Ondansetron is used to treat chemotherapy-induced nausea. Its antiemetic effect is mediated by blocking which receptor in both the gut and the chemoreceptor trigger zone?
- A 5-HT3 receptors on vagal afferents and in the area postrema ✓
- B Histamine H1 receptors
- C Dopamine D2 receptors in the medullary vomiting centre
- D NK-1 receptors on neurons in the nucleus tractus solitarius
Correct answer: A. 5-HT3 receptors on vagal afferents and in the area postrema
Explanation
Cytotoxic chemotherapy triggers serotonin (5-HT) release from enterochromaffin cells in the gut, which activates 5-HT3 receptors on vagal afferent neurons and in the area postrema (chemoreceptor trigger zone), stimulating the vomiting reflex. Ondansetron (and other setrons) block 5-HT3 receptors at both these sites, providing highly effective prevention of acute emesis. Metoclopramide and domperidone block D2 receptors; aprepitant blocks NK-1 receptors (delayed emesis); H1 blockers address vestibular-mediated nausea.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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