dextromethorphan/quinidine (Rx)

Pseudobulbar Affect

Indicated for PBA and symptoms associated with a variety of neurological conditions (eg, MS, ALS) that result in involuntary, sudden, and frequent episodes of laughing and/or crying

PBA occurs secondary to a variety of otherwise unrelated neurologic conditions, and is characterized by involuntary, sudden, and frequent episodes of laughing and/or crying; episodes typically occur out of proportion or incongruent to the underlying emotional state

PBA is a specific condition, distinct from other types of emotional lability that may occur in patients with neurological disease or injury

1 capsule PO qDay for 7days, THEN 1 capsule q12h

Dosage Modifications

Renal impairment

• Mild or moderate: No dose adjustment required
• Severe: Safety and effaicacy not established

Hepatic impairment

• Mild or moderate: No dosage adjustment required; increase in adverse reactions possible with moderate impairment
• Severe: Safety and efficacy not established

Amyotrophic Lateral Sclerosis (Orphan)

Orphan designation for treatment of amyotrophic lateral sclerosis (ALS)

Sponsor

• Avanir Pharmaceuticals; 30 Enterprise, Suite 400; Aliso Viejo, California 92656

Safety and efficacy not established

Dose selection for elderly should be cautious, usually starting at low end of dosing range, reflecting greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy

Contraindicated (72)

• amitriptyline

  quinidine and amitriptyline both increase QTc interval. Contraindicated.

• amoxapine

  quinidine and amoxapine both increase QTc interval. Contraindicated.

• artemether/lumefantrine

  quinidine and artemether/lumefantrine both increase QTc interval. Contraindicated.

• chloroquine

  quinidine will increase the level or effect of chloroquine by Other (see comment). Contraindicated. Quinidine is contraindicated in patients receiving drugs that both prolong the QT interval and are metabolized by CYP2D6, such as chloroquine

• chlorpromazine

  chlorpromazine and quinidine both increase QTc interval. Contraindicated.

• clarithromycin

  quinidine and clarithromycin both increase QTc interval. Contraindicated.

• clomipramine

  quinidine and clomipramine both increase QTc interval. Contraindicated.

• cobimetinib

  quinidine will increase the level or effect of cobimetinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Avoid coadministration with strong CYP3A4 inhibitors with (increases cobimetinib systemic exposure by 6.7-fold).

• conivaptan

  quinidine will increase the level or effect of conivaptan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of conivaptan with strong CYP3A4 inhibitors is contraindicated.

• desipramine

  quinidine and desipramine both increase QTc interval. Contraindicated.

• dihydroergotamine

  quinidine increases levels of dihydroergotamine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

• dihydroergotamine intranasal

  quinidine increases levels of dihydroergotamine intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

• disopyramide

  quinidine and disopyramide both increase QTc interval. Contraindicated.

• dofetilide

  quinidine and dofetilide both increase QTc interval. Contraindicated.
  
  quinidine, dofetilide. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Additive cardiac effects.

• dosulepin

  quinidine and dosulepin both increase QTc interval. Contraindicated.

• doxepin

  quinidine and doxepin both increase QTc interval. Contraindicated.

• dronedarone

  quinidine and dronedarone both increase QTc interval. Contraindicated.

• droperidol

  quinidine and droperidol both increase QTc interval. Contraindicated.

• eliglustat

  quinidine will increase the level or effect of eliglustat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors are contraindicated with eliglustat poor or intermediate metabolizers; reduce eliglustat dose from 84 mg BID to 84 mg once daily in extensive metabolizers; eliglustat is contraindiated if strong or moderate CYP2D6 inhibitors are given concomitantly with strong or moderate CYP3A inhibitors
  
  quinidine increases levels of eliglustat by affecting hepatic enzyme CYP2D6 metabolism. Contraindicated. If coadministered with strong or moderate CYP2D6 inhibitors, reduce eliglustat dose from 84 mg BID to 84 mg once daily in extensive and intermediate metabolizers; eliglustat is contraindiated if strong or moderate CYP2D6 inhibitors are given concomitantly with strong or moderate CYP3A inhibitors.

• epinephrine

  epinephrine and quinidine both increase QTc interval. Contraindicated.

• epinephrine racemic

  epinephrine racemic and quinidine both increase QTc interval. Contraindicated.

• erythromycin base

  quinidine and erythromycin base both increase QTc interval. Contraindicated.

• erythromycin ethylsuccinate

  quinidine and erythromycin ethylsuccinate both increase QTc interval. Contraindicated.

• erythromycin lactobionate

  quinidine and erythromycin lactobionate both increase QTc interval. Contraindicated.

• erythromycin stearate

  quinidine and erythromycin stearate both increase QTc interval. Contraindicated.

• fingolimod

  fingolimod increases effects of quinidine by pharmacodynamic synergism. Contraindicated. Due to increased risk of bradycardia, AV block, and torsade de pointes, concomitant use is contraindicated.

• flibanserin

  quinidine will increase the level or effect of flibanserin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of flibanserin with moderate or strong CYP3A4 inhibitors is contraindicated. Severe hypotension or syncope can occur.

• fluconazole

  fluconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.
  
  quinidine and fluconazole both increase QTc interval. Contraindicated.

• fluphenazine

  fluphenazine and quinidine both increase QTc interval. Contraindicated.

• goserelin

  goserelin increases toxicity of quinidine by QTc interval. Contraindicated. Increases risk of torsades de pointes.

• haloperidol

  quinidine and haloperidol both increase QTc interval. Contraindicated.

• ibutilide

  quinidine and ibutilide both increase QTc interval. Contraindicated.

• imipramine

  quinidine and imipramine both increase QTc interval. Contraindicated.

• indapamide

  quinidine and indapamide both increase QTc interval. Contraindicated.

• isocarboxazid

  isocarboxazid and dextromethorphan both increase serotonin levels. Contraindicated.

• itraconazole

  itraconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Both drugs will increase QT interval. Coadministration of quinidine and itraconazole is contraindicated during and 2 weeks after itraconazole treatment.
  
  quinidine will increase the level or effect of itraconazole by P-glycoprotein (MDR1) efflux transporter. Contraindicated. Both drugs will increase QT interval
  
  quinidine and itraconazole both increase QTc interval. Contraindicated.

• ivabradine

  quinidine will increase the level or effect of ivabradine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of ivabradine with strong CYP3A4 inhibitors is contraindicated.

• ketoconazole

  quinidine and ketoconazole both increase QTc interval. Contraindicated.

• lefamulin

  lefamulin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Lefamulin is contraindicated with CYP3A substrates know to prolong the QT interval.

• leuprolide

  leuprolide increases toxicity of quinidine by QTc interval. Contraindicated. Increases risk of torsades de pointes.

• lofepramine

  quinidine and lofepramine both increase QTc interval. Contraindicated.

• lomitapide

  quinidine increases levels of lomitapide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Increases lomitapide levels several folds.

• lovastatin

  quinidine will increase the level or effect of lovastatin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors increase systemic statin exposure and risk of myopathy, including rhabdomyolysis

• lumefantrine

  quinidine and lumefantrine both increase QTc interval. Contraindicated.

• maprotiline

  quinidine and maprotiline both increase QTc interval. Contraindicated.

• mifepristone

  mifepristone increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Contraindicated with CYP3A substrates that have a narrow therapeutic index; combination may prolong QT interval .

• moxifloxacin

  quinidine and moxifloxacin both increase QTc interval. Contraindicated.

• naloxegol

  quinidine will increase the level or effect of naloxegol by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of naloxegol with strong CYP3A4 inhibitors can significantly increase naloxegol systemic exposure which may precipitate opioid withdrawal symptoms

• nilotinib

  quinidine and nilotinib both increase QTc interval. Contraindicated.

• nortriptyline

  quinidine and nortriptyline both increase QTc interval. Contraindicated.

• octreotide

  quinidine and octreotide both increase QTc interval. Contraindicated.

• octreotide (Antidote)

  quinidine and octreotide (Antidote) both increase QTc interval. Contraindicated.

• pentamidine

  quinidine and pentamidine both increase QTc interval. Contraindicated.

• perphenazine

  perphenazine and quinidine both increase QTc interval. Contraindicated.

• phenelzine

  phenelzine and dextromethorphan both increase serotonin levels. Contraindicated.

• pimozide

  quinidine and pimozide both increase QTc interval. Contraindicated.

• procainamide

  quinidine and procainamide both increase QTc interval. Contraindicated.

• procarbazine

  procarbazine and dextromethorphan both increase serotonin levels. Contraindicated. Combination is contraindicated within 2 weeks of MAOI use.

• prochlorperazine

  prochlorperazine and quinidine both increase QTc interval. Contraindicated.

• promazine

  promazine and quinidine both increase QTc interval. Contraindicated.

• promethazine

  promethazine and quinidine both increase QTc interval. Contraindicated.

• protriptyline

  quinidine and protriptyline both increase QTc interval. Contraindicated.

• rasagiline

  rasagiline and dextromethorphan both increase serotonin levels. Contraindicated. Risk of psychosis episodes or bizarre behavior.

• regorafenib

  quinidine, regorafenib. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors increase regorafenib levels and decrease exposure of the active metabolites M-2 and M-5.

• safinamide

  dextromethorphan, safinamide. Other (see comment). Contraindicated. Comment: Coadministration of MAOIs and dextromethorphan has been reported to cause episodes of psychosis or bizarre behavior.

• saquinavir

  saquinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

• selegiline

  selegiline and dextromethorphan both increase serotonin levels. Contraindicated.

• sotalol

  quinidine and sotalol both increase QTc interval. Contraindicated.

• thioridazine

  thioridazine and quinidine both increase QTc interval. Contraindicated.

• tipranavir

  tipranavir increases levels of quinidine by decreasing metabolism. Contraindicated.
  
  tipranavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

• tranylcypromine

  tranylcypromine and dextromethorphan both increase serotonin levels. Contraindicated.

• trazodone

  quinidine and trazodone both increase QTc interval. Contraindicated.

Serious - Use Alternative (224)

• abametapir

  abametapir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. For 2 weeks after abametapir application, avoid taking drugs that are CYP3A4 substrates. If not feasible, avoid use of abametapir.

• ado-trastuzumab emtansine

  quinidine increases levels of ado-trastuzumab emtansine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. DM1, the cytotoxic component, is metabolized mainly by CYP3A4; strong CYP3A4 inhibitors may increase DM1 exposure and toxicity.

• afatinib

  quinidine increases levels of afatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Reduce afatinib daily dose by 10 mg if not tolerated when coadministered with P-gp inhibitors.

• alfuzosin

  alfuzosin and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• amikacin

  quinidine will increase the level or effect of amikacin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• amiodarone

  quinidine will increase the level or effect of amiodarone by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.
  
  quinidine and amiodarone both increase QTc interval. Avoid or Use Alternate Drug.

• amitriptyline

  amitriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of amitriptyline by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• amoxapine

  amoxapine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• apalutamide

  apalutamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of apalutamide, a strong CYP3A4 inducer, with drugs that are CYP3A4 substrates can result in lower exposure to these medications. Avoid or substitute another drug for these medications when possible. Evaluate for loss of therapeutic effect if medication must be coadministered. Adjust dose according to prescribing information if needed.

• apixaban

  quinidine will increase the level or effect of apixaban by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If taking apixaban dose >2.5 mg BID, decrease dose by 50% if coadministered with strong dual inhibitors of CYP3A4 and P-gp; if currently taking apixaban 2.5 mg PO BID, avoid coadministration with strong dual inhibitors of CYP3A4 and P-gp

• apomorphine

  apomorphine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• aripiprazole

  aripiprazole and quinidine both increase QTc interval. Contraindicated.

• arsenic trioxide

  quinidine and arsenic trioxide both increase QTc interval. Avoid or Use Alternate Drug.

• atomoxetine

  atomoxetine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• atorvastatin

  quinidine will increase the level or effect of atorvastatin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• axitinib

  quinidine increases levels of axitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If unable to avoid coadministration with strong CYP3A4 inhibitors, reduce axitinib dose by 50%.

• bazedoxifene/conjugated estrogens

  quinidine will increase the level or effect of bazedoxifene/conjugated estrogens by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• bedaquiline

  quinidine will increase the level or effect of bedaquiline by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of bedaquiline with strong CYP3A4 inhibitors for >14 consecutive days, unless the benefit of treatment outweighs the risk

• bosutinib

  quinidine increases levels of bosutinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Strong CYP3A4 inhibitors increases bosutinib plasma concentration ~5-fold.
  
  quinidine increases levels of bosutinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• bremelanotide

  bremelanotide will decrease the level or effect of quinidine by Other (see comment). Avoid or Use Alternate Drug. Bremelanotide may slow gastric emptying and potentially reduces the rate and extent of absorption of concomitantly administered oral medications. Avoid use when taking any oral drug that is dependent on threshold concentrations for efficacy. Interactions listed are representative examples and do not include all possible clinical examples.

• brigatinib

  brigatinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Brigatinib induces CYP3A4 in vitro. Coadministration with CYP3A4 substrates, particularly those with a narrow therapeutic index, can result in decreased concentrations and loss of efficacy. If unable to avoid coadministration, monitor CYP3A4 substrate levels and adjust dose as needed.

• budesonide

  quinidine will increase the level or effect of budesonide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• buspirone

  buspirone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• cabozantinib

  quinidine will increase the level or effect of cabozantinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of cabozantinib with strong CYP3A4 inhibitors. If a strong CYP3A4 inhibitor is required, decrease cabozantinib dose by 40 mg/day (Cometriq) or by 20 mg/day (Cabometyx). Resume previous dose 2-3 days after strong CYP3A4 inhibitor discontinued.

• carbamazepine

  carbamazepine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• carvedilol

  quinidine will increase the level or effect of carvedilol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• ceritinib

  quinidine increases levels of ceritinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid if possible; if concomitant use is unavoidable, reduce ceritinib dose by ~33%; after discontinuation of strong CYP3A inhibitor, resume at previous dose.
  
  ceritinib increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concurrent use of CYP3A substrates known to have narrow therapeutic indices or substrates primarily metabolized by CYP3A during treatment with ceritinib; if use of these medications is unavoidable, consider dose.
  
  ceritinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• chloroquine

  chloroquine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.

• chlorpromazine

  quinidine, chlorpromazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• cimetidine

  cimetidine will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of cimetidine by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

• citalopram

  citalopram and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Combination may increase risk of serotonin syndrome or neuroleptic malignant syndrome-like reactions.

• clarithromycin

  clarithromycin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• clobetasone

  quinidine will increase the level or effect of clobetasone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• clomipramine

  clomipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of clomipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• clozapine

  clozapine and quinidine both increase QTc interval. Contraindicated.

• desipramine

  desipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• colchicine

  quinidine will increase the level or effect of colchicine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Avoid use of colchicine with P-gp inhibitors. If coadministration is necessary, decrease colchicine dose or frequency as recommended in prescribing information. Use of any colchicine product in conjunction with P-gp inhibitors is contraindicated in patients with renal or hepatic impairment.

• conjugated estrogens

  quinidine will increase the level or effect of conjugated estrogens by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• conjugated estrogens, vaginal

  quinidine will increase the level or effect of conjugated estrogens, vaginal by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• cortisone

  quinidine will increase the level or effect of cortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• crizotinib

  crizotinib increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of crizotinib with CYP3A substrates with narrow therapeutic indices should be avoided. ECG monitoring is recommended, along with drugs that may prolong the QT interval.
  
  crizotinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• dabrafenib

  quinidine increases levels of dabrafenib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• dapsone topical

  quinidine, dapsone topical. unspecified interaction mechanism. Avoid or Use Alternate Drug. Avoid coadministration of dapsone topical with oral dapsone or antimalarial medications because of the potential for hemolytic reactions.

• dasatinib

  quinidine and dasatinib both increase QTc interval. Avoid or Use Alternate Drug.

• deflazacort

  quinidine will increase the level or effect of deflazacort by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• desipramine

  quinidine will increase the level or effect of desipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• desvenlafaxine

  dextromethorphan and desvenlafaxine both increase serotonin levels. Avoid or Use Alternate Drug.

• dexamethasone

  quinidine will increase the level or effect of dexamethasone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• digoxin

  quinidine will increase the level or effect of digoxin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of digoxin by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

• diphenhydramine

  quinidine, diphenhydramine. Mechanism: pharmacodynamic synergism. Contraindicated. Risk of prolonged QTc interval.

• docetaxel

  quinidine will increase the level or effect of docetaxel by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• dofetilide

  quinidine will increase the level or effect of dofetilide by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.
  
  dofetilide increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.

• dolasetron

  quinidine and dolasetron both increase QTc interval. Avoid or Use Alternate Drug.

• doxepin

  quinidine will increase the level or effect of doxepin by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Both agents increase QTc interval.
  
  doxepin and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• duloxetine

  duloxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of duloxetine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  duloxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• edoxaban

  quinidine will increase the level or effect of edoxaban by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Dose adjustment may be required with strong P-gp inhibitors. DVT/PE treatment: Decrease dose to 30 mg PO once daily. NVAF: No dose reduction recommended

• escitalopram

  escitalopram and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• encorafenib

  encorafenib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Encorafenib is associated with dose-dependent QTc interval prolongation. Avoid with drugs known to prolong QT interval.

• entrectinib

  quinidine and entrectinib both increase QTc interval. Avoid or Use Alternate Drug.

• erdafitinib

  erdafitinib, quinidine. Other (see comment). Avoid or Use Alternate Drug. Comment: Avoid coadministration during initial dosing adjustment period (ie, first 21 days). Increases in serum phosphate levels are a pharmacodynamic effect of FGFR inhibition. Serum phosphate binders may obscure decisions regarding initial dosage increase.
  
  erdafitinib, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration with erdafitinib and sensitive CYP3A4 substrates with narrow therapeutic indices. Erdafitinib may altered plasma concentrations of CYP3A4 substrates, leading to either loss of activity or increased toxicity of the substrate.
  
  erdafitinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If coadministration unavoidable, separate administration by at least 6 hr before or after administration of P-gp substrates with narrow therapeutic index.

• eribulin

  eribulin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Potential for enhanced QTc-prolonging effects; if concurrent use is necessary then ECG monitoring is recommended.

• erlotinib

  quinidine will increase the level or effect of erlotinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• erythromycin base

  erythromycin base will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• erythromycin ethylsuccinate

  erythromycin ethylsuccinate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• erythromycin lactobionate

  erythromycin lactobionate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• erythromycin stearate

  erythromycin stearate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• escitalopram

  escitalopram increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.

• estradiol

  quinidine will increase the level or effect of estradiol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• estrogens conjugated synthetic

  quinidine will increase the level or effect of estrogens conjugated synthetic by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• estropipate

  quinidine will increase the level or effect of estropipate by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• ethinylestradiol

  quinidine will increase the level or effect of ethinylestradiol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• everolimus

  quinidine will increase the level or effect of everolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• fentanyl

  quinidine will increase the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

• fentanyl intranasal

  quinidine will increase the level or effect of fentanyl intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

• fentanyl transdermal

  quinidine will increase the level or effect of fentanyl transdermal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

• fentanyl transmucosal

  quinidine will increase the level or effect of fentanyl transmucosal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

• fexinidazole

  fexinidazole and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Avoid coadministration of fexinidazole with drugs known to block potassium channels and/or prolong QT interval.
  
  fexinidazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Fexinidazole inhibits CYP3A4. Coadministration may increase risk for adverse effects of CYP3A4 substrates.

• flecainide

  quinidine will increase the level or effect of flecainide by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  quinidine and flecainide both increase QTc interval. Avoid or Use Alternate Drug.

• fludrocortisone

  quinidine will increase the level or effect of fludrocortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• fluoxetine

  fluoxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of fluoxetine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  fluoxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  quinidine and fluoxetine both increase QTc interval. Avoid or Use Alternate Drug.

• fluphenazine

  quinidine, fluphenazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• fluvoxamine

  fluvoxamine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• fluticasone intranasal

  quinidine will increase the level or effect of fluticasone intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Strong CYP3A4 inhibitors may increase systemic corticosteroid adverse effects; monitor for signs/symptoms of high corticosteroid concentrations including Cushing type signs/symptoms.

• fluvoxamine

  fluvoxamine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• formoterol

  quinidine and formoterol both increase QTc interval. Avoid or Use Alternate Drug.

• fosamprenavir

  fosamprenavir increases levels of quinidine by unspecified interaction mechanism. Avoid or Use Alternate Drug.

• foscarnet

  quinidine and foscarnet both increase QTc interval. Avoid or Use Alternate Drug.

• gentamicin

  quinidine will increase the level or effect of gentamicin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• glasdegib

  quinidine and glasdegib both increase QTc interval. Avoid or Use Alternate Drug. If coadministration unavoidable, monitor for increased risk of QTc interval prolongation.

• grapefruit

  grapefruit will increase the level or effect of dextromethorphan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• haloperidol

  quinidine will increase the level or effect of haloperidol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• histrelin

  histrelin increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

• hydrocortisone

  quinidine will increase the level or effect of hydrocortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• hydromorphone

  quinidine will increase the level or effect of hydromorphone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• hydroxychloroquine sulfate

  hydroxychloroquine sulfate and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• hydroxyzine

  hydroxyzine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

• ibrutinib

  quinidine increases levels of ibrutinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concomitant use of ibrutinib and strong CYP3A4 inhibitors. If a strong CYP3A4 inhibitor must be used short-term (eg, anti-infectives for =7 days), interrupt ibrutinib therapy until strong CYP3A4 inhibitor is discontinued.

• idelalisib

  quinidine will increase the level or effect of idelalisib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministered with strong CYP3A inhibitors, monitor for signs of idelalisib toxicity; follow recommendations for dosage modifications if adverse reactions occur
  
  idelalisib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Idelalisib is a strong CYP3A inhibitor; avoid coadministration with sensitive CYP3A substrates

• iloperidone

  quinidine will increase the level or effect of iloperidone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  quinidine and iloperidone both increase QTc interval. Avoid or Use Alternate Drug.

