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Synthroid
levothyroxine
Black Box Warnings .
Not for Obesity/Weight Loss
not for obesity/weight loss alone or as combo tx; in euthyroid patients doses within range of daily hormonal requirements ineffective for weight loss; larger doses may cause serious or life-threatening toxicity, especially given in combo with sympathomimetic amines including those with anorectic effects
Adult Dosing .
Dosage forms: TAB: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Dosage Form Details
- [INJ form discontinued in US for this brand; see generic]
Special Note
- [equivalency or interchangeability info]
- Info: for product conversion purposes, 100 mcg levothyroxine = 25 mcg liothyronine = 60-65 mg thyroid (porcine) = 1 grain liotrix
hypothyroidism
- [50-200 mcg PO qd]
- Start: 1.6 mcg/kg/dose PO qd, then adjust dose by 12.5-25 mcg/day q4-6wk; Info: adjust dose based on TFTs; doses >300 mcg/day rarely needed; use lower start dose, then adjust dose q6-8wk in elderly patients and patients with cardiac disease; dose adjustments may be needed during pregnancy and/or immediately postpartum; give on empty stomach, 30-60min before breakfast
TSH suppression
- [individualize dose PO qd]
- Info: for patients with thyrotropin-dependent well-differentiated thyroid CA; adjust dose to suppress TSH to levels based on clinical status; dose adjustments may be needed during pregnancy and/or immediately postpartum; give on empty stomach, 30-60min before breakfast
renal dosing
- [not defined]
- renal impairment: not defined
- HD/PD: not defined
hepatic dosing
- [not defined]
Peds Dosing .
- Dosage forms: TAB: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Dosage Form Details
- [INJ form discontinued in US for this brand; see generic]
Special Note
- [equivalency or interchangeability info]
- Info: for product conversion purposes, 100 mcg levothyroxine = 25 mcg liothyronine = 60-65 mg thyroid (porcine) = 1 grain liotrix
hypothyroidism
- [<3 mo]
- Dose: individualize dose PO qd; Start: 10-15 mcg/kg/dose PO qd, then adjust dose q2wk; Info: adjust dose based on TFTs; use lower start dose and incr. dose q4-6wk if risk for cardiac failure; give on empty stomach, 30-60min before morning meal
- [3-5 mo]
- Dose: individualize dose PO qd; Start: 8-10 mcg/kg/dose PO qd, then adjust dose q2wk; Info: adjust dose based on TFTs; give on empty stomach, 30-60min before morning meal
- [6-11 mo]
- Dose: individualize dose PO qd; Start: 6-8 mcg/kg/dose PO qd, then adjust dose q2wk; Info: adjust dose based on TFTs; give on empty stomach, 30-60min before morning meal
- [1-5 yo]
- Dose: individualize dose PO qd; Start: 5-6 mcg/kg/dose PO qd, then adjust dose q2wk; Info: adjust dose based on TFTs; start 25% usual start dose, then incr. by 25% usual start dose qwk if hyperactivity risk; give on empty stomach, 30-60min before breakfast
- [6-12 yo]
- Dose: individualize dose PO qd; Start: 4-5 mcg/kg/dose PO qd, then adjust dose q2wk; Info: adjust dose based on TFTs; start 25% usual start dose, then incr. by 25% usual start dose qwk if hyperactivity risk; give on empty stomach, 30-60min before breakfast
- [>12 yo, growth/puberty incomplete]
- Dose: individualize dose PO qd; Start: 2-3 mcg/kg/dose PO qd, then adjust dose q2wk; Info: adjust dose based on TFTs; start 25% usual start dose, then incr. by 25% usual start dose qwk if hyperactivity risk; give on empty stomach, 30-60min before breakfast
- [>12 yo, growth/puberty complete]
- Dose: 50-200 mcg PO qd; Start: 1.6 mcg/kg/dose PO qd, then adjust dose by 12.5-25 mcg/day q4-6wk; Info: adjust dose based on TFTs; doses >300 mcg/day rarely needed; use lower start dose, then adjust dose q6-8wk in patients with cardiac disease; start 25% usual start dose, then incr. by 25% usual start dose qwk if hyperactivity risk; dose adjustments may be needed during pregnancy and/or immediately postpartum; give on empty stomach, 30-60min before breakfast
TSH suppression
- [individualize dose PO qd]
- Info: for patients with thyrotropin-dependent well-differentiated thyroid CA; adjust dose to suppress TSH to levels based on clinical status; dose adjustments may be needed during pregnancy and/or immediately postpartum; give on empty stomach, 30-60min before breakfast
renal dosing
- [not defined]
- renal impairment: not defined
- HD/PD: not defined
hepatic dosing
- [not defined]
Contraindications / Cautions .
- hypersensitivity to drug or ingredient
- hypersensitivity to glycerol (PO solution form)
- thyrotoxicosis
- myxedema coma (PO form)
- MI, acute
- adrenal insufficiency, uncorrected
- TSH suppression, pre-existing
- caution: hypersensitivity to tartrazine (some generic forms)
- caution: cardiovascular disease
- caution: diabetes mellitus
- caution: elderly patients
- caution: patients <3 mo (glycerol-containing PO solution form)
- caution: pregnancy
- caution: hyperactivity risk (peds patients)
Drug Interactions .
Overview
levothyroxine
thyroid hormone
- UGT1A1 substrate
- UGT2B4 substrate
- affected by altered fat absorption
- binds to anion exchange resin/polymer
- binds to cation exchange resin/polymer
- binds to polyvalent cations
- gastric pH sensitive
- hyperglycemic effects
- hypertensive effects
- tachycardia
- thyroid hormone
- monitor thyroid function more frequently when starting, adjusting, or stopping other drugs, including short-term therapies, OTC drugs, herbal supplements
Avoid/Use Alternative
- ephedra
- ephedrine oral
- epinephrine inhaled
- furosemide
Monitor/Modify Tx
- acarbose
- acebutolol
- albuterol
- albuterol inhaled
- aliskiren
- alogliptin
- aluminum hydroxide
- amiloride
- amiodarone
- amitriptyline
- amlodipine
- amoxapine
- amphetamine
- apalutamide
- aprocitentan
- arformoterol inhaled
- armodafinil
- atenolol
- atomoxetine
- azilsartan medoxomil
- benazepril
- benzphetamine
- betaxolol
- bexagliflozin
- bisoprolol
- bromocriptine
- bumetanide
- bupropion
- butalbital
- calcium acetate
- calcium carbonate
- calcium citrate
- calcium gluconate
- canagliflozin
- candesartan cilexetil
- captopril
- carbamazepine
- carvedilol
- chlorothiazide
- chlorthalidone
- cholestyramine
- chromium
- cimetidine
- clevidipine
- clomipramine
- clonidine
- cocaine
- colesevelam
- colestipol
- dapagliflozin
- desipramine
- desvenlafaxine
- dexlansoprazole
- dexmethylphenidate
- dextroamphetamine
- diethylpropion
- digoxin
- diltiazem
- dobutamine
- dopamine
- doxazosin
- doxepin
- droxidopa
- dulaglutide
- efavirenz
- empagliflozin
- enalapril
- enalaprilat
- ephedrine injection
- epinephrine
- eplerenone
- ertugliflozin
- esketamine
- esmolol
- esomeprazole
- estetrol (contraceptive)
- estradiol (contraceptive)
- estradiol (hormone replacement)
- estrogens, conjugated (hormone replacement)
- estrogens, esterified (hormone replacement)
- ethacrynic acid
- ethinyl estradiol (contraceptive)
- ethinyl estradiol (hormone replacement)
- exenatide
- famotidine
- felodipine
- fenfluramine
- fenoldopam
- ferric citrate
- ferric maltol
- ferrous fumarate
- ferrous gluconate
- ferrous sulfate
- fexinidazole
- formoterol inhaled
- fosinopril
- fosphenytoin
- glimepiride
- glipizide
- glyburide
- grapefruit
- guanfacine
- hoodia
- hydralazine
- hydrochlorothiazide
- hydroxocobalamin IV
- imatinib
- imipramine
- indapamide
- insulin
- irbesartan
- isoproterenol
- isradipine
- ketamine
- labetalol
- lansoprazole
- lanthanum
- levalbuterol inhaled
- levomilnacipran
- linagliptin
- liraglutide
- lisdexamfetamine
- lisinopril
- lixisenatide
- lomitapide
- lorlatinib
- losartan
- magnesium carbonate
- magnesium citrate
- magnesium hydroxide
- magnesium oxide
- magnesium supplement
- metformin
- methamphetamine
- methyldopa
- methylphenidate
- metolazone
- metoprolol
- midodrine
- miglitol
- milnacipran
- mineral oil
- minoxidil
- mirabegron
- mitapivat
- modafinil
- moexipril
- molindone
- nadolol
- nateglinide
- nebivolol
- nicardipine
- nifedipine
- nimodipine
- nisoldipine
- nizatidine
- norepinephrine
- nortriptyline
- olmesartan medoxomil
- olodaterol inhaled
- omeprazole
- orlistat
- oxcarbazepine
- oxymetazoline nasal
- pantoprazole
- patiromer
- pentobarbital
