Excretion and biotransformation of cisapride in dogs and humans after oral administration

The excretion and biotransformation of cisapride, a novel gastrokinetic drug, were studied after a single po dose of [14C]cisapride in dogs and humans. The excretion of radioactivity amounted to 97% within 4 days after a 1 mg/kg dose in dogs (72% in feces and 25% in urine). After a 10-mg dose in humans, 44% was excreted in the 0-24-hr urine and 37% in the 0-35-hr feces; excretion was complete within 4 days. Excretion of the parent drug was greater in dogs (0.4-1.3% of the dose in urine, 23% in feces) than in humans (0.2% in urine, 4-6% in feces). This was due, at least in part, to a larger proportion of amine glucuronidation and sulfation in dogs. N-Deal-kylation at the piperidine nitrogen resulting in the main urinary metabolite, norcisapride, and aromatic hydroxylation of the 4-fluorophenyl ring were major metabolic pathways in both species. Norcisapride excretion accounted for 14% of the dose in dogs and 41-45% in humans. Minor metabolic pathways were O-dealkylation at the 4-fluorophenoxy group and piperidine oxidation. Peak plasma levels and AUC values of norcisapride in humans were 8-9 times lower than those of cisapride. Apart from more amine conjugation in dogs, the biotransformation of cisapride was similar in dogs and humans.