Absorption characteristics of azasetron from rectal and oral routes in rabbits

The absorption characteristics of azasetron, a serotonin type 3 (5-HT3) receptor antagonist which is used for the treatment of chemotherapy-induced emesis and nausea, were investigated in rabbits. The serum concentrations of azasetron following rectal administration as a suppository increased rapidly and showed the mean tmax value of 0.18 h. The concentrations were greater after rectal administration than those after oral administration. The absolute bioavailability was significantly different between the rectal, 52.9% and oral doses, 21.6%. The mean Cmax and tmax values after the rectal dose were 904.8 ng/ml and 0.18 h, respectively, whereas those after the oral dose averaged 124.7 ng/ml and 0.85 h, respectively. These results indicate that azasetron is absorbed to a greater extent and more rapidly into the systemic circulation via the rectum than via the intestine in rabbits. Consequently, the suppository form of azasetron hydrochloride may be feasible for the treatment of chemotherapy-induced acute emesis and nausea.