A 32-year-old woman undergoing chemotherapy for breast cancer develops severe nausea and vomiting. Which is the most common chemotherapy-induced nausea and vomiting (CINV) receptor mechanism that antiemetic drugs target?

## Most Common CINV Receptor Target **Key Point:** 5-HT₃ receptor antagonists (ondansetron, granisetron) are the most commonly used and most effective antiemetics for chemotherapy-induced nausea and vomiting, particularly for acute CINV (0–24 hours post-chemotherapy). ### Mechanism of Action 5-HT₃ antagonists block serotonin receptors on vagal afferents in the chemoreceptor trigger zone and gastrointestinal tract. Chemotherapy causes massive release of serotonin from enterochromaffin cells, which triggers the vomiting reflex via these receptors. ### Comparative Efficacy in CINV | Antiemetic Class | Receptor Target | Primary Use | Efficacy in Acute CINV | |---|---|---|---| | 5-HT₃ antagonists | Serotonin 5-HT₃ | Acute & delayed CINV | Excellent (gold standard) | | NK₁ antagonists | Neurokinin-1 | Delayed CINV | Good (adjunct) | | Corticosteroids | Glucocorticoid | Delayed CINV | Good (adjunct) | | D₂ antagonists | Dopamine | Post-op nausea | Moderate | | Anticholinergics | Muscarinic | Motion sickness | Moderate | **High-Yield:** 5-HT₃ antagonists are first-line for highly emetogenic chemotherapy (e.g., cisplatin, anthracyclines). They are often combined with NK₁ antagonists (aprepitant) and dexamethasone for delayed CINV prevention. **Clinical Pearl:** Ondansetron is a 5-HT₃ antagonist with rapid onset (30 min IV) and excellent tolerability. It is the most prescribed antiemetic in oncology and perioperative settings worldwide. **Mnemonic:** **SET** = **S**erotonin-**E**mesis-**T**reatment (5-HT₃ antagonists stop serotonin-mediated vomiting).