Thyroid Replacement Hormones (cont.)

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With which drugs do thyroid replacement hormones interact?

Thyroid replacement hormones should be used cautiously in people with diabetes since starting or discontinuing therapy may lead to a loss of control of the blood sugar requiring adjustments in doses of insulin or oral antidiabetic drugs (for example, glyburide [Micronase]). The effects of blood thinners such as warfarin (Coumadin) may be increased by thyroid replacement hormones warranting a decrease in the dose of warfarin in addition to monitoring of blood clotting.

Intravenous epinephrine administration in patients with coronary artery disease who are taking thyroid replacement hormones may increase the risk of complications such as difficulty in breathing and possibly heart attacks. The effectiveness of some beta blockers [for example, metoprolol (Lopressor) orpropranolol (Inderal)] may be reduced when a patient is converted from a state of hypothyroidism (under activity) to a normal state (euthyroid state). It also may be necessary to modify the dose of digoxin (Lanoxin) and theophylline (Slo-Bid) when a patient is converted from hypothyroidism (under activity) to a normal state (euthyroid state). There is increased elimination of theophylline in a euthyroid state compared to a state of hypothyroidism.

The effectiveness of thyroid replacement hormones may be decreased when given with drugs such as calcium carbonate, ferrous sulphate, cholestyramine (Questran) and colestipol (Colestid) that binds thyroid replacement hormones and prevent their absorption. This interaction may be reduced by separating the administration of these drugs from thyroid replacement hormones by four hours.

Medically reviewed by Omudhome Ogbru, PharmD

REFERENCE: FDA Prescribing Information.

Medically Reviewed by a Doctor on 3/27/2015

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