• imatinib

  quinidine will increase the level or effect of imatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• imipramine

  imipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of imipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• indinavir

  quinidine will increase the level or effect of indinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• levomilnacipran

  levomilnacipran and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• inotuzumab

  inotuzumab and quinidine both increase QTc interval. Avoid or Use Alternate Drug. If unable to avoid concomitant use, obtain ECGs and electrolytes before and after initiation of any drug known to prolong QTc, and periodically monitor as clinically indicated during treatment.

• ivermectin

  quinidine will increase the level or effect of ivermectin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• ivosidenib

  ivosidenib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Avoid coadministration of QTc prolonging drugs with ivosidenib or replace with alternate therapies. If coadministration of a QTc prolonging drug is unavoidable, monitor for increased risk of QTc interval prolongation.
  
  ivosidenib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sensitive CYP3A4 substrates with ivosidenib or replace with alternative therapies. If coadministration is unavoidable, monitor patients for loss of therapeutic effect of these drugs.

• ketoconazole

  ketoconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• lapatinib

  quinidine will increase the level or effect of lapatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine and lapatinib both increase QTc interval. Avoid or Use Alternate Drug.

• lasmiditan

  lasmiditan increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• levofloxacin

  quinidine and levofloxacin both increase QTc interval. Avoid or Use Alternate Drug.

• linezolid

  linezolid and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Linezolid may increase serotonin as a result of MAO-A inhibition. If linezolid must be administered, discontinue serotonergic drug immediately and monitor for CNS toxicity. Serotonergic therapy may be resumed 24 hours after last linezolid dose or after 2 weeks of monitoring, whichever comes first.

• lofepramine

  quinidine will increase the level or effect of lofepramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  lofepramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• lonafarnib

  lonafarnib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration with sensitive CYP3A substrates. If coadministration unavoidable, monitor for adverse reactions and reduce CYP3A substrate dose in accordance with product labeling.
  
  quinidine will increase the level or effect of lonafarnib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of lonafarnib (a sensitive CYP3A substrate) with weak CYP3A inhibitors is unavoidable, reduce to, or continue lonafarnib at starting dose. Closely monitor for arrhythmias and events (eg, syncope, heart palpitations) since lonafarnib effect on QT interval is unknown.

• lorcaserin

  dextromethorphan and lorcaserin both increase serotonin levels. Avoid or Use Alternate Drug.

• loperamide

  quinidine will increase the level or effect of loperamide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• lopinavir

  lopinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• lorlatinib

  lorlatinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid use of lorlatinib with CYP3A substrates, where minimal concentration changes may lead to serious therapeutic failures of the substrate. If concomitant use is unavoidable, increase CYP3A substrate dosage in accordance with approved product labeling.

• lovastatin

  quinidine will increase the level or effect of lovastatin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• lumacaftor/ivacaftor

  lumacaftor/ivacaftor will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Lumacaftor is a strong inducer of CYP3A. Avoid coadministration with sensitive CYP3A substrates or CYP3A substrates with a narrow therapeutic index.

• lurasidone

  lurasidone increases toxicity of quinidine by Other (see comment). Avoid or Use Alternate Drug. Comment: Interaction applies only in setting of acute lurasidone overdose. Lurasidone may enhance QTc prolonging effects of quinidine in overdose setting.

• macimorelin

  macimorelin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Macimorelin causes an increase of ~11 msec in the corrected QT interval. Avoid coadministration with drugs that prolong QT interval, which could increase risk for developing torsade de pointes-type ventricular tachycardia. Allow sufficient washout time of drugs that are known to prolong the QT interval before administering macimorelin.

• macitentan

  quinidine will increase the level or effect of macitentan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministering macitentan with strong CYP3A4 inhibitors

• maprotiline

  maprotiline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• maraviroc

  quinidine will increase the level or effect of maraviroc by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• mefloquine

  quinidine, mefloquine. Mechanism: pharmacodynamic synergism. Contraindicated. Risk of ECG abnormalities, cardiac arrest.
  
  mefloquine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Mefloquine may enhance the QTc prolonging effect of high risk QTc prolonging agents.

• memantine

  memantine, dextromethorphan. Either increases toxicity of the other by pharmacodynamic synergism. Contraindicated.

• meperidine

  dextromethorphan and meperidine both increase serotonin levels. Avoid or Use Alternate Drug.

• mestranol

  quinidine will increase the level or effect of mestranol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• methadone

  quinidine and methadone both increase QTc interval. Avoid or Use Alternate Drug.

• methamphetamine

  quinidine will increase the level or effect of methamphetamine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• methylene blue

  methylene blue and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Methylene blue may increase serotonin as a result of MAO-A inhibition. If methylene blue must be administered, discontinue serotonergic drug immediately and monitor for CNS toxicity. Serotonergic therapy may be resumed 24 hours after last methylene blue dose or after 2 weeks of monitoring, whichever comes first.

• methylprednisolone

  quinidine will increase the level or effect of methylprednisolone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• metoclopramide intranasal

  quinidine will increase the level or effect of metoclopramide intranasal by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Concurrent use of metoclopramide intranasal and strong CYP2D6 inhibitors is not recommended since the metoclopramide intranasal dose cannot be adjusted.

• metoprolol

  quinidine will increase the level or effect of metoprolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. If concurrent therapy required, monitor cardiac function carefully (blood pressure, heart rate). A dosage adjustment may be required for both drugs.

• mexiletine

  quinidine will increase the level or effect of mexiletine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• milnacipran

  milnacipran and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• mobocertinib

  mobocertinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If use is unavoidable, increase CYP3A4 substrate dosage in accordance with its prescribing information.
  
  mobocertinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. If coadministration unavoidable, reduce mobocertinib dose and monitor QTc interval more frequently.

• morphine

  quinidine will increase the level or effect of morphine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• nebivolol

  quinidine will increase the level or effect of nebivolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Monitor blood pressure. Reduced doses of nebivolol may be necessary.

• nefazodone

  nefazodone will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  nefazodone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• nelfinavir

  quinidine will increase the level or effect of nelfinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  nelfinavir increases levels of quinidine by decreasing metabolism. Contraindicated.

• nortriptyline

  nortriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• neomycin PO

  quinidine will increase the level or effect of neomycin PO by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• nilotinib

  nilotinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Additive QT prolongation may occur during coadministration of nilotinib and quinidine. Coadministration of nilotinib and a drug that prolongs the QT interval such as dronedarone is not advised
  
  quinidine will increase the level or effect of nilotinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• nortriptyline

  quinidine will increase the level or effect of nortriptyline by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• ofloxacin

  quinidine and ofloxacin both increase QTc interval. Avoid or Use Alternate Drug.

• olaparib

  quinidine will increase the level or effect of olaparib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration with strong CYP3A inhibitors cannot be avoided, reduce olaparib dose to 150 mg (capsule) or 100 mg (tablet) PO BID. Do not substitute tablets with capsules.

• ondansetron

  quinidine and ondansetron both increase QTc interval. Avoid or Use Alternate Drug. Avoid with congenital long QT syndrome; ECG monitoring recommended with concomitant medications that prolong QT interval, electrolyte abnormalities, CHF, or bradyarrhythmias.

• oxycodone

  quinidine will increase the level or effect of oxycodone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  quinidine increases levels of oxycodone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Oxycodone dose reduction may be warranted when coadministered with strong CYP3A4 inhibitors.

• oxymorphone

  quinidine will increase the level or effect of oxymorphone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• paclitaxel

  quinidine will increase the level or effect of paclitaxel by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• paclitaxel protein bound

  quinidine will increase the level or effect of paclitaxel protein bound by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• palbociclib

  quinidine will increase the level or effect of palbociclib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of palbociclib with strong CYP3A inhibitors. If unable to avoid, reduce palbociclib dose to 75 mg/day.

• paliperidone

  quinidine will increase the level or effect of paliperidone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine and paliperidone both increase QTc interval. Avoid or Use Alternate Drug.

• panobinostat

  quinidine and panobinostat both increase QTc interval. Avoid or Use Alternate Drug. Panobinostat is known to significantly prolong QT interval. Panobinostat prescribing information states use with drugs known to prolong QTc is not recommended.

• paromomycin

  quinidine will increase the level or effect of paromomycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• paroxetine

  paroxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  paroxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine and paroxetine both increase QTc interval. Avoid or Use Alternate Drug.

• perphenazine

  quinidine, perphenazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• protriptyline

  protriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• pexidartinib

  quinidine and pexidartinib both increase inhibition of GI absorption. Applies only to oral form of both agents. Avoid or Use Alternate Drug. Pexidartinib can cause hepatotoxicity. Avoid coadministration of pexidartinib with other products know to cause hepatoxicity.
  
  pexidartinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of pexidartinib (a CYP3A4 inducer) with sensitive CYP3A substrates may lead to serious therapeutic failures. If concomitant use is unavoidable, increase the CYP3A substrate dosage in accordance with approved product labeling.

• pimavanserin

  pimavanserin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Coadministration may increase the risk of QT prolongation and cardiac arrhythmia.

• pitolisant

  quinidine and pitolisant both increase QTc interval. Avoid or Use Alternate Drug.

• pomalidomide

  quinidine increases levels of pomalidomide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  quinidine increases levels of pomalidomide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• ponatinib

  quinidine increases levels of ponatinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Decrease ponatinib starting dose to 30 mg qDay if coadministration with strong CYP3A4 inhibitors cannot be avoided.

• ponesimod

  ponesimod, quinidine. Either increases effects of the other by QTc interval. Avoid or Use Alternate Drug. Consult cardiologist if considering treatment. Generally, should not be initiated in patients who are concurrently taking QT prolonging drugs with known arrhythmogenic properties, such as HR-lowering calcium channel blockers (eg, verapamil, diltiazem).

• posaconazole

  posaconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Use of posaconazole in combination with drugs that both prolong the QT interval and are substrates for CYP3A4 is contraindicated
  
  quinidine will increase the level or effect of posaconazole by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine and posaconazole both increase QTc interval. Avoid or Use Alternate Drug.

• prednisolone

  quinidine will increase the level or effect of prednisolone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• prednisone

  quinidine will increase the level or effect of prednisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• pretomanid

  quinidine, pretomanid. Either increases toxicity of the other by Other (see comment). Avoid or Use Alternate Drug. Comment: Pretomanid regimen associated with hepatotoxicity. Avoid alcohol and hepatotoxic agents, including herbal supplements and drugs other than bedaquiline and linezolid.

• procainamide

  quinidine will increase the level or effect of procainamide by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

• prochlorperazine

  quinidine, prochlorperazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• promazine

  quinidine, promazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• promethazine

  quinidine, promethazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• propafenone

  quinidine will increase the level or effect of propafenone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• propranolol

  quinidine will increase the level or effect of propranolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Monitor patients for hypotension, bradycardia, arrhythmias and heart failure.

• ranolazine

  quinidine and ranolazine both increase QTc interval. Avoid or Use Alternate Drug.

• red yeast rice

  quinidine will increase the level or effect of red yeast rice by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. May increase creatine kinase levels and increase risk of myopathy or rhabdomyolysis; red yeast rice contains monocolin K (reportedly identical to lovastatin)

• ribociclib

  ribociclib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• rifabutin

  rifabutin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• rifampin

  rifampin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• rimegepant

  quinidine will increase the level or effect of rimegepant by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• riociguat

  quinidine will increase the level or effect of riociguat by decreasing metabolism. Avoid or Use Alternate Drug. Coadministration of riociguat (substrate of CYP isoenzymes 1A1, 2C8, 3A, 2J2) with strong CYP inhibitors may require a decreased initial dose of 0.5 mg PO TID; monitor for signs of hypotension and reduce dose if needed
  
  quinidine will increase the level or effect of riociguat by Other (see comment). Avoid or Use Alternate Drug. Coadministration of riociguat (an ABCG2 [BCRP] substrate) with strong ABCG2 inhibitors may require a decreased initial dose of 0.5 mg PO TID; monitor for signs of hypotension and reduce dose if needed

• risperidone

  quinidine will increase the level or effect of risperidone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine and risperidone both increase QTc interval. Avoid or Use Alternate Drug.

• ritonavir

  quinidine will increase the level or effect of ritonavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  ritonavir increases levels of quinidine by decreasing metabolism. Contraindicated.

• romidepsin

  quinidine will increase the level or effect of romidepsin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine and romidepsin both increase QTc interval. Avoid or Use Alternate Drug.

• ruxolitinib

  quinidine will increase the level or effect of ruxolitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Reduce ruxolitinib starting dose to 10 mg BID with platelet count 100 X 10^9/L or more and concurrent use of strong CYP3A4 inhibitors; avoid with platelet counts <100 X 10^9/L

• saquinavir

  quinidine will increase the level or effect of saquinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• selegiline transdermal

  selegiline transdermal and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• sertraline

  sertraline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• St John's Wort

  dextromethorphan and St John's Wort both increase serotonin levels. Avoid or Use Alternate Drug.

• silodosin

  quinidine will increase the level or effect of silodosin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• siponimod

  siponimod, quinidine. Either increases effects of the other by QTc interval. Avoid or Use Alternate Drug. Because of the potential additive effects on heart rate, siponimod should generally not be initiated in patients taking QT prolonging drugs with known arrhythmogenic properties, heart rate lowering calcium channel blockers, or other drugs that may decrease heart rate. If treatment considered, obtain cardiology consult regarding switching to non-heart-rate lowering drugs or appropriate monitoring for treatment initiation.

• sirolimus

  quinidine will increase the level or effect of sirolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• sonidegib

  quinidine will increase the level or effect of sonidegib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sonidegib with strong CYP3A4 inhibitors.

• sotorasib

  sotorasib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If use is unavoidable, refer to the prescribing information of the CYP3A4 substrate for dosage modifications
  
  sotorasib will decrease the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If use is unavoidable, refer to the prescribing information of the P-gp substrate for dosage modifications.

• squill

  quinidine increases toxicity of squill by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• St John's Wort

  St John's Wort will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• streptomycin

  quinidine will increase the level or effect of streptomycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• sulfamethoxazole

  quinidine and sulfamethoxazole both increase QTc interval. Avoid or Use Alternate Drug.

• suvorexant

  quinidine increases levels of suvorexant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Suvorexant not recommended with use of strong CYP3A4 inhibitors.

• tacrolimus

  quinidine will increase the level or effect of tacrolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• tamsulosin

  quinidine increases levels of tamsulosin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• telavancin

  quinidine and telavancin both increase QTc interval. Avoid or Use Alternate Drug.

• tepotinib

  tepotinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If concomitant use unavoidable, reduce the P-gp substrate dosage if recommended in its approved product labeling.

• thioridazine

  quinidine will increase the level or effect of thioridazine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  quinidine, thioridazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• timolol

  quinidine will increase the level or effect of timolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• tobramycin

  quinidine will increase the level or effect of tobramycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• tofacitinib

  quinidine increases levels of tofacitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Reduce tofacitinib dose to 5 mg qDay when coadministered with potent CYP3A4 inhibitors.

• tolvaptan

  quinidine will increase the level or effect of tolvaptan by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• topotecan

  quinidine will increase the level or effect of topotecan by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Product labeling for PO topotecan recommends avoiding concomitant use of P-gp inhibitors; the interaction with IV topotecan may be less severe but is still likely of clinical significance

• toremifene

  quinidine and toremifene both increase QTc interval. Avoid or Use Alternate Drug. Concurrent use of toremifene with agents causing QT prolongation should be avoided. If concomitant use is required it's recommended that toremifene be interrupted. If interruption not possible, patients requiring therapy with a drug that prolongs QT should be closely monitored. ECGs should be obtained for high risk patients.

• trazodone

  trazodone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• trifluoperazine

  quinidine, trifluoperazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• trimethoprim

  quinidine and trimethoprim both increase QTc interval. Avoid or Use Alternate Drug.

• trimipramine

  trimipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• triptorelin

  triptorelin increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

• tropisetron

  quinidine and tropisetron both increase QTc interval. Avoid or Use Alternate Drug.

• tucatinib

  tucatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concomitant use of tucatinib with CYP3A substrates, where minimal concentration changes may lead to serious or life-threatening toxicities. If unavoidable, reduce CYP3A substrate dose according to product labeling.

• umeclidinium bromide/vilanterol inhaled

  quinidine increases toxicity of umeclidinium bromide/vilanterol inhaled by QTc interval. Avoid or Use Alternate Drug. Exercise extreme caution when vilanterol coadministered with drugs that prolong QTc interval; adrenergic agonist effects on the cardiovascular system may be potentiated.

• vandetanib

  quinidine, vandetanib. Either increases toxicity of the other by QTc interval. Avoid or Use Alternate Drug. Avoid coadministration with drugs known to prolong QT interval; if a drug known to prolong QT interval must be used, more frequent ECG monitoring is recommended.

• venetoclax

  quinidine will increase the level or effect of venetoclax by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If a P-gp inhibitor must be used, reduce the venetoclax dose by at least 50%. Monitor more closely for signs of venetoclax toxicities.

• venlafaxine

  quinidine and venlafaxine both increase QTc interval. Avoid or Use Alternate Drug.
  
  venlafaxine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  venlafaxine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• vilanterol/fluticasone furoate inhaled

  quinidine increases toxicity of vilanterol/fluticasone furoate inhaled by QTc interval. Avoid or Use Alternate Drug. Exercise extreme caution when vilanterol coadministered with drugs that prolong QTc interval; adrenergic agonist effects on the cardiovascular system may be potentiated.

• vilazodone

  dextromethorphan, vilazodone. Either increases toxicity of the other by serotonin levels. Avoid or Use Alternate Drug. Concomitant therapy should be discontinued immediately if signs or symptoms of serotonin syndrome emerge and supportive symptomatic treatment should be initiated. .

Monitor Closely (287)

• 5-HTP

  5-HTP and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• abiraterone

  abiraterone increases levels of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Avoid coadministration of abiraterone with substrates of CYP2D6. If alternative therapy cannot be used, exercise caution and consider a dose reduction of the CYP2D6 substrate.

• acetazolamide

  acetazolamide will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

• albuterol

  albuterol and quinidine both increase QTc interval. Use Caution/Monitor.

• alfuzosin

  quinidine and alfuzosin both increase QTc interval. Use Caution/Monitor.

• aliskiren

  quinidine will increase the level or effect of aliskiren by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• almotriptan

  almotriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• aluminum hydroxide

  aluminum hydroxide will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

• alvimopan

  quinidine will increase the level or effect of alvimopan by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• amantadine

  quinidine will increase the level or effect of amantadine by decreasing renal clearance. Use Caution/Monitor. Coadministration of quinine or quinidine with amantadine was shown to reduce the renal clearance of amantadine by ~30%.

• amiloride

  amiloride, quinidine. Mechanism: unspecified interaction mechanism. Use Caution/Monitor. Increased risk of arrhythmias in pts. with ventricular tachycardia.

• amobarbital

  amobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• aprepitant

  aprepitant will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• arformoterol

  arformoterol and quinidine both increase QTc interval. Use Caution/Monitor.

• aripiprazole

  dextromethorphan, aripiprazole. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).
  
  quinidine will increase the level or effect of aripiprazole by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• armodafinil

  armodafinil will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of armodafinil by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• artemether/lumefantrine

  artemether/lumefantrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• artemether

  artemether and quinidine both increase QTc interval. Use Caution/Monitor.

• artemether/lumefantrine

  artemether/lumefantrine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• asenapine

  dextromethorphan, asenapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• atazanavir

  atazanavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• atomoxetine

  quinidine will increase the level or effect of atomoxetine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Reduced initial doses of atomoxetine are recommended with strong CYP2D6 inhibitors.

• avapritinib

  quinidine will increase the level or effect of avapritinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• azithromycin

  quinidine and azithromycin both increase QTc interval. Modify Therapy/Monitor Closely.

• bedaquiline

  quinidine and bedaquiline both increase QTc interval. Modify Therapy/Monitor Closely. ECG should be monitored closely

• benzhydrocodone/acetaminophen

  quinidine will increase the level or effect of benzhydrocodone/acetaminophen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Hydromorphone (<3% of the circulating parent hydrocodone [benzhydrocodone is prodrug of hydrocodone]) is mainly formed by CYP2D6 mediated O-demethylation of hydrocodone. Hydromorphone may contribute to the total analgesic effect of hydrocodone.

• berotralstat

  quinidine increases levels of berotralstat by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Reduced berotralstat dose to 110 mg/day when coadministered with P-gp inhibitors.
  
  berotralstat will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor or titrate P-gp substrate dose if coadministered.
  
  berotralstat will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor or titrate substrate dose when berotralstat is coadministered with narrow therapeutic index drugs that are CYP3A substrates.

• betrixaban

  quinidine increases levels of betrixaban by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Decrease betrixaban dose to 80 mg PO once, then 40 mg PO qDay if coadministered with a P-gp inhibitor.

• blinatumomab

  blinatumomab increases levels of quinidine by decreasing metabolism. Modify Therapy/Monitor Closely. Treatment initiation causes transient release of cytokines that may suppress CYP450 enzymes; highest drug-drug interaction risk is during the first 9 days of the first cycle and the first 2 days of the 2nd cycle in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index.

• bosentan

  bosentan will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• bosutinib

  bosutinib increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  bosutinib and quinidine both increase QTc interval. Use Caution/Monitor.

