## Antiemetic Strategy in Highly Emetogenic Chemotherapy ### Correct Statements **High-Yield:** Aprepitant is a neurokinin-1 (NK1) receptor antagonist that readily crosses the blood–brain barrier and blocks substance P, a neuropeptide involved in the emetic response in the chemoreceptor trigger zone and vomiting center. **Clinical Pearl:** Granisetron has a longer elimination half-life (9–12 hours) and slower clearance than ondansetron (4–6 hours), allowing for once-daily dosing or even extended intervals, improving compliance in CINV management. **Key Point:** Dexamethasone is used on days 2–4 after chemotherapy to prevent delayed CINV. Its longer duration of action and anti-inflammatory properties make it ideal for this delayed phase, where substance P and other mediators play a greater role. ### The Incorrect Statement **Warning:** Metoclopramide is **NOT** the preferred first-line agent for acute CINV in highly emetogenic chemotherapy. In fact, metoclopramide is **inferior to 5-HT3 antagonists** for CINV prevention. **Mnemonic:** **HEC = Highly Emetogenic Chemotherapy = 5-HT3 antagonist + NK1 antagonist + Corticosteroid** ### CINV Prevention Algorithm ```mermaid flowchart TD A[Highly Emetogenic Chemotherapy]:::outcome --> B{CINV Prevention Strategy}:::decision B -->|Acute Phase<br/>Day 0| C[5-HT3 antagonist<br/>+ NK1 antagonist<br/>+ Dexamethasone]:::action B -->|Delayed Phase<br/>Days 2-4| D[Dexamethasone<br/>+ NK1 antagonist]:::action C --> E[Ondansetron or Granisetron]:::action E --> F[Aprepitant]:::action D --> G[Prevent delayed CINV]:::outcome H[Metoclopramide alone]:::urgent --> I[Inadequate for HEC]:::urgent ``` ### Comparative Efficacy in CINV | Agent | Class | Efficacy in HEC | Role | | --- | --- | --- | --- | | Ondansetron | 5-HT3 antagonist | High | First-line, acute phase | | Granisetron | 5-HT3 antagonist | High | First-line, longer half-life | | Aprepitant | NK1 antagonist | High | Adjunct, crosses BBB | | Dexamethasone | Corticosteroid | High | Delayed phase, days 2–4 | | **Metoclopramide** | **Dopamine antagonist** | **Low** | **Not recommended for HEC** |
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