warfarin (Rx)

Venous Thrombosis

Prophylaxis and treatment of venous thrombosis and its extension, pulmonary embolism (PE)

Initial dose: 2-5 mg PO/IV qDay for 2 days, OR 10 mg PO for 2 days in healthy individuals

Initiate warfarin on day 1 or 2 of LMWH or unfractionated heparin therapy and overlap until desired INR, THEN discontinue heparin

Check INR after 2 days and adjust dose according to results

Typical maintenance dose ranges between 2 and 10 mg/day

Consider dosage based on genotype (see Genomic Considerations)

DVT and PE treatment

• Initiate warfarin on day 1 or 2 of parenteral anticoagulation therapy (eg, LMWH or unfractionated heparin)
• Overlap warfarin and parenteral anticoagulant for at least 5 days until desired INR (>2.0) maintained for 24 hours, then discontinue parenteral therapy

INR range and treatment duration

• Maintain an INR of 2.0-3.0
• Surgery-provoked DVT or PE: Treatment duration of 3 months
• Transient (reversible) risk factor-induced DVT or PE: Treatment duration of 3 months
• First unprovoked proximal DVT or PE with low or moderate bleeding risk: Extended treatment consideration with periodic (ie, annual) risk-benefit analysis
• First unprovoked proximal DVT or PE with high bleeding risk: Treatment duration of 3 months
• First unprovoked distal DVT regardless of bleeding risk: Treatment duration of 3 months
• Second unprovoked DVT or PE with low or moderate bleeding risk: Extended treatment
• Second unprovoked DVT or PE with high bleeding risk: Treatment duration of 3 months
• DVT/PE and active cancer: Extended treatment, with periodic risk-benefit analysis (ACCP recommends LMWH over vitamin K antagonist therapy)
• Prevention of venous thromboembolism for total knee arthroplasty, total hip arthroplasty, and hip fracture surgery: Minimum treatment duration of 10-14 days, with a recommendation to extend outpatient therapy to 35 days (ACCP recommends LMWH over vitamin K antagonist therapy)

Stroke & Thromboembolism

Prophylaxis and treatment of systemic embolic complications (eg, stroke) associated with atrial fibrillation (AF)

Initial dose: 2-5 mg PO/IV qDay × 2 days, OR 10 mg PO × 2 days in healthy individuals

Check INR after 2 days and adjust dose according to results

Typical maintenance dose ranges between 2-10 mg/day

Consider dosage based on genotype (see Genomic Considerations)

ACCP guidelines recommend dabigatran 150 mg PO BID over adjusted-dose warfarin therapy for AF unless both AF and mitral stenosis are present

INR range and treatment duration

• Nonvalvular AF: Maintain an INR of 2.0-3.0
• AF and stable CAD: Adjusted-dose warfarin therapy (INR 2.0-3.0) without aspirin
• AF with high stroke risk and placement of stent: Triple therapy of dose-adjusted warfarin (INR 2.0-3.0), clopidogrel, and aspirin; for 1 month if bare metal stent; for 3-6 months for drug-eluting stent
• AF with intermediate to high stroke risk without stent placement: 12 months of warfarin therapy (INR 2.0-3.0) with single antiplatelet regimen
• AF for more than 48 hours to undergo cardioversion: Warfarin therapy (INR 2.0-3.0) for 3 weeks prior to and 4 weeks after cardioversion

Indications for indefinite treatment duration

• Persistent or paroxysmal nonvalvular AF in patients with a high risk of stroke: Ie, patients who have risk factors for stroke, such as prior ischemic stroke, transient ischemic attack, or systemic embolism or who have 2 of the following risk factors--age greater than 75 years, moderately or severely impaired left ventricular systolic function and/or heart failure, history of hypertension, or diabetes mellitus
• Persistent or paroxysmal nonvalvular AF in patients with an intermediate risk of ischemic stroke: Ie, patients who have 1 of the following risk factors--age >75 years, moderately or severely impaired left ventricular systolic function and/or heart failure, history of hypertension, or diabetes mellitus
• AF and mitral stenosis
• ≥2 episodes of documented DVT or PE

Cardiac Valve Replacement

Prophylaxis and treatment of thromboembolic complications associated with cardiac valve replacement

Initial dose: 2-5 mg PO/IV qDay × 2 days, OR 10 mg PO × 2 days in healthy individuals

Check INR after 2 days and adjust dose according to results

Typical maintenance dose ranges between 2 and 10 mg/day

Consider dosage based on genotype (see Genomic Considerations)

INR and treatment duration

• Mitral bioprosthetic valve: INR 2.0-3.0 for a 3-month treatment duration; if other risk factors for thromboembolism are present (ie, AF, previous thromboembolism, left ventricular dysfunction), a longer duration may be necessary
• Aortic mechanical valve: INR 2.0-3.0 for indefinite treatment duration
• Mitral mechanical valve, caged ball or caged disk valve, or both aortic and mitral mechanical valves: INR 2.5-3.5 for indefinite treatment duration
• Mechanical valves include bileaflet mechanical valves and Medtronic Hall tilting disk valves

Post-Myocardial Infarction

Reduction in the risk of death, recurrent MI, and thromboembolic events (eg, stroke, systemic embolization) after MI

Initial dose: 2-5 mg PO/IV qDay × 2 days, OR 10 mg PO × 2 days in healthy individuals

Check INR after 2 days and adjust dose according to results

Typical maintenance dose ranges between 2 and 10 mg/day

Consider dosage based on genotype (see Genomic Considerations)

INR and treatment duration

• Maintain INR between 2.0 and 3.0
• In patients who have not had stenting and who have anterior MI and left ventricular (LV) thrombus or high risk of LV thrombus (ie, ejection fraction <40%, anteroapical wall-motion abnormality), treatment involves dual therapy of warfarin (INR 2.0-3.0) and low-dose aspirin 75-100 mg, daily; treatment duration is 3 months, after which warfarin is discontinued
• In patients who have had bare-metal stent placement and who have anterior MI and LV thrombus or high risk of LV thrombus (ejection fraction <40%, anteroapical wall-motion abnormality), treatment involves triple therapy of warfarin (INR 2.0-3.0), low-dose aspirin, and clopidogrel 75 mg, daily for 1 month, followed by warfarin (INR 2.0-3.0) and single antiplatelet therapy for second and third month, after which warfarin is discontinued
• In patients who have had drug-eluting stent placement and who have anterior MI and LV thrombus or high risk of LV thrombus (ejection fraction <40%, anteroapical wall-motion abnormality), treatment involves triple therapy of warfarin (INR 2.0-3.0), low-dose aspirin, and clopidogrel 75 mg, daily for 3-6 months, after which warfarin is discontinued

Rheumatic Valve Disease (Off-label)

Rheumatic valve disease with any of the following: Atrial diameter >55 mm, left atrial thrombus, atrial fibrillation, and previous systemic embolism

Maintain INR 2.0-3.0 indefinitely

Cryptogenic Stroke and Patent Foramen Ovale With DVT (Off-label)

Maintain INR between 2.0 and 3.0 for 3 months

Cardioembolic Stroke or TIA (Off-label)

Maintain INR between 2.0 and 3.0 indefinitely

ACCP guidelines recommend dabigatran 150 mg PO twice daily over dose-adjusted warfarin therapy

Systolic LV Dysfunction (Off-label)

Systolic LV dysfunction without established CAD but with identified acute LV thrombus (eg, Takotsubo cardiomyopathy)

Maintain INR between 2.0 and 3.0 for at least 3 months

Antiphospholipid Antibody Syndrome (Off-label)

Antiphospholipid antibody syndrome with previous arterial or venous thromboembolism

Maintain INR between 2.0 and 3.0 indefinitely

Genomic Considerations

ACCP 2012 guidelines recommend against using pharmacogenetic testing for guiding doses

CYP2C9 and vitamin K epoxide reductase complex, subunit 1 (VKORC1) genotype information can assist in selecting starting dose

If genotype information unavailable, usual starting dose is 2-5 mg/day (modify based on other patient factors)

Range of expected therapeutic doses based on CYP2C9 and VKORC1 genotypes are listed below

VKORC1-GG

• CYP2C9 *1/*1: 5-7 mg
• CYP2C9 *1/*2: 5-7 mg
• CYP2C9 *1/*3: 3-4 mg
• CYP2C9 *2/*2: 3-4 mg
• CYP2C9 *2/*3: 3-4 mg
• CYP2C9 *3/*3: 0.5-2 mg

VKORC1-AG

• CYP2C9 *1/*1: 5-7 mg
• CYP2C9 *1/*2: 3-4 mg
• CYP2C9 *1/*3: 3-4 mg
• CYP2C9 *2/*2: 3-4 mg
• CYP2C9 *2/*3: 0.5-2 mg
• CYP2C9 *3/*3: 0.5-2 mg

VKORC1-AA

• CYP2C9 *1/*1: 3-4 mg
• CYP2C9 *1/*2: 3-4 mg
• CYP2C9 *1/*3: 0.5-2 mg
• CYP2C9 *2/*2: 0.5-2 mg
• CYP2C9 *2/*3: 0.5-2 mg
• CYP2C9 *3/*3: 0.5-2 mg

Dosage Modifications

Hepatic impairment: May potentiate warfarin response because of decreased metabolism and impaired synthesis of clotting factors

Dosing Considerations

Indication determines intensity and duration of therapy

Individualized doses and monitoring of PT/INR are necessary

Monitoring frequency should be daily or once every few days until stabilized; once stable, q4-6 weeks or longer may be appropriate (eg, 12 weeks)

Not all factors causing warfarin dose variability are known, but they include age, race, sex, body weight, concomitant medications, and comorbidities, in addition to genetic factors

Lower starting doses (ie, 2-5 mg/day × 2 days) recommended with the elderly, hepatic impairment, poor nutrition, CHF, high bleeding risk, debilitated patients, heart valve replacement, concomitant medications known to increase warfarin effect, or individuals suspected of having genomic variants

Perioperative management recommendations: Hold warfarin therapy approximately 5 days before surgery; resume warfarin 12-24 hr after surgery; bridge anticoagulation during interruption in patients at high thromboembolism risk

Minor procedures and dental procedures: See ACCP guidelines for specific recommendations

Warfarin has no direct effect on an established thrombus, nor does it reverse ischemic tissue damage

Systemic atheroemboli and cholesterol microemboli; some cases have progressed to necrosis or death; discontinue therapy if such emboli occur

Pregnant women with mechanical heart valves: Therapy may cause fetal harm; however, benefits may outweigh the risks

Thrombosis

Prevention/treatment: If baseline INR is 1.0-1.3, administer loading dose of 0.1-0.2 mg/kg PO qDay × 1 day; check INR on days 2-4 and adjust daily dose to maintain INR between 2.0 and 3.0 (unless valve replacement indicates a higher range)  

Use 0.1 mg/kg to initiate therapy with liver impairment or in patients who have had a Fontan procedure

Typical maintenance dose: 0.09-0.33 mg/kg/day, with infants <12 months old often requiring doses at high end of range

Dosing considerations

• Consistent anticoagulation in children is difficult and requires close supervision and frequent dose adjustments
• Refer to ACCP recommendations or institutional protocol for treatment duration dependent on indication
• Infants and children receiving vitamin K-supplemented nutrition (including infant formulas): May be resistant to warfarin therapy
• Infants with human-milk diet: May be sensitive to warfarin therapy

Dosing Considerations

Hepatic impairment

• Hepatic impairment may potentiate warfarin response because of decreased metabolism and impaired synthesis of clotting factors
• Load: 0.1 mg/kg PO qDay × 2 days
• Typical maintenance dose: 0.1 mg/kg PO qDay; adjust dose to achieve desired INR
• Common maintenance dose range: 0.05-0.34 mg/kg PO qDay

Anticoagulation

Lower doses required to produce therapeutic level of anticoagulation

Initial: ≤5 mg PO qDay

Maintenance: 2-5 mg PO qDay

Dosing Considerations

Elderly show greater than expected PT/INR response to anticoagulant effects of warfarin, possibly because of decreased hepatic function resulting in decreased warfarin metabolism and impaired synthesis of clotting factors

Caution should be used in elderly individuals who have increased risk of hemorrhage

Contraindicated (3)

• apixaban

  warfarin and apixaban both increase anticoagulation. Contraindicated.

• defibrotide

  defibrotide increases effects of warfarin by pharmacodynamic synergism. Contraindicated. Coadministration of defibrotide is contraindicated with antithrombotic/fibrinolytic drugs. This does not include use for routine maintenance or reopening of central venous lines.

• mifepristone

  mifepristone, warfarin. Other (see comment). Contraindicated. Comment: Mifepristone may lead to excessive post abortion bleeding in pts. on anticoagulant therapy.

Serious - Use Alternative (125)

• abciximab

  warfarin, abciximab. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• allopurinol

  allopurinol increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• amiodarone

  amiodarone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• amobarbital

  amobarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.

• anagrelide

  warfarin, anagrelide. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• antithrombin alfa

  antithrombin alfa and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• antithrombin III

  antithrombin III and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• argatroban

  argatroban and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• azithromycin

  azithromycin increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• bazedoxifene/conjugated estrogens

  bazedoxifene/conjugated estrogens decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• bemiparin

  bemiparin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• bivalirudin

  bivalirudin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• bremelanotide

  bremelanotide will decrease the level or effect of warfarin 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.

• butabarbital

  butabarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.

• butalbital

  butalbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.

• capecitabine

  capecitabine increases effects of warfarin by unspecified interaction mechanism. Avoid or Use Alternate Drug. Monitor INR and prothrombin time.

• carbamazepine

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

• cefamandole

  cefamandole increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• cefazolin

  cefazolin increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• cefdinir

  cefdinir increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefditoren

  cefditoren increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefotetan

  cefotetan increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefoxitin

  cefoxitin will increase the level or effect of warfarin by Other (see comment). Avoid or Use Alternate Drug. Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  cefoxitin increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefpodoxime

  cefpodoxime will increase the level or effect of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity

• ceftriaxone

  ceftriaxone increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefuroxime

  cefuroxime will increase the level or effect of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity

• ceritinib

  ceritinib increases levels of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. Avoid concurrent use of CYP2C9 substrates known to have narrow therapeutic indices or substrates primarily metabolized by CYP2C9 during treatment with ceritinib; if use of these medications is unavoidable, consider dose.

• chloral hydrate

  chloral hydrate increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• chloramphenicol

  chloramphenicol increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• cilostazol

  warfarin, cilostazol. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• cimetidine

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

• ciprofibrate

  ciprofibrate increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  ciprofibrate increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• ciprofloxacin

  ciprofloxacin will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Avoid or Use Alternate Drug. Quinolone antibiotics such as ciprofloxacin may enhance the anticoagulant effects of warfarin. Important to monitor INR/prothrombin time and toxic effects of warfarin. Patients receiving this combination should be closely monitored for adverse effects.

• clarithromycin

  clarithromycin increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• clotrimazole

  clotrimazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• conjugated estrogens

  conjugated estrogens decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• dabigatran

  dabigatran and warfarin both increase anticoagulation. Avoid or Use Alternate Drug. Both drugs have the potential to cause bleeding. Concomitant use may increase risk of bleeding.

• dabrafenib

  dabrafenib will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Dabrafenib induces CYP3A4 and possibly other enzymes including CYP2C9 that affect warfarin metabolism

• dalteparin

  dalteparin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• danazol

  danazol increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• dipyridamole

  warfarin, dipyridamole. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• duloxetine

  duloxetine increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• edoxaban

  edoxaban, warfarin. Either increases toxicity of the other by anticoagulation. Avoid or Use Alternate Drug. Both drugs have the potential to cause bleeding, monitor closely. Promptly evaluate any signs or symptoms of blood loss. Long-term concomitant treatment with edoxaban and other anticoagulants is not recommended. Short-term coadministration may be needed for patients transitioning to or from edoxaban.

