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Related to Synthroid: Levothyroxine, hypothyroidism, Eltroxin


trademark for a preparation of levothyroxine sodium, a thyroid hormone.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

levothyroxine sodium (L-thyroxine, T4)

Eltroxin (CA) (UK), Euthyrox (CA), Evotrox (UK), Levo-T, Levolet, Levothroid, Levoxyl, Nu-Thyro (CA), Soloxine, Synthroid, Unithroid

Pharmacologic class: Synthetic thyroxine hormone

Therapeutic class: Thyroid hormone replacement

Pregnancy risk category A

FDA Box Warning

• Drug shouldn't be used alone or with other agents to treat obesity or weight loss. In euthyroid patients, doses within range of daily hormonal requirements are ineffective for weight loss. Larger doses may cause serious or life-threatening toxicity, particularly when given with sympathomimetic amines (such as those used for anorectic effects).


Synthetic form of thyroxine that replaces endogenous thyroxine, increasing thyroid hormone levels. Thyroid hormones help regulate cell growth and differentiation and increase metabolism of lipids, protein, and carbohydrates.


Powder for injection: 200 mcg/vial in 6- and 10-ml vials, 500 mcg/vial in 6- and 10-ml vials

Tablets: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg

Indications and dosages

Hypothyroidism; treatment or prevention of euthyroid goiter

Adults: For healthy adults younger than age 50 and those over age 50 who have recently been treated or undergone short-term therapy, start at full replacement dosage of 1.7 mcg/kg P.O. daily, given 30 minutes to 1 hour before breakfast. For patients older than age 50 or younger than age 50 with heart disease, 25 to 50 mcg P.O. daily, increased q 4 to 6 weeks. In severe hypothyroidism, initial dosage is 12.5 to 25 mcg P.O. daily, adjusted by 25 mcg daily q 2 to 4 weeks. For patients who can't tolerate oral doses, adjust I.M. or I.V. dosage to roughly half of oral dosage.

Congenital hypothyroidism

Children older than age 12 who have completed puberty and growth: 1.7 mcg/kg P.O. daily

Children older than age 12 who have not completed puberty and growth: Up to 150 mcg or 2 to 3 mcg/kg P.O. daily

Children ages 6 to 12: 4 to 5 mcg/kg P.O. daily

Children ages 1 to 5: 5 to 6 mcg/kg P.O. daily

Infants ages 6 to 12 months: 6 to 8 mcg/kg P.O. daily

Infants ages 3 to 6 months: 8 to 10 mcg/kg P.O. daily

Infants up to 3 months old: 10 to 15 mcg/kg P.O. daily

Myxedema coma or stupor

Adults: 200 to 500 mcg I.V. as a solution containing 100 mcg/ml. Additional 100 to 300 mcg may be given on day 2 if significant improvement has not occurred. Convert to P.O. therapy when patient is clinically stable.

Thyroid-stimulating hormone suppression in well-differentiated thyroid cancers and thyroid nodules

Adults: Dosage individualized based on disease and patient

Dosage adjustment

• Cardiovascular disease

• Psychosis or agitation

• Elderly patients


• Hypersensitivity to drug, its components, or tartrazine

• Acute myocardial infarction

• Thyrotoxicosis

• Adrenal insufficiency


Use cautiously in:

• cardiovascular disease, severe renal insufficiency, diabetes mellitus

• elderly patients

• pregnant or breastfeeding patients.


• Be aware that all dosages are highly individualized.

• Give tablets on an empty stomach 30 minutes to 1 hour before first meal of day.

• If patient can't swallow tablets, crush them and sprinkle onto small amount of food, such as applesauce. For infants and children, dissolve tablets in small amount of water, nonsoybean formula, or breast milk and administer immediately.

• Don't give oral form within 4 hours of bile acid sequestrants or antacids.

• Reconstitute Synthroid powder for injection with 5 ml of 0.9% sodium chloride injection. Shake until clear and use immediately.

• For I.V. administration, give each 100 mcg over at least 1 minute.

• Be aware that the various levothyroxine preparations aren't bioequivalent. Patient should consistently use same brand or generic product, with dosing based on weight, age, physical condition, and symptom duration.

• When drug is given for thyroid-stimulating hormone (TSH) suppression test, TSH suppression level is not well established and radioactive iodine (131I) is given before and after treatment course.

