Cytomel® (liothyronine sodium)

Treating low thyroid function. It is also used to treat or preventdifferent types of goiters, as an aid to diagnose certain thyroidconditions, or to treat patients who are allergic to other thyroidmedicines. It may also be used for other conditions as determined byyour doctor.
Cytomel is a naturally occurring hormone produced by the thyroid. It isimportant for normal energy and metabolism. For a variety of reasons,the body may not produce enough of this hormone on its own. In thesecases, liothyronine is taken to replace the body's natural thyroidhormone.

Liothyronine is used to treat hypothyroidism (low thyroid function).Liothyronine is also used to prevent and treat goiter (growth orenlargement of the thyroid gland). Causes of goiter include hormonalimbalances, radiation, surgery, and cancer.

Thyroid hormone drugs are natural or synthetic preparationscontaining tetraiodothyronine (T4, levothyroxine) sodium or triiodothyronine(T3, liothyronine) sodium or both. T4 and T3 areproduced in the human thyroid gland by the iodination and coupling of theamino acid tyrosine. T4 contains four iodine atoms and is formedby the coupling of two molecules of diiodotyrosine (DIT). T3 containsthree atoms of iodine and is formed by the coupling of one molecule of DITwith one molecule of monoiodotyrosine (MIT). Both hormones are stored in thethyroid colloid as thyroglobulin.

Thyroid hormone preparationsbelong to two categories: (1) natural hormonal preparations derived from animalthyroid, and (2) synthetic preparations. Natural preparations include desiccatedthyroid and thyroglobulin. Desiccated thyroid is derived from domesticatedanimals that are used for food by man (either beef or hog thyroid), and thyroglobulinis derived from thyroid glands of the hog. The United States Pharmacopeia(USP) has standardized the total iodine content of natural preparations. ThyroidUSP contains not less than (NLT) 0.17 percent and not more than (NMT) 0.23percent iodine, and thyroglobulin contains not less than (NLT) 0.7 percentof organically bound iodine. Iodine content is only an indirect indicatorof true hormonal biologic activity.

Cytomel (liothyroninesodium) Tablets contain liothyronine (L-triiodothyronine or LT3),a synthetic form of a natural thyroid hormone, and is available as the sodiumsalt.

The structural and empirical formulas and molecular weight of liothyronine sodium are given below.