• efavirenz

  efavirenz will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug.

• enoxaparin

  enoxaparin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug. Additive effects are intended when both drugs are prescribed as indicated for treatment of DVT

• eptifibatide

  warfarin, eptifibatide. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• erdafitinib

  warfarin will increase the level or effect of erdafitinib by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. If coadministration of a strong CYP2C9 inhibitors is unavoidable, closely monitor adverse reactions and modify dose of erdafitinib accordingly. If strong CYP2C9 inhibitor is discontinued, consider increasing erdafitinib dose in the absence of any drug-related toxicities.

• erythromycin base

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

• erythromycin ethylsuccinate

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

• erythromycin lactobionate

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

• erythromycin stearate

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

• escitalopram

  escitalopram increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• estradiol

  estradiol decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• estrogens conjugated synthetic

  estrogens conjugated synthetic decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• estropipate

  estropipate decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• ethinylestradiol

  ethinylestradiol will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Avoid or Use Alternate Drug. The use of estrogen-containing contraceptives and coumarin derivatives should be avoided to avoid risk of thromboembolic disorders.
  
  ethinylestradiol decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• fenofibrate

  fenofibrate increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  fenofibrate increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• fenofibrate micronized

  fenofibrate micronized increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  fenofibrate micronized increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• fenofibric acid

  fenofibric acid increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  fenofibric acid increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• fluconazole

  fluconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• fluoxetine

  fluoxetine increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• fluoxymesterone

  fluoxymesterone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• fluvoxamine

  fluvoxamine will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Avoid or Use Alternate Drug.

• fondaparinux

  fondaparinux and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• gemfibrozil

  gemfibrozil increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  gemfibrozil increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• heparin

  heparin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• ifosfamide

  ifosfamide, warfarin. Either increases toxicity of the other by nephrotoxicity and/or ototoxicity. Avoid or Use Alternate Drug. Monitor for increased INR/effects of coumarin derivatives when ifosfamide is initiated/dose increased, and decreased INR/effects when ifosfamide is discontinued/dose decreased.

• imatinib

  imatinib will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Because warfarin is metabolized by CYP2C9 and CYP3A4, patients taking imatinib who require anticoagulation should receive low-molecular weight or standard heparin instead of warfarin.

• itraconazole

  itraconazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  itraconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• ivosidenib

  ivosidenib will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sensitive CYP2C9 substrates with ivosidenib or replace with alternate therapies. If coadministration is unavoidable, monitor patients for loss of therapeutic effect of these drugs.

• ketoconazole

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

• levomilnacipran

  levomilnacipran, warfarin. Either increases toxicity of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. SNRIs may further impair platelet activity in patients taking antiplatelet or anticoagulant drugs.

• levonorgestrel intrauterine

  levonorgestrel intrauterine, warfarin. Either decreases effects of the other by pharmacodynamic antagonism. Avoid or Use Alternate Drug. Risk of thromboembolic disorders.

• levonorgestrel oral

  levonorgestrel oral, warfarin. Either decreases effects of the other by pharmacodynamic antagonism. Avoid or Use Alternate Drug. Risk of thromboembolic disorders.

• levothyroxine

  levothyroxine increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• liothyronine

  liothyronine increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• lorlatinib

  lorlatinib will decrease the level or effect of warfarin 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.

• mesterolone

  mesterolone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• mestranol

  mestranol decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• metronidazole

  metronidazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• miconazole vaginal

  miconazole vaginal increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• milnacipran

  milnacipran increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• nafcillin

  nafcillin decreases effects of warfarin by increasing hepatic clearance. Avoid or Use Alternate Drug.

• nefazodone

  nefazodone will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  nefazodone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• nitazoxanide

  nitazoxanide, warfarin. Either increases levels of the other by plasma protein binding competition. Avoid or Use Alternate Drug. the active metabolite of nitazoxanide is highly protein bound; avoid use of warfarin with nitazoxanide.

• oxandrolone

  oxandrolone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• oxymetholone

  oxymetholone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• paroxetine

  paroxetine increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• pefloxacin

  pefloxacin will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Avoid or Use Alternate Drug.

• pentobarbital

  pentobarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.

• phenindione

  phenindione and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• phenobarbital

  phenobarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.

• piperacillin

  piperacillin increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. Piperacillin can inhibit platelet aggregation.

• posaconazole

  posaconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• prasugrel

  warfarin, prasugrel. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• primidone

  primidone decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.

• protamine

  protamine and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• quinine

  quinine increases effects of warfarin by unknown mechanism. Avoid or Use Alternate Drug.

• rifabutin

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

• rifampin

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

• ritonavir

  ritonavir, warfarin. Other (see comment). Avoid or Use Alternate Drug. Comment: Variable effect on warfarin levels. Initial frequent monitoring of the INR during co-administration is indicated.

• roxithromycin

  roxithromycin increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• secobarbital

  secobarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.

• sertraline

  sertraline increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• siponimod

  warfarin will increase the level or effect of siponimod by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. Coadministration of siponimod with drugs that cause moderate CYP2C9 AND a moderate or strong CYP3A4 inhibition is not recommended. Caution if siponimod coadministered with moderate CYP2C9 inhibitors alone.

• St John's Wort

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

• sulfadiazine

  sulfadiazine increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.
  
  sulfadiazine increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• sulfamethoxazole

  sulfamethoxazole increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.
  
  sulfamethoxazole increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• sulfisoxazole

  sulfisoxazole increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.
  
  sulfisoxazole increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• tamoxifen

  tamoxifen increases effects of warfarin by unknown mechanism. Avoid or Use Alternate Drug.

• tenecteplase

  warfarin and tenecteplase both increase anticoagulation. Avoid or Use Alternate Drug.

• tesamorelin

  tesamorelin will decrease the level or effect of warfarin by altering metabolism. Avoid or Use Alternate Drug. Monitor INR

• testosterone

  testosterone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• testosterone buccal system

  testosterone buccal system increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• testosterone intranasal

  testosterone intranasal increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug. Androgens may inhibit warfarin metabolism and/or potentiate anticoagulant effects by affecting the coagulation system.

• testosterone topical

  testosterone topical increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• thyroid desiccated

  thyroid desiccated increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• tibolone

  tibolone increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• ticlopidine

  warfarin, ticlopidine. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• tirofiban

  warfarin, tirofiban. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• trazodone

  trazodone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• venlafaxine

  venlafaxine increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• vitamin K1 (phytonadione)

  vitamin K1 (phytonadione) decreases effects of warfarin by pharmacodynamic antagonism. Avoid or Use Alternate Drug. Monitor for decreased prothrombin time or therapeutic effects.

• voriconazole

  voriconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• zanubrutinib

  warfarin, zanubrutinib. Either increases effects of the other by anticoagulation. Avoid or Use Alternate Drug. Zanubrutinib-induced cytopenias increases risk of hemorrhage. Coadministration of zanubritinib with antiplatelets or anticoagulants may further increase this risk.

Monitor Closely (302)

• acalabrutinib

  acalabrutinib increases effects of warfarin by anticoagulation. Use Caution/Monitor. Coadministration of acalabrutinib with antiplatelets or anticoagulants may further increase risk of hemorrhage. Monitor for signs of bleeding and consider the benefit-risk of withholding acalabrutinib for 3-7 days presurgery and postsurgery depending upon the type of surgery and the risk of bleeding.

• aceclofenac

  warfarin and aceclofenac both increase anticoagulation. Modify Therapy/Monitor Closely.

• acemetacin

  warfarin and acemetacin both increase anticoagulation. Modify Therapy/Monitor Closely.

• acetaminophen

  acetaminophen increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• agrimony

  warfarin and agrimony both increase anticoagulation. Modify Therapy/Monitor Closely.

• alfalfa

  warfarin and alfalfa both increase anticoagulation. Modify Therapy/Monitor Closely.

• alpelisib

  warfarin will increase the level or effect of alpelisib by affecting hepatic enzyme CYP2C19 metabolism. Modify Therapy/Monitor Closely.
  
  alpelisib will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Modify Therapy/Monitor Closely.

• alteplase

  warfarin and alteplase both increase anticoagulation. Modify Therapy/Monitor Closely.

• American ginseng

  warfarin and American ginseng both increase anticoagulation. Modify Therapy/Monitor Closely.

• amikacin

  amikacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• amiodarone

  amiodarone will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• amobarbital

  amobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  amobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  amobarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• amoxicillin

  amoxicillin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Amoxicillin may enhance anticoagulant effect of vitamin K antagonists.

• ampicillin

  ampicillin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• anamu

  warfarin and anamu both increase anticoagulation. Use Caution/Monitor.

• anticholinergic/sedative combos

  anticholinergic/sedative combos decreases levels of warfarin by increasing metabolism. Use Caution/Monitor.

• apalutamide

  apalutamide will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Coadministration of apalutamide, a weak CYP2C9 inducer, with drugs that are CYP2C9 substrates can result in lower exposure to these medications. Evaluate for loss of therapeutic effect if medication must be coadministered.

• aprepitant

  aprepitant will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Modify Therapy/Monitor Closely. Aprepitant is a CYP2C9 inducer so coadministration with warfarin may result in a clinically significant decrease in INR. Monitor INR closely in patients on chronic warfarin therapy.

• armodafinil

  armodafinil will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  armodafinil will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• artemether/lumefantrine

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

• aspirin

  warfarin and aspirin both increase anticoagulation. Modify Therapy/Monitor Closely. The need for simultaneous use of low-dose aspirin and warfarin are common for patients with cardiovascular disease; monitor closely.

• aspirin rectal

  warfarin and aspirin rectal both increase anticoagulation. Modify Therapy/Monitor Closely.

• aspirin/citric acid/sodium bicarbonate

  warfarin and aspirin/citric acid/sodium bicarbonate both increase anticoagulation. Modify Therapy/Monitor Closely. The need for simultaneous use of low-dose aspirin and warfarin are common for patients with cardiovascular disease; monitor closely.

• atazanavir

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

• azapropazone

  azapropazone increases effects of warfarin by plasma protein binding competition. Use Caution/Monitor.

• azathioprine

  azathioprine decreases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• azficel-T

  azficel-T, warfarin. Other (see comment). Use Caution/Monitor. Comment: Coadministration with anticoagulants or antiplatelets may increase bruising or bleeding at biopsy and/or injection sites; concomitant use not recommended. Decisions regarding continued use or cessation of anticoagulants or antiplatelets should be made by a physician.

• betrixaban

  warfarin, betrixaban. Either increases levels of the other by anticoagulation. Use Caution/Monitor.

• bicalutamide

  bicalutamide increases effects of warfarin by pharmacodynamic synergism. Use Caution/Monitor. Prothrombin times should be closely monitored in patient already receiving coumarin anticoagulants who are started on bicalutamide.

• blinatumomab

  blinatumomab increases levels of warfarin 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.

• bortezomib

  bortezomib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Use Caution/Monitor. Clinical and laboratory monitoring is warranted in combining bortezomib with agents with narrow therapeutic ranges, such as warfarin.

• bosentan

  bosentan will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  bosentan will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• brodalumab

  brodalumab, warfarin. 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 warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  budesonide, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• bupropion

  bupropion increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Altered PT/INR infrequently associated with hemorrhagic or thrombotic complications were observed when bupropion was administered with warfarin. Monitor INR when bupropion is added to existing warfarin regimen.

• butabarbital

  butabarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  butabarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  butabarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• butalbital

  butalbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  butalbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  butalbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• cannabidiol

  cannabidiol will increase the level or effect of warfarin by decreasing metabolism. Modify Therapy/Monitor Closely. Cannabidiol may potentially inhibit CYP2C9 activity. Consider reducing the dose when concomitantly using CYP2C9 substrates.

• caplacizumab

  caplacizumab, warfarin. Either increases effects of the other by anticoagulation. Use Caution/Monitor.

• carbamazepine

  carbamazepine will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  carbamazepine will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  carbamazepine decreases levels of warfarin by increasing metabolism. Use Caution/Monitor.

• cefaclor

  cefaclor increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefdinir

  cefdinir increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefixime

  cefixime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefotaxime

  cefotaxime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefpodoxime

  cefpodoxime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefprozil

  cefprozil increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• ceftazidime

  ceftazidime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• ceftibuten

  ceftibuten increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• ceftriaxone

  ceftriaxone increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefuroxime

  cefuroxime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• celecoxib

  warfarin and celecoxib both increase anticoagulation. Modify Therapy/Monitor Closely.

• chitosan

  chitosan increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Chitosan can decrease GI absorption of vitamin K, enhancing anticoagulant effects.

• cholestyramine

  cholestyramine decreases levels of warfarin by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

• choline magnesium trisalicylate

  warfarin and choline magnesium trisalicylate both increase anticoagulation. Modify Therapy/Monitor Closely.

• cigarette smoking

  cigarette smoking will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• cimetidine

  cimetidine will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  cimetidine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• cinnamon

  warfarin and cinnamon both increase anticoagulation. Modify Therapy/Monitor Closely.

• citalopram

  citalopram increases levels of warfarin by decreasing metabolism. Use Caution/Monitor. Coadministration of warfarin and citalopram increased prothrombin time by 5%. Use caution with coadministration and monitor patient.

• clarithromycin

  clarithromycin increases toxicity of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Increased risk of hemorrage; monitor INR and prothrombin times frequently.

• clindamycin

  clindamycin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• clopidogrel

  warfarin, clopidogrel. Either increases effects of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Enhanced risk of hemorrhage; additive effects may occur when simultaneous use is clinically required .

• cobicistat

  cobicistat, warfarin. Other (see comment). Use Caution/Monitor. Comment: Effect unknown; monitor INR .

• colesevelam

  colesevelam will decrease the level or effect of warfarin by Mechanism: inhibition of GI absorption. Applies only to oral form of both agents. Modify Therapy/Monitor Closely. Administer warfarin at least 4 hr before colesevelam. Monitor INR frequently during colesevelam initiation or discontinuance.

• collagenase clostridium histolyticum

  warfarin increases toxicity of collagenase clostridium histolyticum by anticoagulation. Use Caution/Monitor. Collagenase clostridium histolyticum has high incidence of ecchymosis/contusion at injection site; avoid concomitant anticoagulants (except for low-dose aspirin, ie, up to 150 mg/day).

• conivaptan

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

• conjugated estrogens, vaginal

  conjugated estrogens, vaginal decreases effects of warfarin by pharmacodynamic antagonism. Modify Therapy/Monitor Closely. Risk of thromboembolic disorders.

• cordyceps

  warfarin and cordyceps both increase anticoagulation. Modify Therapy/Monitor Closely.

• cornsilk

  cornsilk decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor. Cornsilk contains vitamin K; consume a consistent amount daily.

• cortisone

  cortisone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  cortisone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• cyclophosphamide

  cyclophosphamide increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Anticoagulant effect is increased. Monitor coagulation parameters during and after cyclophosphamide therapy. Adjust the warfarin dose as needed.

• cyclosporine

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

• danshen

  warfarin and danshen both increase anticoagulation. Use Caution/Monitor.

• darifenacin

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

• darunavir

  darunavir will decrease the level or effect of warfarin by unspecified interaction mechanism. Use Caution/Monitor. Monitor INR before initiating. Increase monitoring with concurrent therapy.

