Medications and Drugs

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.

PRESCRIPTION: yes

GENERIC AVAILABLE: yes

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

STORAGE:Store tablets at room temperature 20-25°C (68-77°F) and 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 in a test of the thyroid gland to determine if the thyroid is functioning normally.

DOSING: The usual starting dose of liothyronine 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.

Generic and branded tablets of liothyronine may differ in the amount of liothyronine that is absorbed into the body and the distribution of the liothyronine throughout the body. This means that ingestion of 5 mcg of generic or branded liothyronine may not have the same effect on the body as 5 mcg of another generic or branded liothyronine. Practically speaking, this means that when changing between liothyronine manufactured by different pharmaceutical companies, a change in dose may be necessary to maintain the desired effect or to prevent toxicity.

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 should have their blood concentration of theophylline monitored, and doses of theophylline should be adjusted as necessary.

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.

Digoxin (Lanoxin) is a drug that is used to control heart rate. Individuals with hypothyroidism tend to be more sensitive (respond more) to digoxin, and, conversely, individuals with hyperthyroidism are less responsive to digoxin. Therefore, increasing the level of thyroid hormone in the body may warrant an increase in the dose of digoxin. The mechanism for this interaction is not clear, but it may involve changes in the absorption of digoxin, digoxin metabolism, or the effects of thyroid hormone on the heart.

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