• brexpiprazole

  quinidine will increase the level or effect of brexpiprazole by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Administer half of the usual brexpiprazole dose when coadministered with strong CYP2D6 inhibitors. If also administered with a strong/moderate CYP3A4 inhibitor, administer a quarter of brexpiprazole dose. NOTE: In MDD clinical trials, brexpiprazole dosage was not adjusted for strong CYP2D6 inhibitors (eg, paroxetine, fluoxetine); thus, CYP considerations are already factored into general dosing recommendations and brexpiprazole may be administered without dosage adjustment in patients with MDD.
  
  quinidine will increase the level or effect of brexpiprazole by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Administer half of the usual brexpiprazole dose when coadministered with strong CYP3A4 inhibitors. If also administered with a strong/moderate CYP2D6 inhibitor, administer a quarter of brexpiprazole dose.

• brodalumab

  brodalumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, brodalumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of brodalumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• budesonide

  budesonide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• bupivacaine implant

  quinidine, bupivacaine implant. Either increases toxicity of the other by Other (see comment). Use Caution/Monitor. Comment: Local anesthetics may increase the risk of developing methemoglobinemia when concurrently exposed to drugs that also cause methemoglobinemia.

• bupropion

  bupropion will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• butabarbital

  butabarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• butalbital

  butalbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• calcium carbonate

  calcium carbonate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

• capecitabine

  capecitabine and quinidine both increase QTc interval. Use Caution/Monitor.

• cariprazine

  quinidine will increase the level or effect of cariprazine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration with strong CYP3A4 inhibitors requires cariprazine dose reduction. See Dosage Modification section in drug monograph.
  
  dextromethorphan, cariprazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• cenobamate

  cenobamate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Increase dose of CYP3A4 substrate, as needed, when coadministered with cenobamate.

• clobazam

  clobazam will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Lower doses of drugs metabolized by CYP2D6 may be required when used concomitantly.

• ceritinib

  quinidine increases levels of ceritinib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• chlorpromazine

  quinidine will increase the level or effect of chlorpromazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• ciprofloxacin

  ciprofloxacin and quinidine both increase QTc interval. Use Caution/Monitor. Ciprofloxacin elicits minimal effects on QT interval. Caution if used in combination with other drugs known to affect QT interval or in patients with other risk factors.

• citalopram

  quinidine and citalopram both increase QTc interval. Use Caution/Monitor. ECG monitoring is recommended, along with drugs that may prolong the QT interval.

• clozapine

  dextromethorphan, clozapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• cobicistat

  cobicistat will increase the level or effect of quinidine by Other (see comment). Modify Therapy/Monitor Closely. Quinidine is a substrate of CYP3A4 and P-gp, and inhibits CYP2D6 and P-gp; cobicistat is a substrate and inhibitor of both isoenzymes and a P-gp inhibitor
  
  cobicistat will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• cocaine

  cocaine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• codeine

  quinidine will decrease the level or effect of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Prevents conversion of codeine to its active metabolite morphine.

• conivaptan

  conivaptan will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• cortisone

  cortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• crofelemer

  crofelemer increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Crofelemer has the potential to inhibit CYP3A4 at concentrations expected in the gut; unlikely to inhibit systemically because minimally absorbed.

• cyclosporine

  quinidine will increase the level or effect of cyclosporine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  cyclosporine will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• dabigatran

  quinidine will increase the level or effect of dabigatran by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Atrial fibrillation: Avoid coadministering dabigatran with P-gp inhibitors if CrCl <30 mL/min. DVT/PE treatment: Avoid coadministering dabigatran with P-gp inhibitors if CrCl <50 mL/min

• dabrafenib

  dabrafenib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely.

• darifenacin

  darifenacin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• darunavir

  darunavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• dasatinib

  dasatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• daunorubicin

  quinidine will increase the level or effect of daunorubicin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• deferasirox

  deferasirox will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• degarelix

  degarelix and quinidine both increase QTc interval. Use Caution/Monitor.

• desvenlafaxine

  desvenlafaxine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Desvenlafaxine inhibits CYP2D6; with higher desvenlafaxine doses (ie, 400 mg) decrease the CYP2D6 substrate dose by up to 50%; no dosage adjustment needed with desvenlafaxine doses <100 mg

• deutetrabenazine

  quinidine will increase the level or effect of deutetrabenazine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Strong CYP2D6 inhibitors increase the systemic exposure to the active dihydro-metabolites of deutetrabenazine by approximately 3-fold. Do not exceed 18 mg/dose and 36 mg/day of deutetrabenazine if coadministered with strong CYP2D6 inhibitors.
  
  quinidine and deutetrabenazine both increase QTc interval. Modify Therapy/Monitor Closely. Quinidine is a strong CYP2D6 inhibitor and also prolongs the QT interval. Strong CYP2D6 inhibitors increase the systemic exposure to the active dihydro-metabolites of deutetrabenazine by approximately 3-fold. Do not exceed 18 mg/dose and 36 mg/day of deutetrabenazine if coadministered with strong CYP2D6 inhibitors.

• dexamethasone

  dexamethasone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• dexfenfluramine

  dexfenfluramine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.
  
  quinidine will increase the level or effect of dexfenfluramine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• dextroamphetamine

  quinidine will increase the level or effect of dextroamphetamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.
  
  dextroamphetamine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• dextromethorphan

  quinidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• dihydroergotamine

  dextromethorphan and dihydroergotamine both increase serotonin levels. Modify Therapy/Monitor Closely.

• DHEA, herbal

  DHEA, herbal will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• dienogest/estradiol valerate

  quinidine will increase the level or effect of dienogest/estradiol valerate by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor for potential adverse effects such as nausea, irregular uterine bleeding, breast tenderness and headache.

• dihydroergotamine intranasal

  dextromethorphan and dihydroergotamine intranasal both increase serotonin levels. Modify Therapy/Monitor Closely.

• diltiazem

  diltiazem will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of diltiazem by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• donepezil

  quinidine will increase the level or effect of donepezil by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• doxorubicin

  quinidine will increase the level or effect of doxorubicin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• doxorubicin liposomal

  quinidine will increase the level or effect of doxorubicin liposomal by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• dronedarone

  dronedarone will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• dulaglutide

  dulaglutide, quinidine. Other (see comment). Use Caution/Monitor. Comment: Dulaglutide slows gastric emptying and may impact absorption of concomitantly administered oral medications; be particularly cautious when coadministered with drugs that have a narrow therapeutic index.

• dupilumab

  dupilumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, dupilumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of dupilumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• duvelisib

  duvelisib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration with duvelisib increases AUC of a sensitive CYP3A4 substrate which may increase the risk of toxicities of these drugs. Consider reducing the dose of the sensitive CYP3A4 substrate and monitor for signs of toxicities of the coadministered sensitive CYP3A substrate.
  
  quinidine will increase the level or effect of duvelisib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• efavirenz

  efavirenz will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• elagolix

  elagolix will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  elagolix decreases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Elagolix is a weak-to-moderate CYP3A4 inducer. Monitor CYP3A substrates if coadministered. Consider increasing CYP3A substrate dose if needed.

• eletriptan

  eletriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• eliglustat

  eliglustat increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Monitor therapeutic drug concentrations, as indicated, or consider reducing the dosage of the P-gp substrate and titrate to clinical effect.

• eluxadoline

  quinidine increases levels of eluxadoline by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. As a precautionary measure due to incomplete information on the metabolism of eluxadoline, use caution when coadministered with strong CYP2D6 inhibitors.
  
  eluxadoline increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Caution when CYP3A substrates that have a narrow therapeutic index are coadministered with eluxadoline.

• elvitegravir

  quinidine increases levels of elvitegravir by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Elvitegravir is a CYP3A4 substrate; if coadministered with strong CYP3A4 inhibitors may increase levels.

• elvitegravir/cobicistat/emtricitabine/tenofovir DF

  elvitegravir/cobicistat/emtricitabine/tenofovir DF increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Cobicistat is a CYP3A4 inhibitor; contraindicated with CYP3A4 substrates for which elevated plasma concentrations are associated with serious and/or life-threatening events.

• encainide

  quinidine will increase the level or effect of encainide by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• encorafenib

  encorafenib, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Encorafenib both inhibits and induces CYP3A4 at clinically relevant plasma concentrations. Coadministration of encorafenib with sensitive CYP3A4 substrates may result in increased toxicity or decreased efficacy of these agents.

• enzalutamide

  enzalutamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• ergotamine

  dextromethorphan and ergotamine both increase serotonin levels. Modify Therapy/Monitor Closely.

• eslicarbazepine acetate

  eslicarbazepine acetate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• estrogens esterified

  quinidine will increase the level or effect of estrogens esterified by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely.

• ethotoin

  ethotoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

• etoposide

  quinidine will increase the level or effect of etoposide by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• etravirine

  etravirine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• ezogabine

  ezogabine, quinidine. Either increases toxicity of the other by QTc interval. Use Caution/Monitor. Slight and transient QT-prolongation observed with ezogabine, particularly when dose titrated to 1200 mg/day. QT interval should be monitored when ezogabine is prescribed with agents known to increase QT interval.

• fedratinib

  fedratinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Adjust dose of drugs that are CYP3A4 substrates as necessary.

• fenfluramine

  dextromethorphan and fenfluramine both increase serotonin levels. Modify Therapy/Monitor Closely.
  
  fenfluramine, dextromethorphan. Either increases effects of the other by serotonin levels. Use Caution/Monitor. Coadministration with drugs that increase serotoninergic effects may increase the risk of serotonin syndrome.

• ferric maltol

  ferric maltol, quinidine. Either increases levels of the other by unspecified interaction mechanism. Modify Therapy/Monitor Closely. Coadministration of ferric maltol with certain oral medications may decrease the bioavailability of either ferric maltol and some oral drugs. For oral drugs where reductions in bioavailability may cause clinically significant effects on its safety or efficacy, separate administration of ferric maltol from these drugs. Duration of separation may depend on the absorption of the medication concomitantly administered (eg, time to peak concentration, whether the drug is an immediate or extended release product).

• fesoterodine

  quinidine will increase the level or effect of fesoterodine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• fexofenadine

  quinidine will increase the level or effect of fexofenadine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• finerenone

  quinidine will increase the level or effect of finerenone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Monitor serum potassium during initiation and dosage adjustment of either finererone or weak CYP3A4 inhibitors. Adjust finererone dosage as needed.

• fludrocortisone

  fludrocortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• fluphenazine

  quinidine will increase the level or effect of fluphenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.
  
  dextromethorphan, fluphenazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• fluticasone furoate

  quinidine will increase the level or effect of fluticasone furoate by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Strong CYP3A4 inhibitors may increase fluticasone systemic exposure

• frovatriptan

  frovatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• fluticasone inhaled

  quinidine will increase the level or effect of fluticasone inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Strong CYP3A4 inhibitors may increase fluticasone systemic exposure

• fluvoxamine

  quinidine will increase the level or effect of fluvoxamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• fosamprenavir

  fosamprenavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• fosphenytoin

  fosphenytoin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  fosphenytoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

• fostamatinib

  fostamatinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Concomitant use of fostamatinib may increase concentrations of P-gp substrates. Monitor for toxicities of the P-gp substrate drug that may require dosage reduction when given concurrently with fostamatinib.

• fostemsavir

  quinidine and fostemsavir both increase QTc interval. Use Caution/Monitor. QTc prolongation reported with higher than recommended doses of fostemsavir.

• galantamine

  quinidine will increase the level or effect of galantamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• gefitinib

  quinidine increases levels of gefitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration of strong CYP3A4 inhibitors may increase risk for gefitinib adverse effects.

• gemtuzumab

  quinidine and gemtuzumab both increase QTc interval. Use Caution/Monitor.

• glecaprevir/pibrentasvir

  quinidine will increase the level or effect of glecaprevir/pibrentasvir by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  glecaprevir/pibrentasvir will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• glycerol phenylbutyrate

  glycerol phenylbutyrate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Glycerol phenylbutyrate is a weak inducer of CYP3A4. Monitor for decreased efficacy of CYP3A4 substrates that have a narrow therapeutic index.

• grapefruit

  grapefruit will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• griseofulvin

  griseofulvin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• guselkumab

  guselkumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, normalizing the formation of CYP450 enzymes. Upon initiation or discontinuation of guselkumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• haloperidol

  dextromethorphan, haloperidol. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• hawthorn

  hawthorn increases effects of quinidine by pharmacodynamic synergism. Use Caution/Monitor.

• henbane

  henbane, quinidine. unspecified interaction mechanism. Use Caution/Monitor. Combination not recommended by British Herbal Medicine Association.

• hydrochlorothiazide

  quinidine will increase the level or effect of hydrochlorothiazide by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• hydrocodone

  quinidine will increase the level or effect of hydrocodone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Hydromorphone (<3% of the circulating parent hydrocodone) is mainly formed by CYP2D6 mediated O-demethylation of hydrocodone. Hydromorphone may contribute to the total analgesic effect of hydrocodone.

• hydrocortisone

  hydrocortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• iloperidone

  iloperidone increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Iloperidone is a time-dependent CYP3A inhibitor and may lead to increased plasma levels of drugs predominantly eliminated by CYP3A4.
  
  dextromethorphan, iloperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• incobotulinumtoxinA

  quinidine, incobotulinumtoxinA. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Use of anticholinergic drugs after administration of botulinum toxin-containing products may potentiate systemic anticholinergic effects.

• L-tryptophan

  dextromethorphan and L-tryptophan both increase serotonin levels. Modify Therapy/Monitor Closely.

• isoniazid

  dextromethorphan and isoniazid both increase serotonin levels. Modify Therapy/Monitor Closely.

• indacaterol, inhaled

  indacaterol, inhaled, quinidine. QTc interval. Use Caution/Monitor. Drugs that are known to prolong the QTc interval may have an increased the risk of ventricular arrhythmias.

• indinavir

  indinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• isoniazid

  isoniazid will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• istradefylline

  istradefylline will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Istradefylline 40 mg/day increased peak levels and AUC of CYP3A4 substrates in clinical trials. This effect was not observed with istradefylline 20 mg/day. Consider dose reduction of sensitive CYP3A4 substrates.
  
  istradefylline will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Istradefylline 40 mg/day increased peak levels and AUC of P-gp substrates in clinical trials. Consider dose reduction of sensitive P-gp substrates.

• ivacaftor

  ivacaftor increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Ivacaftor and its M1 metabolite has the potential to inhibit P-gp; may significantly increase systemic exposure to sensitive P-gp substrates with a narrow therapeutic index.

• ixekizumab

  ixekizumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, ixekizumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of ixekizumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• lacosamide

  quinidine, lacosamide. Either increases levels of the other by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Consider decreasing lacosamide dose when coadministered with strong CYP3A4 inhibitors.

• lapatinib

  lapatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• lemborexant

  quinidine will increase the level or effect of lemborexant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Lower nightly dose of lemborexant recommended if coadministered with weak CYP3A4 inhibitors. See drug monograph for specific dosage modification.

• lenvatinib

  quinidine and lenvatinib both increase QTc interval. Use Caution/Monitor. Lenvatinib prescribing information recommends monitoring ECG closely when coadministered with QT prolonging drugs.

• letermovir

  letermovir increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  letermovir increases levels of dextromethorphan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• levomilnacipran

  quinidine will increase the level or effect of levomilnacipran by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Do not exceed 80 mg/day of levomilnacipran when coadministered with strong CYP3A4 inhibitors

• lithium

  dextromethorphan and lithium both increase serotonin levels. Modify Therapy/Monitor Closely.

• lofexidine

  quinidine will increase the level or effect of lofexidine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Concomitant use of lofexidine with strong CYP2D6 inhibitors may increase lofexidine plasma levels. Monitor for symptoms of orthostasis and bradycardia if coadministered with a CYP2D6 inhibitor. Consider lofexidine dose reduction.
  
  quinidine and lofexidine both increase QTc interval. Use Caution/Monitor. ECG monitoring is recommended.

• lomitapide

  lomitapide increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Consider reducing dose when used concomitantly with lomitapide.

• lonafarnib

  lonafarnib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Lonafarnib is a weak P-gp inhibitor. Monitor for adverse reactions if coadministered with P-gp substrates where minimal concentration changes may lead to serious or life-threatening toxicities. Reduce P-gp substrate dose if needed.

• loratadine

  quinidine will increase the level or effect of loratadine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of loratadine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• loxapine

  dextromethorphan, loxapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• loxapine inhaled

  dextromethorphan, loxapine inhaled. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• lsd

  dextromethorphan and lsd both increase serotonin levels. Modify Therapy/Monitor Closely.

• lumacaftor/ivacaftor

  quinidine increases levels of lumacaftor/ivacaftor by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Strong CYP3A inhibitors do not impact lumacaftor exposure, but increased ivacaftor exposure by 4.3-fold. Due to the induction effect of lumacaftor on CYP3A, at steady-state the net exposure of ivacaftor is not expected to exceed that when given in the absence of lumacaftor at a dose of 150 mg q12hr (the approved dose of ivacaftor monotherapy). Therefore, no dose adjustment is necessary when CYP3A inhibitors are initiated in patients currently taking lumacaftor/ivacaftor. However, when initiating lumacaftor/ivacaftor in patients taking strong CYP3A inhibitors, reduce the dose to 1 tablet daily (lumacaftor 200 mg/ivacaftor 125 mg total daily dose) for the first week of treatment to allow for the steady-state induction effect of lumacaftor. Following this period, continue with the recommended daily dose. No dose adjustment is required for moderate or weak CYP3A4 inhibitors.

• lumefantrine

  lumefantrine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  lumefantrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• lurasidone

  dextromethorphan, lurasidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• maraviroc

  quinidine will increase the level or effect of maraviroc by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Decrease maraviroc dose to 150 mg BID when coadministered with strong CYP3A4 inhibitors

• marijuana

  marijuana will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• medroxyprogesterone

  quinidine will increase the level or effect of medroxyprogesterone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Use alternative if available.

• memantine

  quinidine will increase the level or effect of memantine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• metformin

  quinidine will increase the level or effect of metformin by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• methyclothiazide

  quinidine will increase the level or effect of methyclothiazide by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• methylprednisolone

  methylprednisolone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• metronidazole

  metronidazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• miconazole vaginal

  miconazole vaginal will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• midazolam intranasal

  quinidine will increase the level or effect of midazolam intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Coadministration of mild CYP3A4 inhibitors with midazolam intranasal may cause higher midazolam systemic exposure, which may prolong sedation.

• midodrine

  quinidine will increase the level or effect of midodrine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• mirtazapine

  dextromethorphan and mirtazapine both increase serotonin levels. Modify Therapy/Monitor Closely.

• mitotane

  mitotane decreases toxicity of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Mitotane is a strong inducer of cytochrome P-4503A4; monitor when coadministered with CYP3A4 substrates for possible dosage adjustments.

• modafinil

  modafinil will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• molindone

  dextromethorphan, molindone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• morphine

  dextromethorphan and morphine both increase serotonin levels. Modify Therapy/Monitor Closely.

• nafcillin

  nafcillin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• naldemedine

  quinidine increases levels of naldemedine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor naldemedine for potential adverse effects if coadministered with P-gp inhibitors.

• naratriptan

  naratriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• nelfinavir

  nelfinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• netupitant/palonosetron

  quinidine will increase the level or effect of netupitant/palonosetron by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Netupitant is mainly metabolized by CYP3A4; no dosage adjustment is required

• nevirapine

  nevirapine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• nifedipine

  nifedipine will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  nifedipine decreases levels of quinidine by increasing elimination. Use Caution/Monitor.
  
  quinidine increases levels of nifedipine by decreasing metabolism. Use Caution/Monitor.

• nintedanib

  quinidine increases levels of nintedanib by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. If nintedanib adverse effects occur, management may require interruption, dose reduction, or discontinuation of therapy .

• ofloxacin

  quinidine will increase the level or effect of ofloxacin by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• olanzapine

  dextromethorphan, olanzapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• oliceridine

  quinidine will increase the level or effect of oliceridine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. If concomitant use is necessary, may require less frequent oliceridine dosing. Closely monitor for respiratory depression and sedation and titrate subsequent doses accordingly. If inhibitor is discontinued, consider increase oliceridine dosage until stable drug effects are achieved. Monitor for signs of opioid withdrawal.

• olodaterol inhaled

  quinidine and olodaterol inhaled both increase QTc interval. Use Caution/Monitor. Drugs that prolong the QTc interval and may potentiate the effects of beta2 agonists on the cardiovascular system; increased risk of ventricular arrhythmias

• ombitasvir/paritaprevir/ritonavir & dasabuvir

  ombitasvir/paritaprevir/ritonavir & dasabuvir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Caution is warranted and therapeutic concentration monitoring (if available) is recommended for antiarrhythmics when coadministered with Viekira Pak

• oritavancin

  oritavancin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Oritavancin is a weak CYP3A4 inducer; caution if coadministered with CYP3A4 substrates that have a narrow therapeutic index

• osilodrostat

  osilodrostat and quinidine both increase QTc interval. Use Caution/Monitor.

• osimertinib

  osimertinib and quinidine both increase QTc interval. Use Caution/Monitor. Conduct periodic monitoring with ECGs and electrolytes in patients taking drugs known to prolong the QTc interval.

• ospemifene

  quinidine increases levels of ospemifene by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• oxaliplatin

  oxaliplatin will increase the level or effect of quinidine by Other (see comment). Use Caution/Monitor. Monitor for ECG changes if therapy is initiated in patients with drugs known to prolong QT interval.

• oxcarbazepine

  oxcarbazepine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• oxycodone

  quinidine decreases effects of oxycodone by decreasing metabolism. Use Caution/Monitor. Decreased conversion of hydrocodone to active metabolite morphine.

• ozanimod

  ozanimod and quinidine both increase QTc interval. Modify Therapy/Monitor Closely. The potential additive effects on heart rate, treatment with ozanimod should generally not be initiated in patients who are concurrently treated with QT prolonging drugs with known arrhythmogenic properties.