• dasatinib

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

• dasiglucagon

  dasiglucagon increases effects of warfarin by unknown mechanism. Use Caution/Monitor. High doses of dasiglucagon may enhance anticoagulant effects of vitamin K antagonists.

• deferasirox

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

• deflazacort

  deflazacort, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• devil's claw

  warfarin and devil's claw both increase anticoagulation. Use Caution/Monitor.

• dexamethasone

  dexamethasone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  dexamethasone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• DHEA, herbal

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

• diclofenac

  warfarin and diclofenac both increase anticoagulation. Modify Therapy/Monitor Closely.

• dicloxacillin

  dicloxacillin decreases levels of warfarin by increasing metabolism. Use Caution/Monitor.

• diflunisal

  warfarin and diflunisal both increase anticoagulation. Modify Therapy/Monitor Closely.
  
  diflunisal increases effects of warfarin by plasma protein binding competition. Use Caution/Monitor.

• disulfiram

  disulfiram will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  disulfiram increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor.

• dong quai

  warfarin and dong quai both increase anticoagulation. Modify Therapy/Monitor Closely.

• dronabinol

  dronabinol increases levels of warfarin by plasma protein binding competition. Modify Therapy/Monitor Closely. Dronabinol is highly bound to plasma proteins and may displace and increase the free fraction of other concomitantly administered highly protein-bound drugs. This has not been confirmed in vivo. Caution with narrow therapeutic index drugs that are highly protein bound when initiating or increasing the dose of dronabinol.

• dronedarone

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

• dulaglutide

  dulaglutide, warfarin. 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, warfarin. 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.

• econazole topical

  econazole topical increases effects of warfarin by decreasing metabolism. Use Caution/Monitor. Most cases reported use of econazole under occlusive bandage, genital application, or application to large body surface area which may increase the systemic absorption.

• efavirenz

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

• elbasvir/grazoprevir

  elbasvir/grazoprevir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• eluxadoline

  eluxadoline increases levels of warfarin 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/cobicistat/emtricitabine/tenofovir DF

  elvitegravir/cobicistat/emtricitabine/tenofovir DF decreases levels of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Elvitegravir is a moderate CYP2C9 inducer.

• epoprostenol

  warfarin and epoprostenol both increase anticoagulation. Modify Therapy/Monitor Closely.

• erythromycin base

  erythromycin base will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• erythromycin ethylsuccinate

  erythromycin ethylsuccinate will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• erythromycin lactobionate

  erythromycin lactobionate will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• erythromycin stearate

  erythromycin stearate will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• eslicarbazepine acetate

  eslicarbazepine acetate will decrease the level or effect of warfarin by increasing metabolism. Use Caution/Monitor. S-warfarin serum concentrations may be decreased. Monitor coagulation parameters (INR) when initiating or discontinuing eslicarbazepine in patients

• estrogens esterified

  estrogens esterified decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor. Estrogens may theoretically reduce the effect of anticoagulants.

• ethanol

  ethanol, warfarin. Mechanism: altering metabolism. Use Caution/Monitor. Avoid alcohol ingestion; acute, excessive EtOH ingestion (binge drinking) decreases .

• ethinylestradiol

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

• ethotoin

  warfarin increases levels of ethotoin by unknown mechanism. Use Caution/Monitor.
  
  ethotoin, warfarin. Other (see comment). Use Caution/Monitor. Comment: Hydantoin anticonvulsants increase anticoagulant effects at first, then decrease those effects with continued use (2+ wks). There are multiple mechanisms involved, including enzyme induction, plasma protein binding site competition, and additive effects on prothrombin time.

• etodolac

  warfarin and etodolac both increase anticoagulation. Modify Therapy/Monitor Closely.

• etravirine

  etravirine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• exenatide injectable solution

  exenatide injectable solution, warfarin. Other (see comment). Use Caution/Monitor. Comment: Exenatide may increase INR and possibly increase bleeding when coadministered with warfarin. Monitor prothrombin (PT) time more frequently after starting or changing dose of exenatide. Once a stable PT time is established, monitor PT times at intervals usually recommended for patients taking warfarin.

• exenatide injectable suspension

  exenatide injectable suspension, warfarin. Other (see comment). Use Caution/Monitor. Comment: Exenatide may increase INR and possibly increase bleeding when coadministered with warfarin. Monitor prothrombin (PT) time more frequently after starting or changing dose of exenatide. Once a stable PT time is established, monitor PT times at intervals usually recommended for patients taking warfarin.

• felbamate

  felbamate will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• fenbufen

  warfarin and fenbufen both increase anticoagulation. Modify Therapy/Monitor Closely.

• fennel

  warfarin and fennel both increase anticoagulation. Modify Therapy/Monitor Closely.

• fenoprofen

  warfarin and fenoprofen both increase anticoagulation. Modify Therapy/Monitor Closely.

• ferric maltol

  ferric maltol, warfarin. 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).

• feverfew

  warfarin and feverfew both increase anticoagulation. Modify Therapy/Monitor Closely.

• fish oil

  fish oil, warfarin. Other (see comment). Use Caution/Monitor. Comment: Patients taking fish oil and an anticoagulant or other drug affecting coagulation should be monitored periodically due to potential increased risk of bleeding. Monitor for changes in INR.

• fish oil triglycerides

  fish oil triglycerides will increase the level or effect of warfarin by anticoagulation. Use Caution/Monitor. Prolonged bleeding reported in patients taking antiplatelet agents or anticoagulants and oral omega-3 fatty acids. Periodically monitor bleeding time in patients receiving fish oil triglycerides and concomitant antiplatelet agents or anticoagulants.

• fleroxacin

  fleroxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• fluconazole

  fluconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  fluconazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• fludrocortisone

  fludrocortisone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  fludrocortisone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• fluorouracil

  fluorouracil increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor. Due to the thrombocytopenic effects of fluorouracil, an additive risk of bleeding may be seen in patients receiving concomitant anticoagulants.

• fluoxetine

  fluoxetine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Use Caution/Monitor.
  
  fluoxetine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• flurbiprofen

  warfarin and flurbiprofen both increase anticoagulation. Modify Therapy/Monitor Closely.

• flutamide

  flutamide increases effects of warfarin by pharmacodynamic synergism. Use Caution/Monitor. Increases in prothrombin time have been noted in patients receiving long-term warfarin therapy after flutamide was initiated. Close monitoring of prothrombin time is recommended.

• fluvastatin

  fluvastatin increases effects of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• fluvoxamine

  fluvoxamine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Use Caution/Monitor.

• food

  food decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor. Specifically, vitamin K rich foods (e.g., dark leafy green vegetables).

• forskolin

  warfarin and forskolin both increase anticoagulation. Modify Therapy/Monitor Closely.

• fosamprenavir

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

• fosphenytoin

  fosphenytoin will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  warfarin increases levels of fosphenytoin by unknown mechanism. Use Caution/Monitor.
  
  fosphenytoin, warfarin. Other (see comment). Use Caution/Monitor. Comment: Hydantoin anticonvulsants increase anticoagulant effects at first, then decrease those effects with continued use (2+ wks). There are multiple mechanisms involved, including enzyme induction, plasma protein binding site competition, and additive effects on prothrombin time.

• garlic

  warfarin and garlic both increase anticoagulation. Modify Therapy/Monitor Closely.

• gefitinib

  gefitinib increases effects of warfarin by unknown mechanism. Modify Therapy/Monitor Closely. Gefitinib prescribing information reports some patients receiving concomitant warfarin experienced increased INR and/or bleeding.

• gemcitabine

  gemcitabine increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor. The anticoagulant effect of warfarin may be increased.

• gemifloxacin

  gemifloxacin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  gemifloxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• ginger

  warfarin and ginger both increase anticoagulation. Modify Therapy/Monitor Closely.

• ginkgo biloba

  warfarin and ginkgo biloba both increase anticoagulation. Modify Therapy/Monitor Closely.

• glecaprevir/pibrentasvir

  glecaprevir/pibrentasvir increases and warfarin decreases Other (see comment). Effect of interaction is not clear, use caution. Use Caution/Monitor. Warfarin is a substrate of OATP and BCRP, which has been suggested to cause fluctuations in warfarin absorption; close monitoring of INR values is recommended during treatment and post-treatment follow-up.

• glucagon

  glucagon increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• glucagon intranasal

  glucagon intranasal increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• grapefruit

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

• green tea

  green tea decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor. Combination may decrease warfarin efficacy. Potential for increased risk of bleeding. Important to monitor INR.

• griseofulvin

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

• guselkumab

  guselkumab, warfarin. 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.

• hemin

  warfarin, hemin. Either increases effects of the other by anticoagulation. Use Caution/Monitor. Hemin degradation product (ie, hematin) may produce coagulopathy (eg, thrombocytopenia, platelet degranulation) and cause mild anticoagulant effects.

• horse chestnut seed

  warfarin and horse chestnut seed both increase anticoagulation. Modify Therapy/Monitor Closely.

• hydrocortisone

  hydrocortisone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  hydrocortisone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• ibrutinib

  ibrutinib will increase the level or effect of warfarin by anticoagulation. Use Caution/Monitor. Ibrutinib may increase the risk of hemorrhage in patients receiving antiplatelet or anticoagulant therapies and monitor for signs of bleeding.

• ibuprofen

  warfarin and ibuprofen both increase anticoagulation. Modify Therapy/Monitor Closely.

• ibuprofen IV

  warfarin and ibuprofen IV both increase anticoagulation. Modify Therapy/Monitor Closely.

• icosapent

  icosapent, warfarin. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Icosapent may prolong bleeding time; monitor periodically if coadministered with other drugs that affect bleeding.

• indinavir

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

• indomethacin

  warfarin and indomethacin both increase anticoagulation. Modify Therapy/Monitor Closely.

• iodine (radioactive)

  iodine (radioactive) decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor.

• isoniazid

  isoniazid will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  isoniazid will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Use Caution/Monitor.
  
  isoniazid will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• ivermectin

  ivermectin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Rare interaction.

• ixekizumab

  ixekizumab, warfarin. 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

  ketoconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• ketoprofen

  warfarin and ketoprofen both increase anticoagulation. Modify Therapy/Monitor Closely.

• ketorolac

  warfarin and ketorolac both increase anticoagulation. Modify Therapy/Monitor Closely.

• ketorolac intranasal

  warfarin and ketorolac intranasal both increase anticoagulation. Modify Therapy/Monitor Closely.

• ledipasvir/sofosbuvir

  ledipasvir/sofosbuvir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• leflunomide

  leflunomide will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• letermovir

  letermovir will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Monitor INR.

• levocarnitine

  levocarnitine will increase the level or effect of warfarin by unknown mechanism. Use Caution/Monitor. INR may increase in patients receiving warfarin therapy; monitor INR levels following initiation of levocarnitine therapy and after dose adjustments

• levofloxacin

  levofloxacin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  levofloxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• lofepramine

  lofepramine increases levels of warfarin by decreasing metabolism. Use Caution/Monitor.

• lomitapide

  lomitapide will increase the level or effect of warfarin by unspecified interaction mechanism. Modify Therapy/Monitor Closely. Increases plasma concentration of R(+)-warfarin and S(-)-warfarin and INR significantly. Monitor INR especially after changing lomitapide dosage. Adjust warfarin dose as necessary.

• lornoxicam

  warfarin and lornoxicam both increase anticoagulation. Modify Therapy/Monitor Closely.

• lovastatin

  lovastatin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• lumacaftor/ivacaftor

  lumacaftor/ivacaftor, warfarin. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. In vitro studies suggest that lumacaftor may induce and ivacaftor may inhibit CYP2C9 substrates. .
  
  lumacaftor/ivacaftor increases levels of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor INR when coadministration required. The less potent warfarin R-enantiomer is metabolized by CYP3A4.

• lumefantrine

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

• marijuana

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

• meclofenamate

  warfarin and meclofenamate both increase anticoagulation. Modify Therapy/Monitor Closely.

• mefenamic acid

  warfarin and mefenamic acid both increase anticoagulation. Modify Therapy/Monitor Closely.

• melatonin

  melatonin increases effects of warfarin by anticoagulation. Use Caution/Monitor. Melatonin may decrease prothrombin time.

• meloxicam

  warfarin and meloxicam both increase anticoagulation. Modify Therapy/Monitor Closely.

• mercaptopurine

  mercaptopurine decreases effects of warfarin by unknown mechanism. Use Caution/Monitor. Inhibition of the anticoagulant effect of warfarin, when given with mercaptopurine, has been reported.

• mesalamine

  mesalamine decreases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• methimazole

  methimazole decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor.

• methylphenidate

  methylphenidate will increase the level or effect of warfarin by unknown mechanism. Use Caution/Monitor.

• methylprednisolone

  methylprednisolone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  methylprednisolone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• methyltestosterone

  methyltestosterone increases levels of warfarin by decreasing metabolism. Use Caution/Monitor. Monitor INR.

• metronidazole

  metronidazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  metronidazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• mexiletine

  mexiletine will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• miconazole vaginal

  miconazole vaginal will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  miconazole vaginal will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• mistletoe

  warfarin increases and mistletoe decreases anticoagulation. Effect of interaction is not clear, use caution. Modify Therapy/Monitor Closely.

• mitotane

  mitotane will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor INR for a change in anticoagulant dosage requirements when warfarin is coadministered with mitotane (strong CYP3A4 inducer)

• modafinil

  modafinil will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  modafinil will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• moxifloxacin

  moxifloxacin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  moxifloxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• nabumetone

  warfarin and nabumetone both increase anticoagulation. Modify Therapy/Monitor Closely.

• naproxen

  warfarin and naproxen both increase anticoagulation. Modify Therapy/Monitor Closely.

• nateglinide

  nateglinide will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• nelfinavir

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

• neomycin PO

  neomycin PO increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• nettle

  warfarin increases and nettle decreases anticoagulation. Effect of interaction is not clear, use caution. Modify Therapy/Monitor Closely.

• nevirapine

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

• nifedipine

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

• nilotinib

  nilotinib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  nilotinib will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• nilutamide

  nilutamide will increase the level or effect of warfarin by decreasing metabolism. Use Caution/Monitor.

• nintedanib

  nintedanib increases effects of warfarin by anticoagulation. Use Caution/Monitor. Nintedanib is a VEGFR inhibitor, and may increase the risk of bleeding; monitor patients on full anticoagulation therapy; monitor closely for bleeding and adjust therapy as needed .

• nitisinone

  nitisinone will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Nitisinone inhibits CYP2C9. Caution if CYP2C9 substrate coadministered, particularly those with a narrow therapeutic index.

• obeticholic acid

  obeticholic acid decreases effects of warfarin by unknown mechanism. Modify Therapy/Monitor Closely. Coadministration has been shown to increase S-warfarin exposure by 13%, but lowered INR by 11%. Monitor INR and adjust warfarin dose accordingly.

• ofloxacin

  ofloxacin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  ofloxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• omadacycline

  omadacycline increases toxicity of warfarin by anticoagulation. Modify Therapy/Monitor Closely. Tetracyclines may interfere with the bactericidal action of penicillins. Monitor for decreased therapeutic effects of penicillins if concomitantly used with a tetracycline.

• ombitasvir/paritaprevir/ritonavir & dasabuvir

  ombitasvir/paritaprevir/ritonavir & dasabuvir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• omega 3 carboxylic acids

  omega 3 carboxylic acids, warfarin. Other (see comment). Use Caution/Monitor. Comment: Patients taking omega-3 acids and an anticoagulant or other drug affecting coagulation should be monitored periodically due to potential increased risk of bleeding.

