Use of plasma levels in evaluation of procainamide dosage.

Plasma procainamide levels achieved by oral procainamide treatment were studied in patients with recent myocardial infarction or ischaemia. Procainamide therapy was started after intravenous lignocaine had been used to control ventricular arrhythmias in the acute phase. A i g loading dose did not provoke toxicity and achieved 4-hour levels in or near the therapeutic range in 79 per cent ofpatients. Some patients with cardiac failure absorbed oral procainamide very slowly. A maintenance regimen of 375 mg 4 hourlyfailed to maintain effective procainamide levels in 73 per cent of patients. On a dosage of 500 mg 4 hourly 36 per cent had ineffective levels before each dose. Measurement of procainamide levels is desirable during treatment, since the variation between patients given a standard dosage is considerable and unpredictable. To maintain adequate procainamide levels frequent doses are necessary but inconvenient.