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Pharmacology · single question

Aspirin's mechanism of action is BEST described as:

  1. Selective COX-2 inhibition
  2. Reversible inhibition of COX-1 and COX-2
  3. Irreversible inhibition of COX-1 and COX-2 by acetylation → prevents thromboxane A2 and prostaglandin synthesis
  4. Inhibition of platelet ADP receptors
Show answer and explanation

Correct answer: C. Irreversible inhibition of COX-1 and COX-2 by acetylation → prevents thromboxane A2 and prostaglandin synthesis

  • A. Selective COX-2 inhibition describes celecoxib (Celebrex) — not aspirin.
  • B. Reversible COX inhibition describes ibuprofen and naproxen — not aspirin.
  • C. Correct. Aspirin irreversibly acetylates the serine residue in the active site of both COX-1 and COX-2 enzymes. COX-1 inhibition prevents thromboxane A2 synthesis in platelets (antiplatelet effect — lasts the platelet's lifetime of ~7–10 days since platelets have no nucleus to make new COX). COX-2 inhibition reduces prostaglandin-mediated pain and fever.
  • D. ADP receptor inhibition (P2Y12 receptor) describes clopidogrel (Plavix) — not aspirin.

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