• omega 3 fatty acids

  omega 3 fatty acids, warfarin. Other (see comment). Use Caution/Monitor. Comment: Patients taking omega-3-fatty acids and an anticoagulant or other drug affecting coagulation should be monitored periodically due to potential increased risk of bleeding. Monitor for changes in INR.

• omeprazole

  omeprazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• oritavancin

  oritavancin will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Oritavancin is a weak CYP2C9 inhibitor; caution if coadministered with CYP2C9 substrates that have a narrow therapeutic index

• orlistat

  orlistat decreases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Orlistat may decrease vitamin K absorption; patients on chronic stable doses of warfarin who are prescribed orlistat should be monitored closely for changes in coagulation parameters.

• ospemifene

  warfarin, ospemifene. Either increases levels of the other by plasma protein binding competition. Modify Therapy/Monitor Closely.

• oxaprozin

  warfarin and oxaprozin both increase anticoagulation. Modify Therapy/Monitor Closely.

• oxcarbazepine

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

• panax ginseng

  warfarin and panax ginseng both increase anticoagulation. Modify Therapy/Monitor Closely.

• parecoxib

  warfarin and parecoxib both increase anticoagulation. Modify Therapy/Monitor Closely.

• paromomycin

  paromomycin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• pau d'arco

  warfarin and pau d'arco both increase anticoagulation. Modify Therapy/Monitor Closely.

• pegaspargase

  pegaspargase increases effects of warfarin by pharmacodynamic synergism. Use Caution/Monitor. Increased risk of bleeding events.

• peginterferon alfa 2a

  peginterferon alfa 2a will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• peginterferon alfa 2b

  peginterferon alfa 2b decreases levels of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. When patients are administered peginterferon alpha-2b with CYP2C9 substrates, the therapeutic effect of these drugs may be altered. .

• pentobarbital

  pentobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  pentobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  pentobarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• pentoxifylline

  pentoxifylline increases effects of warfarin by pharmacodynamic synergism. Use Caution/Monitor.

• phenobarbital

  phenobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  phenobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  phenobarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• phenytoin

  phenytoin will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  warfarin increases levels of phenytoin by unknown mechanism. Use Caution/Monitor.
  
  phenytoin, warfarin. Other (see comment). Use Caution/Monitor. Comment: Hydantoin anticonvulsants increase anticoagulant effects at first, then decrease those effects with continued use (2+ wks). There are multiple mechanisms involved, including enzyme induction, plasma protein binding site competition, and additive effects on prothrombin time.

• phytoestrogens

  warfarin and phytoestrogens both increase anticoagulation. Modify Therapy/Monitor Closely.

• pipemidic acid

  pipemidic acid will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• piroxicam

  warfarin and piroxicam both increase anticoagulation. Modify Therapy/Monitor Closely.

• pitolisant

  pitolisant will decrease the level or effect of warfarin by Other (see comment). Use Caution/Monitor. Pitolisant is a borderline/weak inducer of CYP3A4. Monitor sensitive CYP3A4 substrates for reduced effectiveness if coadministered.

• porfimer

  warfarin decreases effects of porfimer by pharmacodynamic antagonism. Use Caution/Monitor.

• posaconazole

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

• prednisolone

  prednisolone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• prednisone

  prednisone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  prednisone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• primidone

  primidone will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  primidone will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  primidone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• propafenone

  propafenone increases effects of warfarin by decreasing metabolism. Use Caution/Monitor.

• propranolol

  propranolol increases levels of warfarin by decreasing metabolism. Use Caution/Monitor. The anticoagulant effect of warfarin may be increased.

• propylthiouracil

  propylthiouracil decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor.

• quinidine

  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.

• quinupristin/dalfopristin

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

• regorafenib

  regorafenib will increase the level or effect of warfarin by anticoagulation. Use Caution/Monitor. Monitor INR more frequently

• reishi

  warfarin and reishi both increase anticoagulation. Modify Therapy/Monitor Closely.

• reteplase

  warfarin and reteplase both increase anticoagulation. Modify Therapy/Monitor Closely.

• ribociclib

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

• rifabutin

  rifabutin decreases levels of warfarin by increasing metabolism. Use Caution/Monitor.

• rifampin

  rifampin will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  rifampin will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• rifapentine

  rifapentine will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  rifapentine will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• rifaximin

  rifaximin decreases effects of warfarin by increasing metabolism. Use Caution/Monitor. May occur in patients with GI disease that increases intestinal permeability (increased systemic absorption of rifaximin).

• ritonavir

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

• rivaroxaban

  rivaroxaban, warfarin. Either increases effects of the other by anticoagulation. Use Caution/Monitor. Avoid concurrent use of rivaroxaban with other anticoagulants due to increased bleeding risk other than during therapeutic transition periods where patients should be observed closely. Monitor for signs/symptoms of blood loss.

• romidepsin

  romidepsin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Possible elevation of INR.

• rosuvastatin

  rosuvastatin increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor.

• rucaparib

  rucaparib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Modify Therapy/Monitor Closely. Adjust dosage of CYP1A2 substrates, if clinically indicated. If coadministration with warfarin (a CYP2C9 substrate) cannot be avoided, consider increasing the dosing frequency of INR monitoring.

• rufinamide

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

• salicylates (non-asa)

  warfarin and salicylates (non-asa) both increase anticoagulation. Modify Therapy/Monitor Closely.

• salsalate

  warfarin and salsalate both increase anticoagulation. Modify Therapy/Monitor Closely.

• sarecycline

  sarecycline increases toxicity of warfarin by anticoagulation. Modify Therapy/Monitor Closely. Tetracyclines may interfere with the bactericidal action of penicillins. Monitor for decreased therapeutic effects of penicillins if concomitantly used with a tetracycline.

• sarilumab

  sarilumab, warfarin. 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.

• saw palmetto

  saw palmetto increases toxicity of warfarin by unspecified interaction mechanism. Use Caution/Monitor. May increase risk of bleeding.

• schisandra

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

• secobarbital

  secobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  secobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  secobarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• secukinumab

  secukinumab, warfarin. 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.

• selumetinib

  warfarin and selumetinib both increase anticoagulation. Modify Therapy/Monitor Closely. An increased risk of bleeding may occur in patients taking a vitamin-K antagonist or an antiplatelet agent with selumetinib. Monitor for bleeding and INR or PT in patients coadministered a vitamin-K antagonist or an antiplatelet agent with selumetinib.

• Siberian ginseng

  warfarin and Siberian ginseng both increase anticoagulation. Modify Therapy/Monitor Closely.

• siltuximab

  siltuximab, warfarin. 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.

• simvastatin

  simvastatin, warfarin. Either increases effects of the other by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Competition by each drug for CYP3A4-mediated metabolism may result in increased INR and increased risk of rhabdomyolysis.

• smoking

  smoking will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• sodium zirconium cyclosilicate

  sodium zirconium cyclosilicate will increase the level or effect of warfarin by increasing gastric pH. Applies only to oral form of both agents. Modify Therapy/Monitor Closely. Separate administration by at least 2 hr. Medications that are weak acids (eg, warfarin) are more readily absorbed with elevated gastric pH.

• sofosbuvir

  sofosbuvir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• sofosbuvir/velpatasvir

  sofosbuvir/velpatasvir, warfarin. unspecified interaction mechanism. Use Caution/Monitor. Fluctuations in INR reported in patients treated for HCV with direct acting antiviral agents. Close monitoring of INR values recommended during treatment and post-treatment follow-up.

• spironolactone

  spironolactone decreases effects of warfarin by unknown mechanism. Use Caution/Monitor. Interaction is theorized to result from increased concentration of clotting factors as a result of diuresis.

• streptomycin

  streptomycin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• sulfamethoxazole

  sulfamethoxazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• sulfasalazine

  warfarin and sulfasalazine both increase anticoagulation. Modify Therapy/Monitor Closely.

• sulindac

  warfarin and sulindac both increase anticoagulation. Modify Therapy/Monitor Closely.

• tamsulosin

  warfarin, tamsulosin. Other (see comment). Use Caution/Monitor. Comment: Manufacturer's prescribing information states limited in vitro and in vivo studies were inconclusive; caution advised.

• teduglutide

  teduglutide increases levels of warfarin 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.

• teriflunomide

  teriflunomide decreases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor. May decrease INR by 25%; monitor and adjust warfarin dose accordingly.

• ticagrelor

  ticagrelor, warfarin. Either increases effects of the other by anticoagulation. Use Caution/Monitor. Increased risk of bleeding during concomitant use of medications that increase potential for bleeding.

• ticarcillin

  ticarcillin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• ticlopidine

  ticlopidine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• tigecycline

  tigecycline increases levels of warfarin by decreasing elimination. Use Caution/Monitor. Minimal effect on INR; monitor.

• tinidazole

  tinidazole will increase the level or effect of warfarin by anticoagulation. Modify Therapy/Monitor Closely. Enhanced anticoagulation effect may result in a prolongation of prothrombin time. Dosage of warfarin and other coumarin agents may need to be adjusted during coadministration and up to 8 days after discontinuation of tinidazole.

• tipranavir

  tipranavir, warfarin. Mechanism: unspecified interaction mechanism. Use Caution/Monitor. Effect on warfarin levels cannot be predicted; monitor INR frequently upon starting tipranavir Tx. Tipranavir may affect coagulation parameters and platelet aggregation; caution when coadministered w/ drugs that inhibit platelet aggregation or coagulation.

• tobacco use

  tobacco use will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• tobramycin

  tobramycin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• tolfenamic acid

  warfarin and tolfenamic acid both increase anticoagulation. Modify Therapy/Monitor Closely.

• tolmetin

  warfarin and tolmetin both increase anticoagulation. Modify Therapy/Monitor Closely.

• topiramate

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

• toremifene

  toremifene increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor. When concomitant use of anticoagulants with toremifene citrate is necessary, careful monitoring of the prothrombin time is recommended.

• triamcinolone acetonide injectable suspension

  triamcinolone acetonide injectable suspension, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• triclofos

  triclofos increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor.

• ustekinumab

  ustekinumab, warfarin. 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.

• valproic acid

  valproic acid will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• vemurafenib

  vemurafenib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Exercise caution and consider additional INR monitoring when vemurafenib is used concomitantly with warfarin.

• venetoclax

  venetoclax increases effects of warfarin by unknown mechanism. Modify Therapy/Monitor Closely. In a drug-drug interaction study in healthy subjects, administration of a single dose of venetoclax with warfarin resulted in an 18-28% increase in Cmax and AUC of R-warfarin and S-warfarin. Because venetoclax was not dosed to steady state, it is recommended that the INR be monitored closely in patients receiving warfarin. .

• verapamil

  verapamil will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  verapamil will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• vorapaxar

  warfarin, vorapaxar. Either increases effects of the other by anticoagulation. Use Caution/Monitor. Coadministration of anticoagulants, antiplatelets, or other drug affecting coagulation should be monitored periodically due to potential increased risk of bleeding.

• voriconazole

  voriconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  voriconazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• vorinostat

  vorinostat increases effects of warfarin by Mechanism: unspecified interaction mechanism. Use Caution/Monitor. Monitor PT and INR carefully.

• vortioxetine

  warfarin, vortioxetine. Either increases effects of the other by anticoagulation. Use Caution/Monitor.

• voxilaprevir

  voxilaprevir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• zafirlukast

  zafirlukast will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  zafirlukast will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• zileuton

  zileuton will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

Minor (50)

• acetaminophen IV

  acetaminophen IV increases effects of warfarin by unknown mechanism. Minor/Significance Unknown.

• acetaminophen rectal

  acetaminophen rectal increases effects of warfarin by unknown mechanism. Minor/Significance Unknown.

• alprostadil intracavernous/urethral

  alprostadil intracavernous/urethral increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• amobarbital

  amobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• armodafinil

  armodafinil will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• ascorbic acid

  ascorbic acid decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown. Dose >10 g/day vitamin C.

• butabarbital

  butabarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• butalbital

  butalbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• ceftaroline

  ceftaroline increases effects of warfarin by Other (see comment). Minor/Significance Unknown. Comment: Cephalosporins with a methylthiotetrazole (MTT) side ring (eg, cefotetan, cefoperazone) are more frequently associated with hypoprothrombinemic activity.

• chlorella

  chlorella decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown. Theoretical, due to vitamin K content.

• coenzyme Q10

  coenzyme Q10 decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown.

• colestipol

  colestipol decreases levels of warfarin by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

• cranberry

  cranberry increases effects of warfarin by unknown mechanism. Minor/Significance Unknown. Theoretical interaction, based on case reports. Cranberry may inhibit cytochrome P450 2C9.

• demeclocycline

  demeclocycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• dexmethylphenidate

  dexmethylphenidate increases effects of warfarin by decreasing metabolism. Minor/Significance Unknown.

• dimenhydrinate

  dimenhydrinate increases effects of warfarin by unknown mechanism. Minor/Significance Unknown.

• doxycycline

  doxycycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• efavirenz

  efavirenz will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• esomeprazole

  esomeprazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• etravirine

  etravirine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• felbamate

  felbamate will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• felodipine

  felodipine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• fluconazole

  fluconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• glyburide

  glyburide increases effects of warfarin by unspecified interaction mechanism. Minor/Significance Unknown.

• horseradish

  horseradish increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown. Theoretical interaction.

• metronidazole topical

  metronidazole topical will increase the level or effect of warfarin by decreasing metabolism. Minor/Significance Unknown. Oral metronidazole potentiates the effect of warfarin; less likely to occur with topical administration because of low absorption

• metronidazole vaginal

  metronidazole vaginal will increase the level or effect of warfarin by decreasing metabolism. Minor/Significance Unknown. Oral metronidazole potentiates the effect of warfarin; less likely to occur with vaginal administration because of low absorption

• mineral oil

  mineral oil decreases levels of warfarin by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

• minocycline

  minocycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• modafinil

  modafinil will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• omeprazole

  omeprazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• oxcarbazepine

  oxcarbazepine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• oxytetracycline

  oxytetracycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• parecoxib

  parecoxib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• parsley

  parsley increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown. Theoretical interaction.

• pentobarbital

  pentobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• phenobarbital

  phenobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• primidone

  primidone will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• raloxifene

  raloxifene increases effects of warfarin by plasma protein binding competition. Minor/Significance Unknown.

• ribavirin

  ribavirin decreases effects of warfarin by unknown mechanism. Minor/Significance Unknown. Case report.

• rifampin

  rifampin will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• rolapitant

  rolapitant, warfarin. Other (see comment). Minor/Significance Unknown. Comment: Coadministration of IV rolapitant with warfarin did not significantly increase systemic exposure to S-warfarin, the effects on INR and prothrombin time were not studied; monitor INR and prothrombin time and adjust the dosage of warfarin, as needed with concomitant use of rolapitant, to maintain the target INR range.

• rose hips

  rose hips decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown. Dose >10 g/day vitamin C.

• secobarbital

  secobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• sucralfate

  sucralfate decreases levels of warfarin by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

• tetracycline

  tetracycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• verteporfin

  warfarin decreases effects of verteporfin by pharmacodynamic antagonism. Minor/Significance Unknown.

• vitamin E

  vitamin E, warfarin. Mechanism: pharmacodynamic synergism. Minor/Significance Unknown. Vitamin E at RDA does not change INR in pts. on chronic warfarin therapy; megadoses (~10x RDA) may enhance anticoagulant effects in vitamin K deficient pts.

• voriconazole

  voriconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• watercress

  watercress decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown. Theoretical interaction, due to high vitamin K content of watercress.

