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.