• palbociclib

  palbociclib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. The dose of sensitive CYP3A substrates with a narrow therapeutic index may need to be reduced if coadministered with palbociclib

• paliperidone

  dextromethorphan, paliperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• panobinostat

  panobinostat will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Panobinostat can increase the levels and effects of sensitive CYP2D6 substrates or those with a narrow therapeutic index CYP2D6.
  
  quinidine increases levels of panobinostat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Reduce panobinostat starting dose to 10 mg if coadministered with strong CYP3A4 inhibitors.

• paroxetine

  quinidine will increase the level or effect of paroxetine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Monitor patients for signs of paroxetine toxicity. Paroxetine doses may need to be reduced.

• pazopanib

  pazopanib increases levels of dextromethorphan by decreasing metabolism. Use Caution/Monitor.

• pasireotide

  quinidine and pasireotide both increase QTc interval. Modify Therapy/Monitor Closely.

• pazopanib

  quinidine and pazopanib both increase QTc interval. Modify Therapy/Monitor Closely.

• peginterferon alfa 2b

  peginterferon alfa 2b, dextromethorphan. Other (see comment). Use Caution/Monitor. Comment: When patients are administered peginterferon alpha-2b with CYP2D6 substrates, the therapeutic effect of these drugs may be altered. Peginterferon alpha-2b may increase or decrease levels of CYP2D6 substrate.

• pentazocine

  dextromethorphan and pentazocine both increase serotonin levels. Modify Therapy/Monitor Closely.

• pentobarbital

  pentobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• perhexiline

  quinidine will increase the level or effect of perhexiline by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• perphenazine

  dextromethorphan, perphenazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).
  
  quinidine will increase the level or effect of perphenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• phenobarbital

  phenobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• pimavanserin

  dextromethorphan, pimavanserin. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• phenytoin

  phenytoin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  phenytoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

• pimozide

  dextromethorphan, pimozide. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• pitolisant

  quinidine will increase the level or effect of pitolisant by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. If coadministered with strong CYP2D6 inhibitors, initiate pitolisant at 8.9 mg/day and increase after 7 days to maximum of 17.8 mg/day. For patients currently taking pitolisant, reduce pitolisant dose by half upon initiating strong CYP2D6 inhibitors.
  
  pitolisant will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Pitolisant is a borderline/weak inducer of CYP3A4. Monitor sensitive CYP3A4 substrates for reduced effectiveness if coadministered.

• ponatinib

  ponatinib increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• pramipexole

  quinidine will increase the level or effect of pramipexole by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• prednisone

  prednisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• primidone

  primidone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• prochlorperazine

  quinidine will increase the level or effect of prochlorperazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• promazine

  quinidine will increase the level or effect of promazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• promethazine

  quinidine will increase the level or effect of promethazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• quetiapine

  quetiapine, quinidine. Either increases toxicity of the other by QTc interval. Use Caution/Monitor. Avoid use with drugs that prolong QT and in patients with risk factors for prolonged QT interval. Postmarketing cases show QT prolongation with overdose in patients with concomitant illness or with drugs known to cause electrolyte imbalance or prolong QT.
  
  dextromethorphan, quetiapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• quinidine

  quinidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• quinine

  quinidine will increase the level or effect of quinine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.
  
  quinidine and quinine both increase QTc interval. Use Caution/Monitor.

• quinupristin/dalfopristin

  quinupristin/dalfopristin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• ribociclib

  ribociclib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Caution if ribociclib is coadministered with sensitive CYP3A4 substrates that have a narrow therapeutic index. Dose reduction for sensitive CYP3A4 substrates may be needed.

• rifapentine

  rifapentine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• rifaximin

  quinidine increases levels of rifaximin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• rilpivirine

  rilpivirine increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Rilpivirine should be used with caution when co-administered with a drug with a known risk of Torsade de Pointes.

• rimabotulinumtoxinB

  quinidine, rimabotulinumtoxinB. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Anticholinergics may enhance botulinum toxin effects. Closely monitor for increased neuromuscular blockade.

• risperidone

  dextromethorphan, risperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).
  
  quinidine will increase the level or effect of risperidone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• ritonavir

  ritonavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• rizatriptan

  rizatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• rivaroxaban

  quinidine increases levels of rivaroxaban by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Patients with renal impairment receiving rivaroxaban with drugs that are combined P-gp and weak or moderate CYP3A4 inhibitors may have significant increases in exposure compared with patients with normal renal function and no inhibitor use, since both pathways of rivaroxaban elimination are affected. Since these increases may increase bleeding risk, use rivaroxaban in this situation only if the potential benefit justifies the potential risk.

• rolapitant

  rolapitant will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Monitor for adverse reactions when unable to avoid coadministration with narrow therapeutic index CYP2D6 substrates.

• SAMe

  dextromethorphan and SAMe both increase serotonin levels. Modify Therapy/Monitor Closely.

• rucaparib

  rucaparib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Adjust dosage of CYP3A4 substrates, if clinically indicated.

• rufinamide

  rufinamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• sarecycline

  sarecycline will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor for toxicities of P-gp substrates that may require dosage reduction when coadministered with P-gp inhibitors.

• sarilumab

  sarilumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of cytokines such as IL-6. Elevated IL-6 concentration may down-regulate CYP activity, such as in patients with RA, and, hence, increase drug levels compared with subjects without RA. Blockade of IL-6 signaling by IL-6 antagonists (eg, sarilumab) might reverse the inhibitory effect of IL-6 and restore CYP activity, leading to decreased drug concentrations. Caution when initiating or discontinuing sarilumab if coadministered with CYP450 substrates, especially those with a narrow therapeutic index.

• saxagliptin

  quinidine will increase the level or effect of saxagliptin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Limit saxagliptin dose to 2.5 mg/day when coadministered with strong CYP3A4 inhibitors

• schisandra

  schisandra will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• secobarbital

  secobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• secukinumab

  secukinumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, secukinumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of secukinumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• selpercatinib

  selpercatinib increases toxicity of quinidine by QTc interval. Use Caution/Monitor.

• sevelamer

  sevelamer decreases levels of quinidine by increasing elimination. Use Caution/Monitor.

• siltuximab

  siltuximab, quinidine. Other (see comment). Use Caution/Monitor. Comment: CYP450 activity in the liver is down regulated by infection and inflammation stimuli including cytokines (eg, IL-6); inhibition of IL-6 by siltuximab may restore CYP450 enzymatic activity; caution if coadministered with CYP substrates that have a narrow therapeutic index.

• sodium bicarbonate

  sodium bicarbonate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

• sodium citrate/citric acid

  sodium citrate/citric acid will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

• sodium lactate

  sodium lactate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

• sodium sulfate/?magnesium sulfate/potassium chloride

  sodium sulfate/?magnesium sulfate/potassium chloride increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Consider predose and post-colonoscopy ECGs in patients at increased risk of serious cardiac arrhythmias. .

• sodium sulfate/potassium sulfate/magnesium sulfate

  sodium sulfate/potassium sulfate/magnesium sulfate increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Consider predose and post-colonoscopy ECGs in patients at increased risk of serious cardiac arrhythmias. .

• sofosbuvir/velpatasvir

  sofosbuvir/velpatasvir increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Velpatasvir inhibits CYP3A4. Caution if coadministered with drugs with narrow therapeutics indexes.

• sorafenib

  sorafenib and quinidine both increase QTc interval. Use Caution/Monitor.

• stiripentol

  stiripentol, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Stiripentol is a CYP3A4 inhibitor and inducer. Monitor CYP3A4 substrates coadministered with stiripentol for increased or decreased effects. CYP3A4 substrates may require dosage adjustment.
  
  stiripentol will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Consider reducing the dose of P-glycoprotein (P-gp) substrates, if adverse reactions are experienced when administered concomitantly with stiripentol.

• sulfamethoxazole

  quinidine will increase the level or effect of sulfamethoxazole by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• sumatriptan

  sumatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• sumatriptan intranasal

  sumatriptan intranasal and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• talazoparib

  quinidine will increase the level or effect of talazoparib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Talazoparib is a P-glycoprotein (P-gp) substrate; coadministration with P-gp inhibitors may increase talazoparib systemic exposure.

• tamoxifen

  quinidine decreases effects of tamoxifen by decreasing metabolism. Use Caution/Monitor. Inhibition of CYP2D6 metabolism to tamoxifen's active metabolite, endoxifen.

• tamsulosin

  quinidine increases levels of tamsulosin by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• tasimelteon

  quinidine will increase the level or effect of tasimelteon by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• tazemetostat

  tazemetostat will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of tazemetostat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• tecovirimat

  tecovirimat will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Tecovirimat is a weak CYP3A4 inducer. Monitor sensitive CYP3A4 substrates for effectiveness if coadministered.

• teduglutide

  teduglutide increases levels of quinidine by Other (see comment). Use Caution/Monitor. Comment: Teduglutide may increase absorption of concomitant PO medications; caution with with drugs requiring titration or those with a narrow therapeutic index; dose adjustment may be necessary.

• telotristat ethyl

  telotristat ethyl will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Telotristat ethyl induces CYP3A4 and may reduce systemic exposure of sensitive CYP3A4 substrates. Monitor for suboptimal efficacy and consider increasing the dose of the CYP3A4 substrate.

• teniposide

  quinidine will increase the level or effect of teniposide by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• tenofovir DF

  tenofovir DF, quinidine. Either increases levels of the other by decreasing renal clearance. Use Caution/Monitor.

• tetrabenazine

  quinidine increases effects of tetrabenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Decrease tetrabenazine dose by 50% when coadministered with strong CYP2D6 inhibitors.

• thiothixene

  dextromethorphan, thiothixene. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• tinidazole

  quinidine will increase the level or effect of tinidazole by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• tobramycin inhaled

  tobramycin inhaled and quinidine both increase nephrotoxicity and/or ototoxicity. Modify Therapy/Monitor Closely. Avoid concurrent or sequential use to decrease risk for ototoxicity

• tolterodine

  quinidine will increase the level or effect of tolterodine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• topiramate

  topiramate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• tramadol

  quinidine decreases effects of tramadol by decreasing metabolism. Use Caution/Monitor. Decreased conversion of tramadol to active metabolite.
  
  quinidine decreases effects of tramadol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Decreased conversion of tramadol to active metabolite.
  
  dextromethorphan and tramadol both increase serotonin levels. Modify Therapy/Monitor Closely.

• triamterene

  quinidine will increase the level or effect of triamterene by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• trifluoperazine

  dextromethorphan, trifluoperazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• triclabendazole

  triclabendazole and quinidine both increase QTc interval. Use Caution/Monitor.

• trifluoperazine

  quinidine will increase the level or effect of trifluoperazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• trimethoprim

  quinidine will increase the level or effect of trimethoprim by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• tropisetron

  quinidine will increase the level or effect of tropisetron by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• tucatinib

  tucatinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Consider reducing the dosage of P-gp substrates, where minimal concentration changes may lead to serious or life-threatening toxicities.

• umeclidinium bromide/vilanterol inhaled

  quinidine will increase the level or effect of umeclidinium bromide/vilanterol inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Vilanterol is a CYP3A4 substrate; coadministration with potent CYP3A4 inhibitors may increase systemic exposure

• ustekinumab

  ustekinumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, normalizing the formation of CYP450 enzymes. Upon initiation or discontinuation of ustekinumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• valbenazine

  quinidine will increase the level or effect of valbenazine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Consider reducing valbenazine dose based on tolerability if coadministered with a strong CYP2D6 inhibitor.

• vemurafenib

  vemurafenib and quinidine both increase QTc interval. Modify Therapy/Monitor Closely. Concomitant use of vemurafenib with drugs that prolong QT interval is not recommended. Quinidine may also increase vemurafenib levels.

• verapamil

  verapamil will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of verapamil by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• vilanterol/fluticasone furoate inhaled

  quinidine will increase the level or effect of vilanterol/fluticasone furoate inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Fluticasone furoate and vilanterol are both CYP3A4 substrates; coadministration with potent CYP3A4 inhibitors may increase systemic exposure

• voclosporin

  voclosporin, quinidine. Either increases effects of the other by QTc interval. Use Caution/Monitor.

• warfarin

  quinidine increases effects of warfarin by decreasing metabolism. Use Caution/Monitor. Dosage reduction of warfarin may be needed during concurrent administration of quinidine. Monitor INR and adjust the dosage accordingly.

• zafirlukast

  zafirlukast will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• ziprasidone

  dextromethorphan, ziprasidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

Minor (43)

• ambrisentan

  quinidine will increase the level or effect of ambrisentan by P-glycoprotein (MDR1) efflux transporter. Minor/Significance Unknown.

• amiodarone

  amiodarone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• antithrombin alfa

  quinidine increases effects of antithrombin alfa by decreasing metabolism. Minor/Significance Unknown.

• antithrombin III

  quinidine increases effects of antithrombin III by decreasing metabolism. Minor/Significance Unknown.

• argatroban

  quinidine increases effects of argatroban by decreasing metabolism. Minor/Significance Unknown.

• asenapine

  asenapine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• atracurium

  quinidine increases effects of atracurium by pharmacodynamic synergism. Minor/Significance Unknown.

• bemiparin

  quinidine increases effects of bemiparin by decreasing metabolism. Minor/Significance Unknown.

• bivalirudin

  quinidine increases effects of bivalirudin by decreasing metabolism. Minor/Significance Unknown.

• celecoxib

  celecoxib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• chloroquine

  chloroquine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• cimetidine

  cimetidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• cisatracurium

  quinidine increases effects of cisatracurium by pharmacodynamic synergism. Minor/Significance Unknown.

• dalteparin

  quinidine increases effects of dalteparin by decreasing metabolism. Minor/Significance Unknown.

• darifenacin

  darifenacin will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• diphenhydramine

  diphenhydramine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• dronedarone

  dronedarone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• enoxaparin

  quinidine increases effects of enoxaparin by decreasing metabolism. Minor/Significance Unknown.

• fondaparinux

  quinidine increases effects of fondaparinux by decreasing metabolism. Minor/Significance Unknown.

• haloperidol

  haloperidol will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• heparin

  quinidine increases effects of heparin by decreasing metabolism. Minor/Significance Unknown.

• imatinib

  imatinib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• lily of the valley

  quinidine, lily of the valley. Either increases toxicity of the other by pharmacodynamic synergism. Minor/Significance Unknown.

• maraviroc

  maraviroc will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• marijuana

  marijuana will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• nilotinib

  nilotinib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• onabotulinumtoxinA

  quinidine increases effects of onabotulinumtoxinA by pharmacodynamic synergism. Minor/Significance Unknown.

• pancuronium

  quinidine increases effects of pancuronium by pharmacodynamic synergism. Minor/Significance Unknown.

• parecoxib

  parecoxib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• perphenazine

  perphenazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• phenindione

  quinidine increases effects of phenindione by decreasing metabolism. Minor/Significance Unknown.

• propafenone

  propafenone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• protamine

  quinidine increases effects of protamine by decreasing metabolism. Minor/Significance Unknown.

• quinacrine

  quinacrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• ranolazine

  ranolazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• rapacuronium

  quinidine increases effects of rapacuronium by pharmacodynamic synergism. Minor/Significance Unknown.

• ritonavir

  ritonavir will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• rocuronium

  quinidine increases effects of rocuronium by pharmacodynamic synergism. Minor/Significance Unknown.

• sertraline

  sertraline will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• succinylcholine

  quinidine increases effects of succinylcholine by pharmacodynamic synergism. Minor/Significance Unknown.

• thioridazine

  thioridazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• tipranavir

  tipranavir will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• vecuronium

  quinidine increases effects of vecuronium by pharmacodynamic synergism. Minor/Significance Unknown.

• 5-HTP

  Monitor Closely (1)5-HTP and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• abametapir

  Serious - Use Alternative (1)abametapir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. For 2 weeks after abametapir application, avoid taking drugs that are CYP3A4 substrates. If not feasible, avoid use of abametapir.

• abiraterone

  Monitor Closely (1)abiraterone increases levels of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Avoid coadministration of abiraterone with substrates of CYP2D6. If alternative therapy cannot be used, exercise caution and consider a dose reduction of the CYP2D6 substrate.

• acetazolamide

  Monitor Closely (1)acetazolamide will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

• ado-trastuzumab emtansine

  Serious - Use Alternative (1)quinidine increases levels of ado-trastuzumab emtansine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. DM1, the cytotoxic component, is metabolized mainly by CYP3A4; strong CYP3A4 inhibitors may increase DM1 exposure and toxicity.

• afatinib

  Serious - Use Alternative (1)quinidine increases levels of afatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Reduce afatinib daily dose by 10 mg if not tolerated when coadministered with P-gp inhibitors.

• albuterol

  Monitor Closely (1)albuterol and quinidine both increase QTc interval. Use Caution/Monitor.

• alfuzosin

  Monitor Closely (1)quinidine and alfuzosin both increase QTc interval. Use Caution/Monitor.Serious - Use Alternative (1)alfuzosin and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• aliskiren

  Monitor Closely (1)quinidine will increase the level or effect of aliskiren by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• almotriptan

  Monitor Closely (1)almotriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• aluminum hydroxide

  Monitor Closely (1)aluminum hydroxide will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

• alvimopan

  Monitor Closely (1)quinidine will increase the level or effect of alvimopan by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• amantadine

  Monitor Closely (1)quinidine will increase the level or effect of amantadine by decreasing renal clearance. Use Caution/Monitor. Coadministration of quinine or quinidine with amantadine was shown to reduce the renal clearance of amantadine by ~30%.

• ambrisentan

  Minor (1)quinidine will increase the level or effect of ambrisentan by P-glycoprotein (MDR1) efflux transporter. Minor/Significance Unknown.

• amikacin

  Serious - Use Alternative (1)quinidine will increase the level or effect of amikacin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• amiloride

  Monitor Closely (1)amiloride, quinidine. Mechanism: unspecified interaction mechanism. Use Caution/Monitor. Increased risk of arrhythmias in pts. with ventricular tachycardia.

• amiodarone

  Serious - Use Alternative (2)quinidine will increase the level or effect of amiodarone by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.
  
  quinidine and amiodarone both increase QTc interval. Avoid or Use Alternate Drug.Minor (1)amiodarone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• amitriptyline

  Contraindicated (1)quinidine and amitriptyline both increase QTc interval. Contraindicated.Serious - Use Alternative (2)amitriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of amitriptyline by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• amobarbital

  Monitor Closely (1)amobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• amoxapine

  Contraindicated (1)quinidine and amoxapine both increase QTc interval. Contraindicated.Serious - Use Alternative (1)amoxapine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• antithrombin alfa

  Minor (1)quinidine increases effects of antithrombin alfa by decreasing metabolism. Minor/Significance Unknown.

• antithrombin III

  Minor (1)quinidine increases effects of antithrombin III by decreasing metabolism. Minor/Significance Unknown.

• apalutamide

  Serious - Use Alternative (1)apalutamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of apalutamide, a strong CYP3A4 inducer, with drugs that are CYP3A4 substrates can result in lower exposure to these medications. Avoid or substitute another drug for these medications when possible. Evaluate for loss of therapeutic effect if medication must be coadministered. Adjust dose according to prescribing information if needed.

• apixaban

  Serious - Use Alternative (1)quinidine will increase the level or effect of apixaban by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If taking apixaban dose >2.5 mg BID, decrease dose by 50% if coadministered with strong dual inhibitors of CYP3A4 and P-gp; if currently taking apixaban 2.5 mg PO BID, avoid coadministration with strong dual inhibitors of CYP3A4 and P-gp

• apomorphine

  Serious - Use Alternative (1)apomorphine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• aprepitant

  Monitor Closely (1)aprepitant will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• arformoterol

  Monitor Closely (1)arformoterol and quinidine both increase QTc interval. Use Caution/Monitor.

• argatroban

  Minor (1)quinidine increases effects of argatroban by decreasing metabolism. Minor/Significance Unknown.

• aripiprazole

  Monitor Closely (2)quinidine will increase the level or effect of aripiprazole by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.
  
  dextromethorphan, aripiprazole. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Serious - Use Alternative (1)aripiprazole and quinidine both increase QTc interval. Contraindicated.

• armodafinil

  Monitor Closely (2)armodafinil will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of armodafinil by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• arsenic trioxide

  Serious - Use Alternative (1)quinidine and arsenic trioxide both increase QTc interval. Avoid or Use Alternate Drug.

• artemether

  Monitor Closely (1)artemether and quinidine both increase QTc interval. Use Caution/Monitor.

• artemether/lumefantrine

  Contraindicated (1)quinidine and artemether/lumefantrine both increase QTc interval. Contraindicated.Monitor Closely (2)artemether/lumefantrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.
  
  artemether/lumefantrine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• asenapine

  Monitor Closely (1)dextromethorphan, asenapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Minor (1)asenapine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• atazanavir

  Monitor Closely (1)atazanavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• atomoxetine

  Monitor Closely (1)quinidine will increase the level or effect of atomoxetine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Reduced initial doses of atomoxetine are recommended with strong CYP2D6 inhibitors.Serious - Use Alternative (1)atomoxetine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• atorvastatin

  Serious - Use Alternative (1)quinidine will increase the level or effect of atorvastatin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• atracurium

  Minor (1)quinidine increases effects of atracurium by pharmacodynamic synergism. Minor/Significance Unknown.

• avapritinib

  Monitor Closely (1)quinidine will increase the level or effect of avapritinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• axitinib

  Serious - Use Alternative (1)quinidine increases levels of axitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If unable to avoid coadministration with strong CYP3A4 inhibitors, reduce axitinib dose by 50%.

• azithromycin

  Monitor Closely (1)quinidine and azithromycin both increase QTc interval. Modify Therapy/Monitor Closely.

