The fate of orally administered [4-14C]phenytoin in two healthy male volunteers.

A recovery study was conducted to determine whether phenytoin (DPH), like the barbiturates, is metabolized via the recently discovered N-glucosidation pathway. Virtually 100% of the ingested 14C-labelled doses in two subjects could be accounted for in the excreta within 5 days, with 35% in feces and 65% in urine. Radioactivity in the urine was entirely due to free and conjugated 5-(4-hydroxy-phenyl)-5-phenylhydantoin (p-HPPH) and the dihydrodiol, and that in the feces mostly due to the unmetabolized drug. There was no indication of phenytoin N-glucoside being excreted in either the urine or feces of either subject, although one of the subjects was known to possess a particularly strong N-glucosidation capacity for barbiturates. The other subject was a poor metabolizer of debrisoquine and sparteine. Nevertheless, the DPH disappearance from serum and the DPH metabolite excretion in urine were virtually alike in these two subjects, indicating that the debrisoquine 4-hydroxylating and DPH hydroxylating capacities may be separable entities.