Quantitative determination of the urinary excretion of ketobemidone and four of its metabolites after intravenous and oral administration in man.

The urinary excretion of ketobemidone and its metabolites has been quantified in man after intravenous and oral administration. The metabolism of ketobemidone was found to proceed via 4 metabolic pathways: N-demethylation, ring-hydroxylation, O-methylation, and conjugation. The metabolites were isolated and identified after hydrolysis of the corresponding conjugates. A mean total recovery of about 80% of the dose was found in urine as ketobemidone and metabolites after oral and iv administration, conjugated metabolites amounted to 34-68% of the dose. After iv administration the recovery of unchanged ketobemidone in urine was 13-24%, and after oral administration it was 3-10%. Norketobemidone constituted 10-37% of the dose irrespective of route of administration. 4'-Hydroxyketobemidone amounted to 3-12% of the dose. Neither ketobemidone N-oxide nor metabolites formed after reduction of ketobemidone could be detected in the urine. Less than 2% of the dose was found in feces after iv administration.