Combination of antiarrhythmic drugs

Antiarrhythmic treatment with single agents is often ineffective and can be limited by dose-dependent side effects. Therefore, combinations of antiarrhythmic drugs in smaller and well-tolerated doses are advocated in cases refractory to single antiarrhythmic drugs. Basically, substances belonging to the same electrophysiologic class should not be combined. However, drugs of different subsets of class I may be combined. Agents that have pharmacokinetic interactions, such as quinidine and amiodarone, should not be given together because this combination may be associated with a considerable proarrhythmic effect. A combination of beta-adrenoreceptor blockers with class I antiarrhythmic drugs may be effective, mainly in cases in which the arrhythmia is dependent on adrenergic stimulation. The combination of class III and IB substances can be useful in some cases, from the electrophysiological and clinical point of view. Among the successful combinations of this type are amiodarone and mexiletine, sotalol and mexiletine, or sotalol and tocainide. In 34 patients, the reduction of ventricular premature beats by sotalol alone was 28%, and by sotalol plus mexiletine or tocainide was 79%. Complex ventricular arrhythmias were suppressed by sotalol alone by less than 40% and by sotalol plus mexiletine or tocainide by more than 80%. There was no difference in the effectiveness of mexiletine and tocainide (both of them being class IB drugs) in this combination. However, mexiletine was associated with fewer adverse effects than was tocainide. In patients refractory to amiodarone alone or to a combination with mexiletine, the combined treatment with amiodarone and class IC drugs such as flecainide and encainide prolongs the cycle length of ventricular tachycardia, but does not suppress induction of ventricular tachycardia during programmed stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)