Ondansetron prevents chemotherapy-induced nausea and vomiting (CINV) by:
- A Selectively blocking 5-HT3 receptors on vagal afferents in the GI tract and in the CTZ, preventing serotonin-triggered afferent signalling to the vomiting centre ✓
- B Blocking dopamine D2 receptors in the chemoreceptor trigger zone (CTZ) of the area postrema
- C Blocking substance P at neurokinin-1 (NK1) receptors in the nucleus tractus solitarius
- D Inhibiting prostaglandin E2 synthesis in the gastric mucosa, reducing the emetic stimulus
Correct answer: A. Selectively blocking 5-HT3 receptors on vagal afferents in the GI tract and in the CTZ, preventing serotonin-triggered afferent signalling to the vomiting centre
Explanation
Cisplatin and other highly emetogenic chemotherapy agents stimulate enterochromaffin cells to release 5-HT (serotonin). This 5-HT acts on 5-HT3 receptors on vagal afferents in the gut wall, triggering afferent signals to the vomiting centre. 5-HT3 receptors in the CTZ also contribute. Ondansetron selectively blocks these 5-HT3 receptors, interrupting both pathways. Metoclopramide and domperidone are D2 antagonists; aprepitant/fosaprepitant are NK1 antagonists.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.