Liothyronine Sodium (T3; triiodothyronine)

A to Z Drug Facts

 Action Increases metabolic rate of body tissues; is needed for normal growth and maturation.

 Indications Replacement or supplemental therapy in hypothyroidism; TSH suppression for treatment or prevention of euthyroid goiters (eg, thyroid nodules, multinodular goiters and enlargement in chronic thyroiditis); diagnostic agent in suppression tests to differentiate suspected hyperthyroidism from euthyroidism.

 Contraindications Acute MI and thyrotoxicosis uncomplicated by hypothyroidism; coexistence of hypothyroidism and hypoadrenalism (Addison's disease), unless treatment of hypoadrenalism with adrenocortical steroids precedes initiation of thyroid therapy.

 Route/Dosage

Individualize dosage.

Hypothyroidism

ADULTS: PO 25 mcg/day initially, increase by 12.5 to 25 mcg q 1 to 2 wk, if needed. CHILDREN: PO 5 mcg/day initially, increase by 5 mcg q 1 to 2 wk, if needed.

Congenital hypothyroidism

CHILDREN: PO 5 mcg/day initially: PO 5 mcg/day, increase by 5 mcg q 3 to 4 d until desired response achieved.

Simple (nontoxic) goiter

ADULTS: PO 5 mcg/day initially, increase by 5 to 10 mcg q 1 to 2 wk. When 25 mcg/day is reached, increase by 12.5 to 25 mcg q 1 to 2 wk, if needed. CHILDREN: PO 5 mcg/day initially, increase by 5 mcg q 1 to 2 wk, if needed.

Myxedema

ADULTS: PO 5 mcg/day initially, increase by 5 to 10 mcg q 1 to 2 wk. When 25 mcg/day is reached, increase by 12.5 to 25 mcg q 1 to 2 wk, if needed. CHILDREN: PO 5 mcg/day initially, increase by 5 mcg q 1 to 2 wk, if needed.

Myxedema coma/precoma

ADULTS: IV 25 to 50 mcg initially; additional doses administered q 4 to 12 hr, as needed.

TSH suppression test

ADULTS: PO 75 to 100 mcg/day for 7 days.

 Interactions

Anticoagulants, oral: May increase anticoagulant effects. Beta-blockers: May reduce effects of beta-blockers. Cholestyramine, colestipol: May decrease thyroid hormone efficacy. Digitalis glycosides: May reduce effects of glycosides. Theophyllines: Hypothyroidism; may cause decreased theophylline clearance; clearance may return to normal when euthyroid state is achieved.

 Lab Test Interferences Consider changes in thyroxine-binding globulin concentration when interpreting thyroxine (T4) and triiodothyronine (T3) values; medicinal or dietary iodine interferes with all in vivo tests of radioiodine uptake, producing low uptakes that may not reflect true decrease in hormone synthesis.

 Adverse Reactions

CV: Palpitations; tachycardia; cardiac arrhythmias; angina pectoris; cardiac arrest. CNS: Tremors; headache; nervousness; insomnia. GI: Diarrhea; vomiting. OTHER: Hypersensitivity; weight loss; menstrual irregularities; sweating; heat intolerance; fever; decreased bone density (in women using long term).

 Precautions

Pregnancy: Category A. Lactation: Minimal amounts excreted in breast milk. Children: When drug is administered for congenital hypothyroidism, routine determinations of serum T4 or TSH are strongly advised in neonates. In infants, excessive doses of thyroid hormone preparations may produce craniosynostosis. Children may experience transient partial hair loss in first few months of thyroid therapy. Elderly: Therapy should be started with 5 mcg q day and increased by 5 mcg increments at recommended intervals. Cardiovascular disease: Use caution when integrity of cardiovascular system, particularly coronary arteries, is suspect (eg, angina, elderly). Development of chest pain or worsening cardiovascular disease requires decrease in dosage. Endocrine disorders: Therapy in patients with concomitant diabetes mellitus, diabetes insipidus or adrenal insufficiency (Addison's disease) exacerbates intensity of their symptoms. Therapy of myxedema coma requires simultaneous administration of glucocorticoids. Corticosteroids should be used to correct adrenal insufficiency in patients whose hypothyroidism is secondary to hypopituitarism. Hyperthyroid effects: Liothyronine may rarely precipitate hyperthyroid state or may aggravate existing hyperthyroidism. Infertility: Drug is unjustified for treatment of male or female infertility unless condition is accompanied by hypothyroidism. Morphologic hypogonadism and nephrosis: Rule out before therapy. Myxedema coma: Patients are particularly sensitive to thyroid preparations. Sudden administration of large doses is not without cardiovascular risks. Small initial doses are indicated. Obesity: Drug should not be used for weight reduction; may produce serious or life-threatening toxicity in large doses, particularly when given with anorexiants.

 Administration/Storage

• Administer once a day in the early morning to prevent sleep disturbances.
• Administer liothyronine injection IV only, do not give IM or SC.
• Administer with caution to patients with known cardiovascular disease.
• Administer cautiously to patients with possible thyroid gland autonomy as there is danger of an additive effect between the exogenous and endogenous sources.
• Administer only by injection to patients in Myxedema coma and with precoma diagnoses.
• Ensure oral therapy is resumed as soon as patient is stabilized.
• Discontinue IV injection therapy gradually when switching to tablets. Expect a low dosage that will be increased gradually according to response.
• Administer cautiously to elderly patients and patients with known or suspected cardiovascular disease. Note contraindications in some serious cardiovascular conditions and thyrotoxicosis.
• Do not administer large doses of liothyronine with sympathomimetic amines as serious and even life threatening results can occur.
• Administer cholestyramine and thyroid hormones 4 to 5 hrs apart.
• Store tablets in tightly closed container at room temperature; store injectable under refrigeration.

 Assessment/Interventions

• Obtain patient history.
• Prior to initial administration, obtain baseline data of TSH and T4 levels.
• Monitor for signs and symptoms of thyroid deficit or excess.
• Periodically assess thyroid status by using the TSH suppression test.
• Monitor patients on anticoagulants for signs of bleeding.
• Monitor patients on insulin or oral hypoglycemics closely during initiation of thyroid replacement therapy. Increase in insulin or oral hypoglycemic dosage may be required.
• If patient is switching therapies, be aware that liothyronine has a rapid onset of action, but residual effects of other thyroid preparations may persist for the first several weeks of therapy.
• Inform laboratory if patient is pregnant or taking androgens, corticosteroids, estrogens, oral contraceptives, iodine-containing preparations, preparations containing salicylates, or medicinal or dietary iodine as these drugs are known to interfere with tests of patients on liothyronine therapy. Interacting medications may need to be held or discontinued prior to the test.
• Assess for side effects that can occur more rapidly with liothyronine because of its rapid onset.
• Monitor patient on digoxin for signs and symptoms of potential digitalis toxicity as thyroid hormone increases metabolic rate which requires an increased digitalis dosage.

 Patient/Family Education

• Instruct patient to take liothyronine as directed. Do not change or discontinue dosage without consulting health care provider. Explain that liothyronine does not cure hypothyroidism and that therapy will continue for rest of life.
• Instruct patient with diabetes mellitus to closely monitor urinary glucose levels. The daily dosage of antidiabetic medication may need readjustment as thyroid hormone replacement is achieved or if thyroid medication is stopped.
• Explain that partial hair loss may be experienced by children in first few months of therapy, but that this side effect is transient.
• Advise patient to wear Medi-Alert bracelet or necklace and to carry Medi-Alert card in wallet.
• Inform patient that liothyronine's effects are more rapid than levothyroxine, which requires several days before onset of action.
• Teach patient to take pulse and inform the health care provider if signs of tachycardia or dysrhythmias occur.
• Instruct patient to call the health care provider immediately if any adverse symptoms such as chest pain, palpitations, headaches, irritability, increased nervousness, diaphoresis, tachycardia, dysrhythmias or heat intolerance occur.
• Inform patient of possible adverse reactions with other drugs or foods they may be taking. Caution them to inform their healthcare provider of any drugs, including otc drugs, they may be taking or plan to take.
• Emphasize the importance of followup examinations and periodic laboratory tests.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts