Intravenous amiodarone is an effective antiarrhythmic agent that has resulted in good overall conversion rates when used to treat patients with atrial fibrillation (AF). High-dose oral loading (30 to 50 mg per kg) has been reported to suppress supraventricular and ventricular arrhythmias within 24 hours after administration and, clinically, is relatively well tolerated. Peuhkurinen and associates evaluated the efficacy of a single oral dose of amiodarone versus placebo in patients with recent-onset AF.

Inclusion criteria included patients at least 18 years of age with onset of AF within the previous 48 hours whose atrial arrhythmia continued for more than three hours in the hospital, with a ventricular rate between 50 and 150 beats per minute, with hemodynamically stable blood pressure (systolic reading of greater than 95 mm Hg) and a normal serum potassium level. Patients with a history of acute myocardial infarction, acute pulmonary edema, known sick sinus syndrome, high-degree atrioventricular block, anemia, stroke, sepsis, known thyroid disease or severe renal or hepatic disease, those taking class III antiarrhythmics or sotalol, and women of child-bearing age were excluded. All medications that might affect conduction or cardiac rhythm were discontinued before randomization. The 72 patients included in the study were randomized to receive 30 mg per kg of oral amiodarone or placebo. Participants underwent electrocardiography and Holter monitoring for 24 hours. Blood pressure was measured at 11 different time intervals following drug administration and whenever needed. All patients underwent echocardiography before discharge from the hospital.

Of the 72 study participants, 10 were excluded from the final analysis because of sinus rhythm at the beginning of monitoring or technical failure during Holter monitoring. Eight hours following drug administration, approximately 50 percent of the patients who received amiodarone converted to sinus rhythm, compared with 20 percent in the placebo group. After 24 hours, the conversion rates were 87 percent in the Holter-monitored patients in the amiodarone group and 35 percent of patients in the placebo group. No proarrhythmic event (e.g., nonsustained ventricular tachycardia, ventricular fibrillation, episodes of torsades de pointes) was observed in either group. Three patients in the amiodarone group had diarrhea compared with one in the control group. One patient who received amiodarone became bradycardic and hypotensive but recovered rapidly with administration of intravenous fluids. Overall, the number of adverse events was similar in both groups.

Other clinical trials have shown the efficacy of antiarrhythmic medications in converting AF to sinus rhythm. Flecainide and propafenone, given as a single oral or intravenous dose, demonstrated efficacy in converting AF to sinus rhythm, although the safety of these agents is uncertain in patients with left ventricular dysfunction because of negative inotropic effects and increased mortality when used in patients with a history of acute myocardial infarction. Intravenous amiodarone has been demonstrated to be relatively safe in patients with left ventricular dysfunction and acute myocardial infarction. In the acute setting, intravenous amiodarone seems to effectively lower the ventricular rate in patients who do not return to sinus rhythm.

The authors conclude that 30 to 50 mg per kg of oral amiodarone is relatively well tolerated and efficacious in recent-onset AF.