The metabolism of caffeine in three non-human primate species

[814C]-Caffeine was idministered orally to adult male chimpanzees, rhesus mon-keys and galagos and their urine and faeces collected for 24 h. Urinary metabolites were separated by ion exchange and HPLC and quantitated by scintillation count-ing. Urinary elimination was 50 % of dose by the chimpanzee, 38 % by the rhesus monkey, 56 % in galagos, with <1% in the faeces of each. In all cases, caffeine was extensively metabolized accounting for <1% of urinary 14C. The pattern of major metabolites differed appreciably between the species. In the chimpanzee, the major products were uric acids (69 % of urinary 14C) mostly as dimethyluric acids. Xanthines totalled 13 %. In the rhesus monkey uric acids accounted for 48 %, the bulk in the form of dimethyluric acids (30 %) and xanthines accounted for 41 % equally divided between the mono— and dimethylxanthines, 38 % of urinary 14C in the galago was in the form of xanthines, principally as monomethyl-xanthines (26 %), and 35 % was as uric acids, mainly dimethyluric acids (22 %).