Dosing & Uses
Dosage Forms & Strengths
tablet (Levo-T, Levoxyl, Unithroid, generic)
- 25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 112mcg
- 125mcg, 137mcg, 150mcg, 175mcg, 200mcg, 300mcg
capsule (Tirosint, generic)
- 13mcg, 25mcg, 50mcg, 75mcg, 88mcg
- 100mcg, 112 mcg, 125mcg, 137 mcg, 150mcg
oral solution
-
Tirosint-SOL
- 13mcg/mL, 25mcg/mL, 37.5mcg/mL, 44mcg/mL, 50mcg/mL, 62.5mcg/mL
- 75mcg/mL, 88mcg/mL, 100mcg/mL, 112mcg/mL, 125mcg/mL, 137mcg/mL
- 150mcg/mL, 175mcg/mL, 200mcg/mL
-
Thyquidity
- 20mcg/mL
injection, lyophilized powder for reconstitution
- 100mcg/vial
- 200mcg/vial
- 500mcg/vial
injection, solution
- 100mcg/mL
Mild Hypothyroidism
1.7 mcg/kg or 100-125 mcg PO qDay; not to exceed 300 mcg/day
>50 years (or <50 yr with CV disease)
- Usual initial dose: 25-50 mcg/day
- May adjust dose by 12.5-25 mcg q6-8Week
>50 years with CV disease
- Usual initial dose: 12.5-25 mcg PO qDay
- May adjust dose by 12.5-25 mcg q4-6weeks until patient becomes euthyroid and serum TSH concentration normalized; adjustments q6-8weeks also used
- Dose range: 100-125 mcg PO qDay
Severe Hypothyroidism
Initial: 12.5-25 mcg PO qDay
Adjust dose by 25 mcg/day q2-4Week PRN
Subclinical Hypothyroidism
Initial: 1 mcg/kg PO qDay may be adequate, OR
If replacement therapy not initiated, monitor patient annually for clinical status
Myxedema Coma
300-500 mcg IV once, THEN 50-100 mcg qDay until patient is able to tolerate oral administration; may consider smaller doses in patients with cardiovascular disease
Organ Preservation (Orphan)
Preservation of organ function in brain-dead organ donors
Orphan indication sponsor
- Fera Pharmaceuticals, LLC; 134 Birch Hill Road; Locust Valley, NY 11560
Dosing Considerations
Lower dose of Tirosint capsules may be required compared with standard T4 tablets for hypothyroidism in patients with impaired gastric acid secretion to reach their target TSH levels; Tirosint has shown improved absorption compared with conventional T4 tablets
Check for bioequivalence if switching brands/generics, OR every week after switching from one levothyroxine sodium preparation to another
Monitor serum thyroid levels; patient may be asymptomatic
Monitoring
- Initially evaluate patients q6-8Week
- Once normalization of thyroid function and serum TSH conc achieved, evaluate q6-12mo
Limitations of use
- IV: Relative bioavailability has not been established; use caution when converting patients from PO to IV
-
PO
- Not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients, as there are no clinical benefits and overtreatment with levothyroxine may induce hyperthyroidism
- Not indicated for treatment of hypothyroidism during recovery phase of subacute thyroiditis
Dosage Forms & Strengths
Dosage Forms & Strengths
tablet (Levo-T, Levoxyl, Unithroid, generic)
- 25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 112mcg
- 125mcg, 137mcg, 150mcg, 175mcg, 200mcg, 300mcg
capsule (Tirosint, generic)
- 13mcg, 25mcg, 50mcg, 75mcg, 88mcg
- 100mcg, 112 mcg, 125mcg, 137 mcg, 150mcg
oral solution
-
Tirosint-SOL
- 13mcg/mL, 25mcg/mL, 37.5mcg/mL, 44mcg/mL, 50mcg/mL, 62.5mcg/mL
- 75mcg/mL, 88mcg/mL, 100mcg/mL, 112mcg/mL, 125mcg/mL, 137mcg/mL
- 150mcg/mL, 175mcg/mL, 200mcg/mL
-
Thyquidity
- 20mcg/mL
injection, lyophilized powder for reconstitution
- 100mcg/vial
- 200mcg/vial
Hypothyroidism
Indicated in patients from birth to <17 years of age:
- As a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism
- As an adjunct to surgery and radioiodine therapy in management of thyrotropin-dependent well-differentiated thyroid cancer
Age 1-3 months
- 10-15 mcg/kg/day PO
- 5-7.5 mcg/kg/day IV/IM
- Use lower starting dose (25 mcg/day) if patient at risk of cardiac failure; if initial serum T4 lower than 5 mcg/dL begin treatment at higher dose (50 mcg/day)
Age 3-6 months
Age 6-12 months
Age 1-5 years
Age 6-12 years
>12 years
Dosing considerations
- Check for bioequivalence if switching brands/generics
- May minimize hyperactivity in older children by initiating dose at 1/4 of recommended dose; increase by that amount each week until full dose achieved
- Start children with severe or chronic hypothyroidism at 25 mcg/day; adjust dose by 25 mcg qweek
