Distribution and excretion of methamphetamine and its metabolites in rats II. Time-course of concentration in blood and distribution after multiple oral administration

The time-course of total blood radioactivity after oral administration of 3H-methamphetamine, following multiple oral administration of non-radioactive methamphetamine for 7 and 14 days to rats, was examined to elucidate the effects of multiple administration on enterohepatic circulation. Whole-body autoradiographs of rats after oral administration of 14C-methamphetamine showed high levels of radioactivity in contents of stomach and small intestine, bladder urine, liver, and various glands. Distribution of methamphetamine and the major metabolite in tissues during multiple dosing was investigated; accumulation occurred in brain, liver, testis and fat. Multiple oral administration of methamphetamine to rats slightly induced enzyme activities of N-demethylation and aromatic hydroxylation of methamphetamine in rat-liver 9000 g supernatant.