• abciximab

  Serious - Use Alternative (1)warfarin, abciximab. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• acalabrutinib

  Monitor Closely (1)acalabrutinib increases effects of warfarin by anticoagulation. Use Caution/Monitor. Coadministration of acalabrutinib with antiplatelets or anticoagulants may further increase risk of hemorrhage. Monitor for signs of bleeding and consider the benefit-risk of withholding acalabrutinib for 3-7 days presurgery and postsurgery depending upon the type of surgery and the risk of bleeding.

• aceclofenac

  Monitor Closely (1)warfarin and aceclofenac both increase anticoagulation. Modify Therapy/Monitor Closely.

• acemetacin

  Monitor Closely (1)warfarin and acemetacin both increase anticoagulation. Modify Therapy/Monitor Closely.

• acetaminophen

  Monitor Closely (1)acetaminophen increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• acetaminophen IV

  Minor (1)acetaminophen IV increases effects of warfarin by unknown mechanism. Minor/Significance Unknown.

• acetaminophen rectal

  Minor (1)acetaminophen rectal increases effects of warfarin by unknown mechanism. Minor/Significance Unknown.

• agrimony

  Monitor Closely (1)warfarin and agrimony both increase anticoagulation. Modify Therapy/Monitor Closely.

• alfalfa

  Monitor Closely (1)warfarin and alfalfa both increase anticoagulation. Modify Therapy/Monitor Closely.

• allopurinol

  Serious - Use Alternative (1)allopurinol increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• alpelisib

  Monitor Closely (2)warfarin will increase the level or effect of alpelisib by affecting hepatic enzyme CYP2C19 metabolism. Modify Therapy/Monitor Closely.
  
  alpelisib will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Modify Therapy/Monitor Closely.

• alprostadil intracavernous/urethral

  Minor (1)alprostadil intracavernous/urethral increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• alteplase

  Monitor Closely (1)warfarin and alteplase both increase anticoagulation. Modify Therapy/Monitor Closely.

• American ginseng

  Monitor Closely (1)warfarin and American ginseng both increase anticoagulation. Modify Therapy/Monitor Closely.

• amikacin

  Monitor Closely (1)amikacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• amiodarone

  Monitor Closely (1)amiodarone will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)amiodarone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• amobarbital

  Monitor Closely (3)amobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  amobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  amobarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)amobarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.Minor (1)amobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• amoxicillin

  Monitor Closely (1)amoxicillin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Amoxicillin may enhance anticoagulant effect of vitamin K antagonists.

• ampicillin

  Monitor Closely (1)ampicillin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• anagrelide

  Serious - Use Alternative (1)warfarin, anagrelide. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• anamu

  Monitor Closely (1)warfarin and anamu both increase anticoagulation. Use Caution/Monitor.

• anticholinergic/sedative combos

  Monitor Closely (1)anticholinergic/sedative combos decreases levels of warfarin by increasing metabolism. Use Caution/Monitor.

• antithrombin alfa

  Serious - Use Alternative (1)antithrombin alfa and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• antithrombin III

  Serious - Use Alternative (1)antithrombin III and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• apalutamide

  Monitor Closely (1)apalutamide will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Coadministration of apalutamide, a weak CYP2C9 inducer, with drugs that are CYP2C9 substrates can result in lower exposure to these medications. Evaluate for loss of therapeutic effect if medication must be coadministered.

• apixaban

  Contraindicated (1)warfarin and apixaban both increase anticoagulation. Contraindicated.

• aprepitant

  Monitor Closely (1)aprepitant will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Modify Therapy/Monitor Closely. Aprepitant is a CYP2C9 inducer so coadministration with warfarin may result in a clinically significant decrease in INR. Monitor INR closely in patients on chronic warfarin therapy.

• argatroban

  Serious - Use Alternative (1)argatroban and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• armodafinil

  Monitor Closely (2)armodafinil will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  armodafinil will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Minor (1)armodafinil will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• artemether/lumefantrine

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

• ascorbic acid

  Minor (1)ascorbic acid decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown. Dose >10 g/day vitamin C.

• aspirin

  Monitor Closely (1)warfarin and aspirin both increase anticoagulation. Modify Therapy/Monitor Closely. The need for simultaneous use of low-dose aspirin and warfarin are common for patients with cardiovascular disease; monitor closely.

• aspirin rectal

  Monitor Closely (1)warfarin and aspirin rectal both increase anticoagulation. Modify Therapy/Monitor Closely.

• aspirin/citric acid/sodium bicarbonate

  Monitor Closely (1)warfarin and aspirin/citric acid/sodium bicarbonate both increase anticoagulation. Modify Therapy/Monitor Closely. The need for simultaneous use of low-dose aspirin and warfarin are common for patients with cardiovascular disease; monitor closely.

• atazanavir

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

• azapropazone

  Monitor Closely (1)azapropazone increases effects of warfarin by plasma protein binding competition. Use Caution/Monitor.

• azathioprine

  Monitor Closely (1)azathioprine decreases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• azficel-T

  Monitor Closely (1)azficel-T, warfarin. Other (see comment). Use Caution/Monitor. Comment: Coadministration with anticoagulants or antiplatelets may increase bruising or bleeding at biopsy and/or injection sites; concomitant use not recommended. Decisions regarding continued use or cessation of anticoagulants or antiplatelets should be made by a physician.

• azithromycin

  Serious - Use Alternative (1)azithromycin increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• bazedoxifene/conjugated estrogens

  Serious - Use Alternative (1)bazedoxifene/conjugated estrogens decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• bemiparin

  Serious - Use Alternative (1)bemiparin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• betrixaban

  Monitor Closely (1)warfarin, betrixaban. Either increases levels of the other by anticoagulation. Use Caution/Monitor.

• bicalutamide

  Monitor Closely (1)bicalutamide increases effects of warfarin by pharmacodynamic synergism. Use Caution/Monitor. Prothrombin times should be closely monitored in patient already receiving coumarin anticoagulants who are started on bicalutamide.

• bivalirudin

  Serious - Use Alternative (1)bivalirudin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• blinatumomab

  Monitor Closely (1)blinatumomab increases levels of warfarin 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.

• bortezomib

  Monitor Closely (1)bortezomib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Use Caution/Monitor. Clinical and laboratory monitoring is warranted in combining bortezomib with agents with narrow therapeutic ranges, such as warfarin.

• bosentan

  Monitor Closely (2)bosentan will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  bosentan will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• bremelanotide

  Serious - Use Alternative (1)bremelanotide will decrease the level or effect of warfarin 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.

• brodalumab

  Monitor Closely (1)brodalumab, warfarin. 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 (2)budesonide will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  budesonide, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• bupropion

  Monitor Closely (1)bupropion increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Altered PT/INR infrequently associated with hemorrhagic or thrombotic complications were observed when bupropion was administered with warfarin. Monitor INR when bupropion is added to existing warfarin regimen.

• butabarbital

  Monitor Closely (3)butabarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  butabarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  butabarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)butabarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.Minor (1)butabarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• butalbital

  Monitor Closely (3)butalbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  butalbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  butalbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)butalbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.Minor (1)butalbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• cannabidiol

  Monitor Closely (1)cannabidiol will increase the level or effect of warfarin by decreasing metabolism. Modify Therapy/Monitor Closely. Cannabidiol may potentially inhibit CYP2C9 activity. Consider reducing the dose when concomitantly using CYP2C9 substrates.

• capecitabine

  Serious - Use Alternative (1)capecitabine increases effects of warfarin by unspecified interaction mechanism. Avoid or Use Alternate Drug. Monitor INR and prothrombin time.

• caplacizumab

  Monitor Closely (1)caplacizumab, warfarin. Either increases effects of the other by anticoagulation. Use Caution/Monitor.

• carbamazepine

  Monitor Closely (3)carbamazepine will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  carbamazepine will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  carbamazepine decreases levels of warfarin by increasing metabolism. Use Caution/Monitor.Serious - Use Alternative (1)carbamazepine will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• cefaclor

  Monitor Closely (1)cefaclor increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefamandole

  Serious - Use Alternative (1)cefamandole increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• cefazolin

  Serious - Use Alternative (1)cefazolin increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• cefdinir

  Monitor Closely (1)cefdinir increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.Serious - Use Alternative (1)cefdinir increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefditoren

  Serious - Use Alternative (1)cefditoren increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefixime

  Monitor Closely (1)cefixime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefotaxime

  Monitor Closely (1)cefotaxime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• cefotetan

  Serious - Use Alternative (1)cefotetan increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefoxitin

  Serious - Use Alternative (2)cefoxitin will increase the level or effect of warfarin by Other (see comment). Avoid or Use Alternate Drug. Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  cefoxitin increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefpodoxime

  Monitor Closely (1)cefpodoxime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.Serious - Use Alternative (1)cefpodoxime will increase the level or effect of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity

• cefprozil

  Monitor Closely (1)cefprozil increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• ceftaroline

  Minor (1)ceftaroline increases effects of warfarin by Other (see comment). Minor/Significance Unknown. Comment: Cephalosporins with a methylthiotetrazole (MTT) side ring (eg, cefotetan, cefoperazone) are more frequently associated with hypoprothrombinemic activity.

• ceftazidime

  Monitor Closely (1)ceftazidime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• ceftibuten

  Monitor Closely (1)ceftibuten increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• ceftriaxone

  Monitor Closely (1)ceftriaxone increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.Serious - Use Alternative (1)ceftriaxone increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity.

• cefuroxime

  Monitor Closely (1)cefuroxime increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.Serious - Use Alternative (1)cefuroxime will increase the level or effect of warfarin by anticoagulation. Avoid or Use Alternate Drug. cephalosporins may decrease prothrombin activity

• celecoxib

  Monitor Closely (1)warfarin and celecoxib both increase anticoagulation. Modify Therapy/Monitor Closely.

• ceritinib

  Serious - Use Alternative (1)ceritinib increases levels of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. Avoid concurrent use of CYP2C9 substrates known to have narrow therapeutic indices or substrates primarily metabolized by CYP2C9 during treatment with ceritinib; if use of these medications is unavoidable, consider dose.

• chitosan

  Monitor Closely (1)chitosan increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Chitosan can decrease GI absorption of vitamin K, enhancing anticoagulant effects.

• chloral hydrate

  Serious - Use Alternative (1)chloral hydrate increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• chloramphenicol

  Serious - Use Alternative (1)chloramphenicol increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• chlorella

  Minor (1)chlorella decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown. Theoretical, due to vitamin K content.

• cholestyramine

  Monitor Closely (1)cholestyramine decreases levels of warfarin by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

• choline magnesium trisalicylate

  Monitor Closely (1)warfarin and choline magnesium trisalicylate both increase anticoagulation. Modify Therapy/Monitor Closely.

• cigarette smoking

  Monitor Closely (1)cigarette smoking will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• cilostazol

  Serious - Use Alternative (1)warfarin, cilostazol. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• cimetidine

  Monitor Closely (2)cimetidine will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  cimetidine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)cimetidine will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• cinnamon

  Monitor Closely (1)warfarin and cinnamon both increase anticoagulation. Modify Therapy/Monitor Closely.

• ciprofibrate

  Serious - Use Alternative (2)ciprofibrate increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  ciprofibrate increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• ciprofloxacin

  Serious - Use Alternative (1)ciprofloxacin will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Avoid or Use Alternate Drug. Quinolone antibiotics such as ciprofloxacin may enhance the anticoagulant effects of warfarin. Important to monitor INR/prothrombin time and toxic effects of warfarin. Patients receiving this combination should be closely monitored for adverse effects.

• citalopram

  Monitor Closely (1)citalopram increases levels of warfarin by decreasing metabolism. Use Caution/Monitor. Coadministration of warfarin and citalopram increased prothrombin time by 5%. Use caution with coadministration and monitor patient.

• clarithromycin

  Monitor Closely (1)clarithromycin increases toxicity of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Increased risk of hemorrage; monitor INR and prothrombin times frequently.Serious - Use Alternative (1)clarithromycin increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• clindamycin

  Monitor Closely (1)clindamycin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• clopidogrel

  Monitor Closely (1)warfarin, clopidogrel. Either increases effects of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Enhanced risk of hemorrhage; additive effects may occur when simultaneous use is clinically required .

• clotrimazole

  Serious - Use Alternative (1)clotrimazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• cobicistat

  Monitor Closely (1)cobicistat, warfarin. Other (see comment). Use Caution/Monitor. Comment: Effect unknown; monitor INR .

• coenzyme Q10

  Minor (1)coenzyme Q10 decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown.

• colesevelam

  Monitor Closely (1)colesevelam will decrease the level or effect of warfarin by Mechanism: inhibition of GI absorption. Applies only to oral form of both agents. Modify Therapy/Monitor Closely. Administer warfarin at least 4 hr before colesevelam. Monitor INR frequently during colesevelam initiation or discontinuance.

• colestipol

  Minor (1)colestipol decreases levels of warfarin by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

• collagenase clostridium histolyticum

  Monitor Closely (1)warfarin increases toxicity of collagenase clostridium histolyticum by anticoagulation. Use Caution/Monitor. Collagenase clostridium histolyticum has high incidence of ecchymosis/contusion at injection site; avoid concomitant anticoagulants (except for low-dose aspirin, ie, up to 150 mg/day).

• conivaptan

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

• conjugated estrogens

  Serious - Use Alternative (1)conjugated estrogens decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• conjugated estrogens, vaginal

  Monitor Closely (1)conjugated estrogens, vaginal decreases effects of warfarin by pharmacodynamic antagonism. Modify Therapy/Monitor Closely. Risk of thromboembolic disorders.

• cordyceps

  Monitor Closely (1)warfarin and cordyceps both increase anticoagulation. Modify Therapy/Monitor Closely.

• cornsilk

  Monitor Closely (1)cornsilk decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor. Cornsilk contains vitamin K; consume a consistent amount daily.

• cortisone

  Monitor Closely (2)cortisone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  cortisone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• cranberry

  Minor (1)cranberry increases effects of warfarin by unknown mechanism. Minor/Significance Unknown. Theoretical interaction, based on case reports. Cranberry may inhibit cytochrome P450 2C9.

• cyclophosphamide

  Monitor Closely (1)cyclophosphamide increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Anticoagulant effect is increased. Monitor coagulation parameters during and after cyclophosphamide therapy. Adjust the warfarin dose as needed.

• cyclosporine

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

• dabigatran

  Serious - Use Alternative (1)dabigatran and warfarin both increase anticoagulation. Avoid or Use Alternate Drug. Both drugs have the potential to cause bleeding. Concomitant use may increase risk of bleeding.

• dabrafenib

  Serious - Use Alternative (1)dabrafenib will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Dabrafenib induces CYP3A4 and possibly other enzymes including CYP2C9 that affect warfarin metabolism

• dalteparin

  Serious - Use Alternative (1)dalteparin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• danazol

  Serious - Use Alternative (1)danazol increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• danshen

  Monitor Closely (1)warfarin and danshen both increase anticoagulation. Use Caution/Monitor.

• darifenacin

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

• darunavir

  Monitor Closely (1)darunavir will decrease the level or effect of warfarin by unspecified interaction mechanism. Use Caution/Monitor. Monitor INR before initiating. Increase monitoring with concurrent therapy.

• dasatinib

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

• dasiglucagon

  Monitor Closely (1)dasiglucagon increases effects of warfarin by unknown mechanism. Use Caution/Monitor. High doses of dasiglucagon may enhance anticoagulant effects of vitamin K antagonists.

