Question

Which of the following drugs acts as a neurokinin-1 (NK1) receptor antagonist to prevent chemotherapy-induced vomiting?

• A. Ondansetron
• B. Aprepitant
• C. Dronabinol
• D. Metoclopramide

Hint:

Chemotherapy-induced nausea and vomiting (CINV) is controlled by drugs acting on several receptor systems. Substance P, acting on neurokinin-1 (NK1) receptors, is a key mediator of the delayed phase of vomiting.

Answer 1

The Correct Option is B

Step 1: What is the question about?
We need to identify the drug that prevents chemotherapy-induced vomiting by blocking neurokinin-1 (NK₁) receptors.

Step 2: The role of NK₁ receptors in vomiting.
NK₁ receptors are receptors for substance P, a neuropeptide involved in the delayed phase of chemotherapy-induced nausea and vomiting (CINV). Substance P, released in the gut and the brain, activates the vomiting reflex especially 24-48 hours after chemotherapy. Blocking NK₁ receptors prevents this delayed vomiting.

Step 3: Evaluate Option 2 - Aprepitant.
Aprepitant is the first NK₁ receptor antagonist approved for prevention of CINV. It is used in combination with a 5-HT₃ antagonist and dexamethasone for highly emetogenic chemotherapy. This is the correct answer.

Step 4: Evaluate Option 1 - Ondansetron.
Ondansetron is a 5-HT₃ receptor antagonist, not an NK₁ blocker. It is effective against acute-phase CINV.

Step 5: Evaluate Option 3 - Dronabinol.
Dronabinol is a cannabinoid (delta-9-THC) that acts on CB₁ receptors to reduce nausea. Not an NK₁ antagonist.

Step 6: Evaluate Option 4 - Metoclopramide and Conclusion.
Metoclopramide is a dopamine D₂ blocker with some 5-HT₄ agonist activity. Not an NK₁ antagonist. Only Aprepitant targets NK₁ receptors.
Answer: Option (2) — Aprepitant