Encainide versus flecainide in the treatment of chronic resistant paroxysmal atrial tachyarrhythmias.

To determine the relative safety and efficacy of oral encainide, ten patients with a long (mean 10 years) history of resistant paroxysmal atrial tachyarrhythmias that were finally controlled with flecainide were selected. All patients were resistant to previously used Class 1A antiarrhythmic drugs, and amiodarone was ineffective or insufficient in eight. Flecainide (mean 200 mg/day) given alone in five patients, or combined with amiodarone in four, and nadolol in one had been used for a mean of 19 months (range, 4-48). The clinical efficacy was considered good in five patients and fair in five, and tolerance was good in four, fair in three, and poor in three. Flecainide was replaced with encainide (153 mg/day; range, 50-225 mg/day) for a mean duration of 6.2 months (range, 0.5-14.2 months). Encainide was effective in five patients, partly effective in two, and ineffective in three. Tolerance was good, except for vertigo reported by two patients. Flecainide was clearly or slightly more effective than encainide in five patients, equally as effective as encainide in three, and less effective than encainide in two. Tolerance of encainide was better than flecainide in six patients, equal to flecainide in two, and worse in two. The results of the present study may be biased because the patients were selected on the basis of flecainide efficacy and tolerance. However, the results reflect the equivalence of the two drugs in clinical practice for the treatment of particularly resistant arrhythmias.