• bazedoxifene/conjugated estrogens

  Serious - Use Alternative (1)quinidine will increase the level or effect of bazedoxifene/conjugated estrogens by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• bedaquiline

  Monitor Closely (1)quinidine and bedaquiline both increase QTc interval. Modify Therapy/Monitor Closely. ECG should be monitored closelySerious - Use Alternative (1)quinidine will increase the level or effect of bedaquiline by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of bedaquiline with strong CYP3A4 inhibitors for >14 consecutive days, unless the benefit of treatment outweighs the risk

• bemiparin

  Minor (1)quinidine increases effects of bemiparin by decreasing metabolism. Minor/Significance Unknown.

• benzhydrocodone/acetaminophen

  Monitor Closely (1)quinidine will increase the level or effect of benzhydrocodone/acetaminophen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Hydromorphone (<3% of the circulating parent hydrocodone [benzhydrocodone is prodrug of hydrocodone]) is mainly formed by CYP2D6 mediated O-demethylation of hydrocodone. Hydromorphone may contribute to the total analgesic effect of hydrocodone.

• berotralstat

  Monitor Closely (3)berotralstat will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor or titrate P-gp substrate dose if coadministered.
  
  berotralstat will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor or titrate substrate dose when berotralstat is coadministered with narrow therapeutic index drugs that are CYP3A substrates.
  
  quinidine increases levels of berotralstat by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Reduced berotralstat dose to 110 mg/day when coadministered with P-gp inhibitors.

• betrixaban

  Monitor Closely (1)quinidine increases levels of betrixaban by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Decrease betrixaban dose to 80 mg PO once, then 40 mg PO qDay if coadministered with a P-gp inhibitor.

• bivalirudin

  Minor (1)quinidine increases effects of bivalirudin by decreasing metabolism. Minor/Significance Unknown.

• blinatumomab

  Monitor Closely (1)blinatumomab increases levels of quinidine by decreasing metabolism. Modify Therapy/Monitor Closely. Treatment initiation causes transient release of cytokines that may suppress CYP450 enzymes; highest drug-drug interaction risk is during the first 9 days of the first cycle and the first 2 days of the 2nd cycle in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index.

• bosentan

  Monitor Closely (1)bosentan will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• bosutinib

  Monitor Closely (2)bosutinib increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  bosutinib and quinidine both increase QTc interval. Use Caution/Monitor.Serious - Use Alternative (2)quinidine increases levels of bosutinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Strong CYP3A4 inhibitors increases bosutinib plasma concentration ~5-fold.
  
  quinidine increases levels of bosutinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• bremelanotide

  Serious - Use Alternative (1)bremelanotide will decrease the level or effect of quinidine by Other (see comment). Avoid or Use Alternate Drug. Bremelanotide may slow gastric emptying and potentially reduces the rate and extent of absorption of concomitantly administered oral medications. Avoid use when taking any oral drug that is dependent on threshold concentrations for efficacy. Interactions listed are representative examples and do not include all possible clinical examples.

• brexpiprazole

  Monitor Closely (2)quinidine will increase the level or effect of brexpiprazole by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Administer half of the usual brexpiprazole dose when coadministered with strong CYP2D6 inhibitors. If also administered with a strong/moderate CYP3A4 inhibitor, administer a quarter of brexpiprazole dose. NOTE: In MDD clinical trials, brexpiprazole dosage was not adjusted for strong CYP2D6 inhibitors (eg, paroxetine, fluoxetine); thus, CYP considerations are already factored into general dosing recommendations and brexpiprazole may be administered without dosage adjustment in patients with MDD.
  
  quinidine will increase the level or effect of brexpiprazole by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Administer half of the usual brexpiprazole dose when coadministered with strong CYP3A4 inhibitors. If also administered with a strong/moderate CYP2D6 inhibitor, administer a quarter of brexpiprazole dose.

• brigatinib

  Serious - Use Alternative (1)brigatinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Brigatinib induces CYP3A4 in vitro. Coadministration with CYP3A4 substrates, particularly those with a narrow therapeutic index, can result in decreased concentrations and loss of efficacy. If unable to avoid coadministration, monitor CYP3A4 substrate levels and adjust dose as needed.

• brodalumab

  Monitor Closely (1)brodalumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, brodalumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of brodalumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• budesonide

  Monitor Closely (1)budesonide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine will increase the level or effect of budesonide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• bupivacaine implant

  Monitor Closely (1)quinidine, bupivacaine implant. Either increases toxicity of the other by Other (see comment). Use Caution/Monitor. Comment: Local anesthetics may increase the risk of developing methemoglobinemia when concurrently exposed to drugs that also cause methemoglobinemia.

• bupropion

  Monitor Closely (1)bupropion will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• buspirone

  Serious - Use Alternative (1)buspirone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• butabarbital

  Monitor Closely (1)butabarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• butalbital

  Monitor Closely (1)butalbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• cabozantinib

  Serious - Use Alternative (1)quinidine will increase the level or effect of cabozantinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of cabozantinib with strong CYP3A4 inhibitors. If a strong CYP3A4 inhibitor is required, decrease cabozantinib dose by 40 mg/day (Cometriq) or by 20 mg/day (Cabometyx). Resume previous dose 2-3 days after strong CYP3A4 inhibitor discontinued.

• calcium carbonate

  Monitor Closely (1)calcium carbonate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

• capecitabine

  Monitor Closely (1)capecitabine and quinidine both increase QTc interval. Use Caution/Monitor.

• carbamazepine

  Serious - Use Alternative (1)carbamazepine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• cariprazine

  Monitor Closely (2)quinidine will increase the level or effect of cariprazine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration with strong CYP3A4 inhibitors requires cariprazine dose reduction. See Dosage Modification section in drug monograph.
  
  dextromethorphan, cariprazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• carvedilol

  Serious - Use Alternative (1)quinidine will increase the level or effect of carvedilol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• celecoxib

  Minor (1)celecoxib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• cenobamate

  Monitor Closely (1)cenobamate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Increase dose of CYP3A4 substrate, as needed, when coadministered with cenobamate.

• ceritinib

  Monitor Closely (1)quinidine increases levels of ceritinib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.Serious - Use Alternative (3)ceritinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.
  
  quinidine increases levels of ceritinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid if possible; if concomitant use is unavoidable, reduce ceritinib dose by ~33%; after discontinuation of strong CYP3A inhibitor, resume at previous dose.
  
  ceritinib increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concurrent use of CYP3A substrates known to have narrow therapeutic indices or substrates primarily metabolized by CYP3A during treatment with ceritinib; if use of these medications is unavoidable, consider dose.

• chloroquine

  Contraindicated (1)quinidine will increase the level or effect of chloroquine by Other (see comment). Contraindicated. Quinidine is contraindicated in patients receiving drugs that both prolong the QT interval and are metabolized by CYP2D6, such as chloroquineSerious - Use Alternative (1)chloroquine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.Minor (1)chloroquine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• chlorpromazine

  Contraindicated (1)chlorpromazine and quinidine both increase QTc interval. Contraindicated.Monitor Closely (1)quinidine will increase the level or effect of chlorpromazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine, chlorpromazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• cimetidine

  Serious - Use Alternative (2)quinidine will increase the level or effect of cimetidine by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.
  
  cimetidine will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.Minor (1)cimetidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• ciprofloxacin

  Monitor Closely (1)ciprofloxacin and quinidine both increase QTc interval. Use Caution/Monitor. Ciprofloxacin elicits minimal effects on QT interval. Caution if used in combination with other drugs known to affect QT interval or in patients with other risk factors.

• cisatracurium

  Minor (1)quinidine increases effects of cisatracurium by pharmacodynamic synergism. Minor/Significance Unknown.

• citalopram

  Monitor Closely (1)quinidine and citalopram both increase QTc interval. Use Caution/Monitor. ECG monitoring is recommended, along with drugs that may prolong the QT interval.Serious - Use Alternative (1)citalopram and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Combination may increase risk of serotonin syndrome or neuroleptic malignant syndrome-like reactions.

• clarithromycin

  Contraindicated (1)quinidine and clarithromycin both increase QTc interval. Contraindicated.Serious - Use Alternative (1)clarithromycin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• clobazam

  Monitor Closely (1)clobazam will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Lower doses of drugs metabolized by CYP2D6 may be required when used concomitantly.

• clobetasone

  Serious - Use Alternative (1)quinidine will increase the level or effect of clobetasone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• clomipramine

  Contraindicated (1)quinidine and clomipramine both increase QTc interval. Contraindicated.Serious - Use Alternative (2)clomipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of clomipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• clozapine

  Monitor Closely (1)dextromethorphan, clozapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Serious - Use Alternative (1)clozapine and quinidine both increase QTc interval. Contraindicated.

• cobicistat

  Monitor Closely (2)cobicistat will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  cobicistat will increase the level or effect of quinidine by Other (see comment). Modify Therapy/Monitor Closely. Quinidine is a substrate of CYP3A4 and P-gp, and inhibits CYP2D6 and P-gp; cobicistat is a substrate and inhibitor of both isoenzymes and a P-gp inhibitor

• cobimetinib

  Contraindicated (1)quinidine will increase the level or effect of cobimetinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Avoid coadministration with strong CYP3A4 inhibitors with (increases cobimetinib systemic exposure by 6.7-fold).

• cocaine

  Monitor Closely (1)cocaine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• codeine

  Monitor Closely (1)quinidine will decrease the level or effect of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Prevents conversion of codeine to its active metabolite morphine.

• colchicine

  Serious - Use Alternative (1)quinidine will increase the level or effect of colchicine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Avoid use of colchicine with P-gp inhibitors. If coadministration is necessary, decrease colchicine dose or frequency as recommended in prescribing information. Use of any colchicine product in conjunction with P-gp inhibitors is contraindicated in patients with renal or hepatic impairment.

• conivaptan

  Contraindicated (1)quinidine will increase the level or effect of conivaptan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of conivaptan with strong CYP3A4 inhibitors is contraindicated.Monitor Closely (1)conivaptan will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• conjugated estrogens

  Serious - Use Alternative (1)quinidine will increase the level or effect of conjugated estrogens by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• conjugated estrogens, vaginal

  Serious - Use Alternative (1)quinidine will increase the level or effect of conjugated estrogens, vaginal by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• cortisone

  Monitor Closely (1)cortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine will increase the level or effect of cortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• crizotinib

  Serious - Use Alternative (2)crizotinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.
  
  crizotinib increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of crizotinib with CYP3A substrates with narrow therapeutic indices should be avoided. ECG monitoring is recommended, along with drugs that may prolong the QT interval.

• crofelemer

  Monitor Closely (1)crofelemer increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Crofelemer has the potential to inhibit CYP3A4 at concentrations expected in the gut; unlikely to inhibit systemically because minimally absorbed.

• cyclosporine

  Monitor Closely (2)quinidine will increase the level or effect of cyclosporine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  cyclosporine will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• dabigatran

  Monitor Closely (1)quinidine will increase the level or effect of dabigatran by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Atrial fibrillation: Avoid coadministering dabigatran with P-gp inhibitors if CrCl <30 mL/min. DVT/PE treatment: Avoid coadministering dabigatran with P-gp inhibitors if CrCl <50 mL/min

• dabrafenib

  Monitor Closely (1)dabrafenib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely.Serious - Use Alternative (1)quinidine increases levels of dabrafenib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• dalteparin

  Minor (1)quinidine increases effects of dalteparin by decreasing metabolism. Minor/Significance Unknown.

• dapsone topical

  Serious - Use Alternative (1)quinidine, dapsone topical. unspecified interaction mechanism. Avoid or Use Alternate Drug. Avoid coadministration of dapsone topical with oral dapsone or antimalarial medications because of the potential for hemolytic reactions.

• darifenacin

  Monitor Closely (1)darifenacin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Minor (1)darifenacin will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• darunavir

  Monitor Closely (1)darunavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• dasatinib

  Monitor Closely (1)dasatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine and dasatinib both increase QTc interval. Avoid or Use Alternate Drug.

• daunorubicin

  Monitor Closely (1)quinidine will increase the level or effect of daunorubicin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• deferasirox

  Monitor Closely (1)deferasirox will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• deflazacort

  Serious - Use Alternative (1)quinidine will increase the level or effect of deflazacort by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• degarelix

  Monitor Closely (1)degarelix and quinidine both increase QTc interval. Use Caution/Monitor.

• desipramine

  Contraindicated (1)quinidine and desipramine both increase QTc interval. Contraindicated.Serious - Use Alternative (2)quinidine will increase the level or effect of desipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  desipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• desvenlafaxine

  Monitor Closely (1)desvenlafaxine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Desvenlafaxine inhibits CYP2D6; with higher desvenlafaxine doses (ie, 400 mg) decrease the CYP2D6 substrate dose by up to 50%; no dosage adjustment needed with desvenlafaxine doses <100 mgSerious - Use Alternative (1)dextromethorphan and desvenlafaxine both increase serotonin levels. Avoid or Use Alternate Drug.

• deutetrabenazine

  Monitor Closely (2)quinidine will increase the level or effect of deutetrabenazine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Strong CYP2D6 inhibitors increase the systemic exposure to the active dihydro-metabolites of deutetrabenazine by approximately 3-fold. Do not exceed 18 mg/dose and 36 mg/day of deutetrabenazine if coadministered with strong CYP2D6 inhibitors.
  
  quinidine and deutetrabenazine both increase QTc interval. Modify Therapy/Monitor Closely. Quinidine is a strong CYP2D6 inhibitor and also prolongs the QT interval. Strong CYP2D6 inhibitors increase the systemic exposure to the active dihydro-metabolites of deutetrabenazine by approximately 3-fold. Do not exceed 18 mg/dose and 36 mg/day of deutetrabenazine if coadministered with strong CYP2D6 inhibitors.

• dexamethasone

  Monitor Closely (1)dexamethasone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine will increase the level or effect of dexamethasone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• dexfenfluramine

  Monitor Closely (2)dexfenfluramine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.
  
  quinidine will increase the level or effect of dexfenfluramine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• dextroamphetamine

  Monitor Closely (2)quinidine will increase the level or effect of dextroamphetamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.
  
  dextroamphetamine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• dextromethorphan

  Monitor Closely (1)quinidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• DHEA, herbal

  Monitor Closely (1)DHEA, herbal will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• dienogest/estradiol valerate

  Monitor Closely (1)quinidine will increase the level or effect of dienogest/estradiol valerate by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor for potential adverse effects such as nausea, irregular uterine bleeding, breast tenderness and headache.

• digoxin

  Serious - Use Alternative (2)quinidine will increase the level or effect of digoxin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of digoxin by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

• dihydroergotamine

  Contraindicated (1)quinidine increases levels of dihydroergotamine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.Monitor Closely (1)dextromethorphan and dihydroergotamine both increase serotonin levels. Modify Therapy/Monitor Closely.

• dihydroergotamine intranasal

  Contraindicated (1)quinidine increases levels of dihydroergotamine intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.Monitor Closely (1)dextromethorphan and dihydroergotamine intranasal both increase serotonin levels. Modify Therapy/Monitor Closely.

• diltiazem

  Monitor Closely (2)diltiazem will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of diltiazem by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• diphenhydramine

  Serious - Use Alternative (1)quinidine, diphenhydramine. Mechanism: pharmacodynamic synergism. Contraindicated. Risk of prolonged QTc interval.Minor (1)diphenhydramine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• disopyramide

  Contraindicated (1)quinidine and disopyramide both increase QTc interval. Contraindicated.

• docetaxel

  Serious - Use Alternative (1)quinidine will increase the level or effect of docetaxel by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• dofetilide

  Contraindicated (2)quinidine and dofetilide both increase QTc interval. Contraindicated.
  
  quinidine, dofetilide. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Additive cardiac effects.Serious - Use Alternative (2)dofetilide increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of dofetilide by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

• dolasetron

  Serious - Use Alternative (1)quinidine and dolasetron both increase QTc interval. Avoid or Use Alternate Drug.

• donepezil

  Monitor Closely (1)quinidine will increase the level or effect of donepezil by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• dosulepin

  Contraindicated (1)quinidine and dosulepin both increase QTc interval. Contraindicated.

• doxepin

  Contraindicated (1)quinidine and doxepin both increase QTc interval. Contraindicated.Serious - Use Alternative (2)quinidine will increase the level or effect of doxepin by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Both agents increase QTc interval.
  
  doxepin and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• doxorubicin

  Monitor Closely (1)quinidine will increase the level or effect of doxorubicin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• doxorubicin liposomal

  Monitor Closely (1)quinidine will increase the level or effect of doxorubicin liposomal by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• dronedarone

  Contraindicated (1)quinidine and dronedarone both increase QTc interval. Contraindicated.Monitor Closely (1)dronedarone will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Minor (1)dronedarone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• droperidol

  Contraindicated (1)quinidine and droperidol both increase QTc interval. Contraindicated.

• dulaglutide

  Monitor Closely (1)dulaglutide, quinidine. Other (see comment). Use Caution/Monitor. Comment: Dulaglutide slows gastric emptying and may impact absorption of concomitantly administered oral medications; be particularly cautious when coadministered with drugs that have a narrow therapeutic index.

• duloxetine

  Serious - Use Alternative (3)duloxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of duloxetine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  duloxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• dupilumab

  Monitor Closely (1)dupilumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, dupilumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of dupilumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• duvelisib

  Monitor Closely (2)quinidine will increase the level or effect of duvelisib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  duvelisib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration with duvelisib increases AUC of a sensitive CYP3A4 substrate which may increase the risk of toxicities of these drugs. Consider reducing the dose of the sensitive CYP3A4 substrate and monitor for signs of toxicities of the coadministered sensitive CYP3A substrate.

• edoxaban

  Serious - Use Alternative (1)quinidine will increase the level or effect of edoxaban by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Dose adjustment may be required with strong P-gp inhibitors. DVT/PE treatment: Decrease dose to 30 mg PO once daily. NVAF: No dose reduction recommended

• efavirenz

  Monitor Closely (1)efavirenz will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• elagolix

  Monitor Closely (2)elagolix will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  elagolix decreases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Elagolix is a weak-to-moderate CYP3A4 inducer. Monitor CYP3A substrates if coadministered. Consider increasing CYP3A substrate dose if needed.

• eletriptan

  Monitor Closely (1)eletriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• eliglustat

  Contraindicated (2)quinidine will increase the level or effect of eliglustat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors are contraindicated with eliglustat poor or intermediate metabolizers; reduce eliglustat dose from 84 mg BID to 84 mg once daily in extensive metabolizers; eliglustat is contraindiated if strong or moderate CYP2D6 inhibitors are given concomitantly with strong or moderate CYP3A inhibitors
  
  quinidine increases levels of eliglustat by affecting hepatic enzyme CYP2D6 metabolism. Contraindicated. If coadministered with strong or moderate CYP2D6 inhibitors, reduce eliglustat dose from 84 mg BID to 84 mg once daily in extensive and intermediate metabolizers; eliglustat is contraindiated if strong or moderate CYP2D6 inhibitors are given concomitantly with strong or moderate CYP3A inhibitors.Monitor Closely (1)eliglustat increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Monitor therapeutic drug concentrations, as indicated, or consider reducing the dosage of the P-gp substrate and titrate to clinical effect.

• eluxadoline

  Monitor Closely (2)quinidine increases levels of eluxadoline by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. As a precautionary measure due to incomplete information on the metabolism of eluxadoline, use caution when coadministered with strong CYP2D6 inhibitors.
  
  eluxadoline increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Caution when CYP3A substrates that have a narrow therapeutic index are coadministered with eluxadoline.

• elvitegravir

  Monitor Closely (1)quinidine increases levels of elvitegravir by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Elvitegravir is a CYP3A4 substrate; if coadministered with strong CYP3A4 inhibitors may increase levels.

• elvitegravir/cobicistat/emtricitabine/tenofovir DF

  Monitor Closely (1)elvitegravir/cobicistat/emtricitabine/tenofovir DF increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Cobicistat is a CYP3A4 inhibitor; contraindicated with CYP3A4 substrates for which elevated plasma concentrations are associated with serious and/or life-threatening events.

• encainide

  Monitor Closely (1)quinidine will increase the level or effect of encainide by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• encorafenib

  Monitor Closely (1)encorafenib, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Encorafenib both inhibits and induces CYP3A4 at clinically relevant plasma concentrations. Coadministration of encorafenib with sensitive CYP3A4 substrates may result in increased toxicity or decreased efficacy of these agents.Serious - Use Alternative (1)encorafenib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Encorafenib is associated with dose-dependent QTc interval prolongation. Avoid with drugs known to prolong QT interval.

• enoxaparin

  Minor (1)quinidine increases effects of enoxaparin by decreasing metabolism. Minor/Significance Unknown.

• entrectinib

  Serious - Use Alternative (1)quinidine and entrectinib both increase QTc interval. Avoid or Use Alternate Drug.

• enzalutamide

  Monitor Closely (1)enzalutamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• epinephrine

  Contraindicated (1)epinephrine and quinidine both increase QTc interval. Contraindicated.

• epinephrine racemic

  Contraindicated (1)epinephrine racemic and quinidine both increase QTc interval. Contraindicated.

• erdafitinib

  Serious - Use Alternative (3)erdafitinib, quinidine. Other (see comment). Avoid or Use Alternate Drug. Comment: Avoid coadministration during initial dosing adjustment period (ie, first 21 days). Increases in serum phosphate levels are a pharmacodynamic effect of FGFR inhibition. Serum phosphate binders may obscure decisions regarding initial dosage increase.
  
  erdafitinib, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration with erdafitinib and sensitive CYP3A4 substrates with narrow therapeutic indices. Erdafitinib may altered plasma concentrations of CYP3A4 substrates, leading to either loss of activity or increased toxicity of the substrate.
  
  erdafitinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If coadministration unavoidable, separate administration by at least 6 hr before or after administration of P-gp substrates with narrow therapeutic index.

• ergotamine

  Monitor Closely (1)dextromethorphan and ergotamine both increase serotonin levels. Modify Therapy/Monitor Closely.