• deferasirox

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

• defibrotide

  Contraindicated (1)defibrotide increases effects of warfarin by pharmacodynamic synergism. Contraindicated. Coadministration of defibrotide is contraindicated with antithrombotic/fibrinolytic drugs. This does not include use for routine maintenance or reopening of central venous lines.

• deflazacort

  Monitor Closely (1)deflazacort, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• demeclocycline

  Minor (1)demeclocycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• devil's claw

  Monitor Closely (1)warfarin and devil's claw both increase anticoagulation. Use Caution/Monitor.

• dexamethasone

  Monitor Closely (2)dexamethasone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  dexamethasone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• dexmethylphenidate

  Minor (1)dexmethylphenidate increases effects of warfarin by decreasing metabolism. Minor/Significance Unknown.

• DHEA, herbal

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

• diclofenac

  Monitor Closely (1)warfarin and diclofenac both increase anticoagulation. Modify Therapy/Monitor Closely.

• dicloxacillin

  Monitor Closely (1)dicloxacillin decreases levels of warfarin by increasing metabolism. Use Caution/Monitor.

• diflunisal

  Monitor Closely (2)diflunisal increases effects of warfarin by plasma protein binding competition. Use Caution/Monitor.
  
  warfarin and diflunisal both increase anticoagulation. Modify Therapy/Monitor Closely.

• dimenhydrinate

  Minor (1)dimenhydrinate increases effects of warfarin by unknown mechanism. Minor/Significance Unknown.

• dipyridamole

  Serious - Use Alternative (1)warfarin, dipyridamole. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• disulfiram

  Monitor Closely (2)disulfiram will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  disulfiram increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor.

• dong quai

  Monitor Closely (1)warfarin and dong quai both increase anticoagulation. Modify Therapy/Monitor Closely.

• doxycycline

  Minor (1)doxycycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• dronabinol

  Monitor Closely (1)dronabinol increases levels of warfarin by plasma protein binding competition. Modify Therapy/Monitor Closely. Dronabinol is highly bound to plasma proteins and may displace and increase the free fraction of other concomitantly administered highly protein-bound drugs. This has not been confirmed in vivo. Caution with narrow therapeutic index drugs that are highly protein bound when initiating or increasing the dose of dronabinol.

• dronedarone

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

• dulaglutide

  Monitor Closely (1)dulaglutide, warfarin. 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 (1)duloxetine increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• dupilumab

  Monitor Closely (1)dupilumab, warfarin. 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.

• econazole topical

  Monitor Closely (1)econazole topical increases effects of warfarin by decreasing metabolism. Use Caution/Monitor. Most cases reported use of econazole under occlusive bandage, genital application, or application to large body surface area which may increase the systemic absorption.

• edoxaban

  Serious - Use Alternative (1)edoxaban, warfarin. Either increases toxicity of the other by anticoagulation. Avoid or Use Alternate Drug. Both drugs have the potential to cause bleeding, monitor closely. Promptly evaluate any signs or symptoms of blood loss. Long-term concomitant treatment with edoxaban and other anticoagulants is not recommended. Short-term coadministration may be needed for patients transitioning to or from edoxaban.

• efavirenz

  Monitor Closely (1)efavirenz will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)efavirenz will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug.Minor (1)efavirenz will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• elbasvir/grazoprevir

  Monitor Closely (1)elbasvir/grazoprevir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• eluxadoline

  Monitor Closely (1)eluxadoline increases levels of warfarin 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/cobicistat/emtricitabine/tenofovir DF

  Monitor Closely (1)elvitegravir/cobicistat/emtricitabine/tenofovir DF decreases levels of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Elvitegravir is a moderate CYP2C9 inducer.

• enoxaparin

  Serious - Use Alternative (1)enoxaparin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug. Additive effects are intended when both drugs are prescribed as indicated for treatment of DVT

• epoprostenol

  Monitor Closely (1)warfarin and epoprostenol both increase anticoagulation. Modify Therapy/Monitor Closely.

• eptifibatide

  Serious - Use Alternative (1)warfarin, eptifibatide. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• erdafitinib

  Serious - Use Alternative (1)warfarin will increase the level or effect of erdafitinib by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. If coadministration of a strong CYP2C9 inhibitors is unavoidable, closely monitor adverse reactions and modify dose of erdafitinib accordingly. If strong CYP2C9 inhibitor is discontinued, consider increasing erdafitinib dose in the absence of any drug-related toxicities.

• erythromycin base

  Monitor Closely (1)erythromycin base will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)erythromycin base will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  erythromycin base increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• erythromycin ethylsuccinate

  Monitor Closely (1)erythromycin ethylsuccinate will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)erythromycin ethylsuccinate will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  erythromycin ethylsuccinate increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• erythromycin lactobionate

  Monitor Closely (1)erythromycin lactobionate will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)erythromycin lactobionate will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  erythromycin lactobionate increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• erythromycin stearate

  Monitor Closely (1)erythromycin stearate will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)erythromycin stearate will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  erythromycin stearate increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• escitalopram

  Serious - Use Alternative (1)escitalopram increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• eslicarbazepine acetate

  Monitor Closely (1)eslicarbazepine acetate will decrease the level or effect of warfarin by increasing metabolism. Use Caution/Monitor. S-warfarin serum concentrations may be decreased. Monitor coagulation parameters (INR) when initiating or discontinuing eslicarbazepine in patients

• esomeprazole

  Minor (1)esomeprazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• estradiol

  Serious - Use Alternative (1)estradiol decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• estrogens conjugated synthetic

  Serious - Use Alternative (1)estrogens conjugated synthetic decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• estrogens esterified

  Monitor Closely (1)estrogens esterified decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor. Estrogens may theoretically reduce the effect of anticoagulants.

• estropipate

  Serious - Use Alternative (1)estropipate decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• ethanol

  Monitor Closely (1)ethanol, warfarin. Mechanism: altering metabolism. Use Caution/Monitor. Avoid alcohol ingestion; acute, excessive EtOH ingestion (binge drinking) decreases .

• ethinylestradiol

  Monitor Closely (1)ethinylestradiol will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)ethinylestradiol decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.
  
  ethinylestradiol will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Avoid or Use Alternate Drug. The use of estrogen-containing contraceptives and coumarin derivatives should be avoided to avoid risk of thromboembolic disorders.

• ethotoin

  Monitor Closely (2)warfarin increases levels of ethotoin by unknown mechanism. Use Caution/Monitor.
  
  ethotoin, warfarin. Other (see comment). Use Caution/Monitor. Comment: Hydantoin anticonvulsants increase anticoagulant effects at first, then decrease those effects with continued use (2+ wks). There are multiple mechanisms involved, including enzyme induction, plasma protein binding site competition, and additive effects on prothrombin time.

• etodolac

  Monitor Closely (1)warfarin and etodolac both increase anticoagulation. Modify Therapy/Monitor Closely.

• etravirine

  Monitor Closely (1)etravirine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Minor (1)etravirine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• exenatide injectable solution

  Monitor Closely (1)exenatide injectable solution, warfarin. Other (see comment). Use Caution/Monitor. Comment: Exenatide may increase INR and possibly increase bleeding when coadministered with warfarin. Monitor prothrombin (PT) time more frequently after starting or changing dose of exenatide. Once a stable PT time is established, monitor PT times at intervals usually recommended for patients taking warfarin.

• exenatide injectable suspension

  Monitor Closely (1)exenatide injectable suspension, warfarin. Other (see comment). Use Caution/Monitor. Comment: Exenatide may increase INR and possibly increase bleeding when coadministered with warfarin. Monitor prothrombin (PT) time more frequently after starting or changing dose of exenatide. Once a stable PT time is established, monitor PT times at intervals usually recommended for patients taking warfarin.

• felbamate

  Monitor Closely (1)felbamate will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Minor (1)felbamate will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• felodipine

  Minor (1)felodipine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• fenbufen

  Monitor Closely (1)warfarin and fenbufen both increase anticoagulation. Modify Therapy/Monitor Closely.

• fennel

  Monitor Closely (1)warfarin and fennel both increase anticoagulation. Modify Therapy/Monitor Closely.

• fenofibrate

  Serious - Use Alternative (2)fenofibrate increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  fenofibrate increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• fenofibrate micronized

  Serious - Use Alternative (2)fenofibrate micronized increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  fenofibrate micronized increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• fenofibric acid

  Serious - Use Alternative (2)fenofibric acid increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  fenofibric acid increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• fenoprofen

  Monitor Closely (1)warfarin and fenoprofen both increase anticoagulation. Modify Therapy/Monitor Closely.

• ferric maltol

  Monitor Closely (1)ferric maltol, warfarin. 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).

• feverfew

  Monitor Closely (1)warfarin and feverfew both increase anticoagulation. Modify Therapy/Monitor Closely.

• fish oil

  Monitor Closely (1)fish oil, warfarin. Other (see comment). Use Caution/Monitor. Comment: Patients taking fish oil and an anticoagulant or other drug affecting coagulation should be monitored periodically due to potential increased risk of bleeding. Monitor for changes in INR.

• fish oil triglycerides

  Monitor Closely (1)fish oil triglycerides will increase the level or effect of warfarin by anticoagulation. Use Caution/Monitor. Prolonged bleeding reported in patients taking antiplatelet agents or anticoagulants and oral omega-3 fatty acids. Periodically monitor bleeding time in patients receiving fish oil triglycerides and concomitant antiplatelet agents or anticoagulants.

• fleroxacin

  Monitor Closely (1)fleroxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• fluconazole

  Monitor Closely (2)fluconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  fluconazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)fluconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.Minor (1)fluconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• fludrocortisone

  Monitor Closely (2)fludrocortisone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  fludrocortisone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• fluorouracil

  Monitor Closely (1)fluorouracil increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor. Due to the thrombocytopenic effects of fluorouracil, an additive risk of bleeding may be seen in patients receiving concomitant anticoagulants.

• fluoxetine

  Monitor Closely (2)fluoxetine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Use Caution/Monitor.
  
  fluoxetine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)fluoxetine increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• fluoxymesterone

  Serious - Use Alternative (1)fluoxymesterone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• flurbiprofen

  Monitor Closely (1)warfarin and flurbiprofen both increase anticoagulation. Modify Therapy/Monitor Closely.

• flutamide

  Monitor Closely (1)flutamide increases effects of warfarin by pharmacodynamic synergism. Use Caution/Monitor. Increases in prothrombin time have been noted in patients receiving long-term warfarin therapy after flutamide was initiated. Close monitoring of prothrombin time is recommended.

• fluvastatin

  Monitor Closely (1)fluvastatin increases effects of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• fluvoxamine

  Monitor Closely (1)fluvoxamine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)fluvoxamine will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Avoid or Use Alternate Drug.

• fondaparinux

  Serious - Use Alternative (1)fondaparinux and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• food

  Monitor Closely (1)food decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor. Specifically, vitamin K rich foods (e.g., dark leafy green vegetables).

• forskolin

  Monitor Closely (1)warfarin and forskolin both increase anticoagulation. Modify Therapy/Monitor Closely.

• fosamprenavir

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

• fosphenytoin

  Monitor Closely (3)fosphenytoin will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  warfarin increases levels of fosphenytoin by unknown mechanism. Use Caution/Monitor.
  
  fosphenytoin, warfarin. Other (see comment). Use Caution/Monitor. Comment: Hydantoin anticonvulsants increase anticoagulant effects at first, then decrease those effects with continued use (2+ wks). There are multiple mechanisms involved, including enzyme induction, plasma protein binding site competition, and additive effects on prothrombin time.

• garlic

  Monitor Closely (1)warfarin and garlic both increase anticoagulation. Modify Therapy/Monitor Closely.

• gefitinib

  Monitor Closely (1)gefitinib increases effects of warfarin by unknown mechanism. Modify Therapy/Monitor Closely. Gefitinib prescribing information reports some patients receiving concomitant warfarin experienced increased INR and/or bleeding.

• gemcitabine

  Monitor Closely (1)gemcitabine increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor. The anticoagulant effect of warfarin may be increased.

• gemfibrozil

  Serious - Use Alternative (2)gemfibrozil increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
  
  gemfibrozil increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• gemifloxacin

  Monitor Closely (2)gemifloxacin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  gemifloxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• ginger

  Monitor Closely (1)warfarin and ginger both increase anticoagulation. Modify Therapy/Monitor Closely.

• ginkgo biloba

  Monitor Closely (1)warfarin and ginkgo biloba both increase anticoagulation. Modify Therapy/Monitor Closely.

• glecaprevir/pibrentasvir

  Monitor Closely (1)glecaprevir/pibrentasvir increases and warfarin decreases Other (see comment). Effect of interaction is not clear, use caution. Use Caution/Monitor. Warfarin is a substrate of OATP and BCRP, which has been suggested to cause fluctuations in warfarin absorption; close monitoring of INR values is recommended during treatment and post-treatment follow-up.

• glucagon

  Monitor Closely (1)glucagon increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• glucagon intranasal

  Monitor Closely (1)glucagon intranasal increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• glyburide

  Minor (1)glyburide increases effects of warfarin by unspecified interaction mechanism. Minor/Significance Unknown.

• grapefruit

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

• green tea

  Monitor Closely (1)green tea decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor. Combination may decrease warfarin efficacy. Potential for increased risk of bleeding. Important to monitor INR.

• griseofulvin

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

• guselkumab

  Monitor Closely (1)guselkumab, warfarin. 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.

• hemin

  Monitor Closely (1)warfarin, hemin. Either increases effects of the other by anticoagulation. Use Caution/Monitor. Hemin degradation product (ie, hematin) may produce coagulopathy (eg, thrombocytopenia, platelet degranulation) and cause mild anticoagulant effects.

• heparin

  Serious - Use Alternative (1)heparin and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• horse chestnut seed

  Monitor Closely (1)warfarin and horse chestnut seed both increase anticoagulation. Modify Therapy/Monitor Closely.

• horseradish

  Minor (1)horseradish increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown. Theoretical interaction.

• hydrocortisone

  Monitor Closely (2)hydrocortisone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  hydrocortisone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• ibrutinib

  Monitor Closely (1)ibrutinib will increase the level or effect of warfarin by anticoagulation. Use Caution/Monitor. Ibrutinib may increase the risk of hemorrhage in patients receiving antiplatelet or anticoagulant therapies and monitor for signs of bleeding.

• ibuprofen

  Monitor Closely (1)warfarin and ibuprofen both increase anticoagulation. Modify Therapy/Monitor Closely.

• ibuprofen IV

  Monitor Closely (1)warfarin and ibuprofen IV both increase anticoagulation. Modify Therapy/Monitor Closely.

• icosapent

  Monitor Closely (1)icosapent, warfarin. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Icosapent may prolong bleeding time; monitor periodically if coadministered with other drugs that affect bleeding.

• ifosfamide

  Serious - Use Alternative (1)ifosfamide, warfarin. Either increases toxicity of the other by nephrotoxicity and/or ototoxicity. Avoid or Use Alternate Drug. Monitor for increased INR/effects of coumarin derivatives when ifosfamide is initiated/dose increased, and decreased INR/effects when ifosfamide is discontinued/dose decreased.

• imatinib

  Serious - Use Alternative (1)imatinib will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Because warfarin is metabolized by CYP2C9 and CYP3A4, patients taking imatinib who require anticoagulation should receive low-molecular weight or standard heparin instead of warfarin.

• indinavir

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

• indomethacin

  Monitor Closely (1)warfarin and indomethacin both increase anticoagulation. Modify Therapy/Monitor Closely.

• iodine (radioactive)

  Monitor Closely (1)iodine (radioactive) decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor.

