1. After administration of [C-14]-carbazeran by oral gavage to guinea
pigs, 48% of the dosed radioactivity was recovered in urine and 46% in
faeces after 144h. 2. The major urinary metabolite was identified by
infrared spectroscopy and mass spectrometry as the O-glucuronide of O-
desmethyl-4-oxocarbazeran, O-demethylation having taken place at the 6
- or 7-position. The corresponding aglycone was identified as the majo
r faecal metabolite. 3. A minor metabolite in urine was identified as
the 4-oxo-4'-hydroxy derivative of carbazeran. 4. In animals pretreate
d with hydralazine, an aldehyde oxidase inhibitor, less radioactivity
was extracted in the urine and a significant decrease was observed in
the levels of the major urinary metabolite. 5. These results show that
aldehyde oxidase plays a key role in the metabolism of carbazeran in
guinea pig as it does in man. The similarity of man and guinea pig liv
er aldehyde oxidase has been observed previously in vitro.