Acetylator phenotype and the clinical pharmacology of slow-release procainamide.

Slow-release procainamide given 8-hourly is shown to produce plasma levels generally accepted as giving effective prophylaxis against ventricular dysrhythmias occurring after recent myocardial infarction. Patients can be classified into 'slow' and 'fast' acetylators of procainamide. Knowledge of acetylator status is helpful in determining the dose of procainamide necessary to attain effective steady-state plasma levels while avoiding toxic ones. Acetylator status cannot be assessed accurately using sulphadimidine when the patients are also taking procainamide.