Ondansetron is commonly used for chemotherapy-induced nausea. Its antiemetic mechanism relies on blockade of which receptor subtype?

• A 5-HT3 receptors on vagal afferents in the GI tract and in the chemoreceptor trigger zone ✓
• B 5-HT4 receptors in the GI tract, reducing gastric motility
• C D2 dopamine receptors in the area postrema
• D NK1 neurokinin receptors in the nucleus tractus solitarius

Explanation

Ondansetron (a setron) selectively antagonises 5-HT3 receptors, which are ligand-gated ion channels (unlike most other serotonin receptors which are GPCRs). Cisplatin and other cytotoxics trigger enterochromaffin cells to release serotonin, which activates 5-HT3 receptors on vagal afferents (triggering the vomiting reflex) and in the area postrema/CTZ. Blocking these receptors prevents acute chemotherapy-induced emesis. 5-HT4 agonism (metoclopramide component) prokinetic. D2 blockade is the mechanism of metoclopramide and haloperidol. NK1 blockade is the mechanism of aprepitant (used for delayed emesis).

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.