Thyroid Supplements

More than 3 million chronic users in USA.

T ₄ prescribed for pts with chronic hypothyroidism.

T ₃ used in myxedema coma.

T ₃ successfully used as rescue therapy for cardiogenic shock after CPB.

T ₃ favorably administered to brain-dead donors before organ harvesting for heart or heart-lung transplantation. (Prophylactic use of T ₃ has shown no benefit in recent randomized trials.)

T ₄ is generally administered PO; T ₄ and T ₃ can be administered IV.

Drugs (amiodarone, lithium, herbal supplements, catecholamines, radiopaque contrast media) and also cirrhosis, renal failure, sepsis, and operation (CPB) can induce euthyroid sick syndrome (reduced peripheral conversion of T ₄ to T ₃ ); may also precipitate myxedema coma.

Amiodarone, a potent class III antiarrhythmic drug, is an iodine-rich compound with a structural resemblance to T ₃ and T ₄ and causes substantial iodine overload; with continued administration, may produce either thyrotoxicosis or hypothyroidism.

T ₄ or T ₃ can aggravate symptoms of myocardial ischemia.