For high-emetogenic risk regimens, which antiemetic addition may be used beyond ondansetron and dexamethasone?

• A. Metoclopramide.
• B. Dexamethasone.
• C. Ondansetron plus dexamethasone; NK1 antagonist may be added for high emetogenic risk.
• D. Aprepitant alone.

Answer: (C)

In highly emetogenic chemotherapy, preventing nausea and vomiting relies on a three-drug approach: a serotonin-3 receptor antagonist, a corticosteroid, and an NK1 receptor antagonist. The NK1 blocker adds protection by inhibiting the substance P signaling that contributes to both acute and delayed CINV, improving control beyond what ondansetron (a 5-HT3 blocker) and dexamethasone provide alone. That makes adding an NK1 antagonist the appropriate step for high-risk regimens.

Metoclopramide can be used as an adjunct, but it doesn’t offer the same level of protection as incorporating an NK1 antagonist in this setting. Using dexamethasone alone misses the serotonin receptor blockade that's central to first-line prevention, and an NK1 antagonist by itself isn’t sufficient either since a 5-HT3 blocker and corticosteroid are also needed for optimal control.