Most effective antiemetic for chemotherapy – induced vomiting is _____________.

Explanation

## Correct Answer: A. Granisetron Granisetron is a **5-HT3 receptor antagonist** (5-HT3 blocker) and represents the gold-standard antiemetic for chemotherapy-induced nausea and vomiting (CINV). Chemotherapy agents (especially cisplatin, doxorubicin) cause massive serotonin release from intestinal enterochromaffin cells, which then stimulates 5-HT3 receptors on vagal afferents and chemoreceptor trigger zone neurons, triggering the vomiting reflex. Granisetron selectively blocks these 5-HT3 receptors, preventing both acute (within 24 hours) and delayed CINV (days 2–5 post-chemotherapy). It is highly effective for highly emetogenic chemotherapy regimens used in Indian cancer centres. The drug has rapid onset, good oral bioavailability, and minimal side effects compared to older antiemetics. According to Indian oncology guidelines and KD Tripathi pharmacology, 5-HT3 antagonists (granisetron, ondansetron) are the first-line agents for CINV, often combined with NK1 antagonists and corticosteroids for optimal control. Granisetron's superior efficacy over other antiemetics in this context is well-established in clinical trials and forms the backbone of CINV prophylaxis in Indian cancer treatment protocols. ## Why the other options are wrong **B. Tegaserod** — Tegaserod is a **5-HT4 agonist** used for irritable bowel syndrome with constipation, not for CINV. It acts on the enteric nervous system to promote motility and has no antiemetic properties. NBE may trap students who confuse serotonergic agents; tegaserod's serotonin involvement is mechanistically opposite to what CINV requires. **C. Domperidone** — Domperidone is a **dopamine antagonist** (D2 blocker) effective for postoperative nausea, gastroesophageal reflux, and functional dyspepsia—but ineffective for CINV. It cannot cross the blood–brain barrier significantly and does not block the serotonin pathway activated by chemotherapy. It is a second-line agent for milder emetic triggers, not chemotherapy. **D. Doxylamine** — Doxylamine is a **first-generation antihistamine** (H1 antagonist) used for motion sickness and insomnia-related nausea, not CINV. It has no activity against 5-HT3 receptors and lacks the potency and specificity required for highly emetogenic chemotherapy. NBE includes this to test whether students confuse antihistamines with serotonin antagonists. ## High-Yield Facts - **5-HT3 antagonists** (granisetron, ondansetron) are first-line agents for chemotherapy-induced nausea and vomiting (CINV), blocking serotonin release from enterochromaffin cells. - Granisetron is effective for both **acute CINV** (within 24 hours) and **delayed CINV** (days 2–5), unlike older antiemetics. - **Highly emetogenic chemotherapy** (cisplatin, doxorubicin, cyclophosphamide) requires 5-HT3 antagonists ± NK1 antagonists ± corticosteroids for optimal prophylaxis. - Domperidone (dopamine antagonist) is ineffective for CINV because it does not block the serotonin pathway and cannot cross the blood–brain barrier adequately. - Granisetron has minimal side effects (headache, constipation rare) and superior tolerability compared to metoclopramide or older antiemetics in Indian cancer centres. ## Mnemonics **5-HT3 for CINV** **5-HT3 blocker = Serotonin Stopper for Chemo-vomiting.** Chemotherapy → serotonin surge → 5-HT3 activation → vomiting. Block the 5-HT3, block the vomit. Use this when you see 'chemotherapy' + 'nausea' in the stem. **CINV Prophylaxis Ladder (Indian DOC)** **5-HT3 (granisetron) + NK1 (aprepitant) + Steroid (dexamethasone).** For highly emetogenic regimens in Indian oncology units, this triple combination is standard. Granisetron is the backbone. ## NBE Trap NBE pairs serotonergic agents (tegaserod, granisetron) to trap students who know 'serotonin = antiemetic' but confuse receptor subtypes. Tegaserod (5-HT4 agonist) sounds plausible but is mechanistically opposite to what CINV requires. The trap tests depth of pharmacology, not just drug class recognition. ## Clinical Pearl In Indian cancer centres, granisetron is routinely given IV 30 minutes before cisplatin-based chemotherapy. Patients receiving highly emetogenic regimens without 5-HT3 prophylaxis suffer severe CINV, leading to dehydration, electrolyte imbalance, and poor chemotherapy adherence—a major quality-of-life issue in resource-limited Indian oncology settings. _Reference: KD Tripathi Pharmacology Ch. 48 (GIT Agents); Harrison Ch. 100 (Nausea & Vomiting); Robbins Ch. 9 (Neoplasia & chemotherapy side effects)_