Adverse reactions

CNS: insomnia, irritability, nervousness, headache

CV: tachycardia, angina pectoris, hypotension, hypertension, increased cardiac output, arrhythmias, cardiovascular collapse

GI: vomiting, diarrhea, abdominal cramps

GU: menstrual irregularities

Metabolic: hyperthyroidism

Musculoskeletal: accelerated bone maturation (in children), decreased bone density (in women on long-term therapy)

Skin: alopecia (in children), diaphoresis

Other: heat intolerance, weight loss


Drug-drug. Aminoglutethimide, amiodarone, anabolic steroids, antithyroid drugs, asparaginase, barbiturates, carbamazepine, chloral hydrate, cholestyramine, clofibrate, colestipol, corticosteroids, danazol, diazepam, estrogens, ethionamide, fluorouracil, heparin (with I.V. use), insulin, lithium, methadone, mitotane, nitroprusside, oxyphenbutazone, perphenazine, phenylbutazone, phenytoin, propranolol, salicylates (large doses), sulfonylureas, thiazides: altered thyroid function test results

Antacids, bile acid sequestrants: interference with levothyroxine absorption

Anticoagulants: increased anticoagulant action

Beta-adrenergic blockers (selected): decreased beta blocker action

Cardiac glycosides: decreased cardiac glycoside blood level

Cholestyramine, colestipol: levothyroxine inefficacy

Theophyllines: decreased theophylline clearance

Drug-diagnostic tests. Thyroid function tests: decreased values

Drug-food. Foods high in iron or fiber, soybeans: decreased drug absorption

Patient monitoring

• Check vital signs and ECG routinely.

• Monitor thyroid and liver function tests.

Evaluate for signs and symptoms of overdose, including those of hyperthyroidism (weight loss, cardiac symptoms, abdominal cramps).

• Monitor closely for drug efficacy.

• Check patients with Addison's disease or diabetes mellitus for worsening of these conditions.

Watch for signs and symptoms of bleeding tendency, especially in patients receiving anticoagulants concurrently.

Patient teaching

• Explain that patient may require lifelong therapy and must undergo regular blood testing.

• Tell patient or parent to report adverse effects, including signs or symptoms of hyperthyroidism or hypothyroidism.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• Advise patient to avoid getting overheated, as in hot environments or during vigorous exercise.

• Tell parents that child being treated may lose hair during first few months of therapy. Reassure them that this effect usually is transient.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and foods mentioned above.

McGraw-Hill Nurse's Drug Handbook, 7th Ed. Copyright © 2013 by The McGraw-Hill Companies, Inc. All rights reserved


A trademark for the drug levothyroxine sodium.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
References in periodicals archive ?
Its major products are Humira for arthritis, Norvir for HIV, Depakote, an anticonvulsant and Synthroid for thyroid.
Current American guidelines for the treatment of thyroid disease calls for the use of TSH-only testing and for levothyroxine sodium (such as brand name Synthroid) to be administered to all hypothyroid patients.
Thyroid hormone medications, including levothyroxine (Levothroid, Levoxyl, Synthroid), liothyronine (Cytomel) and liotrix (Euthroid, Thyrolar), are given when blood tests show that you have hypothyroidism,.
A blood test will detect an underactive thyroid, which may require a medication like Synthroid. In this case, new research suggests this drug is most effective when taken at night, contrary to routine recommendations.
"Often they give patients synthroid and send them on their way but that doesn't work for everyone.
The 'Happy Feet Two' star, who is now raising awareness about the disease, said that after using Synthroid, she has never had a problem and never had any symptoms.
According to MayoClinic recommendations, standard treatment for hypothyroidism involves daily use of the synthetic thyroid hormone levothyroxine (Levothroid, Synthroid, or others).
The research-based pharmaceutical company has approximately USD18bn in annual revenues currently and will have a sustainable portfolio of market-leading brands, including Humira, Lupron, Synagis, Kaletra, Creon and Synthroid. In addition, a pipeline of R&D assets in important specialty therapeutic areas such as Hepatitis C, immunology, chronic kidney disease, women's health, oncology and neuroscience is expected to drive its future growth.
The research company currently has about USD18bn (EUR13bn) in annual revenue and its portfolio will comprised brands like Humira, Lupron, Synagis, Kaletra, Creon and Synthroid. It will specialise in research in new medicines and formulations, including more than 20 new compounds or indications in Phase II or III in areas like immunology, chronic kidney disease, women's health, Hepatitis C, oncology and neuroscience.
"I know I will need to take my calcium at the same time I take my Synthroid."
When Jan Root's 88-year-old mother broke her hip last year, "in the hoopla of admitting her to the emergency room, we forgot to tell the doctor that she takes Synthroid, a thyroid medicine," Root recalls.