Biotransformation of the antipsychotic agent, mazapertine, in dog - mass spectral characterization and identification of metabolites

1. Biotransformation of the antipsychotic agent, mazapertine, was studied a fter a single oral administration of C-14-mazapertine succinate (10 mg/kg, free base) to six beagle dogs (three male, three female). 2. Following oral administration of C-14-mazapertine, plasma (0-48 h), urin e (0-7 days), and faeces (0-7 days) were collected. Recoveries of total rad ioactivity in urine and faeces were 26.9 and 62.0% of the dose, respectivel y. 3. Unchanged mazapertine plus 14 metabolites were isolated and identified, which accounted for > 60% of the sample radioactivity in the plasma, 17% of the dose in urine and 28% of the dose in faecal extract. 4. Unchanged mazapertine accounted for <4% of the radioactive dose in excre ta samples and <21% of the sample radioactivity present in plasma samples. 5. Seven metabolic pathways for the formation of metabolites were identifie d including: (1) phenyl hydroxylation, (2) piperidyl oxidation, (3) O-dealk ylation, (4) N-dephenylation, (5) oxidative N-debenzylation, (6) depiperidy lation and (7) conjugation. 6. Pathways 1, 2, 5 and 6 produced 4-OH-piperidyl, OH-phenyl-OH-piperidyl, carboxybenzoyl piperidine and depiperidyl analogues of mazapertine as major metabolites.