• isoniazid

  Monitor Closely (3)isoniazid will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  isoniazid will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Use Caution/Monitor.
  
  isoniazid will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• itraconazole

  Serious - Use Alternative (2)itraconazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  itraconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• ivermectin

  Monitor Closely (1)ivermectin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Rare interaction.

• ivosidenib

  Serious - Use Alternative (1)ivosidenib will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sensitive CYP2C9 substrates with ivosidenib or replace with alternate therapies. If coadministration is unavoidable, monitor patients for loss of therapeutic effect of these drugs.

• ixekizumab

  Monitor Closely (1)ixekizumab, warfarin. 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

  Monitor Closely (1)ketoconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)ketoconazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  ketoconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• ketoprofen

  Monitor Closely (1)warfarin and ketoprofen both increase anticoagulation. Modify Therapy/Monitor Closely.

• ketorolac

  Monitor Closely (1)warfarin and ketorolac both increase anticoagulation. Modify Therapy/Monitor Closely.

• ketorolac intranasal

  Monitor Closely (1)warfarin and ketorolac intranasal both increase anticoagulation. Modify Therapy/Monitor Closely.

• ledipasvir/sofosbuvir

  Monitor Closely (1)ledipasvir/sofosbuvir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• leflunomide

  Monitor Closely (1)leflunomide will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• letermovir

  Monitor Closely (1)letermovir will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Monitor INR.

• levocarnitine

  Monitor Closely (1)levocarnitine will increase the level or effect of warfarin by unknown mechanism. Use Caution/Monitor. INR may increase in patients receiving warfarin therapy; monitor INR levels following initiation of levocarnitine therapy and after dose adjustments

• levofloxacin

  Monitor Closely (2)levofloxacin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  levofloxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• levomilnacipran

  Serious - Use Alternative (1)levomilnacipran, warfarin. Either increases toxicity of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. SNRIs may further impair platelet activity in patients taking antiplatelet or anticoagulant drugs.

• levonorgestrel intrauterine

  Serious - Use Alternative (1)levonorgestrel intrauterine, warfarin. Either decreases effects of the other by pharmacodynamic antagonism. Avoid or Use Alternate Drug. Risk of thromboembolic disorders.

• levonorgestrel oral

  Serious - Use Alternative (1)levonorgestrel oral, warfarin. Either decreases effects of the other by pharmacodynamic antagonism. Avoid or Use Alternate Drug. Risk of thromboembolic disorders.

• levothyroxine

  Serious - Use Alternative (1)levothyroxine increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• liothyronine

  Serious - Use Alternative (1)liothyronine increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• lofepramine

  Monitor Closely (1)lofepramine increases levels of warfarin by decreasing metabolism. Use Caution/Monitor.

• lomitapide

  Monitor Closely (1)lomitapide will increase the level or effect of warfarin by unspecified interaction mechanism. Modify Therapy/Monitor Closely. Increases plasma concentration of R(+)-warfarin and S(-)-warfarin and INR significantly. Monitor INR especially after changing lomitapide dosage. Adjust warfarin dose as necessary.

• lorlatinib

  Serious - Use Alternative (1)lorlatinib will decrease the level or effect of warfarin 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.

• lornoxicam

  Monitor Closely (1)warfarin and lornoxicam both increase anticoagulation. Modify Therapy/Monitor Closely.

• lovastatin

  Monitor Closely (1)lovastatin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• lumacaftor/ivacaftor

  Monitor Closely (2)lumacaftor/ivacaftor, warfarin. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. In vitro studies suggest that lumacaftor may induce and ivacaftor may inhibit CYP2C9 substrates. .
  
  lumacaftor/ivacaftor increases levels of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor INR when coadministration required. The less potent warfarin R-enantiomer is metabolized by CYP3A4.

• lumefantrine

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

• marijuana

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

• meclofenamate

  Monitor Closely (1)warfarin and meclofenamate both increase anticoagulation. Modify Therapy/Monitor Closely.

• mefenamic acid

  Monitor Closely (1)warfarin and mefenamic acid both increase anticoagulation. Modify Therapy/Monitor Closely.

• melatonin

  Monitor Closely (1)melatonin increases effects of warfarin by anticoagulation. Use Caution/Monitor. Melatonin may decrease prothrombin time.

• meloxicam

  Monitor Closely (1)warfarin and meloxicam both increase anticoagulation. Modify Therapy/Monitor Closely.

• mercaptopurine

  Monitor Closely (1)mercaptopurine decreases effects of warfarin by unknown mechanism. Use Caution/Monitor. Inhibition of the anticoagulant effect of warfarin, when given with mercaptopurine, has been reported.

• mesalamine

  Monitor Closely (1)mesalamine decreases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• mesterolone

  Serious - Use Alternative (1)mesterolone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• mestranol

  Serious - Use Alternative (1)mestranol decreases effects of warfarin by pharmacodynamic antagonism. Contraindicated. Risk of thromboembolic disorders.

• methimazole

  Monitor Closely (1)methimazole decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor.

• methylphenidate

  Monitor Closely (1)methylphenidate will increase the level or effect of warfarin by unknown mechanism. Use Caution/Monitor.

• methylprednisolone

  Monitor Closely (2)methylprednisolone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  methylprednisolone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• methyltestosterone

  Monitor Closely (1)methyltestosterone increases levels of warfarin by decreasing metabolism. Use Caution/Monitor. Monitor INR.

• metronidazole

  Monitor Closely (2)metronidazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  metronidazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)metronidazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• metronidazole topical

  Minor (1)metronidazole topical will increase the level or effect of warfarin by decreasing metabolism. Minor/Significance Unknown. Oral metronidazole potentiates the effect of warfarin; less likely to occur with topical administration because of low absorption

• metronidazole vaginal

  Minor (1)metronidazole vaginal will increase the level or effect of warfarin by decreasing metabolism. Minor/Significance Unknown. Oral metronidazole potentiates the effect of warfarin; less likely to occur with vaginal administration because of low absorption

• mexiletine

  Monitor Closely (1)mexiletine will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• miconazole vaginal

  Monitor Closely (2)miconazole vaginal will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  miconazole vaginal will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)miconazole vaginal increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• mifepristone

  Contraindicated (1)mifepristone, warfarin. Other (see comment). Contraindicated. Comment: Mifepristone may lead to excessive post abortion bleeding in pts. on anticoagulant therapy.

• milnacipran

  Serious - Use Alternative (1)milnacipran increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• mineral oil

  Minor (1)mineral oil decreases levels of warfarin by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

• minocycline

  Minor (1)minocycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• mistletoe

  Monitor Closely (1)warfarin increases and mistletoe decreases anticoagulation. Effect of interaction is not clear, use caution. Modify Therapy/Monitor Closely.

• mitotane

  Monitor Closely (1)mitotane will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor INR for a change in anticoagulant dosage requirements when warfarin is coadministered with mitotane (strong CYP3A4 inducer)

• modafinil

  Monitor Closely (2)modafinil will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  modafinil will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Minor (1)modafinil will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• moxifloxacin

  Monitor Closely (2)moxifloxacin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  moxifloxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• nabumetone

  Monitor Closely (1)warfarin and nabumetone both increase anticoagulation. Modify Therapy/Monitor Closely.

• nafcillin

  Serious - Use Alternative (1)nafcillin decreases effects of warfarin by increasing hepatic clearance. Avoid or Use Alternate Drug.

• naproxen

  Monitor Closely (1)warfarin and naproxen both increase anticoagulation. Modify Therapy/Monitor Closely.

• nateglinide

  Monitor Closely (1)nateglinide will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• nefazodone

  Serious - Use Alternative (2)nefazodone will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.
  
  nefazodone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• nelfinavir

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

• neomycin PO

  Monitor Closely (1)neomycin PO increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• nettle

  Monitor Closely (1)warfarin increases and nettle decreases anticoagulation. Effect of interaction is not clear, use caution. Modify Therapy/Monitor Closely.

• nevirapine

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

• nifedipine

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

• nilotinib

  Monitor Closely (2)nilotinib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  nilotinib will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• nilutamide

  Monitor Closely (1)nilutamide will increase the level or effect of warfarin by decreasing metabolism. Use Caution/Monitor.

• nintedanib

  Monitor Closely (1)nintedanib increases effects of warfarin by anticoagulation. Use Caution/Monitor. Nintedanib is a VEGFR inhibitor, and may increase the risk of bleeding; monitor patients on full anticoagulation therapy; monitor closely for bleeding and adjust therapy as needed .

• nitazoxanide

  Serious - Use Alternative (1)nitazoxanide, warfarin. Either increases levels of the other by plasma protein binding competition. Avoid or Use Alternate Drug. the active metabolite of nitazoxanide is highly protein bound; avoid use of warfarin with nitazoxanide.

• nitisinone

  Monitor Closely (1)nitisinone will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Nitisinone inhibits CYP2C9. Caution if CYP2C9 substrate coadministered, particularly those with a narrow therapeutic index.

• obeticholic acid

  Monitor Closely (1)obeticholic acid decreases effects of warfarin by unknown mechanism. Modify Therapy/Monitor Closely. Coadministration has been shown to increase S-warfarin exposure by 13%, but lowered INR by 11%. Monitor INR and adjust warfarin dose accordingly.

• ofloxacin

  Monitor Closely (2)ofloxacin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.
  
  ofloxacin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Ciprofloxacin, norfloxacin, & ofloxacin are most likely to interact w/warfarin; data for other quinolones is conflicting. Monitor INR closely.

• omadacycline

  Monitor Closely (1)omadacycline increases toxicity of warfarin by anticoagulation. Modify Therapy/Monitor Closely. Tetracyclines may interfere with the bactericidal action of penicillins. Monitor for decreased therapeutic effects of penicillins if concomitantly used with a tetracycline.

• ombitasvir/paritaprevir/ritonavir & dasabuvir

  Monitor Closely (1)ombitasvir/paritaprevir/ritonavir & dasabuvir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• omega 3 carboxylic acids

  Monitor Closely (1)omega 3 carboxylic acids, warfarin. Other (see comment). Use Caution/Monitor. Comment: Patients taking omega-3 acids and an anticoagulant or other drug affecting coagulation should be monitored periodically due to potential increased risk of bleeding.

• omega 3 fatty acids

  Monitor Closely (1)omega 3 fatty acids, warfarin. Other (see comment). Use Caution/Monitor. Comment: Patients taking omega-3-fatty acids and an anticoagulant or other drug affecting coagulation should be monitored periodically due to potential increased risk of bleeding. Monitor for changes in INR.

• omeprazole

  Monitor Closely (1)omeprazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Minor (1)omeprazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• oritavancin

  Monitor Closely (1)oritavancin will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Oritavancin is a weak CYP2C9 inhibitor; caution if coadministered with CYP2C9 substrates that have a narrow therapeutic index

• orlistat

  Monitor Closely (1)orlistat decreases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Orlistat may decrease vitamin K absorption; patients on chronic stable doses of warfarin who are prescribed orlistat should be monitored closely for changes in coagulation parameters.

• ospemifene

  Monitor Closely (1)warfarin, ospemifene. Either increases levels of the other by plasma protein binding competition. Modify Therapy/Monitor Closely.

• oxandrolone

  Serious - Use Alternative (1)oxandrolone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• oxaprozin

  Monitor Closely (1)warfarin and oxaprozin both increase anticoagulation. Modify Therapy/Monitor Closely.

• oxcarbazepine

  Monitor Closely (1)oxcarbazepine will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Minor (1)oxcarbazepine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• oxymetholone

  Serious - Use Alternative (1)oxymetholone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• oxytetracycline

  Minor (1)oxytetracycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• panax ginseng

  Monitor Closely (1)warfarin and panax ginseng both increase anticoagulation. Modify Therapy/Monitor Closely.

• parecoxib

  Monitor Closely (1)warfarin and parecoxib both increase anticoagulation. Modify Therapy/Monitor Closely.Minor (1)parecoxib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• paromomycin

  Monitor Closely (1)paromomycin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• paroxetine

  Serious - Use Alternative (1)paroxetine increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• parsley

  Minor (1)parsley increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown. Theoretical interaction.

• pau d'arco

  Monitor Closely (1)warfarin and pau d'arco both increase anticoagulation. Modify Therapy/Monitor Closely.

• pefloxacin

  Serious - Use Alternative (1)pefloxacin will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Avoid or Use Alternate Drug.

• pegaspargase

  Monitor Closely (1)pegaspargase increases effects of warfarin by pharmacodynamic synergism. Use Caution/Monitor. Increased risk of bleeding events.

• peginterferon alfa 2a

  Monitor Closely (1)peginterferon alfa 2a will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• peginterferon alfa 2b

  Monitor Closely (1)peginterferon alfa 2b decreases levels of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. When patients are administered peginterferon alpha-2b with CYP2C9 substrates, the therapeutic effect of these drugs may be altered. .

• pentobarbital

  Monitor Closely (3)pentobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  pentobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  pentobarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)pentobarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.Minor (1)pentobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• pentoxifylline

  Monitor Closely (1)pentoxifylline increases effects of warfarin by pharmacodynamic synergism. Use Caution/Monitor.

• phenindione

  Serious - Use Alternative (1)phenindione and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• phenobarbital

  Monitor Closely (3)phenobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  phenobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  phenobarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)phenobarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.Minor (1)phenobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• phenytoin

  Monitor Closely (3)phenytoin will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  warfarin increases levels of phenytoin by unknown mechanism. Use Caution/Monitor.
  
  phenytoin, warfarin. Other (see comment). Use Caution/Monitor. Comment: Hydantoin anticonvulsants increase anticoagulant effects at first, then decrease those effects with continued use (2+ wks). There are multiple mechanisms involved, including enzyme induction, plasma protein binding site competition, and additive effects on prothrombin time.

• phytoestrogens

  Monitor Closely (1)warfarin and phytoestrogens both increase anticoagulation. Modify Therapy/Monitor Closely.

• pipemidic acid

  Monitor Closely (1)pipemidic acid will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• piperacillin

  Serious - Use Alternative (1)piperacillin increases effects of warfarin by anticoagulation. Avoid or Use Alternate Drug. Piperacillin can inhibit platelet aggregation.

• piroxicam

  Monitor Closely (1)warfarin and piroxicam both increase anticoagulation. Modify Therapy/Monitor Closely.

• pitolisant

  Monitor Closely (1)pitolisant will decrease the level or effect of warfarin by Other (see comment). Use Caution/Monitor. Pitolisant is a borderline/weak inducer of CYP3A4. Monitor sensitive CYP3A4 substrates for reduced effectiveness if coadministered.

• porfimer

  Monitor Closely (1)warfarin decreases effects of porfimer by pharmacodynamic antagonism. Use Caution/Monitor.

• posaconazole

  Monitor Closely (1)posaconazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)posaconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• prasugrel

  Serious - Use Alternative (1)warfarin, prasugrel. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• prednisolone

  Monitor Closely (1)prednisolone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• prednisone

  Monitor Closely (2)prednisone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.
  
  prednisone, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• primidone

  Monitor Closely (3)primidone will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  primidone will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  primidone will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)primidone decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.Minor (1)primidone will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• propafenone

  Monitor Closely (1)propafenone increases effects of warfarin by decreasing metabolism. Use Caution/Monitor.

• propranolol

  Monitor Closely (1)propranolol increases levels of warfarin by decreasing metabolism. Use Caution/Monitor. The anticoagulant effect of warfarin may be increased.

• propylthiouracil

  Monitor Closely (1)propylthiouracil decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor.

• protamine

  Serious - Use Alternative (1)protamine and warfarin both increase anticoagulation. Avoid or Use Alternate Drug.