• eribulin

  Serious - Use Alternative (1)eribulin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Potential for enhanced QTc-prolonging effects; if concurrent use is necessary then ECG monitoring is recommended.

• erlotinib

  Serious - Use Alternative (1)quinidine will increase the level or effect of erlotinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• erythromycin base

  Contraindicated (1)quinidine and erythromycin base both increase QTc interval. Contraindicated.Serious - Use Alternative (1)erythromycin base will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• erythromycin ethylsuccinate

  Contraindicated (1)quinidine and erythromycin ethylsuccinate both increase QTc interval. Contraindicated.Serious - Use Alternative (1)erythromycin ethylsuccinate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• erythromycin lactobionate

  Contraindicated (1)quinidine and erythromycin lactobionate both increase QTc interval. Contraindicated.Serious - Use Alternative (1)erythromycin lactobionate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• erythromycin stearate

  Contraindicated (1)quinidine and erythromycin stearate both increase QTc interval. Contraindicated.Serious - Use Alternative (1)erythromycin stearate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• escitalopram

  Serious - Use Alternative (2)escitalopram increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.
  
  escitalopram and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• eslicarbazepine acetate

  Monitor Closely (1)eslicarbazepine acetate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• estradiol

  Serious - Use Alternative (1)quinidine will increase the level or effect of estradiol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• estrogens conjugated synthetic

  Serious - Use Alternative (1)quinidine will increase the level or effect of estrogens conjugated synthetic by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• estrogens esterified

  Monitor Closely (1)quinidine will increase the level or effect of estrogens esterified by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely.

• estropipate

  Serious - Use Alternative (1)quinidine will increase the level or effect of estropipate by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• ethinylestradiol

  Serious - Use Alternative (1)quinidine will increase the level or effect of ethinylestradiol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• ethotoin

  Monitor Closely (1)ethotoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

• etoposide

  Monitor Closely (1)quinidine will increase the level or effect of etoposide by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• etravirine

  Monitor Closely (1)etravirine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• everolimus

  Serious - Use Alternative (1)quinidine will increase the level or effect of everolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• ezogabine

  Monitor Closely (1)ezogabine, quinidine. Either increases toxicity of the other by QTc interval. Use Caution/Monitor. Slight and transient QT-prolongation observed with ezogabine, particularly when dose titrated to 1200 mg/day. QT interval should be monitored when ezogabine is prescribed with agents known to increase QT interval.

• fedratinib

  Monitor Closely (1)fedratinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Adjust dose of drugs that are CYP3A4 substrates as necessary.

• fenfluramine

  Monitor Closely (2)fenfluramine, dextromethorphan. Either increases effects of the other by serotonin levels. Use Caution/Monitor. Coadministration with drugs that increase serotoninergic effects may increase the risk of serotonin syndrome.
  
  dextromethorphan and fenfluramine both increase serotonin levels. Modify Therapy/Monitor Closely.

• fentanyl

  Serious - Use Alternative (1)quinidine will increase the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

• fentanyl intranasal

  Serious - Use Alternative (1)quinidine will increase the level or effect of fentanyl intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

• fentanyl transdermal

  Serious - Use Alternative (1)quinidine will increase the level or effect of fentanyl transdermal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

• fentanyl transmucosal

  Serious - Use Alternative (1)quinidine will increase the level or effect of fentanyl transmucosal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

• ferric maltol

  Monitor Closely (1)ferric maltol, quinidine. Either increases levels of the other by unspecified interaction mechanism. Modify Therapy/Monitor Closely. Coadministration of ferric maltol with certain oral medications may decrease the bioavailability of either ferric maltol and some oral drugs. For oral drugs where reductions in bioavailability may cause clinically significant effects on its safety or efficacy, separate administration of ferric maltol from these drugs. Duration of separation may depend on the absorption of the medication concomitantly administered (eg, time to peak concentration, whether the drug is an immediate or extended release product).

• fesoterodine

  Monitor Closely (1)quinidine will increase the level or effect of fesoterodine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• fexinidazole

  Serious - Use Alternative (2)fexinidazole and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Avoid coadministration of fexinidazole with drugs known to block potassium channels and/or prolong QT interval.
  
  fexinidazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Fexinidazole inhibits CYP3A4. Coadministration may increase risk for adverse effects of CYP3A4 substrates.

• fexofenadine

  Monitor Closely (1)quinidine will increase the level or effect of fexofenadine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• finerenone

  Monitor Closely (1)quinidine will increase the level or effect of finerenone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Monitor serum potassium during initiation and dosage adjustment of either finererone or weak CYP3A4 inhibitors. Adjust finererone dosage as needed.

• fingolimod

  Contraindicated (1)fingolimod increases effects of quinidine by pharmacodynamic synergism. Contraindicated. Due to increased risk of bradycardia, AV block, and torsade de pointes, concomitant use is contraindicated.

• flecainide

  Serious - Use Alternative (2)quinidine and flecainide both increase QTc interval. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of flecainide by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• flibanserin

  Contraindicated (1)quinidine will increase the level or effect of flibanserin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of flibanserin with moderate or strong CYP3A4 inhibitors is contraindicated. Severe hypotension or syncope can occur.

• fluconazole

  Contraindicated (2)fluconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.
  
  quinidine and fluconazole both increase QTc interval. Contraindicated.

• fludrocortisone

  Monitor Closely (1)fludrocortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine will increase the level or effect of fludrocortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• fluoxetine

  Serious - Use Alternative (4)quinidine will increase the level or effect of fluoxetine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  fluoxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  fluoxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  quinidine and fluoxetine both increase QTc interval. Avoid or Use Alternate Drug.

• fluphenazine

  Contraindicated (1)fluphenazine and quinidine both increase QTc interval. Contraindicated.Monitor Closely (2)quinidine will increase the level or effect of fluphenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.
  
  dextromethorphan, fluphenazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Serious - Use Alternative (1)quinidine, fluphenazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• fluticasone furoate

  Monitor Closely (1)quinidine will increase the level or effect of fluticasone furoate by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Strong CYP3A4 inhibitors may increase fluticasone systemic exposure

• fluticasone inhaled

  Monitor Closely (1)quinidine will increase the level or effect of fluticasone inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Strong CYP3A4 inhibitors may increase fluticasone systemic exposure

• fluticasone intranasal

  Serious - Use Alternative (1)quinidine will increase the level or effect of fluticasone intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Strong CYP3A4 inhibitors may increase systemic corticosteroid adverse effects; monitor for signs/symptoms of high corticosteroid concentrations including Cushing type signs/symptoms.

• fluvoxamine

  Monitor Closely (1)quinidine will increase the level or effect of fluvoxamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)fluvoxamine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.
  
  fluvoxamine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• fondaparinux

  Minor (1)quinidine increases effects of fondaparinux by decreasing metabolism. Minor/Significance Unknown.

• formoterol

  Serious - Use Alternative (1)quinidine and formoterol both increase QTc interval. Avoid or Use Alternate Drug.

• fosamprenavir

  Monitor Closely (1)fosamprenavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)fosamprenavir increases levels of quinidine by unspecified interaction mechanism. Avoid or Use Alternate Drug.

• foscarnet

  Serious - Use Alternative (1)quinidine and foscarnet both increase QTc interval. Avoid or Use Alternate Drug.

• fosphenytoin

  Monitor Closely (2)fosphenytoin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  fosphenytoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

• fostamatinib

  Monitor Closely (1)fostamatinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Concomitant use of fostamatinib may increase concentrations of P-gp substrates. Monitor for toxicities of the P-gp substrate drug that may require dosage reduction when given concurrently with fostamatinib.

• fostemsavir

  Monitor Closely (1)quinidine and fostemsavir both increase QTc interval. Use Caution/Monitor. QTc prolongation reported with higher than recommended doses of fostemsavir.

• frovatriptan

  Monitor Closely (1)frovatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• galantamine

  Monitor Closely (1)quinidine will increase the level or effect of galantamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• gefitinib

  Monitor Closely (1)quinidine increases levels of gefitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration of strong CYP3A4 inhibitors may increase risk for gefitinib adverse effects.

• gemtuzumab

  Monitor Closely (1)quinidine and gemtuzumab both increase QTc interval. Use Caution/Monitor.

• gentamicin

  Serious - Use Alternative (1)quinidine will increase the level or effect of gentamicin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• glasdegib

  Serious - Use Alternative (1)quinidine and glasdegib both increase QTc interval. Avoid or Use Alternate Drug. If coadministration unavoidable, monitor for increased risk of QTc interval prolongation.

• glecaprevir/pibrentasvir

  Monitor Closely (2)quinidine will increase the level or effect of glecaprevir/pibrentasvir by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.
  
  glecaprevir/pibrentasvir will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• glycerol phenylbutyrate

  Monitor Closely (1)glycerol phenylbutyrate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Glycerol phenylbutyrate is a weak inducer of CYP3A4. Monitor for decreased efficacy of CYP3A4 substrates that have a narrow therapeutic index.

• goserelin

  Contraindicated (1)goserelin increases toxicity of quinidine by QTc interval. Contraindicated. Increases risk of torsades de pointes.

• grapefruit

  Monitor Closely (1)grapefruit will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)grapefruit will increase the level or effect of dextromethorphan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• griseofulvin

  Monitor Closely (1)griseofulvin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• guselkumab

  Monitor Closely (1)guselkumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, normalizing the formation of CYP450 enzymes. Upon initiation or discontinuation of guselkumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• haloperidol

  Contraindicated (1)quinidine and haloperidol both increase QTc interval. Contraindicated.Monitor Closely (1)dextromethorphan, haloperidol. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Serious - Use Alternative (1)quinidine will increase the level or effect of haloperidol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.Minor (1)haloperidol will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• hawthorn

  Monitor Closely (1)hawthorn increases effects of quinidine by pharmacodynamic synergism. Use Caution/Monitor.

• henbane

  Monitor Closely (1)henbane, quinidine. unspecified interaction mechanism. Use Caution/Monitor. Combination not recommended by British Herbal Medicine Association.

• heparin

  Minor (1)quinidine increases effects of heparin by decreasing metabolism. Minor/Significance Unknown.

• histrelin

  Serious - Use Alternative (1)histrelin increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

• hydrochlorothiazide

  Monitor Closely (1)quinidine will increase the level or effect of hydrochlorothiazide by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• hydrocodone

  Monitor Closely (1)quinidine will increase the level or effect of hydrocodone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Hydromorphone (<3% of the circulating parent hydrocodone) is mainly formed by CYP2D6 mediated O-demethylation of hydrocodone. Hydromorphone may contribute to the total analgesic effect of hydrocodone.

• hydrocortisone

  Monitor Closely (1)hydrocortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine will increase the level or effect of hydrocortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• hydromorphone

  Serious - Use Alternative (1)quinidine will increase the level or effect of hydromorphone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• hydroxychloroquine sulfate

  Serious - Use Alternative (1)hydroxychloroquine sulfate and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• hydroxyzine

  Serious - Use Alternative (1)hydroxyzine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

• ibrutinib

  Serious - Use Alternative (1)quinidine increases levels of ibrutinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concomitant use of ibrutinib and strong CYP3A4 inhibitors. If a strong CYP3A4 inhibitor must be used short-term (eg, anti-infectives for =7 days), interrupt ibrutinib therapy until strong CYP3A4 inhibitor is discontinued.

• ibutilide

  Contraindicated (1)quinidine and ibutilide both increase QTc interval. Contraindicated.

• idelalisib

  Serious - Use Alternative (2)quinidine will increase the level or effect of idelalisib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministered with strong CYP3A inhibitors, monitor for signs of idelalisib toxicity; follow recommendations for dosage modifications if adverse reactions occur
  
  idelalisib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Idelalisib is a strong CYP3A inhibitor; avoid coadministration with sensitive CYP3A substrates

• iloperidone

  Monitor Closely (2)iloperidone increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Iloperidone is a time-dependent CYP3A inhibitor and may lead to increased plasma levels of drugs predominantly eliminated by CYP3A4.
  
  dextromethorphan, iloperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Serious - Use Alternative (2)quinidine and iloperidone both increase QTc interval. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of iloperidone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• imatinib

  Serious - Use Alternative (1)quinidine will increase the level or effect of imatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.Minor (1)imatinib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• imipramine

  Contraindicated (1)quinidine and imipramine both increase QTc interval. Contraindicated.Serious - Use Alternative (2)quinidine will increase the level or effect of imipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  imipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• incobotulinumtoxinA

  Monitor Closely (1)quinidine, incobotulinumtoxinA. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Use of anticholinergic drugs after administration of botulinum toxin-containing products may potentiate systemic anticholinergic effects.

• indacaterol, inhaled

  Monitor Closely (1)indacaterol, inhaled, quinidine. QTc interval. Use Caution/Monitor. Drugs that are known to prolong the QTc interval may have an increased the risk of ventricular arrhythmias.

• indapamide

  Contraindicated (1)quinidine and indapamide both increase QTc interval. Contraindicated.

• indinavir

  Monitor Closely (1)indinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine will increase the level or effect of indinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• inotuzumab

  Serious - Use Alternative (1)inotuzumab and quinidine both increase QTc interval. Avoid or Use Alternate Drug. If unable to avoid concomitant use, obtain ECGs and electrolytes before and after initiation of any drug known to prolong QTc, and periodically monitor as clinically indicated during treatment.

• isocarboxazid

  Contraindicated (1)isocarboxazid and dextromethorphan both increase serotonin levels. Contraindicated.

• isoniazid

  Monitor Closely (2)dextromethorphan and isoniazid both increase serotonin levels. Modify Therapy/Monitor Closely.
  
  isoniazid will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• istradefylline

  Monitor Closely (2)istradefylline will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Istradefylline 40 mg/day increased peak levels and AUC of CYP3A4 substrates in clinical trials. This effect was not observed with istradefylline 20 mg/day. Consider dose reduction of sensitive CYP3A4 substrates.
  
  istradefylline will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Istradefylline 40 mg/day increased peak levels and AUC of P-gp substrates in clinical trials. Consider dose reduction of sensitive P-gp substrates.

• itraconazole

  Contraindicated (3)itraconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Both drugs will increase QT interval. Coadministration of quinidine and itraconazole is contraindicated during and 2 weeks after itraconazole treatment.
  
  quinidine will increase the level or effect of itraconazole by P-glycoprotein (MDR1) efflux transporter. Contraindicated. Both drugs will increase QT interval
  
  quinidine and itraconazole both increase QTc interval. Contraindicated.

• ivabradine

  Contraindicated (1)quinidine will increase the level or effect of ivabradine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of ivabradine with strong CYP3A4 inhibitors is contraindicated.

• ivacaftor

  Monitor Closely (1)ivacaftor increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Ivacaftor and its M1 metabolite has the potential to inhibit P-gp; may significantly increase systemic exposure to sensitive P-gp substrates with a narrow therapeutic index.

• ivermectin

  Serious - Use Alternative (1)quinidine will increase the level or effect of ivermectin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• ivosidenib

  Serious - Use Alternative (2)ivosidenib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Avoid coadministration of QTc prolonging drugs with ivosidenib or replace with alternate therapies. If coadministration of a QTc prolonging drug is unavoidable, monitor for increased risk of QTc interval prolongation.
  
  ivosidenib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sensitive CYP3A4 substrates with ivosidenib or replace with alternative therapies. If coadministration is unavoidable, monitor patients for loss of therapeutic effect of these drugs.

• ixekizumab

  Monitor Closely (1)ixekizumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, ixekizumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of ixekizumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• ketoconazole

  Contraindicated (1)quinidine and ketoconazole both increase QTc interval. Contraindicated.Serious - Use Alternative (1)ketoconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• L-tryptophan

  Monitor Closely (1)dextromethorphan and L-tryptophan both increase serotonin levels. Modify Therapy/Monitor Closely.

• lacosamide

  Monitor Closely (1)quinidine, lacosamide. Either increases levels of the other by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Consider decreasing lacosamide dose when coadministered with strong CYP3A4 inhibitors.

• lapatinib

  Monitor Closely (1)lapatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)quinidine and lapatinib both increase QTc interval. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of lapatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• lasmiditan

  Serious - Use Alternative (1)lasmiditan increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• lefamulin

  Contraindicated (1)lefamulin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Lefamulin is contraindicated with CYP3A substrates know to prolong the QT interval.

• lemborexant

  Monitor Closely (1)quinidine will increase the level or effect of lemborexant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Lower nightly dose of lemborexant recommended if coadministered with weak CYP3A4 inhibitors. See drug monograph for specific dosage modification.

• lenvatinib

  Monitor Closely (1)quinidine and lenvatinib both increase QTc interval. Use Caution/Monitor. Lenvatinib prescribing information recommends monitoring ECG closely when coadministered with QT prolonging drugs.

• letermovir

  Monitor Closely (2)letermovir increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  letermovir increases levels of dextromethorphan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• leuprolide

  Contraindicated (1)leuprolide increases toxicity of quinidine by QTc interval. Contraindicated. Increases risk of torsades de pointes.

• levofloxacin

  Serious - Use Alternative (1)quinidine and levofloxacin both increase QTc interval. Avoid or Use Alternate Drug.

• levomilnacipran

  Monitor Closely (1)quinidine will increase the level or effect of levomilnacipran by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Do not exceed 80 mg/day of levomilnacipran when coadministered with strong CYP3A4 inhibitorsSerious - Use Alternative (1)levomilnacipran and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• lily of the valley

  Minor (1)quinidine, lily of the valley. Either increases toxicity of the other by pharmacodynamic synergism. Minor/Significance Unknown.

• linezolid

  Serious - Use Alternative (1)linezolid and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Linezolid may increase serotonin as a result of MAO-A inhibition. If linezolid must be administered, discontinue serotonergic drug immediately and monitor for CNS toxicity. Serotonergic therapy may be resumed 24 hours after last linezolid dose or after 2 weeks of monitoring, whichever comes first.

• lithium

  Monitor Closely (1)dextromethorphan and lithium both increase serotonin levels. Modify Therapy/Monitor Closely.

• lofepramine

  Contraindicated (1)quinidine and lofepramine both increase QTc interval. Contraindicated.Serious - Use Alternative (2)quinidine will increase the level or effect of lofepramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  lofepramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• lofexidine

  Monitor Closely (2)quinidine and lofexidine both increase QTc interval. Use Caution/Monitor. ECG monitoring is recommended.
  
  quinidine will increase the level or effect of lofexidine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Concomitant use of lofexidine with strong CYP2D6 inhibitors may increase lofexidine plasma levels. Monitor for symptoms of orthostasis and bradycardia if coadministered with a CYP2D6 inhibitor. Consider lofexidine dose reduction.

• lomitapide

  Contraindicated (1)quinidine increases levels of lomitapide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Increases lomitapide levels several folds.Monitor Closely (1)lomitapide increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Consider reducing dose when used concomitantly with lomitapide.

• lonafarnib

  Monitor Closely (1)lonafarnib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Lonafarnib is a weak P-gp inhibitor. Monitor for adverse reactions if coadministered with P-gp substrates where minimal concentration changes may lead to serious or life-threatening toxicities. Reduce P-gp substrate dose if needed.Serious - Use Alternative (2)lonafarnib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration with sensitive CYP3A substrates. If coadministration unavoidable, monitor for adverse reactions and reduce CYP3A substrate dose in accordance with product labeling.
  
  quinidine will increase the level or effect of lonafarnib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of lonafarnib (a sensitive CYP3A substrate) with weak CYP3A inhibitors is unavoidable, reduce to, or continue lonafarnib at starting dose. Closely monitor for arrhythmias and events (eg, syncope, heart palpitations) since lonafarnib effect on QT interval is unknown.

• loperamide

  Serious - Use Alternative (1)quinidine will increase the level or effect of loperamide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• lopinavir

  Serious - Use Alternative (1)lopinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• loratadine

  Monitor Closely (2)quinidine will increase the level or effect of loratadine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of loratadine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• lorcaserin

  Serious - Use Alternative (1)dextromethorphan and lorcaserin both increase serotonin levels. Avoid or Use Alternate Drug.

• lorlatinib

  Serious - Use Alternative (1)lorlatinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid use of lorlatinib with CYP3A substrates, where minimal concentration changes may lead to serious therapeutic failures of the substrate. If concomitant use is unavoidable, increase CYP3A substrate dosage in accordance with approved product labeling.

• lovastatin

  Contraindicated (1)quinidine will increase the level or effect of lovastatin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors increase systemic statin exposure and risk of myopathy, including rhabdomyolysisSerious - Use Alternative (1)quinidine will increase the level or effect of lovastatin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• loxapine

  Monitor Closely (1)dextromethorphan, loxapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• loxapine inhaled

  Monitor Closely (1)dextromethorphan, loxapine inhaled. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• lsd

  Monitor Closely (1)dextromethorphan and lsd both increase serotonin levels. Modify Therapy/Monitor Closely.

• lumacaftor/ivacaftor

  Monitor Closely (1)quinidine increases levels of lumacaftor/ivacaftor by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Strong CYP3A inhibitors do not impact lumacaftor exposure, but increased ivacaftor exposure by 4.3-fold. Due to the induction effect of lumacaftor on CYP3A, at steady-state the net exposure of ivacaftor is not expected to exceed that when given in the absence of lumacaftor at a dose of 150 mg q12hr (the approved dose of ivacaftor monotherapy). Therefore, no dose adjustment is necessary when CYP3A inhibitors are initiated in patients currently taking lumacaftor/ivacaftor. However, when initiating lumacaftor/ivacaftor in patients taking strong CYP3A inhibitors, reduce the dose to 1 tablet daily (lumacaftor 200 mg/ivacaftor 125 mg total daily dose) for the first week of treatment to allow for the steady-state induction effect of lumacaftor. Following this period, continue with the recommended daily dose. No dose adjustment is required for moderate or weak CYP3A4 inhibitors.Serious - Use Alternative (1)lumacaftor/ivacaftor will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Lumacaftor is a strong inducer of CYP3A. Avoid coadministration with sensitive CYP3A substrates or CYP3A substrates with a narrow therapeutic index.