Because of increased prevalence of cardiovascular disease among the elderly, initiate therapy at less than full replacement dose; atrial arrhythmias can occur in elderly patients; atrial fibrillation is the most common of arrhythmias observed with levothyroxine overtreatment in the elderly
Interactions
Interaction Checker
No Results
Contraindicated
Serious - Use Alternative
Significant - Monitor Closely
Minor
Contraindicated (2)
- sodium iodide I-131
levothyroxine will decrease the level or effect of sodium iodide I-131 by Other (see comment). Contraindicated. Use of thyroid products or iodine before and during treatment with sodium iodide I-131 decreases uptake of sodium iodide I-131 by the thyroid gland
- sucroferric oxyhydroxide
sucroferric oxyhydroxide decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Contraindicated. No interaction anticipated with parenteral levothyroxine.
Serious - Use Alternative (11)
- antithrombin alfa
levothyroxine increases effects of antithrombin alfa by pharmacodynamic synergism. Avoid or Use Alternate Drug.
- antithrombin III
levothyroxine increases effects of antithrombin III by pharmacodynamic synergism. Avoid or Use Alternate Drug.
- argatroban
levothyroxine increases effects of argatroban by pharmacodynamic synergism. Avoid or Use Alternate Drug.
- bemiparin
levothyroxine increases effects of bemiparin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
- bivalirudin
levothyroxine increases effects of bivalirudin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
- bremelanotide
bremelanotide will decrease the level or effect of levothyroxine 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.
- fondaparinux
levothyroxine increases effects of fondaparinux by pharmacodynamic synergism. Avoid or Use Alternate Drug.
- heparin
levothyroxine increases effects of heparin by pharmacodynamic synergism. Avoid or Use Alternate Drug.
- lycopus
lycopus decreases effects of levothyroxine by pharmacodynamic antagonism. Contraindicated. Lycopus blocks peripheral conversion of T4 to T3.
- phenindione
levothyroxine increases effects of phenindione by pharmacodynamic synergism. Avoid or Use Alternate Drug.
- protamine
levothyroxine increases effects of protamine by pharmacodynamic synergism. Avoid or Use Alternate Drug.
Monitor Closely (55)
- amitriptyline
levothyroxine increases effects of amitriptyline by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- amoxapine
levothyroxine increases effects of amoxapine by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- apalutamide
apalutamide will decrease the level or effect of levothyroxine by increasing elimination. Use Caution/Monitor. Apalutamide induces UGT and may decrease systemic exposure of drugs that are UGT substrates.
- caffeine
caffeine decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. COFFEE binds levothyroxine in the GI tract. Separate by 2 hours.
- calcium acetate
calcium acetate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. Separate administration by 4 hours.
- calcium carbonate
calcium carbonate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. Separate by 2 hours.
- calcium chloride
calcium chloride decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. Separate by 2 hours.
- calcium citrate
calcium citrate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. Separate by 2 hours.
- calcium gluconate
calcium gluconate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. Separate by 2 hours.
- carbonyl iron
carbonyl iron decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- cholestyramine
cholestyramine decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- clomipramine
levothyroxine increases effects of clomipramine by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- colesevelam
colesevelam decreases levels of levothyroxine by drug binding in GI tract. Use Caution/Monitor. Concomitant administration decreases levothyroxine absorption; however, absorption is not reduced when levothyroxine is administered 4 hr before colesevelam.
- crofelemer
crofelemer increases levels of levothyroxine by Other (see comment). Use Caution/Monitor. Comment: Crofelemer has the potential to inhibit transporters MRP2 and OATP1A2 at concentrations expected in the gut; unlikely to inhibit systemically because minimally absorbed.
- desipramine
levothyroxine increases effects of desipramine by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- didanosine
didanosine will decrease the level or effect of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. Applies to didanosine chewable tablets and powder for oral solution; administer 2 hr before or several hours after didanosine oral solution or chewable tablet administration
- digoxin
levothyroxine decreases effects of digoxin by unknown mechanism. Use Caution/Monitor.
- doxepin
levothyroxine increases effects of doxepin by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- doxepin cream
levothyroxine increases effects of doxepin cream by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- dulaglutide
dulaglutide, levothyroxine. 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.
- eluxadoline
eluxadoline increases levels of levothyroxine by decreasing metabolism. Use Caution/Monitor. Eluxadoline may increase the systemic exposure of coadministered OATP1B1 substrates.
- epinephrine
levothyroxine will increase the level or effect of epinephrine by unspecified interaction mechanism. Use Caution/Monitor.
- ferric maltol
ferric maltol decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
ferric maltol, levothyroxine. Either increases effects 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). - ferrous fumarate
ferrous fumarate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- ferrous gluconate
ferrous gluconate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- ferrous sulfate
ferrous sulfate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- food
food decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. COFFEE binds levothyroxine in the GI tract. Separate by 2 hours.
- imipramine
levothyroxine increases effects of imipramine by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- insulin degludec
levothyroxine decreases effects of insulin degludec by pharmacodynamic antagonism. Use Caution/Monitor. Thyroid hormones regulate carbohydrate metabolism, gluconeogenesis, and glycogen stores mobilization; dose of antidiabetic agents may need adjustment and increased frequency of glucose monitoring may be required.
- insulin degludec/insulin aspart
levothyroxine decreases effects of insulin degludec/insulin aspart by pharmacodynamic antagonism. Use Caution/Monitor. Thyroid hormones regulate carbohydrate metabolism, gluconeogenesis, and glycogen stores mobilization; dose of antidiabetic agents may need adjustment and increased frequency of glucose monitoring may be required.
- insulin inhaled
levothyroxine decreases effects of insulin inhaled by pharmacodynamic antagonism. Use Caution/Monitor. Thyroid hormones regulate carbohydrate metabolism, gluconeogenesis, and glycogen stores mobilization; dose of antidiabetic agents may need adjustment and increased frequency of glucose monitoring may be required.
- iron dextran complex
iron dextran complex decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- iron sucrose
iron sucrose decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- ketamine
levothyroxine increases toxicity of ketamine by unspecified interaction mechanism. Use Caution/Monitor. Coadministration may cause marked hypertension and tachycardia.
- lanthanum carbonate
lanthanum carbonate decreases levels of levothyroxine by cation binding in GI tract. Use Caution/Monitor. Administer oral thyroid products at least 2 hr before or after lanthanum. Interaction applies only to oral thyroid products only. .
- letermovir
letermovir increases levels of levothyroxine by Other (see comment). Use Caution/Monitor. Comment: Letermovir, an OATP1B1/3 inhibitor may increase plasma concentrations of coadministered OATP1B1/3 substrates.
- levonorgestrel oral/ethinylestradiol/ferrous bisglycinate
levonorgestrel oral/ethinylestradiol/ferrous bisglycinate will decrease the level or effect of levothyroxine by unknown mechanism. Modify Therapy/Monitor Closely. The estrogen component of combined hormonal contraceptives (CHCs) may raise the serum concentrations of thyroxine-binding globulin. Women on thyroid hormone replacement therapy may need increased doses of thyroid hormone with use of CHCs.
- magnesium supplement
magnesium supplement will decrease the level or effect of levothyroxine by Other (see comment). Modify Therapy/Monitor Closely. Drug may adsorb to magnesium; may decrease absorption by the intestinal tract; applies to oral forms; may separate administration of drugs by 4 hr
- metformin
levothyroxine decreases effects of metformin by pharmacodynamic antagonism. Use Caution/Monitor. Patient should be closely observed for loss of blood glucose control; when drugs are withdrawn from a patient receiving metformin, patient should be observed closely for hypoglycemia.
- nateglinide
levothyroxine decreases effects of nateglinide by pharmacodynamic antagonism. Use Caution/Monitor. Coadministration may reduce nateglinide's hypoglycemic action.