• quinidine

  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.

• quinine

  Serious - Use Alternative (1)quinine increases effects of warfarin by unknown mechanism. Avoid or Use Alternate Drug.

• quinupristin/dalfopristin

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

• raloxifene

  Minor (1)raloxifene increases effects of warfarin by plasma protein binding competition. Minor/Significance Unknown.

• regorafenib

  Monitor Closely (1)regorafenib will increase the level or effect of warfarin by anticoagulation. Use Caution/Monitor. Monitor INR more frequently

• reishi

  Monitor Closely (1)warfarin and reishi both increase anticoagulation. Modify Therapy/Monitor Closely.

• reteplase

  Monitor Closely (1)warfarin and reteplase both increase anticoagulation. Modify Therapy/Monitor Closely.

• ribavirin

  Minor (1)ribavirin decreases effects of warfarin by unknown mechanism. Minor/Significance Unknown. Case report.

• ribociclib

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

• rifabutin

  Monitor Closely (1)rifabutin decreases levels of warfarin by increasing metabolism. Use Caution/Monitor.Serious - Use Alternative (1)rifabutin will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• rifampin

  Monitor Closely (2)rifampin will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  rifampin will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)rifampin will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.Minor (1)rifampin will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• rifapentine

  Monitor Closely (2)rifapentine will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  rifapentine will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• rifaximin

  Monitor Closely (1)rifaximin decreases effects of warfarin by increasing metabolism. Use Caution/Monitor. May occur in patients with GI disease that increases intestinal permeability (increased systemic absorption of rifaximin).

• ritonavir

  Monitor Closely (1)ritonavir will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)ritonavir, warfarin. Other (see comment). Avoid or Use Alternate Drug. Comment: Variable effect on warfarin levels. Initial frequent monitoring of the INR during co-administration is indicated.

• rivaroxaban

  Monitor Closely (1)rivaroxaban, warfarin. Either increases effects of the other by anticoagulation. Use Caution/Monitor. Avoid concurrent use of rivaroxaban with other anticoagulants due to increased bleeding risk other than during therapeutic transition periods where patients should be observed closely. Monitor for signs/symptoms of blood loss.

• rolapitant

  Minor (1)rolapitant, warfarin. Other (see comment). Minor/Significance Unknown. Comment: Coadministration of IV rolapitant with warfarin did not significantly increase systemic exposure to S-warfarin, the effects on INR and prothrombin time were not studied; monitor INR and prothrombin time and adjust the dosage of warfarin, as needed with concomitant use of rolapitant, to maintain the target INR range.

• romidepsin

  Monitor Closely (1)romidepsin increases effects of warfarin by unknown mechanism. Use Caution/Monitor. Possible elevation of INR.

• rose hips

  Minor (1)rose hips decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown. Dose >10 g/day vitamin C.

• rosuvastatin

  Monitor Closely (1)rosuvastatin increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor.

• roxithromycin

  Serious - Use Alternative (1)roxithromycin increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• rucaparib

  Monitor Closely (1)rucaparib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Modify Therapy/Monitor Closely. Adjust dosage of CYP1A2 substrates, if clinically indicated. If coadministration with warfarin (a CYP2C9 substrate) cannot be avoided, consider increasing the dosing frequency of INR monitoring.

• rufinamide

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

• salicylates (non-asa)

  Monitor Closely (1)warfarin and salicylates (non-asa) both increase anticoagulation. Modify Therapy/Monitor Closely.

• salsalate

  Monitor Closely (1)warfarin and salsalate both increase anticoagulation. Modify Therapy/Monitor Closely.

• sarecycline

  Monitor Closely (1)sarecycline increases toxicity of warfarin by anticoagulation. Modify Therapy/Monitor Closely. Tetracyclines may interfere with the bactericidal action of penicillins. Monitor for decreased therapeutic effects of penicillins if concomitantly used with a tetracycline.

• sarilumab

  Monitor Closely (1)sarilumab, warfarin. 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.

• saw palmetto

  Monitor Closely (1)saw palmetto increases toxicity of warfarin by unspecified interaction mechanism. Use Caution/Monitor. May increase risk of bleeding.

• schisandra

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

• secobarbital

  Monitor Closely (3)secobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  secobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  secobarbital will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)secobarbital decreases effects of warfarin by increasing metabolism. Avoid or Use Alternate Drug.Minor (1)secobarbital will decrease the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• secukinumab

  Monitor Closely (1)secukinumab, warfarin. 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.

• selumetinib

  Monitor Closely (1)warfarin and selumetinib both increase anticoagulation. Modify Therapy/Monitor Closely. An increased risk of bleeding may occur in patients taking a vitamin-K antagonist or an antiplatelet agent with selumetinib. Monitor for bleeding and INR or PT in patients coadministered a vitamin-K antagonist or an antiplatelet agent with selumetinib.

• sertraline

  Serious - Use Alternative (1)sertraline increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• Siberian ginseng

  Monitor Closely (1)warfarin and Siberian ginseng both increase anticoagulation. Modify Therapy/Monitor Closely.

• siltuximab

  Monitor Closely (1)siltuximab, warfarin. 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.

• simvastatin

  Monitor Closely (1)simvastatin, warfarin. Either increases effects of the other by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Competition by each drug for CYP3A4-mediated metabolism may result in increased INR and increased risk of rhabdomyolysis.

• siponimod

  Serious - Use Alternative (1)warfarin will increase the level or effect of siponimod by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. Coadministration of siponimod with drugs that cause moderate CYP2C9 AND a moderate or strong CYP3A4 inhibition is not recommended. Caution if siponimod coadministered with moderate CYP2C9 inhibitors alone.

• smoking

  Monitor Closely (1)smoking will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• sodium zirconium cyclosilicate

  Monitor Closely (1)sodium zirconium cyclosilicate will increase the level or effect of warfarin by increasing gastric pH. Applies only to oral form of both agents. Modify Therapy/Monitor Closely. Separate administration by at least 2 hr. Medications that are weak acids (eg, warfarin) are more readily absorbed with elevated gastric pH.

• sofosbuvir

  Monitor Closely (1)sofosbuvir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• sofosbuvir/velpatasvir

  Monitor Closely (1)sofosbuvir/velpatasvir, warfarin. unspecified interaction mechanism. Use Caution/Monitor. Fluctuations in INR reported in patients treated for HCV with direct acting antiviral agents. Close monitoring of INR values recommended during treatment and post-treatment follow-up.

• spironolactone

  Monitor Closely (1)spironolactone decreases effects of warfarin by unknown mechanism. Use Caution/Monitor. Interaction is theorized to result from increased concentration of clotting factors as a result of diuresis.

• St John's Wort

  Serious - Use Alternative (1)St John's Wort will decrease the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

• streptomycin

  Monitor Closely (1)streptomycin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• sucralfate

  Minor (1)sucralfate decreases levels of warfarin by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

• sulfadiazine

  Serious - Use Alternative (2)sulfadiazine increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.
  
  sulfadiazine increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• sulfamethoxazole

  Monitor Closely (1)sulfamethoxazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Serious - Use Alternative (2)sulfamethoxazole increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.
  
  sulfamethoxazole increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• sulfasalazine

  Monitor Closely (1)warfarin and sulfasalazine both increase anticoagulation. Modify Therapy/Monitor Closely.

• sulfisoxazole

  Serious - Use Alternative (2)sulfisoxazole increases effects of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.
  
  sulfisoxazole increases effects of warfarin by plasma protein binding competition. Avoid or Use Alternate Drug.

• sulindac

  Monitor Closely (1)warfarin and sulindac both increase anticoagulation. Modify Therapy/Monitor Closely.

• tamoxifen

  Serious - Use Alternative (1)tamoxifen increases effects of warfarin by unknown mechanism. Avoid or Use Alternate Drug.

• tamsulosin

  Monitor Closely (1)warfarin, tamsulosin. Other (see comment). Use Caution/Monitor. Comment: Manufacturer's prescribing information states limited in vitro and in vivo studies were inconclusive; caution advised.

• teduglutide

  Monitor Closely (1)teduglutide increases levels of warfarin 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.

• tenecteplase

  Serious - Use Alternative (1)warfarin and tenecteplase both increase anticoagulation. Avoid or Use Alternate Drug.

• teriflunomide

  Monitor Closely (1)teriflunomide decreases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor. May decrease INR by 25%; monitor and adjust warfarin dose accordingly.

• tesamorelin

  Serious - Use Alternative (1)tesamorelin will decrease the level or effect of warfarin by altering metabolism. Avoid or Use Alternate Drug. Monitor INR

• testosterone

  Serious - Use Alternative (1)testosterone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• testosterone buccal system

  Serious - Use Alternative (1)testosterone buccal system increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• testosterone intranasal

  Serious - Use Alternative (1)testosterone intranasal increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug. Androgens may inhibit warfarin metabolism and/or potentiate anticoagulant effects by affecting the coagulation system.

• testosterone topical

  Serious - Use Alternative (1)testosterone topical increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• tetracycline

  Minor (1)tetracycline increases effects of warfarin by pharmacodynamic synergism. Minor/Significance Unknown.

• thyroid desiccated

  Serious - Use Alternative (1)thyroid desiccated increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• tibolone

  Serious - Use Alternative (1)tibolone increases effects of warfarin by pharmacodynamic synergism. Avoid or Use Alternate Drug.

• ticagrelor

  Monitor Closely (1)ticagrelor, warfarin. Either increases effects of the other by anticoagulation. Use Caution/Monitor. Increased risk of bleeding during concomitant use of medications that increase potential for bleeding.

• ticarcillin

  Monitor Closely (1)ticarcillin increases effects of warfarin by Other (see comment). Use Caution/Monitor. Comment: Decr vitamin K-producing intestinal flora may increase INR after a few days.

• ticlopidine

  Monitor Closely (1)ticlopidine will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)warfarin, ticlopidine. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• tigecycline

  Monitor Closely (1)tigecycline increases levels of warfarin by decreasing elimination. Use Caution/Monitor. Minimal effect on INR; monitor.

• tinidazole

  Monitor Closely (1)tinidazole will increase the level or effect of warfarin by anticoagulation. Modify Therapy/Monitor Closely. Enhanced anticoagulation effect may result in a prolongation of prothrombin time. Dosage of warfarin and other coumarin agents may need to be adjusted during coadministration and up to 8 days after discontinuation of tinidazole.

• tipranavir

  Monitor Closely (1)tipranavir, warfarin. Mechanism: unspecified interaction mechanism. Use Caution/Monitor. Effect on warfarin levels cannot be predicted; monitor INR frequently upon starting tipranavir Tx. Tipranavir may affect coagulation parameters and platelet aggregation; caution when coadministered w/ drugs that inhibit platelet aggregation or coagulation.

• tirofiban

  Serious - Use Alternative (1)warfarin, tirofiban. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Enhanced risk of hemorrhage.

• tobacco use

  Monitor Closely (1)tobacco use will decrease the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.

• tobramycin

  Monitor Closely (1)tobramycin increases effects of warfarin by unknown mechanism. Use Caution/Monitor.

• tolfenamic acid

  Monitor Closely (1)warfarin and tolfenamic acid both increase anticoagulation. Modify Therapy/Monitor Closely.

• tolmetin

  Monitor Closely (1)warfarin and tolmetin both increase anticoagulation. Modify Therapy/Monitor Closely.

• topiramate

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

• toremifene

  Monitor Closely (1)toremifene increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor. When concomitant use of anticoagulants with toremifene citrate is necessary, careful monitoring of the prothrombin time is recommended.

• trazodone

  Serious - Use Alternative (1)trazodone increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• triamcinolone acetonide injectable suspension

  Monitor Closely (1)triamcinolone acetonide injectable suspension, warfarin. Other (see comment). Use Caution/Monitor. Comment: Corticosteroids may decrease anticoagulant effects by increasing blood coagulability; conversely, they may impair vascular integrity, thus increasing bleeding risk. Monitor INR closely.

• triclofos

  Monitor Closely (1)triclofos increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor.

• ustekinumab

  Monitor Closely (1)ustekinumab, warfarin. 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.

• valproic acid

  Monitor Closely (1)valproic acid will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

• vemurafenib

  Monitor Closely (1)vemurafenib will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Exercise caution and consider additional INR monitoring when vemurafenib is used concomitantly with warfarin.

• venetoclax

  Monitor Closely (1)venetoclax increases effects of warfarin by unknown mechanism. Modify Therapy/Monitor Closely. In a drug-drug interaction study in healthy subjects, administration of a single dose of venetoclax with warfarin resulted in an 18-28% increase in Cmax and AUC of R-warfarin and S-warfarin. Because venetoclax was not dosed to steady state, it is recommended that the INR be monitored closely in patients receiving warfarin. .

• venlafaxine

  Serious - Use Alternative (1)venlafaxine increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.

• verapamil

  Monitor Closely (2)verapamil will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.
  
  verapamil will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• verteporfin

  Minor (1)warfarin decreases effects of verteporfin by pharmacodynamic antagonism. Minor/Significance Unknown.

• vitamin E

  Minor (1)vitamin E, warfarin. Mechanism: pharmacodynamic synergism. Minor/Significance Unknown. Vitamin E at RDA does not change INR in pts. on chronic warfarin therapy; megadoses (~10x RDA) may enhance anticoagulant effects in vitamin K deficient pts.

• vitamin K1 (phytonadione)

  Serious - Use Alternative (1)vitamin K1 (phytonadione) decreases effects of warfarin by pharmacodynamic antagonism. Avoid or Use Alternate Drug. Monitor for decreased prothrombin time or therapeutic effects.

• vorapaxar

  Monitor Closely (1)warfarin, vorapaxar. Either increases effects of the other by anticoagulation. Use Caution/Monitor. Coadministration of anticoagulants, antiplatelets, or other drug affecting coagulation should be monitored periodically due to potential increased risk of bleeding.

• voriconazole

  Monitor Closely (2)voriconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  voriconazole will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.Serious - Use Alternative (1)voriconazole increases levels of warfarin by decreasing metabolism. Avoid or Use Alternate Drug.Minor (1)voriconazole will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C19 metabolism. Minor/Significance Unknown.

• vorinostat

  Monitor Closely (1)vorinostat increases effects of warfarin by Mechanism: unspecified interaction mechanism. Use Caution/Monitor. Monitor PT and INR carefully.

• vortioxetine

  Monitor Closely (1)warfarin, vortioxetine. Either increases effects of the other by anticoagulation. Use Caution/Monitor.

• voxilaprevir

  Monitor Closely (1)voxilaprevir increases toxicity of warfarin by anticoagulation. Use Caution/Monitor. Fluctuations in INR values may occur in patients receiving warfarin concomitant with HCV treatment; frequent monitoring of INR values recommended during treatment and post-treatment follow-up.

• watercress

  Minor (1)watercress decreases effects of warfarin by pharmacodynamic antagonism. Minor/Significance Unknown. Theoretical interaction, due to high vitamin K content of watercress.

• zafirlukast

  Monitor Closely (2)zafirlukast will increase the level or effect of warfarin by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.
  
  zafirlukast will increase the level or effect of warfarin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

• zanubrutinib

  Serious - Use Alternative (1)warfarin, zanubrutinib. Either increases effects of the other by anticoagulation. Avoid or Use Alternate Drug. Zanubrutinib-induced cytopenias increases risk of hemorrhage. Coadministration of zanubritinib with antiplatelets or anticoagulants may further increase this risk.

• zileuton

  Monitor Closely (1)zileuton will increase the level or effect of warfarin by affecting hepatic enzyme CYP1A2 metabolism. Use Caution/Monitor.