liothyronine sodium, Cytomel, Triostat

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GENERIC NAME: liothyronine sodium

BRAND NAME: Cytomel, Triostat

DRUG CLASS AND MECHANISM: Liothyronine sodium is a synthetic (man-made) version of one of the two hormones made by the thyroid gland, triiodothyronine. It is used for treating individuals who are hypothyroid (do not produce enough thyroid hormones). Thyroid hormones increase the metabolism (activity) of all cells in the body. In the fetus, newborn infant and child, thyroid hormones promote growth and development of tissues. In adults, thyroid hormones help to maintain the function of the brain, the use of food by the body, and body temperature. The FDA approved liothyronine in May 1956.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 5, 25, and 50 mcg. Injection: 10 mcg/ml

STORAGE: Tablets should be stored at room temperature 20-25 C (68-77°F) and the injectable preparation between 2-8 C (36-46 F )

PRESCRIBED FOR: Liothyronine is used to treat hypothyroidism (low production of thyroid hormone) in adults and children. Prolonged hypothyroidism can result in a condition called myxedema in which patients develop swollen lips, thickened nose, and unusual deposits of material in the skin that are dry and waxy. These deposits also may appear in body tissues other than the skin. Liothyronine also is used for suppressing production of thyroid stimulating hormone in patients with goiters and for testing how well the thyroid gland is functioning.

DOSING: The usual starting dose of liothyronine for treating hypothyroidism is 5 to 25 mcg per day. The dose then is adjusted based on the patient's response and the blood levels of thyroid hormone. Optimal liothyronine doses are different for each patient and vary depending on the patient's age, weight, symptoms, blood levels of thyroid hormone and underlying conditions such as heart disease. Individuals who are hypothyroid will require thyroid hormone for life.

DRUG INTERACTIONS: Thyroid hormone affects the body's handling of many drugs. Generally, hypothyroidism (decreased concentration of thyroid hormone) reduces the effects of the body on drugs (metabolism of drugs) while hyperthyroidism (increased concentration of thyroid hormone) increases the effects. Therefore, individuals who are hypothyroid will eliminate drugs more slowly, and those with hyperthyroidism will eliminate drugs faster compared with individuals with normal levels of thyroid hormone.

This principle also applies to the metabolism of drugs that must be metabolized (changed) by the body into their active forms in order to have an effect. Therefore, liothyronine and other thyroid hormones may change the action of many drugs. The elimination of theophylline (Theo-Dur) and similar drugs increases as the dose of thyroid hormone increases. Individuals who are hypothyroid have slower theophylline elimination. Therefore, when the concentration of thyroid hormone is returned to normal with liothyronine, the elimination of theophylline is increased. This reduces the concentration of theophylline in the body and can reduce the effectiveness of theophylline. Patients who are treated for thyroid conditions and who are taking theophylline should have their blood concentration of theophylline monitored, and doses of theophylline should be adjusted as necessary.

Cholestyramine (Questran) binds liothyronine and other thyroid in hormones in the intestine, reducing the absorption and levels of liothyronine. Thyroid hormones should not be administered for 4 to 5 hours after administering cholestyramine.

The administration of liothyronine increases the action of the blood thinning drug, warfarin (Coumadin). Warfarin acts by reducing the concentration of factors in the body that are necessary for blood to clot. The concentration of these clotting factors in the body is determined by the body's rate of metabolism. In theory, by increasing the body's metabolism (elimination) of these clotting factors, thyroid hormones reduce the body's ability to clot and therefore enhance the effects of warfarin. Since this can lead to excessive bleeding, the dose of warfarin may need to be reduced.




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