- perindopril
- phendimetrazine
- phenobarbital
- phenoxybenzamine
- phentermine
- phentolamine
- phenylephrine
- phenylephrine injection
- phenylephrine nasal
- phenylephrine ophthalmic
- phenylephrine rectal
- phenytoin
- pindolol
- pioglitazone
- pramlintide
- prazosin
- primidone
- propranolol
- protriptyline
- pseudoephedrine
- quinapril
- rabeprazole
- raloxifene
- ramipril
- repaglinide
- rifampin
- rifapentine
- ritonavir
- ropinirole
- rosiglitazone
- rotigotine transdermal
- salmeterol inhaled
- saxagliptin
- semaglutide
- sertraline
- sevelamer
- simethicone
- sitagliptin
- sodium bicarbonate
- sodium citrate
- sodium polystyrene sulfonate
- solriamfetol
- soy
- spironolactone
- sucralfate
- sucroferric oxyhydroxide
- sulfate bowel prep
- telmisartan
- terazosin
- terbutaline
- timolol
- tipranavir
- tirzepatide
- torsemide
- trandolapril
- triamterene
- trimipramine
- valproic acid
- valsartan
- venlafaxine
- verapamil
- vilanterol inhaled
- viloxazine
- vonoprazan
- warfarin
- yohimbe
- zinc oral
Adverse Reactions .
Serious Reactions
- hypersensitivity reaction
- arrhythmia
- CHF
- HTN
- angina
- pseudotumor cerebri (peds patients)
- craniosynostosis (infants)
- premature epiphyseal closure
- seizures
Common Reactions
- palpitations
- appetite incr.
- tachycardia
- nervousness
- tremor
- weight loss
- diaphoresis
- diarrhea
- abdominal cramps
- insomnia
- fever
- headache
- alopecia
- heat intolerance
- menstrual irregularities
- nausea
- anxiety
- dyspnea
- rash
- muscle spasm
Safety/Monitoring .
Monitoring Parameters
ECG, cardiac exam closely in infants during 1st 2wk of tx
Look/Sound-Alike Drug Names
Synthroid confused with: Symmetrel; thyroid
levothyroxine confused with: amantadine; digoxin; lamoTRIgine; Lanoxin; leucovorin; Levaquin; levoFLOXacin; levonorgestrel; levorphanol; liothyronine
Pregnancy/Lactation .
Pregnancy
Clinical Summary
Hypothyroidism Use: may use during pregnancy; drug of choice during pregnancy; start 1.6 mcg/kg/dose PO qd if TSH >10 milliunits/L; start 1 mcg/kg/dose PO qd if TSH <10 milliunits/L; dose adjustment may be needed during pregnancy and/or immediately postpartum; no known risk of teratogenicity based on human data; possible risk of decr. drug levels, efficacy in pregnant patients
All Other Uses: may use during pregnancy; dose adjustment may be needed during pregnancy and/or immediately postpartum; no known risk of teratogenicity based on human data; possible risk of decr. drug levels, efficacy in pregnant patients
Lactation
Clinical Summary
may use while breastfeeding; no known risk of infant harm based on limited human data and drug properties; no human data available, though adverse effects on milk production not expected based on drug's mechanism of action
Pharmacology .
Metabolism: for levothyroxine: liver primarily, kidney, tissues; CYP450: unknown
Excretion: for levothyroxine: urine primarily, feces; Half-life: 6-7 days (euthyroid), 3-4 days (hyperthyroid), 9-10 days (hypothyroid)
Subclass: Thyroid Disorders: Hypothyroidism
Mechanism of Action
for levothyroxine: replaces thyroxine, an endogenous thyroid hormone involved in metabolism, growth, and development (synthetic T4)
Formulary .
No Formulary Selected
Manufacturer/Pricing .
Manufacturer: AbbVie Inc.
DEA/FDA: Rx
Retail Price
Estimated prices only. For current pricing, visit GoodRx.
oral tablet:
- 25 mcg (30 ea): $47.00
- 50 mcg (30 ea): $47.00
- 75 mcg (30 ea): $47.00
- 88 mcg (30 ea): $47.00
- 100 mcg (30 ea): $47.00
- 112 mcg (30 ea): $47.00
- 125 mcg (30 ea): $47.00
- 137 mcg (30 ea): $47.00
- 150 mcg (30 ea): $47.00
- 175 mcg (30 ea): $47.00
- 200 mcg (30 ea): $47.00
- 300 mcg (30 ea): $47.00
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