Ondansetron is a selective 5-HT3 receptor antagonist. While its mechanism of action has not been fully characterized, ondansetron is not a dopamine-receptor antagonist. Serotonin receptors of the 5-HT3 type are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema. It is not certain whether ondansetron’s antiemetic action is mediated centrally, peripherally, or in both sites. However, cytotoxic chemotherapy appears to be associated with release of serotonin from the enterochromaffin cells of the small intestine.
(in Tablet form)
Adult: Usual dose: 8 mg tid. Undergoing total body irradiation: 8 mg 1-2 hr prior to each fraction of therapy daily. Undergoing single high-dose fraction radiation therapy to the abdomen: 8 mg 1-2 hr prior to radiation, repeat dose 8 hrly for 1-2 days after completion of therapy. Undergoing daily fractioned radiation to the abdomen: 8 mg 1-2 hr prior to radiation, then 8 hrly; repeat therapy daily.
Elderly: No dosage adjustment needed.
Manufacturer: Square Pharmaceutical Ltd.