A patient is given ondansetron for chemotherapy-induced vomiting. It acts at which receptor subtype?
- A 5-HT2A
- B 5-HT3 ✓
- C 5-HT4
- D Dopamine D2
Correct answer: B. 5-HT3
Explanation
Ondansetron, granisetron, and similar -setrons are selective 5-HT3 receptor antagonists. Chemotherapy activates enterochromaffin cells in the gut to release serotonin (5-HT), which stimulates vagal afferents via 5-HT3 receptors, triggering the vomiting reflex. Blocking 5-HT3 receptors peripherally and in the area postrema prevents this. 5-HT3 is the only ligand-gated ion channel among serotonin receptors. Metoclopramide is a D2 antagonist; cisapride acts via 5-HT4.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.