Sulphamethoxazole acetylation in fast and slow acetylators.

Acetylation of sulphamethoxazole was studied in 22 subjects previously phenotyped with sulphadimidine. Sulphamethoxazole and its acetylated metabolite were measured in 6 h plasma and 0-6 h urine samples. Percentage of plasma acetylated-sulphamethoxazole did not correlate with the percentage of urinary acetylated-sulphamethoxazole. There was also no correlation between the percentage of acetylated-sulphadimidine and percentage of acetylated-sulphamethoxazole in plasma. The finding suggest that the acetylation of sulphamethoxazole has no predictive value in determining acetylator status.