Drug Interactions Newsletter

Volume 1, Issue 48, 12/15/2009

Question

Why is it so important to consider several dosage reductions in a patient on stable doses of the oral anticoagulant, warfarin (Coumadin, Jantoven), when initiating amiodarone (Cordarone, Pacerone)?

Answer

Warfarin (Coumadin, Jantoven) is an oral anticoagulant most commonly used for the prevention and treatment of thromboembolic events (blood clots) in patients with atrial fibrillation, prosthetic heart valves, venous thrombosis and/or pulmonary embolism.(1)  As a complication of their diagnosis, some patients taking warfarin will also develop supraventricular or ventricular arrhythmias which may require treatment with an antiarrhythmic medication.  Amiodarone (Cordarone, Pacerone) is considered one of the first-line antiarrhythmics for these conditions.(2,3)  Therefore, many patients will have an indication for concomitant warfarin and amiodarone therapy.

The reason for considering a dosage reduction of warfarin when initiating amiodarone is the effect of amiodarone on...

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