liothyronine sodium, Cytomel, Triostat (cont.)

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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.

PREGNANCY: Thyroid hormones do not easily cross the placenta and, therefore, are safe for pregnant women to take.

NURSING MOTHERS: Very small amounts of thyroid hormone may be excreted in breast milk. This is not a serious problem for breastfed infants.

Medically reviewed by Eni Williams, PharmD

Reference: FDA Prescribing Information

Medically Reviewed by a Doctor on 1/28/2015

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