Human metabolism of dolasetron mesylate, a 5-HT3 receptor antagonist.

Dolasetron mesylate is a selective and potent 5-HT3 receptor antagonist. This drug is currently in development for the treatment of nausea and vomiting in chemotherapy. The metabolism of dolasetron mesylate was studied in six healthy male volunteers who were given a single 300 mg oral dose of [14C]dolasetron mesylate. An average of 59% of the total radioactivity was recovered in the urine and 25% in the feces. Metabolites were quantitated in urine samples taken up to 36 hr postdose. Reduced dolasetron (RD) accounted for 17-54% of the dose in urine. Hydroxylated metabolites of RD made up no more than 9% of the dose in urine. Most of the remaining urinary radioactivity consisted of conjugated metabolites of RD and hydroxy RD. Hydrolysis of selected urine samples showed that the glucuronide of RD was the most abundant conjugate in urine. A small percentage of the dose (< 1%) in urine was identified as the N-oxide of RD. Analysis of urine samples by chiral HPLC indicated that the R(+):S(-) ratio of RD was approximately 9:1.