Pronunciation:

(lye oh THYE roe neen)

U.S. Brand Names:

Synonyms:

Generic Available:

Canadian Brand Names:

Use:

Oral: Replacement or supplemental therapy in hypothyroidism; management of nontoxic goiter; a diagnostic aid

I.V.: Treatment of myxedema coma/precoma

Pregnancy Risk Factor:

Pregnancy Implications:

Lactation:

Contraindications:

Warnings/Precautions:

Adverse Reactions:

1% to 10%: Cardiovascular: Arrhythmia (6%), tachycardia (3%), cardiopulmonary arrest (2%), hypotension (2%), MI (2%)

<1%: Allergic skin reactions, angina, CHF, fever, hypertension, phlebitis, twitching

Overdosage/Toxicology:

Reduce dose or temporarily discontinue therapy. Normal hypothalamic-pituitary-thyroid axis will return to normal in 6-8 weeks. Serum T4 levels do not correlate well with toxicity. In massive acute ingestion, reduce GI absorption and give general supportive care. Excessive adrenergic activity (tachycardia) requires propranolol 1-3 mg I.V. over 10 minutes or 80-160 mg orally/day.

Drug Interactions:

Aluminum- and magnesium-containing antacids, calcium carbonate, simethicone, or sucralfate: May decrease T4 absorption; separate dose from thyroid hormones by at least 4 hours.

Antidiabetic agents (biguanides, meglitinides, sulfonylureas, thiazolidinediones, insulin): Changes in thyroid function may alter requirements of antidiabetic agent. Monitor closely at initiation of therapy, or when dose is changed or discontinued.

Cholestyramine and colestipol: Decrease T4 absorption; separate dose from thyroid hormones by at least 2 hours.

Digoxin: Digoxin levels may be reduced in hyperthyroidism; therapeutic effect may be reduced. Impact of thyroid replacement should be monitored.

Estrogens: May decrease serum free-thyroxine concentrations.

Iron: Decreases T4 absorption; separate dose from thyroid hormones by at least 4 hours

Kayexalate®: Decreases T4 absorption; separate dose from thyroid hormones by at least 4 hours

Ketamine: May cause marked hypertension and tachycardia; monitor

Theophylline, caffeine: Decreased theophylline clearance in hypothyroid patients; monitor during thyroid replacement.

Tricyclic and tetracyclic antidepressants: Therapeutic and toxic effects of thyroid hormones and the antidepressant are increased.

Warfarin (and other oral anticoagulants): The hypoprothrombinemic response to warfarin may be altered by a change in thyroid function or replacement. Replacement may dramatically increase response to warfarin. However, initiation of warfarin in a patient stabilized on a dose of thyroid hormones does not appear to require a significantly different approach.

Ethanol/Nutrition/Herb Interactions:

Stability:

Mechanism of Action:

Pharmacodynamics/Kinetics:

Onset of action: 2-4 hours

Peak response: 2-3 days

Absorption: Oral: Well absorbed (95% in 4 hours)

Half-life elimination: 2.5 days

Excretion: Urine

Dosage:

Children: Congenital hypothyroidism: Oral: 5 mcg/day increase by 5 mcg every 3-4 days until the desired response is achieved. Usual maintenance dose: 20 mcg/day for infants, 50 mcg/day for children 1-3 years of age, and adult dose for children >3 years.

Adults:

Hypothyroidism: Oral: 25 mcg/day increase by increments of 12.5-25 mcg/day every 1-2 weeks to a maximum of 100 mcg/day; usual maintenance dose: 25-75 mcg/day.

Patients with cardiovascular disease: Refer to Elderly dosing.

T3 suppression test: Oral: 75-100 mcg/day for 7 days; use lowest dose for elderly

Myxedema: Oral: Initial: 5 mcg/day; increase in increments of 5-10 mcg/day every 1-2 weeks. When 25 mcg/day is reached, dosage may be increased at intervals of 5-25 mcg/day every 1-2 weeks. Usual maintenance dose: 50-100 mcg/day.

Myxedema coma: I.V.: 25-50 mcg

Patients with known or suspected cardiovascular disease: 10-20 mcg

Note: Normally, at least 4 hours should be allowed between doses to adequately assess therapeutic response and no more than 12 hours should elapse between doses to avoid fluctuations in hormone levels. Oral therapy should be resumed as soon as the clinical situation has been stabilized and the patient is able to take oral medication. If levothyroxine rather than liothyronine sodium is used in initiating oral therapy, the physician should bear in mind that there is a delay of several days in the onset of levothyroxine activity and that I.V. therapy should be discontinued gradually.

Simple (nontoxic) goiter: Oral: Initial: 5 mcg/day; increase by 5-10 mcg every 1-2 weeks; after 25 mcg/day is reached, may increase dose by 12.5-25 mcg. Usual maintenance dose: 75 mcg/day

Elderly: Oral: 5 mcg/day; increase by 5 mcg/day every 2 weeks

Administration:

Administer doses at least 4 hours, and no more than 12 hours, apart

Resume oral therapy as soon as the clinical situation has been stabilized and the patient is able to take oral medication

When switching to tablets, discontinue the injectable, initiate oral therapy at a low dosage and increase gradually according to response

If levothyroxine is used for oral therapy, there is a delay of several days in the onset of activity; therefore, discontinue I.V. therapy gradually

Monitoring Parameters:

Reference Range:

Patient Education:

Additional Information:

Equivalent doses: Thyroid USP 60 mg ~ levothyroxine 0.05-0.06 mg ~ liothyronine 0.015-0.0375 mg

50-60 mg thyroid ~ 50-60 mcg levothyroxine and 12.5-15 mcg liothyronine

A synthetic form of L-Triiodothyronine (T3) can be used in patients allergic to products derived from pork or beef.

Note: Several medications have effects on thyroid production or conversion. The impact in thyroid replacement has not been specifically evaluated, but patient response should be monitored:

Methimazole: Decreases thyroid hormone secretion, while propylthiouracil decrease thyroid hormone secretion and decreases conversion of T4 to T3.

Beta-adrenergic antagonists: Decrease conversion of T4 to T3 (dose related, propranolol 160 mg/day); patients may be clinically euthyroid.

Iodide, iodine-containing radiographic contrast agents may decrease thyroid hormone secretion; may also increase thyroid hormone secretion, especially in patients with Graves' disease.

Other agents reported to impact on thyroid production/conversion include aminoglutethimide, amiodarone, chloral hydrate, diazepam, ethionamide, interferon-alpha, interleukin-2, lithium, lovastatin (case report), glucocorticoids (dose-related), mercaptopurine, sulfonamides, thiazide diuretics, and tolbutamide.

In addition, a number of medications have been noted to cause transient depression in TSH secretion, which may complicate interpretation of monitoring tests for thyroid hormones, including corticosteroids, octreotide, and dopamine. Metoclopramide may increase TSH secretion.

Anesthesia and Critical Care Concerns/Other Considerations:

Dental Health: Effects on Dental Treatment:

Dental Health: Vasoconstrictor/Local Anesthetic Precautions:

Mental Health: Effects on Mental Status:

Mental Health: Effects on Psychiatric Treatment:

Dosage Forms:

Injection, solution, as sodium (Triostat®): 10 mcg/mL (1 mL) [contains alcohol 6.8%]

Tablet, as sodium (Cytomel®): 5 mcg, 25 mcg, 50 mcg

International Brand Names: