indication

Used as replacement or supplemental therapy in patients with hypothyroidism of any etiology, except transient hypothyrodism during the recovery phase of subacute thyroiditis.

pharmacology

Thyroid hormone drugs are natural or synthetic preparations containing T₄ or T₃ or both. T₄ and T₃ are produced in the human thyroid gland by the iodination and coupling of the amino acid tyrosine. Liothyronine (T₃) contains three atoms of iodine and is formed by the coupling of one molecule of diiodotyrosine (DIT) with one molecule of monoiodotyrosine (MIT). These hormones enhance oxygen consumption by most tissues of the body and increase the basal metabolic rate and the metabolism of carbohydrates, lipids and proteins. Thus, they exert a profound influence on every organ system in the body and are of particular importance in the development of the central nervous system.

mechanism of action

The hormones, T₄ and T₃, are tyrosine-based hormones produced by the thyroid gland. Iodine is an important component in their synthesis. The major form of thyroid hormone in the blood is thyroxine (T4). This is converted to the more active liothyronine form by deiodinases in peripheral tissues. Liothyronine acts on the body to increase the basal metabolic rate, affect protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline). The thyroid hormones are essential to proper development and differentiation of all cells of the human body. To various extents T₄ and T₃ regulate protein, fat and carbohydrate metabolism. Their most pronounced effect is on how human cells use energetic compounds. The thyroid hormone derivatives bind to the thyroid hormone receptors initially to initiate their downstream effects.

absorption

95% in 4 hours

half life

2.5 days

drug interactions

Calcium Acetate: Calcium salts such as calcium acetate may diminish the therapeutic effect of thyroid products such as liothyronine. Separate the doses of the thyroid product and the oral calcium supplement by at least 4 hours. Monitor for decreased therapeutic effects of thyroid products if an oral calcium supplement is initiated/dose increased, or increased effects if an oral calcium supplement is discontinued/dose decreased.

Calcium Chloride: Calcium salts such as calcium chloride may diminish the therapeutic effect of thyroid products such as liothyronine. Separate the doses of the thyroid product and the oral calcium supplement by at least 4 hours. Monitor for decreased therapeutic effects of thyroid products if an oral calcium supplement is initiated/dose increased, or increased effects if an oral calcium supplement is discontinued/dose decreased.

Cholestyramine: The resin, cholestyramine, decreases the absorption of the thyroid hormones, liothyronine.

Colestipol: The resin, colestipol, decreases the absorption of the thyroid hormone, liothyronine.

Digoxin: The thyroid hormone, liothyronine, decreases the effect of digoxin.

Warfarin: Liothyronine may contribute to the anticoagulant effect of warfarin by increasing the metabolism of vitamin K-dependent clotting factors. Monitor for changes in prothrombin time and anticoagulant effects if liothyronine is initiated, discontinued or dose changed.