Which NSAID is considered an "irreversible" Cox inhibitor?

Which NSAID is considered an "irreversible" Cox inhibitor?

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

Answer: (A)

The key idea is that some NSAIDs inhibit COX enzymes permanently, while others only block them temporarily. Aspirin acts by covalently acetylating a serine in the COX enzyme, which irreversibly inactivates it. In platelets, this is especially important because they can’t synthesize new COX, so the anti-platelet effect lasts for the platelet’s entire lifespan (about 7–10 days). That lasting effect is what makes aspirin stand out as an irreversible COX inhibitor. In contrast, ibuprofen and naproxen bind reversibly to COX, so once the drug is cleared, COX activity returns quickly. Celecoxib also binds reversibly, though it’s selective for COX-2. So aspirin is the irreversible COX inhibitor among the options.

The key idea is that some NSAIDs inhibit COX enzymes permanently, while others only block them temporarily. Aspirin acts by covalently acetylating a serine in the COX enzyme, which irreversibly inactivates it. In platelets, this is especially important because they can’t synthesize new COX, so the anti-platelet effect lasts for the platelet’s entire lifespan (about 7–10 days). That lasting effect is what makes aspirin stand out as an irreversible COX inhibitor. In contrast, ibuprofen and naproxen bind reversibly to COX, so once the drug is cleared, COX activity returns quickly. Celecoxib also binds reversibly, though it’s selective for COX-2. So aspirin is the irreversible COX inhibitor among the options.