A 55-year-old man receiving cisplatin-based chemotherapy for non-small cell lung cancer develops persistent vomiting on day 3 after infusion despite ondansetron. This delayed emesis is predominantly mediated by:
- A Substance P binding to NK1 receptors in the vomiting center ✓
- B Dopamine receptor activation in the chemoreceptor trigger zone
- C Acetylcholine stimulation of the vestibular nucleus
- D Serotonin acting on vagal afferents in the gastrointestinal mucosa
Correct answer: A. Substance P binding to NK1 receptors in the vomiting center
Explanation
Delayed chemotherapy-induced nausea and vomiting (occurring >24 hours post-chemotherapy) is primarily mediated by Substance P binding to neurokinin-1 (NK1) receptors in the nucleus tractus solitarius and vomiting center. Aprepitant, an NK1 receptor antagonist, is the cornerstone of delayed emesis prophylaxis and is combined with 5-HT3 antagonists and dexamethasone for highly emetogenic agents like cisplatin. The 5-HT3 pathway is more relevant to acute emesis.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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