Ondansetron Mechanism — FRCA Primary MCQ
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Correct answer: D — 5-HT3 serotonin
Ondansetron is a potent, highly selective antagonist at the serotonin 5-HT3 receptor. It inhibits emetic signalling at peripheral 5-HT3 receptors on vagal afferent neurons and at 5-HT3 receptors within central emetic pathways, including the area postrema. Dopamine D2 antagonism is associated with drugs such as droperidol and metoclopramide; muscarinic M1 antagonism with hyoscine; neurokinin NK1 antagonism with aprepitant; and histamine H1 antagonism with agents such as cyclizine. Therefore, 5-HT3 is the single best answer.
Reference: Electronic Medicines Compendium, Ondansetron 2 mg/ml solution for injection/infusion, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties, text revised 23 December 2025. https://www.medicines.org.uk/emc/product/101465/smpc