Aspirin has a plasma half-life of only 15 to 20 minutes, yet its antiplatelet effect persists for 7 to 10 days after a single dose. The reason is:

• A Aspirin accumulates in megakaryocytes and is released slowly
• B Aspirin permanently depletes circulating thromboxane A2 receptors
• C Active metabolite salicylic acid has a 7-day half-life in platelets
• D Irreversible acetylation of platelet COX-1, and anucleate platelets cannot synthesize new enzyme ✓

Explanation

Aspirin irreversibly acetylates a serine residue of cyclooxygenase-1, permanently disabling thromboxane A2 synthesis in the exposed platelet. Because platelets are anucleate and cannot regenerate the enzyme, recovery depends on replacement by newly formed platelets, taking 7 to 10 days. Salicylic acid itself lacks meaningful antiplatelet activity, and thromboxane receptors are not depleted by aspirin.

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

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