Massive doses of procainamide for ventricular tachyarrhythmias due to myocardial infarction.

Three patients are described in whom malignant ventricular arrhythmias appeared in connection with a reinfarction some days after hospitalization for an acute myocardial infarction and in whom massive doses of procainamide, up to 7.5 g/day i.v., were necessary to prevent these arrhythmias. The serum concentration of procainamide was 2--4 times higher than the recommended upper level, but no side-effects were observed. With the dose given, one would have expected still higher serum concentrations. Several reasons for this finding are discussed, including the effects of renal function, intestinal leakage, storage of the drug in tissues and hitherto unknown metabolic pathways of procainamide in patients, who are slow acetylators.