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Pharmacology · single question

What is the primary mechanism of action of aspirin (acetylsalicylic acid)?

  1. Reversibly inhibits cyclooxygenase enzymes to reduce prostaglandin synthesis
  2. Irreversibly inhibits platelet COX-1, preventing thromboxane A2 formation and platelet aggregation
  3. Blocks leukotriene receptors to reduce inflammation
  4. Inhibits phospholipase A2 to prevent arachidonic acid release
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Correct answer: B. Irreversibly inhibits platelet COX-1, preventing thromboxane A2 formation and platelet aggregation

Aspirin irreversibly acetylates and inhibits cyclooxygenase (COX-1 and COX-2) enzymes. In platelets, irreversible COX-1 inhibition permanently prevents thromboxane A2 (TXA2) synthesis for the lifespan of the platelet (7-10 days). Since platelets lack nuclei and cannot synthesize new COX-1, a single dose of aspirin (81 mg) provides sustained antiplatelet effects. This is clinically significant in dentistry: patients on low-dose aspirin for cardiovascular prophylaxis should NOT have aspirin discontinued before dental procedures, as the risk of thrombotic events outweighs the modest increase in bleeding. Ibuprofen (NSAID) inhibits COX reversibly. Corticosteroids inhibit phospholipase A2.

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