Amiodarone is a benzofuran derivative approved for the treatment of cardiac arrhythmias. Traditionally classified as a class III antiarrhythmic agent, amiodarone possesses electrophysiologic properties of all four Vaughan–Williams classes. This drug, however, has high iodine content, and this feature plus the intrinsic effects on the body make amiodarone especially toxic to the thyroid gland. Treatment can result in a range of effects from mild derangements in thyroid function to overt hypothyroidism or thyrotoxicosis. The diagnosis and treatment of amiodarone-induced hypothyroidism is usually straightforward, whereas that of amiodarone-induced thyrotoxicosis and the ability to distinguish between the type 1 and type 2 forms of the disease are much more challenging. Dronedarone was approved in 2009 for the treatment of patients with atrial fibrillation. As amiodarone, dronedarone is a benzofuran derivative with similar electrophysiologic properties. In contrast to amiodarone, however, dronedarone is structurally devoid of iodine and has a notably shorter half-life. In studies reported before FDA approval, dronedarone proved to be associated with significantly fewer adverse effects than amiodarone, making it a more attractive choice for patients with atrial fibrillation or flutter, who are at risk of developing amiodarone-induced thyroid dysfunction.
Amiodarone, an iodine-rich benzofuran derivative, is approved for the treatment of ventricular arrhythmias, but is often used in the treatment of atrial fibrillation
Amiodarone and its active metabolite desethylamiodarone have multiple electrophysiologic effects
Untoward effects associated with amiodarone use, including effects on the pulmonary, gastrointestinal, ophthalmologic, neurologic, dermatologic and thyroid systems, are prevalent and have resulted in decreased use of the drug
Amiodarone-induced thyroid dysfunction, including hypothyroidism and hyperthyroidism, may be due to iodine effects or to intrinsic drug effects
Treatment of amiodarone-induced thyrotoxicosis (AIT) varies depending on the type of AIT and does not necessarily include discontinuation of amiodarone treatment
Dronedarone, a benzofuran derivative that does not contain iodine, has been approved by the FDA for the treatment of atrial fibrillation and demonstrates less thyroid-related toxic effects than amiodarone
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The authors, the Journal Editor V. Heath and the CME questions author Désirée Lie declare no competing interests.
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Cohen-Lehman, J., Dahl, P., Danzi, S. et al. Effects of amiodarone therapy on thyroid function. Nat Rev Endocrinol 6, 34–41 (2010). https://doi.org/10.1038/nrendo.2009.225
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