Acetylation polymorphism of caffeine in a Japanese population.

The frequency distribution of N-acetylation of caffeine was determined in 140 unrelated healthy Japanese subjects by measuring the amount of two main metabolites of caffeine, 5-acetylamino-6-formyl-amino-3-methyluracil (AFMU) and 1-methylxanthine (1X), in urine after an oral dose of caffeine. N-Acetylation capacity for caffeine appeared to be polymorphic: 15 subjects (10.7%) were phenotyped as slow acetylators, whereas 125 subjects (89.3%) were phenotyped as rapid ones. The urinary molar excretion ratio of AFMU (AFMU/1X) in 2 hours-urine samples ranged from 0.03 (slow acetylators) to 2.66 (rapid acetylators). The frequency of slow acetylators in this study was similar to that reported previously for the isoniazid and dapsone polymorphism in Japanese populations.