- nortriptyline
levothyroxine increases effects of nortriptyline by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- orlistat
orlistat decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. Risk of hypothyroidism. Separate by 4 hours.
- patiromer
patiromer will decrease the level or effect of levothyroxine by drug binding in GI tract. Use Caution/Monitor. May administer 3 hours apart
- polysaccharide iron
polysaccharide iron decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- protriptyline
levothyroxine increases effects of protriptyline by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- raloxifene
raloxifene decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- ropeginterferon alfa 2b
ropeginterferon alfa 2b will increase the level or effect of levothyroxine by Other (see comment). Use Caution/Monitor. Certain proinflammatory cytokines, including interferons, can suppress CYP450 enzymes resulting in increased exposures of some CYP substrates. Therefore, monitor patients who are receiving concomitant drugs that are CYP450 substrates with a narrow therapeutic index from toxicities to such drugs.
- rose hips
rose hips decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- sodium sulfate/?magnesium sulfate/potassium chloride
sodium sulfate/?magnesium sulfate/potassium chloride decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Modify Therapy/Monitor Closely. Administer levothyroxine at least 4 hr after each dose to avoid chelation with magnesium. .
- sodium sulfate/potassium sulfate/magnesium sulfate
sodium sulfate/potassium sulfate/magnesium sulfate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Modify Therapy/Monitor Closely. Administer levothyroxine at least 4 hr after each dose to avoid chelation with magnesium. .
- teduglutide
teduglutide increases levels of levothyroxine 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.
- trimagnesium citrate anhydrous
trimagnesium citrate anhydrous decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
- trimipramine
levothyroxine increases effects of trimipramine by Other (see comment). Use Caution/Monitor. Comment: Increased catecholamine receptor sensitivity; may increase CNS and cardiovascular effects, including arrhythmias.
- ustekinumab
ustekinumab, levothyroxine. 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.
- warfarin
levothyroxine increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor.
Minor (31)
- alendronate
levothyroxine decreases levels of alendronate by unspecified interaction mechanism. Minor/Significance Unknown. Bioavailability of alendronate decreases slightly.
- amobarbital
amobarbital decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- butabarbital
butabarbital decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- butalbital
butalbital decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- carbamazepine
carbamazepine decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- colestipol
colestipol decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.
- dexlansoprazole
dexlansoprazole decreases levels of levothyroxine by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- eptifibatide
levothyroxine decreases levels of eptifibatide by increasing renal clearance. Minor/Significance Unknown.
- eslicarbazepine acetate
eslicarbazepine acetate decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- esomeprazole
esomeprazole decreases levels of levothyroxine by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- ethotoin
ethotoin decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
ethotoin decreases levels of levothyroxine by plasma protein binding competition. Minor/Significance Unknown. - fosphenytoin
fosphenytoin decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
fosphenytoin decreases levels of levothyroxine by plasma protein binding competition. Minor/Significance Unknown. - furosemide
furosemide increases toxicity of levothyroxine by Other (see comment). Minor/Significance Unknown. Comment: High doses (greater than 80 mg) of furosemide may inhibit binding of thyroid hormones to carrier proteins and result in transient increase in free thyroid hormones, followed by overall decrease in total thyroid hormone levels.
- glandular products
glandular products increases effects of levothyroxine by pharmacodynamic synergism. Minor/Significance Unknown. Additive effects with thyroid glandular extract.
- guggul
guggul decreases effects of levothyroxine by pharmacodynamic antagonism. Minor/Significance Unknown.
- lansoprazole
lansoprazole decreases levels of levothyroxine by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- omeprazole
omeprazole decreases levels of levothyroxine by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- oxcarbazepine
oxcarbazepine decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- pantoprazole
pantoprazole decreases levels of levothyroxine by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- pentobarbital
pentobarbital decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- phenobarbital
phenobarbital decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- phenytoin
phenytoin decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
phenytoin decreases levels of levothyroxine by plasma protein binding competition. Minor/Significance Unknown. - piracetam
piracetam, levothyroxine. Mechanism: unknown. Minor/Significance Unknown. Combination of piracetam and T3+T4 produced confusion, sleep disorder in single case.
- primidone
primidone decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- rabeprazole
rabeprazole decreases levels of levothyroxine by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- rifampin
rifampin decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- secobarbital
secobarbital decreases levels of levothyroxine by increasing metabolism. Minor/Significance Unknown.
