Subject para-aminobenzoic acid

MM Drucker, SJ Blondheim, L Wislicki, Factors affecting acetylation in vivo of para-aminobenzoic acid by human subjects. Clin Sci 27 133-141, 1964. 

A single case report found that para-aminobenzoic acid (PABA) increased the serum levels of procainamide and reduced the serum levels of the procainamide metabolite N-acetylprocainamide. In contrast, a later pharmacokinetic study in healthy subjects found that PABA had no effect on serum procainamide levels, and increased serum IV-acetylprocainamide levels. 

A 61-year-old man who had sustained ventrieular tachycardia, which did not respond adequately to oral procainamide, was found to be a fast acetylator of procainamide, which resulted in particularly high serum levels of the procainamide metabolite (7V-acetylprocainamide) when compared with the procainamide levels. When he was also given para-aminobenzoic acid (PABA) 1.5 g every 6 hours for 30 hours, to suppress the production of this metabolite, the serum level of procainamide increased, that of Al-acetylproeainamide decreased, and control of his arrhythmia improved. However, a later study in 10 healthy subjects, who were also fast acety lators, found that PABA did not significantly affect the pharmacokinetics of procainamide. In addition, although PABA inhibited the production of A-acetylprocainamide, it also inhibited renal excretion, so that the AUC and elimination half-life were increased. This suggests that PABA may in fact not be useful for increasing the efficacy and safety of procainamide. ... 

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