Aspirin irreversibly acetylates cyclooxygenase-1 in platelets. The antiplatelet effect persists for 7 to 10 days after stopping the drug because:

• A Platelets lack nuclei and cannot synthesise new COX-1 ✓
• B Aspirin remains bound to platelet COX-1 throughout the platelet lifespan
• C Acetylated COX-1 slowly regenerates over one week
• D Bone marrow suppression delays release of fresh platelets

Explanation

Anucleate platelets have minimal capacity for protein synthesis, so once COX-1 is irreversibly acetylated, thromboxane B2 production is abolished for that platelet's lifespan of 7 to 10 days. Function returns only when new platelets enter the circulation from marrow megakaryocytes. Option B is wrong because the drug dissociates; the enzyme itself stays inactive. This underlies aspirin's use as once-daily therapy despite a short half-life.

Reference: Ganong's Review of Medical Physiology, 27th ed.

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