Significance of the acetylation phenotype and the therapeutic effect of procainamide.

In order to estimate the relative anti-arrhythmic effect of procainamide and N-acetyl-procainamide, 18 randomly selected, patients with arrhythmia were divided into two groups; the first was treated with Pronestyl in the first half of the investigation period, followed by Duretter in the second half, and the second group began with Duretter and terminated with Pronestyl. The concentrations of procainamide and N-acetylprocainamide were measured twice a day during the steady state part of each treatment period. The acetylation phenotype of the patients was determined with sulfadimidine, and compared with the relative serum concentrations of procainamide and N-acetylprocainamide. N-acetylprocainamide was found to antagonize the action of procainamide.