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Amiodarone and thyroid dysfunction

Douglas S Ross, MD
Section Editor
David S Cooper, MD
Deputy Editor
Jean E Mulder, MD


Amiodarone, a class III anti-arrhythmic drug, has multiple effects on myocardial depolarization and repolarization that make it an extremely effective antiarrhythmic drug. However, amiodarone is associated with a number of side effects, including thyroid dysfunction (both hypo- and hyperthyroidism), which is due to amiodarone's high iodine content and its direct toxic effect on the thyroid. This topic will review the major effects of amiodarone on thyroid function. The clinical use and other side effects of amiodarone are reviewed elsewhere. (See "Clinical uses of amiodarone" and "Monitoring and management of amiodarone side effects".)


Amiodarone contains two iodine atoms. It is estimated that amiodarone metabolism in the liver releases approximately 3 mg of inorganic iodine into the systemic circulation per 100 mg of amiodarone ingested. The average iodine content in a typical American diet is about 0.3 mg/day. Thus, 6 mg of iodine associated with a 200 mg dose of amiodarone markedly increases the daily iodine load [1,2].

Amiodarone is very lipophilic and is concentrated in adipose tissue, cardiac and skeletal muscle, and the thyroid. Elimination from the body occurs with a half-life of about 100 days [3]. Amiodarone toxicity can therefore occur well after drug withdrawal [4].

The effects of amiodarone on thyroid function can be divided into those effects that are intrinsic properties of the drug, and those effects that are due to iodine.

Intrinsic drug effects

Amiodarone inhibits outer ring 5'-monodeiodination of thyroxine (T4), thus decreasing triiodothyronine (T3) production; reverse T3 accumulates since it is not metabolized to T2 [5].

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Literature review current through: Nov 2017. | This topic last updated: Nov 02, 2017.
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