Dronedarone, a derivative of amiodarone with similar mechanisms of action (blocking calcium, potassium and sodium channels in addition to having anti-adrenergic effects) does not contain iodine and has shown no thyroid toxicity in its clinical trials, has fewer drug interactions than amiodarone, and has rare if any proven pulmonary toxicity.^1-8  Very rarely, dronedarone has produced severe hepatic failure – not shown predictable by routine hepatic function test monitoring in its clinical trials (see the package insert for details).  Dronedarone’s effects on blocking the L-type calcium current are dose/concentration dependent and require higher levels than its effects on the sodium channel and on potassium channels.^{1 (and, Belardinalli and Zeng, 2012 personal communication)}  Dronedarone is approved for the treatment of atrial fibrillation (see below); has had limited studies for other arrhythmias; and has no adverse drug-ICD interactions reported.