<prompt> Which one of the following is a 5-HT3 antagonist?OndansetronOrlestatClozapineErgotamine  <response>: A Ondansetron ANTAGONISTS IN CHEMOTHERAPY-INDUCED NAUSEAEMESISDRUGCHEMICAL NATURERECEPTOR INTERACTIONST12DOSE IVOndansetronCarbazole derivative5-HT3 antagonist and weak 5-HT4 antagonist3.9 hours0.15 mgkgGranisetronIndazole5-HT3 antagonist9-11.6 hours10 ugkgDolasetronIndole moiety5-HT3 antagonist7-9 hours0.6-3 mgkgPalonosetronIsoquinoline5-HT3 antagonist; highest affinity for 5-HT3 receptor in this class40 hours0.25 mgRamosetronBenzidazolyl derivative5-HT3 antagonist5.8 hours300 ugkg Ondansetron is a serotonin 5-HT3 receptor antagonist used mainly to treat nausea and vomiting following chemotherapy. Its effects are thought to be on both peripheral and central nerves. One part is to reduce the activity of the vagus nerve, which is a nerve that activates the vomiting center in the medulla oblongata, the other is a blockage of serotonin receptors in the chemoreceptor trigger zone. It does not have much effect on vomiting that is due to motion sickness. This drug does not have any effect on dopamine receptors or muscarinic receptors. 5-HT3-Receptor Antagonists: Chemistry, Pharmacological Effects, and Mechanism of Action. Ondansetron ZOFRAN is the prototypical drug in this class. Since their introduction in the early 1990s, the 5-HT3-receptor antagonists have become the most widely used drugs for chemotherapy-induced emesis. Other agents in this class include granisetron KYTRIL, dolasetron ANZEMET, palonosetron ALOXI; intravenous use only and tropisetron The differences among these agents are related mainly to their chemical structures, 5-HT3 receptor affinities pharmacokinetic profiles 