- shepherd's purse
shepherd's purse decreases effects of levothyroxine by unspecified interaction mechanism. Minor/Significance Unknown. Theoretical interaction.
- sodium polystyrene sulfonate
sodium polystyrene sulfonate decreases levels of levothyroxine by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.
- theophylline
levothyroxine decreases levels of theophylline by increasing elimination. Minor/Significance Unknown.
- tirofiban
levothyroxine decreases levels of tirofiban by increasing renal clearance. Minor/Significance Unknown.
Adverse Effects
Frequency Not Defined
Angina pectoris
Arthralgia
Congestive heart failure
Flushing
Increased pulse
Myocardial infarction
Palpitations
Arrhythmias
Cramps
Diarrhea
Nervousness
Anxiety
Choking sensation
Emotional lability
Headache
Heat intolerance
Insomnia
Myasthenia
Pseudotumor cerebri
Alopecia
Weight loss
Infertility
Dyspnea
Fever
Tachycardia
Tremor
Decreased bone mineral density
Postmarketing Reports
Musculoskeletal: Muscle weakness, muscle spasm
Dermatologic: Hair loss, rash
Slipped capital femoral epiphysis (children)
Warnings
Black Box Warnings
Thyroid hormones, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss
In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction; larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects
Contraindications
Hypersensitivity to thyroid hormone or other ingredients
Uncorrected adrenal insufficiency
Cautions
Proper dose titration and careful monitoring is critical to prevent persistence of hypothyroidism or development of hyperthyroidism
Generally, do not use levothyroxine sodium preparations interchangeably, owing to narrow therapeutic index; check for bioequivalence if switching brands/generics; if formulations are changed, monitor TSH and adjust dose if needed
Synthroid and Unithroid tabs contain lactose
Pediatric use
- In pediatric patients, rapid restoration of normal serum T4 concentrations is essential for preventing adverse effects of congenital hypothyroidism on cognitive development as well as on overall physical growth and maturation; therefore, initiate therapy immediately upon diagnosis; levothyroxine is generally continued for life in these patients
- Closely monitor infants during first 2 weeks of therapy for cardiac overload and arrhythmias
Cardiovascular
- Over-treatment with levothyroxine may cause increase in heart rate, cardiac wall thickness, and cardiac contractility; may precipitate angina or arrhythmias, particularly in patients with cardiovascular disease and in elderly patients
- Initiate with lower doses in elderly patients than the recommended dose for younger individuals or patients without cardiac disease
- Monitor patients receiving concomitant levothyroxine and sympathomimetic agents for signs and symptoms of coronary insufficiency
Myxedema coma
- Myxedema coma is a life-threatening emergency characterized by poor circulation and hypometabolism, and may result in unpredictable GI absorption of levothyroxine
- Use of oral thyroid hormone drug products is not recommended to treat myxedema coma
- Treat myxedema coma with IV thyroid products
Acute adrenal crisis in patients with concomitant adrenal insufficiency
- Thyroid hormone increases metabolic clearance of glucocorticoids
- Initiation of thyroid hormone therapy before initiating glucocorticoid therapy may precipitate an acute adrenal crisis in patients with adrenal insufficiency
- Treat patients with adrenal insufficiency with replacement glucocorticoids before initiating
Prevention of hyperthyroidism or incomplete treatment of hypothyroidism
- Levothyroxine has a narrow therapeutic index
- Over- or undertreatment may have negative effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and on glucose and lipid metabolism in adult or pediatric patients
- In pediatric patients with congenital and acquired hypothyroidism, undertreatment may adversely affect cognitive development and linear growth, and overtreatment is associated with craniosynostosis and acceleration of bone age
- Titrate dose carefully and monitor response to titration to avoid these effects; consider potential for food or drug interactions and adjust administration or dosage as needed
Worsening diabetic control
- Addition of levothyroxine therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements
- Carefully monitor glycemic control after starting, changing, or discontinuing levothyroxine
Decreased bone mineral density with over-replacement
- Increased bone resorption and decreased bone mineral density may occur as a result of over-replacement, particularly in post-menopausal women
- Increased bone resorption may be associated with increased serum levels and urinary excretion of calcium and phosphorous, elevations in bone alkaline phosphatase, and suppressed serum parathyroid hormone levels
- Administer minimum dose of levothyroxine that achieves desired clinical and biochemical response to mitigate against this risk
