Identify the drug that suppresses platelet aggregation by inhibiting cyclooxygenase 1.

• A. Aspirin
• B. Warfarin
• C. Clopidogrel
• D. Heparin

Answer: (A)

Inhibiting cyclooxygenase 1 in platelets reduces production of thromboxane A2, a key driver of platelet aggregation. Aspirin does this by irreversibly acetylating COX-1 in platelets, blocking thromboxane A2 synthesis. Because platelets have no nucleus, they can’t synthesize new COX-1, so the anti-platelet effect lasts for the platelet’s lifespan (about 7–10 days) until new platelets are made. Warfarin acts on vitamin K–dependent clotting factors in the coagulation cascade, not on platelets. Clopidogrel blocks the P2Y12 ADP receptor on platelets, inhibiting aggregation through a different pathway. Heparin enhances antithrombin III to inhibit thrombin and factor Xa, also within the coagulation cascade rather than via COX-1. Therefore, aspirin is the drug that suppresses platelet aggregation by inhibiting cyclooxygenase 1.