A study of the metabolism of theobromine, theophylline, and caffeine in man.

Previous studies (1, 2) have shown that after the ingestion of caffeine or theophylline by man there was an increased urinary excretion of material which gave a blue color with the alkaline arsenophosphotungstate reagents used in the determination of uric acid. Myers and Wardell (3) and Buchanan, Christman, and Block (1) presented evidence that this extra color was caused by methyluric acids rather than by an increase in true uric acid excretion. When similar amounts of theobromine were taken, there was no increase in the excretion of chromogenic material. Subsequent work (2) demonstrated the presence of l-methyl and 1,3dimethyluric acids in urine after the administration of caffeine and theophylline. The excretion of 7-methylxanthine, 1-methylxanthine, and 1,7-dimethylxanthine after the ingestion of caffeine has recently been reported by Weissmann et al. (4). The present investigation concerns the identification and quantitative determination of the methyluric acids and methylxanthines excreted in the urine of man after the ingestion of theobromine, theophylline, and caffeine. 65 to 75 per cent of 1 gm. oral doses of these compounds were accounted for in the urine as methyluric acids or methylxanthines.