Drug-food interactions
- Evaluate need for dose adjustments when regularly administering within 1 hr of certain foods that affect levothyroxine absorption
- Decreases GI absorption: Soybean flour (infant formula), cottonseed meal, walnuts, and dietary fiber
- Delayed GI absorption, reduced biovailability: Grapefruit juice
Drug interaction overview
-
Drugs that may decrease T4 absorption
- Concurrent use may reduce levothyroxine efficacy by binding and delaying or preventing absorption, potentially resulting in hypothyroidism
- Calcium carbonate, ferrous sulfate, bile acid sequestrants, ion exchange resins: Administer at least 4 hr apart
- Orlistat: Monitor for changes in thyroid function
- PPIs, sucralfate, antacids: Hypochlorhydria and altered gastric pH may reduce levothyroxine absorption; monitor
-
Drugs that may alter T4 and T3 transport
- Typically patients remain euthyroid
- Clofibrate, estrogen, heroin, methadone, 5-fluorouracil, mitotane, tamoxifen: May increase thyroxine binding globulin (TBG) concentration
- Androgens, anabolic steroids, asparaginase, glucocorticoids, slow-release nicotinic acid: may decrease TBG concentration
- Salicylates: Inhibit binding of T4 and T3 to TBG and transthyretin; initial increase in serum FT4 followed by return of FT4 to normal levels with sustained therapeutic serum salicylate concentrations, although total T4 levels may decrease by up to 30%
- Carbamazepine, furosemide, heparin, hydantoins, NSADs , fenamates: May cause protein binding site displacement of levothyroxine
-
Drugs that may alter hepatic metabolism
- May increase levothyroxine dose requirements
- Phenobarbital, rifampin: Stimulate hepatic microsomal drug-metabolizing enzyme activity and may cause increased hepatic degradation of levothyroxine
-
Drugs that may decreased conversion of T4 to T3
- Beta blockers: Large doses of propranolol (>160 mg/day), T3 and T4 levels change slightly, TSH levels remain normal, and patients are clinically euthyroid; beta-adrenergic antagonists may be impaired when hypothyroid patient is converted to the euthyroid state
- Glucocorticoids: Short-term administration of large doses of glucocorticoids may decrease serum T3 concentrations by 30% with minimal change in serum T4 levels; however, long-term glucocorticoid therapy may result in slightly decreased T3 and T4 levels due to decreased TBG production
- Amiodarone: Inhibits peripheral conversion of T4 to T3 and may cause isolated biochemical changes (increase in serum free-T4, and decreased or normal free-T3) in clinically euthyroid patients
-
Antidiabetics
- Monitor glycemic control when levothyroxine started, changed, or discontinued
- Levothyroxine may worsen glycemic control and result in increased antidiabetic agent or insulin requirements
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Oral anticoagulants
- Decreased anticoagulant dose may be required
- Levothyroxine increases response to oral anticoagulant
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Digoxin
- Increased digoxin dose may be required
- Levothyroxine may reduce therapeutic effects of digoxin; serum digoxin levels may be decreased when a hypothyroid patient becomes euthyroid
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Antidepressants
- Concurrent use of tricyclic or tetracyclic antidepressants and levothyroxine may increase therapeutic and toxic effects of both drugs, possibly due to increased receptor sensitivity to catecholamines
- Sertraline administration in patients stabilized on levothyroxine may result in increased levothyroxine requirements
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Ketamine
- Closely monitor blood pressure
- Coadministration may produce marked hypertension and tachycardia
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Sympathomimetics
- Increased effects of sympathomimetics or thyroid hormone
- Thyroid hormones may increase risk of coronary insufficiency when sympathomimetic agents are administered to patients with coronary artery disease
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Tyrosine kinase inhibitors
- Closely monitor TSH levels
- Coadministration may cause hypothyroidism
Pregnancy & Lactation
Pregnancy
Experience with levothyroxine use in pregnant women, including data from post-marketing studies, in pregnant women treated with oral levothyroxine to maintain euthyroid state, have not reported increased rates of major birth defects or miscarriages; there are risks to mother and fetus associated with untreated hypothyroidism in pregnancy; since TSH levels may increase during pregnancy, TSH should be monitored and levothyroxine dosage adjusted during pregnancy; untreated maternal hypothyroidism may have adverse effect on fetal neurocognitive development