• lumefantrine

  Contraindicated (1)quinidine and lumefantrine both increase QTc interval. Contraindicated.Monitor Closely (2)lumefantrine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  lumefantrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• lurasidone

  Monitor Closely (1)dextromethorphan, lurasidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Serious - Use Alternative (1)lurasidone increases toxicity of quinidine by Other (see comment). Avoid or Use Alternate Drug. Comment: Interaction applies only in setting of acute lurasidone overdose. Lurasidone may enhance QTc prolonging effects of quinidine in overdose setting.

• macimorelin

  Serious - Use Alternative (1)macimorelin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Macimorelin causes an increase of ~11 msec in the corrected QT interval. Avoid coadministration with drugs that prolong QT interval, which could increase risk for developing torsade de pointes-type ventricular tachycardia. Allow sufficient washout time of drugs that are known to prolong the QT interval before administering macimorelin.

• macitentan

  Serious - Use Alternative (1)quinidine will increase the level or effect of macitentan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministering macitentan with strong CYP3A4 inhibitors

• maprotiline

  Contraindicated (1)quinidine and maprotiline both increase QTc interval. Contraindicated.Serious - Use Alternative (1)maprotiline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• maraviroc

  Monitor Closely (1)quinidine will increase the level or effect of maraviroc by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Decrease maraviroc dose to 150 mg BID when coadministered with strong CYP3A4 inhibitorsSerious - Use Alternative (1)quinidine will increase the level or effect of maraviroc by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.Minor (1)maraviroc will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• marijuana

  Monitor Closely (1)marijuana will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Minor (1)marijuana will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• medroxyprogesterone

  Monitor Closely (1)quinidine will increase the level or effect of medroxyprogesterone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Use alternative if available.

• mefloquine

  Serious - Use Alternative (2)mefloquine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Mefloquine may enhance the QTc prolonging effect of high risk QTc prolonging agents.
  
  quinidine, mefloquine. Mechanism: pharmacodynamic synergism. Contraindicated. Risk of ECG abnormalities, cardiac arrest.

• memantine

  Monitor Closely (1)quinidine will increase the level or effect of memantine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.Serious - Use Alternative (1)memantine, dextromethorphan. Either increases toxicity of the other by pharmacodynamic synergism. Contraindicated.

• meperidine

  Serious - Use Alternative (1)dextromethorphan and meperidine both increase serotonin levels. Avoid or Use Alternate Drug.

• mestranol

  Serious - Use Alternative (1)quinidine will increase the level or effect of mestranol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• metformin

  Monitor Closely (1)quinidine will increase the level or effect of metformin by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• methadone

  Serious - Use Alternative (1)quinidine and methadone both increase QTc interval. Avoid or Use Alternate Drug.

• methamphetamine

  Serious - Use Alternative (1)quinidine will increase the level or effect of methamphetamine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• methyclothiazide

  Monitor Closely (1)quinidine will increase the level or effect of methyclothiazide by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• methylene blue

  Serious - Use Alternative (1)methylene blue and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Methylene blue may increase serotonin as a result of MAO-A inhibition. If methylene blue must be administered, discontinue serotonergic drug immediately and monitor for CNS toxicity. Serotonergic therapy may be resumed 24 hours after last methylene blue dose or after 2 weeks of monitoring, whichever comes first.

• methylprednisolone

  Monitor Closely (1)methylprednisolone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine will increase the level or effect of methylprednisolone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• metoclopramide intranasal

  Serious - Use Alternative (1)quinidine will increase the level or effect of metoclopramide intranasal by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Concurrent use of metoclopramide intranasal and strong CYP2D6 inhibitors is not recommended since the metoclopramide intranasal dose cannot be adjusted.

• metoprolol

  Serious - Use Alternative (1)quinidine will increase the level or effect of metoprolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. If concurrent therapy required, monitor cardiac function carefully (blood pressure, heart rate). A dosage adjustment may be required for both drugs.

• metronidazole

  Monitor Closely (1)metronidazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• mexiletine

  Serious - Use Alternative (1)quinidine will increase the level or effect of mexiletine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• miconazole vaginal

  Monitor Closely (1)miconazole vaginal will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• midazolam intranasal

  Monitor Closely (1)quinidine will increase the level or effect of midazolam intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Coadministration of mild CYP3A4 inhibitors with midazolam intranasal may cause higher midazolam systemic exposure, which may prolong sedation.

• midodrine

  Monitor Closely (1)quinidine will increase the level or effect of midodrine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• mifepristone

  Contraindicated (1)mifepristone increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Contraindicated with CYP3A substrates that have a narrow therapeutic index; combination may prolong QT interval .

• milnacipran

  Serious - Use Alternative (1)milnacipran and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• mirtazapine

  Monitor Closely (1)dextromethorphan and mirtazapine both increase serotonin levels. Modify Therapy/Monitor Closely.

• mitotane

  Monitor Closely (1)mitotane decreases toxicity of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Mitotane is a strong inducer of cytochrome P-4503A4; monitor when coadministered with CYP3A4 substrates for possible dosage adjustments.

• mobocertinib

  Serious - Use Alternative (2)mobocertinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If use is unavoidable, increase CYP3A4 substrate dosage in accordance with its prescribing information.
  
  mobocertinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. If coadministration unavoidable, reduce mobocertinib dose and monitor QTc interval more frequently.

• modafinil

  Monitor Closely (1)modafinil will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• molindone

  Monitor Closely (1)dextromethorphan, molindone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• morphine

  Monitor Closely (1)dextromethorphan and morphine both increase serotonin levels. Modify Therapy/Monitor Closely.Serious - Use Alternative (1)quinidine will increase the level or effect of morphine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• moxifloxacin

  Contraindicated (1)quinidine and moxifloxacin both increase QTc interval. Contraindicated.

• nafcillin

  Monitor Closely (1)nafcillin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• naldemedine

  Monitor Closely (1)quinidine increases levels of naldemedine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor naldemedine for potential adverse effects if coadministered with P-gp inhibitors.

• naloxegol

  Contraindicated (1)quinidine will increase the level or effect of naloxegol by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of naloxegol with strong CYP3A4 inhibitors can significantly increase naloxegol systemic exposure which may precipitate opioid withdrawal symptoms

• naratriptan

  Monitor Closely (1)naratriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• nebivolol

  Serious - Use Alternative (1)quinidine will increase the level or effect of nebivolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Monitor blood pressure. Reduced doses of nebivolol may be necessary.

• nefazodone

  Serious - Use Alternative (2)nefazodone will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  nefazodone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• nelfinavir

  Monitor Closely (1)nelfinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)nelfinavir increases levels of quinidine by decreasing metabolism. Contraindicated.
  
  quinidine will increase the level or effect of nelfinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• neomycin PO

  Serious - Use Alternative (1)quinidine will increase the level or effect of neomycin PO by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• netupitant/palonosetron

  Monitor Closely (1)quinidine will increase the level or effect of netupitant/palonosetron by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Netupitant is mainly metabolized by CYP3A4; no dosage adjustment is required

• nevirapine

  Monitor Closely (1)nevirapine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• nifedipine

  Monitor Closely (3)nifedipine will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  nifedipine decreases levels of quinidine by increasing elimination. Use Caution/Monitor.
  
  quinidine increases levels of nifedipine by decreasing metabolism. Use Caution/Monitor.

• nilotinib

  Contraindicated (1)quinidine and nilotinib both increase QTc interval. Contraindicated.Serious - Use Alternative (2)nilotinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Additive QT prolongation may occur during coadministration of nilotinib and quinidine. Coadministration of nilotinib and a drug that prolongs the QT interval such as dronedarone is not advised
  
  quinidine will increase the level or effect of nilotinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.Minor (1)nilotinib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• nintedanib

  Monitor Closely (1)quinidine increases levels of nintedanib by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. If nintedanib adverse effects occur, management may require interruption, dose reduction, or discontinuation of therapy .

• nortriptyline

  Contraindicated (1)quinidine and nortriptyline both increase QTc interval. Contraindicated.Serious - Use Alternative (2)nortriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of nortriptyline by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• octreotide

  Contraindicated (1)quinidine and octreotide both increase QTc interval. Contraindicated.

• octreotide (Antidote)

  Contraindicated (1)quinidine and octreotide (Antidote) both increase QTc interval. Contraindicated.

• ofloxacin

  Monitor Closely (1)quinidine will increase the level or effect of ofloxacin by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.Serious - Use Alternative (1)quinidine and ofloxacin both increase QTc interval. Avoid or Use Alternate Drug.

• olanzapine

  Monitor Closely (1)dextromethorphan, olanzapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• olaparib

  Serious - Use Alternative (1)quinidine will increase the level or effect of olaparib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration with strong CYP3A inhibitors cannot be avoided, reduce olaparib dose to 150 mg (capsule) or 100 mg (tablet) PO BID. Do not substitute tablets with capsules.

• oliceridine

  Monitor Closely (1)quinidine will increase the level or effect of oliceridine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. If concomitant use is necessary, may require less frequent oliceridine dosing. Closely monitor for respiratory depression and sedation and titrate subsequent doses accordingly. If inhibitor is discontinued, consider increase oliceridine dosage until stable drug effects are achieved. Monitor for signs of opioid withdrawal.

• olodaterol inhaled

  Monitor Closely (1)quinidine and olodaterol inhaled both increase QTc interval. Use Caution/Monitor. Drugs that prolong the QTc interval and may potentiate the effects of beta2 agonists on the cardiovascular system; increased risk of ventricular arrhythmias

• ombitasvir/paritaprevir/ritonavir & dasabuvir

  Monitor Closely (1)ombitasvir/paritaprevir/ritonavir & dasabuvir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Caution is warranted and therapeutic concentration monitoring (if available) is recommended for antiarrhythmics when coadministered with Viekira Pak

• onabotulinumtoxinA

  Minor (1)quinidine increases effects of onabotulinumtoxinA by pharmacodynamic synergism. Minor/Significance Unknown.

• ondansetron

  Serious - Use Alternative (1)quinidine and ondansetron both increase QTc interval. Avoid or Use Alternate Drug. Avoid with congenital long QT syndrome; ECG monitoring recommended with concomitant medications that prolong QT interval, electrolyte abnormalities, CHF, or bradyarrhythmias.

• oritavancin

  Monitor Closely (1)oritavancin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Oritavancin is a weak CYP3A4 inducer; caution if coadministered with CYP3A4 substrates that have a narrow therapeutic index

• osilodrostat

  Monitor Closely (1)osilodrostat and quinidine both increase QTc interval. Use Caution/Monitor.

• osimertinib

  Monitor Closely (1)osimertinib and quinidine both increase QTc interval. Use Caution/Monitor. Conduct periodic monitoring with ECGs and electrolytes in patients taking drugs known to prolong the QTc interval.

• ospemifene

  Monitor Closely (1)quinidine increases levels of ospemifene by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• oxaliplatin

  Monitor Closely (1)oxaliplatin will increase the level or effect of quinidine by Other (see comment). Use Caution/Monitor. Monitor for ECG changes if therapy is initiated in patients with drugs known to prolong QT interval.

• oxcarbazepine

  Monitor Closely (1)oxcarbazepine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• oxycodone

  Monitor Closely (1)quinidine decreases effects of oxycodone by decreasing metabolism. Use Caution/Monitor. Decreased conversion of hydrocodone to active metabolite morphine.Serious - Use Alternative (2)quinidine will increase the level or effect of oxycodone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  quinidine increases levels of oxycodone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Oxycodone dose reduction may be warranted when coadministered with strong CYP3A4 inhibitors.

• oxymorphone

  Serious - Use Alternative (1)quinidine will increase the level or effect of oxymorphone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• ozanimod

  Monitor Closely (1)ozanimod and quinidine both increase QTc interval. Modify Therapy/Monitor Closely. The potential additive effects on heart rate, treatment with ozanimod should generally not be initiated in patients who are concurrently treated with QT prolonging drugs with known arrhythmogenic properties.

• paclitaxel

  Serious - Use Alternative (1)quinidine will increase the level or effect of paclitaxel by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• paclitaxel protein bound

  Serious - Use Alternative (1)quinidine will increase the level or effect of paclitaxel protein bound by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• palbociclib

  Monitor Closely (1)palbociclib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. The dose of sensitive CYP3A substrates with a narrow therapeutic index may need to be reduced if coadministered with palbociclibSerious - Use Alternative (1)quinidine will increase the level or effect of palbociclib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of palbociclib with strong CYP3A inhibitors. If unable to avoid, reduce palbociclib dose to 75 mg/day.

• paliperidone

  Monitor Closely (1)dextromethorphan, paliperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Serious - Use Alternative (2)quinidine and paliperidone both increase QTc interval. Avoid or Use Alternate Drug.
  
  quinidine will increase the level or effect of paliperidone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• pancuronium

  Minor (1)quinidine increases effects of pancuronium by pharmacodynamic synergism. Minor/Significance Unknown.

• panobinostat

  Monitor Closely (2)panobinostat will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Panobinostat can increase the levels and effects of sensitive CYP2D6 substrates or those with a narrow therapeutic index CYP2D6.
  
  quinidine increases levels of panobinostat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Reduce panobinostat starting dose to 10 mg if coadministered with strong CYP3A4 inhibitors.Serious - Use Alternative (1)quinidine and panobinostat both increase QTc interval. Avoid or Use Alternate Drug. Panobinostat is known to significantly prolong QT interval. Panobinostat prescribing information states use with drugs known to prolong QTc is not recommended.

• parecoxib

  Minor (1)parecoxib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• paromomycin

  Serious - Use Alternative (1)quinidine will increase the level or effect of paromomycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• paroxetine

  Monitor Closely (1)quinidine will increase the level or effect of paroxetine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Monitor patients for signs of paroxetine toxicity. Paroxetine doses may need to be reduced.Serious - Use Alternative (3)paroxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.
  
  paroxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  quinidine and paroxetine both increase QTc interval. Avoid or Use Alternate Drug.

• pasireotide

  Monitor Closely (1)quinidine and pasireotide both increase QTc interval. Modify Therapy/Monitor Closely.

• pazopanib

  Monitor Closely (2)pazopanib increases levels of dextromethorphan by decreasing metabolism. Use Caution/Monitor.
  
  quinidine and pazopanib both increase QTc interval. Modify Therapy/Monitor Closely.

• peginterferon alfa 2b

  Monitor Closely (1)peginterferon alfa 2b, dextromethorphan. Other (see comment). Use Caution/Monitor. Comment: When patients are administered peginterferon alpha-2b with CYP2D6 substrates, the therapeutic effect of these drugs may be altered. Peginterferon alpha-2b may increase or decrease levels of CYP2D6 substrate.

• pentamidine

  Contraindicated (1)quinidine and pentamidine both increase QTc interval. Contraindicated.

• pentazocine

  Monitor Closely (1)dextromethorphan and pentazocine both increase serotonin levels. Modify Therapy/Monitor Closely.

• pentobarbital

  Monitor Closely (1)pentobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• perhexiline

  Monitor Closely (1)quinidine will increase the level or effect of perhexiline by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• perphenazine

  Contraindicated (1)perphenazine and quinidine both increase QTc interval. Contraindicated.Monitor Closely (2)dextromethorphan, perphenazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).
  
  quinidine will increase the level or effect of perphenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine, perphenazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.Minor (1)perphenazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• pexidartinib

  Serious - Use Alternative (2)quinidine and pexidartinib both increase inhibition of GI absorption. Applies only to oral form of both agents. Avoid or Use Alternate Drug. Pexidartinib can cause hepatotoxicity. Avoid coadministration of pexidartinib with other products know to cause hepatoxicity.
  
  pexidartinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of pexidartinib (a CYP3A4 inducer) with sensitive CYP3A substrates may lead to serious therapeutic failures. If concomitant use is unavoidable, increase the CYP3A substrate dosage in accordance with approved product labeling.

• phenelzine

  Contraindicated (1)phenelzine and dextromethorphan both increase serotonin levels. Contraindicated.

• phenindione

  Minor (1)quinidine increases effects of phenindione by decreasing metabolism. Minor/Significance Unknown.

• phenobarbital

  Monitor Closely (1)phenobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• phenytoin

  Monitor Closely (2)phenytoin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  phenytoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

• pimavanserin

  Monitor Closely (1)dextromethorphan, pimavanserin. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).Serious - Use Alternative (1)pimavanserin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Coadministration may increase the risk of QT prolongation and cardiac arrhythmia.

• pimozide

  Contraindicated (1)quinidine and pimozide both increase QTc interval. Contraindicated.Monitor Closely (1)dextromethorphan, pimozide. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• pitolisant

  Monitor Closely (2)pitolisant will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Pitolisant is a borderline/weak inducer of CYP3A4. Monitor sensitive CYP3A4 substrates for reduced effectiveness if coadministered.
  
  quinidine will increase the level or effect of pitolisant by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. If coadministered with strong CYP2D6 inhibitors, initiate pitolisant at 8.9 mg/day and increase after 7 days to maximum of 17.8 mg/day. For patients currently taking pitolisant, reduce pitolisant dose by half upon initiating strong CYP2D6 inhibitors.Serious - Use Alternative (1)quinidine and pitolisant both increase QTc interval. Avoid or Use Alternate Drug.

• pomalidomide

  Serious - Use Alternative (2)quinidine increases levels of pomalidomide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  quinidine increases levels of pomalidomide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• ponatinib

  Monitor Closely (1)ponatinib increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.Serious - Use Alternative (1)quinidine increases levels of ponatinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Decrease ponatinib starting dose to 30 mg qDay if coadministration with strong CYP3A4 inhibitors cannot be avoided.

• ponesimod

  Serious - Use Alternative (1)ponesimod, quinidine. Either increases effects of the other by QTc interval. Avoid or Use Alternate Drug. Consult cardiologist if considering treatment. Generally, should not be initiated in patients who are concurrently taking QT prolonging drugs with known arrhythmogenic properties, such as HR-lowering calcium channel blockers (eg, verapamil, diltiazem).

• posaconazole

  Serious - Use Alternative (3)quinidine and posaconazole both increase QTc interval. Avoid or Use Alternate Drug.
  
  posaconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Use of posaconazole in combination with drugs that both prolong the QT interval and are substrates for CYP3A4 is contraindicated
  
  quinidine will increase the level or effect of posaconazole by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• pramipexole

  Monitor Closely (1)quinidine will increase the level or effect of pramipexole by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• prednisolone

  Serious - Use Alternative (1)quinidine will increase the level or effect of prednisolone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• prednisone

  Monitor Closely (1)prednisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine will increase the level or effect of prednisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• pretomanid

  Serious - Use Alternative (1)quinidine, pretomanid. Either increases toxicity of the other by Other (see comment). Avoid or Use Alternate Drug. Comment: Pretomanid regimen associated with hepatotoxicity. Avoid alcohol and hepatotoxic agents, including herbal supplements and drugs other than bedaquiline and linezolid.

• primidone

  Monitor Closely (1)primidone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• procainamide

  Contraindicated (1)quinidine and procainamide both increase QTc interval. Contraindicated.Serious - Use Alternative (1)quinidine will increase the level or effect of procainamide by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

• procarbazine

  Contraindicated (1)procarbazine and dextromethorphan both increase serotonin levels. Contraindicated. Combination is contraindicated within 2 weeks of MAOI use.

• prochlorperazine

  Contraindicated (1)prochlorperazine and quinidine both increase QTc interval. Contraindicated.Monitor Closely (1)quinidine will increase the level or effect of prochlorperazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine, prochlorperazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• promazine

  Contraindicated (1)promazine and quinidine both increase QTc interval. Contraindicated.Monitor Closely (1)quinidine will increase the level or effect of promazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine, promazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• promethazine

  Contraindicated (1)promethazine and quinidine both increase QTc interval. Contraindicated.Monitor Closely (1)quinidine will increase the level or effect of promethazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine, promethazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• propafenone

  Serious - Use Alternative (1)quinidine will increase the level or effect of propafenone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.Minor (1)propafenone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• propranolol

  Serious - Use Alternative (1)quinidine will increase the level or effect of propranolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Monitor patients for hypotension, bradycardia, arrhythmias and heart failure.

• protamine

  Minor (1)quinidine increases effects of protamine by decreasing metabolism. Minor/Significance Unknown.

• protriptyline

  Contraindicated (1)quinidine and protriptyline both increase QTc interval. Contraindicated.Serious - Use Alternative (1)protriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• quetiapine

  Monitor Closely (2)quetiapine, quinidine. Either increases toxicity of the other by QTc interval. Use Caution/Monitor. Avoid use with drugs that prolong QT and in patients with risk factors for prolonged QT interval. Postmarketing cases show QT prolongation with overdose in patients with concomitant illness or with drugs known to cause electrolyte imbalance or prolong QT.
  
  dextromethorphan, quetiapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• quinacrine

  Minor (1)quinacrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• quinidine

  Monitor Closely (1)quinidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• quinine

  Monitor Closely (2)quinidine will increase the level or effect of quinine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.
  
  quinidine and quinine both increase QTc interval. Use Caution/Monitor.

• quinupristin/dalfopristin

  Monitor Closely (1)quinupristin/dalfopristin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• ranolazine

  Serious - Use Alternative (1)quinidine and ranolazine both increase QTc interval. Avoid or Use Alternate Drug.Minor (1)ranolazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• rapacuronium

  Minor (1)quinidine increases effects of rapacuronium by pharmacodynamic synergism. Minor/Significance Unknown.

• rasagiline

  Contraindicated (1)rasagiline and dextromethorphan both increase serotonin levels. Contraindicated. Risk of psychosis episodes or bizarre behavior.

