Question

Aprepitant, a drug used to prevent late-onset chemotherapy-induced nausea and vomiting, acts through which of the following mechanisms?

• A. NK-1 antagonist
• B. NK-1 agonist
• C. NK-3 antagonist
• D. NK-2 antagonist

Hint:

Aprepitant is an NK-1 antagonist, effective in preventing chemotherapy-induced nausea and vomiting by blocking the action of substance P.

Answer 1

The Correct Option is A

Answer: NK-1 antagonist.

Start with the job of the drug. Aprepitant is given to stop the delayed (late-onset) vomiting that follows chemotherapy. Vomiting starts when a chemical called substance P binds to the NK-1 (neurokinin-1) receptor in the brain's vomiting centre. So a drug that blocks this receptor will switch the signal off.

An antagonist blocks a receptor; an agonist turns it on. To stop vomiting we must block it, not turn it on, so the answer has to be an antagonist. That removes option 2 (NK-1 agonist), which would instead cause vomiting.

Now choose the right receptor number. Substance P acts on NK-1, so the drug must target NK-1, not NK-2 or NK-3. That removes option 3 (NK-3) and option 4 (NK-2).

Only one choice is both an antagonist and aimed at NK-1. Aprepitant is an NK-1 antagonist (option 1). In real use it is added to a 5-HT3 blocker and a steroid for stronger control of chemotherapy sickness.