Reduced acetylation of procainamide by para-aminobenzoic acid.

Acetylation is the major route of metabolism of many drugs including the antiarrhythmic agent procainamide. Coadministration of para-aminobenzoic acid was observed to decrease the biotransformation of procainamide to N-acetylprocainamide in a patient with rapid acetylation kinetics. In view of the distinct antiarrhythmic and toxic properties of procainamide and N-acetylprocainamide, the observed drug interference may have great clinical relevance in long-term oral antiarrhythmic therapy and in instances where other drugs converge for acetylation.