NOT a reversible COX I and II inhibitor?

NOT a reversible COX I and II inhibitor?

• A. Aspirin
• B. Ibuprofen
• C. Naproxen
• D. Indomethacin

Answer: (A)

A key point here is the difference between reversible and irreversible inhibition of cyclooxygenase. The three drugs listed—ibuprofen, naproxen, and indomethacin—bind reversibly to COX, meaning their inhibitory effect ends when the drug dissociates or is cleared. Aspirin acts differently: it permanently acetylates a serine residue in COX-1 (and COX-2), forming a covalent bond that inactivates the enzyme for its lifetime. Because platelets are anucleate and cannot synthesize new COX, aspirin’s antiplatelet effect lasts for the life of the platelet, about 7–10 days, even after the drug has been cleared. So aspirin is not a reversible COX-1 and COX-2 inhibitor, making it the correct choice.

A key point here is the difference between reversible and irreversible inhibition of cyclooxygenase. The three drugs listed—ibuprofen, naproxen, and indomethacin—bind reversibly to COX, meaning their inhibitory effect ends when the drug dissociates or is cleared.

Aspirin acts differently: it permanently acetylates a serine residue in COX-1 (and COX-2), forming a covalent bond that inactivates the enzyme for its lifetime. Because platelets are anucleate and cannot synthesize new COX, aspirin’s antiplatelet effect lasts for the life of the platelet, about 7–10 days, even after the drug has been cleared.

So aspirin is not a reversible COX-1 and COX-2 inhibitor, making it the correct choice.