Tropisetron (Tropisetron-AFT) is a potent and selective serotonin 3 (5-hydroxytryptamine3; 5-HT3) receptor antagonist with antiemetic properties, probably mediated via antagonism of receptors both at peripheral sites and in the central nervous system. Surgery and treatment with certain substances, including some chemotherapeutic agents, may trigger the release of serotonin from enterochromaffin-like cells in the visceral mucosa and initiate the emesis reflex and its accompanying feeling of nausea. Tropisetron (Tropisetron-AFT) selectively blocks the excitation of the presynaptic 5-HT3 receptors of the peripheral neurons in this reflex, and may exert additional direct actions within the CNS on 5-HT3 receptors mediating the actions of vagal input to the area postrema.

Ondansetron (ZOFRAN®) is a selective 5-HT3 receptor antagonist. It is effective in the treatment of nausea and vomiting caused by radiotherapy, anesthesia, surgery or cytotoxic chemotherapy drugs, including cisplatin, and has reported anxiolytic and neuroleptic properties. While its mechanism of action has not been fully characterized, ondansetron is not a dopamine-receptor antagonist. 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. The released serotonin may stimulate the vagal afferents through the 5-HT3 receptors and initiate the vomiting reflex.