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Pharmacology · single question

What is the mechanism of action of aspirin?

  1. Selective inhibition of COX-2 only
  2. Reversible inhibition of COX-1 and COX-2
  3. Direct inhibition of thromboxane A2 synthase
  4. Irreversible inhibition of COX-1 and COX-2
Show answer and explanation

Correct answer: D. Irreversible inhibition of COX-1 and COX-2

Aspirin (acetylsalicylic acid) IRREVERSIBLY inhibits both COX-1 and COX-2 by acetylation. COX-1 inhibition → no thromboxane A2 in platelets → permanent antiplatelet effect for platelet lifespan (~10 days). Source confirms: 'Aspirin MOA: Inhibit platelets aggregation — Irreversible COX 1–2.'
  • A. Selective COX-2 inhibition = coxibs (celecoxib) — not aspirin.
  • B. Reversible COX inhibition = mechanism of NSAIDs like ibuprofen — NOT aspirin.
  • C. Aspirin inhibits COX enzymes; the net result includes reduced TXA2, but the mechanism is COX inhibition, not direct TXA2 synthase inhibition.
  • D. CORRECT. Aspirin = IRREVERSIBLE COX-1 and COX-2 inhibition via acetylation. Platelet function doesn't recover until new platelets form (~10 days).

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