Delayed hypersensitivity reactions are among the most severe adverse effects of the sulfonamides in current clinical use. These reactions appear to occur because of differences in the metabolism and detoxification of reactive metabolites of the sulfonamides. N-Acetylation is a major metabolic pathway for the sulfonamides. Slow acetylation phenotype might be a risk factor for the development of these reactions. We determined the acetylation phenotype of 21 patients who had suffered hypersensitivity reactions to the sulfonamides. There were 11 females and 10 males in the group, with a mean age of 15 years (age range, 1.8 to 50 years). Their acetylator phenotype was determined by determining the ratio of urinary caffeine metabolites (1-methylxanthine to 5-amino-6-formylmethyluracil after an oral dose of 50 mg caffeine). Nineteen (90%) of the patients were slow acetylators compared to a 55% incidence of slow acetylators in a race-matched control population (p less than 0.008). This suggests that a slow acetylator phenotype is a risk factor for the development of sulfonamide hypersensitivity reactions and provides further support for the role of imbalances in genetically determined pathways of metabolism and detoxification of the sulfonamides in the pathogenesis of these reactions.
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