Which antiemetic is added to a 5-HT3 antagonist and dexamethasone regimen specifically because of superior control of the DELAYED phase of chemotherapy-induced vomiting?
- A Metoclopramide
- B Aprepitant ✓
- C Scopolamine
- D Promethazine
Correct answer: B. Aprepitant
Explanation
Aprepitant is a neurokinin-1 (substance P) receptor antagonist acting centrally in the medullary vomiting centre. Substance P signalling dominates the delayed phase of cisplatin-induced emesis occurring 24 hours or more after chemotherapy, so aprepitant added to a 5-HT3 antagonist plus dexamethasone improves delayed-phase control. It is metabolised by CYP3A4 and inhibits CYP3A4, warranting dose adjustment of drugs like dexamethasone. Metoclopramide was historically used for delayed emesis but is inferior and carries dystonia risk.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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