Maternal hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, and premature delivery; untreated maternal hypothyroidism may have adverse effect on fetal neurocognitive development
Pregnancy may increase thyroid hormone requirements. serum TSH level should be monitored and the dosage adjusted during pregnancy; since postpartum TSH levels are similar to preconception values, the dosage should return to the pre-pregnancy dose immediately after delivery
Animal data
- Animal reproductive studies have not been conducted with levothyroxine sodium; therapy should not be discontinued during pregnancy and hypothyroidism diagnosed during pregnancy should be promptly treated
Lactation
Limited published studies report that levothyroxine is present in human milk; however, there is insufficient information to determine effects of levothyroxine on breastfed infant and no adverse effects on breastfed infant reported and there is no information on effects of levothyroxine on milk production; adequate levothyroxine treatment during lactation may normalize milk production in hypothyroid lactating mothers with low milk supply; developmental and health benefits of breastfeeding should be considered along with mother’s clinical need for levothyroxine and any potential adverse effects on breastfed infant from levothyroxine or from underlying maternal condition
Pregnancy Categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk. C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done. D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk. X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist. NA: Information not available.Pharmacology
Mechanism of Action
Synthetic T4; thyroid hormone increases basal metabolic rate, increases utilization and mobilization of glycogen stores, promotes gluconeogenesis; involved in growth development and stimulates protein synthesis
Absorption
40-80% from GI tract (PO)
Bioavailability: 64% (nonfasting); 79-81% (fasting)
Peak plasma time: 2-4 hr (PO)
Duration: Hypothyroidism, several weeks
Onset, hypothyroidism
- Initial response: 3-5 days (PO); 6-8 hr (IV)
- Maximum effect: Several weeks
- Peak effect: 24 hr (IV)
Onset, myxedema coma
- Initial response: 6-12 hr (IV)
- Peak effect: 24 hr
Distribution
Protein bound: 99%
Vd: 9-10 L
Metabolism
Deiodinated in blood and then 50% converted to active metabolite, triiodothyronine (T3), also by liver
Metabolites: T3 (active)
Elimination
Half-life: 9-10 days (hypothyroid); 3-4 days (hyperthyroid); 6-7 days (euthyroid)
Total body clearance: 0.8-1.4 L/day
Excretion: Urine (major), feces (20%)
Administration
IV Preparation
Reconstitution of lyophilized powder
- Add 5 mL of 0.9% NaCl vial containing 200 or 500 mcg and shake until a clear solution is obtained; resultant solutions contain ~40 or 100 mcg/mL, respectively
- Use reconstituted solutions immediately; discard any unused portions
- Alternatively, add 2 mL 0.9% NaCl to vial containing 200 mcg to produce solution containing ~100 mcg/mL
- Do not admix with IV infusion solutions
Oral Administration
Take tabs with full glass of water preferably 30 min to 1 hr before breakfast on empty stomach to avoid choking or gagging
Evaluate need for dose adjustments when regularly administering within 1 hr of certain foods that may affect absorption
Do not use foods that decrease absorption (soybean products) for administering levothyroxine
Administer oral levothyroxine >4 hr apart from drugs known to interfere with absorption
IV/IM: Administer 50% of PO dose
Patients unable to swallow intact tabs
- Crush appropriate dose and place in 5-10 mL of water
- Administer resultant suspension by spoon or dropper immediately, do NOT store
Images
Patient Handout
levothyroxine intravenous
NO MONOGRAPH AVAILABLE AT THIS TIME
USES: Consult your pharmacist.
HOW TO USE: Consult your pharmacist.
SIDE EFFECTS: Consult your pharmacist.In the US -Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.
PRECAUTIONS: Consult your pharmacist.
DRUG INTERACTIONS: Consult your pharmacist.Keep a list of all your medications with you, and share the list with your doctor and pharmacist.
OVERDOSE: If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center.
NOTES: No monograph available at this time.
MISSED DOSE: Consult your pharmacist.
STORAGE: Consult your pharmacist.Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.
Information last revised July 2016. Copyright(c) 2022 First Databank, Inc.
IMPORTANT: HOW TO USE THIS INFORMATION: This is a summary and does NOT have all possible information about this product. This information does not assure that this product is safe, effective, or appropriate for you. This information is not individual medical advice and does not substitute for the advice of your health care professional. Always ask your health care professional for complete information about this product and your specific health needs.
Formulary
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