Abstract

The absorption and metabolism of a novel antianxiety drug candidate, CP-93,393, ((7S,9aS)-2-(pyrimidin-2-yl)-7-(succinimidomethyl)-octahydro-1H-pyrido[1,2-a]pyrazine) were investigated in bile-cannulated Long Evans rats after oral administration of a single 30 mg/kg base equivalent dose of¹⁴C-CP-93,393 (HCl salt). Urine, bile, plasma, and feces were collected and assayed for total radioactivity. Plasma samples were also analyzed for unchanged drug using an LC/MS/MS assay. Metabolic profiles of ¹⁴C-CP-93,393 were obtained in urine, bile, and plasma. Structural characterization of metabolites was carried out by LC/MS using a combination of full scan, product ion, constant neutral loss, and multiple reaction ion monitoring techniques. CP-93,393 was completely absorbed, as less than 1% of the administered radioactivity was recovered in the feces. The major portion of the radioactivity was recovered in bile, suggesting that the biliary route was the primary route of excretion. Total recovery of administered dose was 97.4 ± 3.3% from male rats and 85.3 ± 9.6% from female rats. Approximately 32% of the administered radioactive dose was recovered in urine of female rats, while only 20% was recovered in urine of male rats. In contrast, biliary recoveries of the radioactivity were higher for male rats (approximately 77% for males and 53% for females). MeanC_max values for the unchanged CP-93,393 and total radioactivity were significantly higher in the female rats than in the male rats. Similarly, mean AUC_(0-t)values for the unchanged drug and radioactivity were also higher in female rats. These findings suggested that CP-93,393 was eliminated more rapidly in the male rats than in the female rats.

CP-93,393 and a total of 16 metabolites were identified in urine, bile, and plasma. Based on the structures of oxidative metabolites, four metabolic pathways of CP-93,393 were identified: hydroxylation at the pyrimidine ring, hydroxylation at the succinimide ring, hydroxylation alpha to the nitrogen of the piperazine ring, and hydrolysis of amide bond of the succinimide ring. The major oxidative metabolites were excreted as sulfate and/or glucuronide conjugates. The structures of regioisomeric glucuronides were established by a novel tandem mass spectrometric technique. The glucuronides were dissociated at the orifice, and the resulting aglycones were then analyzed by MS/MS studies. The identified metabolites accounted for >90% of the total radioactivity present in urine, bile, and plasma.