Aspirin at low dose (75 to 150 mg daily) produces antiplatelet effects lasting for the entire 7 to 10 day lifespan of the platelet. This sustained duration is best explained by:

• A Enterohepatic recirculation of aspirin metabolites within platelets
• B Slow release of aspirin from bone marrow megakaryocyte stores
• C High-affinity binding of salicylic acid to the thromboxane A2 receptor
• D Irreversible acetylation of COX-1 in anucleate platelets that cannot resynthesize the enzyme ✓

Explanation

Aspirin irreversibly acetylates a serine residue of COX-1, permanently blocking thromboxane A2 synthesis in that platelet. Platelets are anucleate and cannot regenerate the enzyme, so inhibition lasts until new platelets are produced from megakaryocytes, roughly 7 to 10 days. Salicylic acid itself does not inhibit COX irreversibly and has no antiplatelet action, which rules out option C.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.