• red yeast rice

  Serious - Use Alternative (1)quinidine will increase the level or effect of red yeast rice by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. May increase creatine kinase levels and increase risk of myopathy or rhabdomyolysis; red yeast rice contains monocolin K (reportedly identical to lovastatin)

• regorafenib

  Contraindicated (1)quinidine, regorafenib. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors increase regorafenib levels and decrease exposure of the active metabolites M-2 and M-5.

• ribociclib

  Monitor Closely (1)ribociclib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Caution if ribociclib is coadministered with sensitive CYP3A4 substrates that have a narrow therapeutic index. Dose reduction for sensitive CYP3A4 substrates may be needed.Serious - Use Alternative (1)ribociclib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

• rifabutin

  Serious - Use Alternative (1)rifabutin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• rifampin

  Serious - Use Alternative (1)rifampin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• rifapentine

  Monitor Closely (1)rifapentine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• rifaximin

  Monitor Closely (1)quinidine increases levels of rifaximin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• rilpivirine

  Monitor Closely (1)rilpivirine increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Rilpivirine should be used with caution when co-administered with a drug with a known risk of Torsade de Pointes.

• rimabotulinumtoxinB

  Monitor Closely (1)quinidine, rimabotulinumtoxinB. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Anticholinergics may enhance botulinum toxin effects. Closely monitor for increased neuromuscular blockade.

• rimegepant

  Serious - Use Alternative (1)quinidine will increase the level or effect of rimegepant by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• riociguat

  Serious - Use Alternative (2)quinidine will increase the level or effect of riociguat by decreasing metabolism. Avoid or Use Alternate Drug. Coadministration of riociguat (substrate of CYP isoenzymes 1A1, 2C8, 3A, 2J2) with strong CYP inhibitors may require a decreased initial dose of 0.5 mg PO TID; monitor for signs of hypotension and reduce dose if needed
  
  quinidine will increase the level or effect of riociguat by Other (see comment). Avoid or Use Alternate Drug. Coadministration of riociguat (an ABCG2 [BCRP] substrate) with strong ABCG2 inhibitors may require a decreased initial dose of 0.5 mg PO TID; monitor for signs of hypotension and reduce dose if needed

• risperidone

  Monitor Closely (2)dextromethorphan, risperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).
  
  quinidine will increase the level or effect of risperidone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)quinidine will increase the level or effect of risperidone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine and risperidone both increase QTc interval. Avoid or Use Alternate Drug.

• ritonavir

  Monitor Closely (1)ritonavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)ritonavir increases levels of quinidine by decreasing metabolism. Contraindicated.
  
  quinidine will increase the level or effect of ritonavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.Minor (1)ritonavir will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• rivaroxaban

  Monitor Closely (1)quinidine increases levels of rivaroxaban by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Patients with renal impairment receiving rivaroxaban with drugs that are combined P-gp and weak or moderate CYP3A4 inhibitors may have significant increases in exposure compared with patients with normal renal function and no inhibitor use, since both pathways of rivaroxaban elimination are affected. Since these increases may increase bleeding risk, use rivaroxaban in this situation only if the potential benefit justifies the potential risk.

• rizatriptan

  Monitor Closely (1)rizatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• rocuronium

  Minor (1)quinidine increases effects of rocuronium by pharmacodynamic synergism. Minor/Significance Unknown.

• rolapitant

  Monitor Closely (1)rolapitant will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Monitor for adverse reactions when unable to avoid coadministration with narrow therapeutic index CYP2D6 substrates.

• romidepsin

  Serious - Use Alternative (2)quinidine will increase the level or effect of romidepsin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.
  
  quinidine and romidepsin both increase QTc interval. Avoid or Use Alternate Drug.

• rucaparib

  Monitor Closely (1)rucaparib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Adjust dosage of CYP3A4 substrates, if clinically indicated.

• rufinamide

  Monitor Closely (1)rufinamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• ruxolitinib

  Serious - Use Alternative (1)quinidine will increase the level or effect of ruxolitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Reduce ruxolitinib starting dose to 10 mg BID with platelet count 100 X 10^9/L or more and concurrent use of strong CYP3A4 inhibitors; avoid with platelet counts <100 X 10^9/L

• safinamide

  Contraindicated (1)dextromethorphan, safinamide. Other (see comment). Contraindicated. Comment: Coadministration of MAOIs and dextromethorphan has been reported to cause episodes of psychosis or bizarre behavior.

• SAMe

  Monitor Closely (1)dextromethorphan and SAMe both increase serotonin levels. Modify Therapy/Monitor Closely.

• saquinavir

  Contraindicated (1)saquinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.Serious - Use Alternative (1)quinidine will increase the level or effect of saquinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• sarecycline

  Monitor Closely (1)sarecycline will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor for toxicities of P-gp substrates that may require dosage reduction when coadministered with P-gp inhibitors.

• sarilumab

  Monitor Closely (1)sarilumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of cytokines such as IL-6. Elevated IL-6 concentration may down-regulate CYP activity, such as in patients with RA, and, hence, increase drug levels compared with subjects without RA. Blockade of IL-6 signaling by IL-6 antagonists (eg, sarilumab) might reverse the inhibitory effect of IL-6 and restore CYP activity, leading to decreased drug concentrations. Caution when initiating or discontinuing sarilumab if coadministered with CYP450 substrates, especially those with a narrow therapeutic index.

• saxagliptin

  Monitor Closely (1)quinidine will increase the level or effect of saxagliptin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Limit saxagliptin dose to 2.5 mg/day when coadministered with strong CYP3A4 inhibitors

• schisandra

  Monitor Closely (1)schisandra will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• secobarbital

  Monitor Closely (1)secobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• secukinumab

  Monitor Closely (1)secukinumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, secukinumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of secukinumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• selegiline

  Contraindicated (1)selegiline and dextromethorphan both increase serotonin levels. Contraindicated.

• selegiline transdermal

  Serious - Use Alternative (1)selegiline transdermal and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• selpercatinib

  Monitor Closely (1)selpercatinib increases toxicity of quinidine by QTc interval. Use Caution/Monitor.

• sertraline

  Serious - Use Alternative (1)sertraline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.Minor (1)sertraline will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• sevelamer

  Monitor Closely (1)sevelamer decreases levels of quinidine by increasing elimination. Use Caution/Monitor.

• silodosin

  Serious - Use Alternative (1)quinidine will increase the level or effect of silodosin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• siltuximab

  Monitor Closely (1)siltuximab, quinidine. Other (see comment). Use Caution/Monitor. Comment: CYP450 activity in the liver is down regulated by infection and inflammation stimuli including cytokines (eg, IL-6); inhibition of IL-6 by siltuximab may restore CYP450 enzymatic activity; caution if coadministered with CYP substrates that have a narrow therapeutic index.

• siponimod

  Serious - Use Alternative (1)siponimod, quinidine. Either increases effects of the other by QTc interval. Avoid or Use Alternate Drug. Because of the potential additive effects on heart rate, siponimod should generally not be initiated in patients taking QT prolonging drugs with known arrhythmogenic properties, heart rate lowering calcium channel blockers, or other drugs that may decrease heart rate. If treatment considered, obtain cardiology consult regarding switching to non-heart-rate lowering drugs or appropriate monitoring for treatment initiation.

• sirolimus

  Serious - Use Alternative (1)quinidine will increase the level or effect of sirolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• sodium bicarbonate

  Monitor Closely (1)sodium bicarbonate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

• sodium citrate/citric acid

  Monitor Closely (1)sodium citrate/citric acid will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

• sodium lactate

  Monitor Closely (1)sodium lactate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

• sodium sulfate/?magnesium sulfate/potassium chloride

  Monitor Closely (1)sodium sulfate/?magnesium sulfate/potassium chloride increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Consider predose and post-colonoscopy ECGs in patients at increased risk of serious cardiac arrhythmias. .

• sodium sulfate/potassium sulfate/magnesium sulfate

  Monitor Closely (1)sodium sulfate/potassium sulfate/magnesium sulfate increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Consider predose and post-colonoscopy ECGs in patients at increased risk of serious cardiac arrhythmias. .

• sofosbuvir/velpatasvir

  Monitor Closely (1)sofosbuvir/velpatasvir increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Velpatasvir inhibits CYP3A4. Caution if coadministered with drugs with narrow therapeutics indexes.

• sonidegib

  Serious - Use Alternative (1)quinidine will increase the level or effect of sonidegib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sonidegib with strong CYP3A4 inhibitors.

• sorafenib

  Monitor Closely (1)sorafenib and quinidine both increase QTc interval. Use Caution/Monitor.

• sotalol

  Contraindicated (1)quinidine and sotalol both increase QTc interval. Contraindicated.

• sotorasib

  Serious - Use Alternative (2)sotorasib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If use is unavoidable, refer to the prescribing information of the CYP3A4 substrate for dosage modifications
  
  sotorasib will decrease the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If use is unavoidable, refer to the prescribing information of the P-gp substrate for dosage modifications.

• squill

  Serious - Use Alternative (1)quinidine increases toxicity of squill by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• St John's Wort

  Serious - Use Alternative (1)St John's Wort will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• stiripentol

  Monitor Closely (2)stiripentol, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Stiripentol is a CYP3A4 inhibitor and inducer. Monitor CYP3A4 substrates coadministered with stiripentol for increased or decreased effects. CYP3A4 substrates may require dosage adjustment.
  
  stiripentol will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Consider reducing the dose of P-glycoprotein (P-gp) substrates, if adverse reactions are experienced when administered concomitantly with stiripentol.

• streptomycin

  Serious - Use Alternative (1)quinidine will increase the level or effect of streptomycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• succinylcholine

  Minor (1)quinidine increases effects of succinylcholine by pharmacodynamic synergism. Minor/Significance Unknown.

• sulfamethoxazole

  Monitor Closely (1)quinidine will increase the level or effect of sulfamethoxazole by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.Serious - Use Alternative (1)quinidine and sulfamethoxazole both increase QTc interval. Avoid or Use Alternate Drug.

• sumatriptan

  Monitor Closely (1)sumatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• sumatriptan intranasal

  Monitor Closely (1)sumatriptan intranasal and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

• suvorexant

  Serious - Use Alternative (1)quinidine increases levels of suvorexant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Suvorexant not recommended with use of strong CYP3A4 inhibitors.

• tacrolimus

  Serious - Use Alternative (1)quinidine will increase the level or effect of tacrolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• talazoparib

  Monitor Closely (1)quinidine will increase the level or effect of talazoparib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Talazoparib is a P-glycoprotein (P-gp) substrate; coadministration with P-gp inhibitors may increase talazoparib systemic exposure.

• tamoxifen

  Monitor Closely (1)quinidine decreases effects of tamoxifen by decreasing metabolism. Use Caution/Monitor. Inhibition of CYP2D6 metabolism to tamoxifen's active metabolite, endoxifen.

• tamsulosin

  Monitor Closely (1)quinidine increases levels of tamsulosin by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine increases levels of tamsulosin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• tasimelteon

  Monitor Closely (1)quinidine will increase the level or effect of tasimelteon by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• tazemetostat

  Monitor Closely (2)tazemetostat will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of tazemetostat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• tecovirimat

  Monitor Closely (1)tecovirimat will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Tecovirimat is a weak CYP3A4 inducer. Monitor sensitive CYP3A4 substrates for effectiveness if coadministered.

• teduglutide

  Monitor Closely (1)teduglutide increases levels of quinidine by Other (see comment). Use Caution/Monitor. Comment: Teduglutide may increase absorption of concomitant PO medications; caution with with drugs requiring titration or those with a narrow therapeutic index; dose adjustment may be necessary.

• telavancin

  Serious - Use Alternative (1)quinidine and telavancin both increase QTc interval. Avoid or Use Alternate Drug.

• telotristat ethyl

  Monitor Closely (1)telotristat ethyl will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Telotristat ethyl induces CYP3A4 and may reduce systemic exposure of sensitive CYP3A4 substrates. Monitor for suboptimal efficacy and consider increasing the dose of the CYP3A4 substrate.

• teniposide

  Monitor Closely (1)quinidine will increase the level or effect of teniposide by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

• tenofovir DF

  Monitor Closely (1)tenofovir DF, quinidine. Either increases levels of the other by decreasing renal clearance. Use Caution/Monitor.

• tepotinib

  Serious - Use Alternative (1)tepotinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If concomitant use unavoidable, reduce the P-gp substrate dosage if recommended in its approved product labeling.

• tetrabenazine

  Monitor Closely (1)quinidine increases effects of tetrabenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Decrease tetrabenazine dose by 50% when coadministered with strong CYP2D6 inhibitors.

• thioridazine

  Contraindicated (1)thioridazine and quinidine both increase QTc interval. Contraindicated.Serious - Use Alternative (2)quinidine, thioridazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.
  
  quinidine will increase the level or effect of thioridazine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.Minor (1)thioridazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• thiothixene

  Monitor Closely (1)dextromethorphan, thiothixene. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• timolol

  Serious - Use Alternative (1)quinidine will increase the level or effect of timolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• tinidazole

  Monitor Closely (1)quinidine will increase the level or effect of tinidazole by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• tipranavir

  Contraindicated (2)tipranavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.
  
  tipranavir increases levels of quinidine by decreasing metabolism. Contraindicated.Minor (1)tipranavir will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

• tobramycin

  Serious - Use Alternative (1)quinidine will increase the level or effect of tobramycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• tobramycin inhaled

  Monitor Closely (1)tobramycin inhaled and quinidine both increase nephrotoxicity and/or ototoxicity. Modify Therapy/Monitor Closely. Avoid concurrent or sequential use to decrease risk for ototoxicity

• tofacitinib

  Serious - Use Alternative (1)quinidine increases levels of tofacitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Reduce tofacitinib dose to 5 mg qDay when coadministered with potent CYP3A4 inhibitors.

• tolterodine

  Monitor Closely (1)quinidine will increase the level or effect of tolterodine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

• tolvaptan

  Serious - Use Alternative (1)quinidine will increase the level or effect of tolvaptan by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• topiramate

  Monitor Closely (1)topiramate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• topotecan

  Serious - Use Alternative (1)quinidine will increase the level or effect of topotecan by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Product labeling for PO topotecan recommends avoiding concomitant use of P-gp inhibitors; the interaction with IV topotecan may be less severe but is still likely of clinical significance

• toremifene

  Serious - Use Alternative (1)quinidine and toremifene both increase QTc interval. Avoid or Use Alternate Drug. Concurrent use of toremifene with agents causing QT prolongation should be avoided. If concomitant use is required it's recommended that toremifene be interrupted. If interruption not possible, patients requiring therapy with a drug that prolongs QT should be closely monitored. ECGs should be obtained for high risk patients.

• tramadol

  Monitor Closely (3)quinidine decreases effects of tramadol by decreasing metabolism. Use Caution/Monitor. Decreased conversion of tramadol to active metabolite.
  
  quinidine decreases effects of tramadol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Decreased conversion of tramadol to active metabolite.
  
  dextromethorphan and tramadol both increase serotonin levels. Modify Therapy/Monitor Closely.

• tranylcypromine

  Contraindicated (1)tranylcypromine and dextromethorphan both increase serotonin levels. Contraindicated.

• trazodone

  Contraindicated (1)quinidine and trazodone both increase QTc interval. Contraindicated.Serious - Use Alternative (1)trazodone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• triamterene

  Monitor Closely (1)quinidine will increase the level or effect of triamterene by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• triclabendazole

  Monitor Closely (1)triclabendazole and quinidine both increase QTc interval. Use Caution/Monitor.

• trifluoperazine

  Contraindicated (1)trifluoperazine and quinidine both increase QTc interval. Contraindicated.Monitor Closely (2)dextromethorphan, trifluoperazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).
  
  quinidine will increase the level or effect of trifluoperazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine, trifluoperazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

• trimethoprim

  Monitor Closely (1)quinidine will increase the level or effect of trimethoprim by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.Serious - Use Alternative (1)quinidine and trimethoprim both increase QTc interval. Avoid or Use Alternate Drug.

• trimipramine

  Contraindicated (1)quinidine and trimipramine both increase QTc interval. Contraindicated.Serious - Use Alternative (1)trimipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

• triptorelin

  Serious - Use Alternative (1)triptorelin increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

• tropisetron

  Monitor Closely (1)quinidine will increase the level or effect of tropisetron by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)quinidine and tropisetron both increase QTc interval. Avoid or Use Alternate Drug.

• tucatinib

  Monitor Closely (1)tucatinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Consider reducing the dosage of P-gp substrates, where minimal concentration changes may lead to serious or life-threatening toxicities.Serious - Use Alternative (1)tucatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concomitant use of tucatinib with CYP3A substrates, where minimal concentration changes may lead to serious or life-threatening toxicities. If unavoidable, reduce CYP3A substrate dose according to product labeling.

• umeclidinium bromide/vilanterol inhaled

  Monitor Closely (1)quinidine will increase the level or effect of umeclidinium bromide/vilanterol inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Vilanterol is a CYP3A4 substrate; coadministration with potent CYP3A4 inhibitors may increase systemic exposureSerious - Use Alternative (1)quinidine increases toxicity of umeclidinium bromide/vilanterol inhaled by QTc interval. Avoid or Use Alternate Drug. Exercise extreme caution when vilanterol coadministered with drugs that prolong QTc interval; adrenergic agonist effects on the cardiovascular system may be potentiated.

• ustekinumab

  Monitor Closely (1)ustekinumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, normalizing the formation of CYP450 enzymes. Upon initiation or discontinuation of ustekinumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

• valbenazine

  Monitor Closely (1)quinidine will increase the level or effect of valbenazine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Consider reducing valbenazine dose based on tolerability if coadministered with a strong CYP2D6 inhibitor.

• vandetanib

  Serious - Use Alternative (1)quinidine, vandetanib. Either increases toxicity of the other by QTc interval. Avoid or Use Alternate Drug. Avoid coadministration with drugs known to prolong QT interval; if a drug known to prolong QT interval must be used, more frequent ECG monitoring is recommended.

• vecuronium

  Minor (1)quinidine increases effects of vecuronium by pharmacodynamic synergism. Minor/Significance Unknown.

• vemurafenib

  Monitor Closely (1)vemurafenib and quinidine both increase QTc interval. Modify Therapy/Monitor Closely. Concomitant use of vemurafenib with drugs that prolong QT interval is not recommended. Quinidine may also increase vemurafenib levels.

• venetoclax

  Serious - Use Alternative (1)quinidine will increase the level or effect of venetoclax by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If a P-gp inhibitor must be used, reduce the venetoclax dose by at least 50%. Monitor more closely for signs of venetoclax toxicities.

• venlafaxine

  Serious - Use Alternative (3)quinidine and venlafaxine both increase QTc interval. Avoid or Use Alternate Drug.
  
  venlafaxine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.
  
  venlafaxine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

• verapamil

  Monitor Closely (2)verapamil will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  quinidine will increase the level or effect of verapamil by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

• vilanterol/fluticasone furoate inhaled

  Monitor Closely (1)quinidine will increase the level or effect of vilanterol/fluticasone furoate inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Fluticasone furoate and vilanterol are both CYP3A4 substrates; coadministration with potent CYP3A4 inhibitors may increase systemic exposureSerious - Use Alternative (1)quinidine increases toxicity of vilanterol/fluticasone furoate inhaled by QTc interval. Avoid or Use Alternate Drug. Exercise extreme caution when vilanterol coadministered with drugs that prolong QTc interval; adrenergic agonist effects on the cardiovascular system may be potentiated.

• vilazodone

  Serious - Use Alternative (2)dextromethorphan, vilazodone. Either increases toxicity of the other by serotonin levels. Avoid or Use Alternate Drug. Concomitant therapy should be discontinued immediately if signs or symptoms of serotonin syndrome emerge and supportive symptomatic treatment should be initiated. .
  
  quinidine increases levels of vilazodone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Strong CYP3A4 inhibitors may increase vilazodone plasma levels by 50% - Reduce daily dose to 20 mg.

• vinblastine

  Serious - Use Alternative (1)quinidine will increase the level or effect of vinblastine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• vincristine

  Serious - Use Alternative (1)quinidine will increase the level or effect of vincristine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• vincristine liposomal

  Serious - Use Alternative (1)quinidine will increase the level or effect of vincristine liposomal by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

• voclosporin

  Monitor Closely (1)voclosporin, quinidine. Either increases effects of the other by QTc interval. Use Caution/Monitor.

• vorapaxar

  Serious - Use Alternative (1)quinidine increases levels of vorapaxar by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• voriconazole

  Contraindicated (2)voriconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Elevated and toxic levels of quinidine may occur potentiating the risk for QT prolongation and cardiac arrhythmias.
  
  quinidine and voriconazole both increase QTc interval. Contraindicated.

• vortioxetine

  Serious - Use Alternative (1)quinidine increases levels of vortioxetine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Decrease vortioxetine dose by 50% when coadministered with strong CYP2D6 inhibitors.

• voxelotor

  Serious - Use Alternative (1)voxelotor will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Voxelotor increases systemic exposure of sensitive CYP3A4 substrates. Avoid coadministration with sensitive CYP3A4 substrates with a narrow therapeutic index. Consider dose reduction of the sensitive CYP3A4 substrate(s) if unable to avoid.

• warfarin

  Monitor Closely (1)quinidine increases effects of warfarin by decreasing metabolism. Use Caution/Monitor. Dosage reduction of warfarin may be needed during concurrent administration of quinidine. Monitor INR and adjust the dosage accordingly.

• zafirlukast

  Monitor Closely (1)zafirlukast will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• ziprasidone

  Contraindicated (1)quinidine and ziprasidone both increase QTc interval. Contraindicated.Monitor Closely (1)dextromethorphan, ziprasidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

• zolmitriptan

  Monitor Closely (1)zolmitriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.