About Granisetron Selective 5HT3 receptor antagonist, Tropane derivative, Antiemetic, antinauseant. Mechanism of Action of Granisetron Granisetron is a selective 5HT3 receptor antagonist. 5HT3 receptors are present in vagal nerve terminals and chemoreceptor trigger zone of area postrema of the brain. Cytotoxic chemotherapy is associated with release of Serotonin from Enterochromaffin cells in the small intestine. Serotonin triggers vomiting through 5HT3 vagal receptor that activates the vomiting reflex. Since Granisetron is a 5HT3 receptor antagonist, it is indicated for the prevention of nausea and vomiting associated in chemotherapy. Indications for Granisetron 1.Nausea and vomiting associated with cytotoxic chemotherapy or radiotherapy.