The metabolism of sulforidazine was studied in female dogs and adult male humans after oral administration of 37.5 mg and 25.0 mg, respectively. 2. Metabolites in organic extracts of dog urine were separated by h.p.l.c. and individually collected prior to mass spectrometric analysis, while organic extracts of human urine were directly subjected to plasmaspray h.p.l.c.-mass spectrometric determination. In the case of phenolic metabolites, the urinary extracts from both species were derivatized with a silylating reagent (with or without prior enzymic hydrolysis) and subsequently analysed by h.p.l.c.-mass spectrometry. The structures of metabolites with the exception of phenols were confirmed by comparison of their mass spectra and chromatographic behaviours with those of authentic standards. 3. The compounds identified in urine of both species were sulforidazine, two diastereomers of sulforidazine ring sulphoxide, the lactam of sulforidazine ring sulphoxide and a phenolic derivative of sulforidazine, whereas sulforidazine N-oxide and the lactam of sulforidazine were identified only in human urine. Moreover the phenolic metabolite was present in human urine in both unconjugated and conjugated forms, whereas dog urine had only the conjugated form. 4. Sulforidazine and some of its major metabolites were quantified by an h.p.l.c. method. The mean urinary excretions (0-48 h) of sulforidazine were similar in human (n = 3) and dog (n = 3) (5.9 +/- 0.7% and 7.2 +/- 1.9%), as were the excretions of sulforidazine ring sulphoxide (13.2 +/- 4.6% and 13.3 +/- 4.4%), while the lactam of sulforidazine ring sulphoxide was a major metabolite only in human (7.5 +/- 2.8% and < 0.1%). The lactam of sulforidazine was a minor metabolite in human. 5. The metabolites observed in human urine were similar to those previously reported in rat, except that sulforidazine N-oxide was found only in human, whereas the two diastereomers of N-desmethylsulforidazine ring sulphoxide were observed only in rat. These data suggest that rat may be a more suitable animal than dog for further study of the metabolism of the piperidine ring of sulforidazine.
