Ondansetron prevents chemotherapy-induced nausea by blocking 5-HT3 receptors. In which anatomical location is 5-HT3 receptor blockade MOST critical for preventing acute chemotherapy-induced emesis?

• A Cerebral cortex higher emesis centers
• B Vestibular nuclei in the brainstem
• C Area postrema (chemoreceptor trigger zone) and vagal afferents in the gut wall ✓
• D Dopamine D2 receptors in the nucleus tractus solitarius

Explanation

Cytotoxic chemotherapy causes enterochromaffin cells in the gut to release large amounts of serotonin (5-HT), which activates 5-HT3 receptors on vagal afferent nerve fibers in the gut wall, transmitting emetic signals to the nucleus tractus solitarius and vomiting center. Additionally, serotonin in the area postrema directly stimulates 5-HT3 receptors there. Ondansetron blocking both these peripheral and central 5-HT3 sites is the basis of its efficacy; this is most effective for acute emesis within the first 24 hours.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.