What is the mechanism and rationale for using aspirin in suspected ACS?

• A. Irreversibly inhibits COX-1, reducing thromboxane A2 and platelet aggregation
• B. Reversibly inhibits COX-2 to decrease inflammation
• C. Increases platelet production to promote healing
• D. Antagonizes ADP receptors on platelets

Answer: (A)

In suspected ACS, the vital action of aspirin is to shut down a key pathway in platelets that drives clot formation. It does this by irreversibly acetylating COX-1 in platelets, which stops the production of thromboxane A2, a substance that promotes platelet aggregation and vasoconstriction. Because platelets have no nucleus, they can’t make new COX-1, so the antiplatelet effect lasts for the platelet’s entire lifespan (about 7–10 days). This rapid, durable reduction in thromboxane A2 limits thrombus growth at the culprit coronary lesion and helps preserve blood flow to the heart muscle, which is crucial in ACS. The other ideas—reversible COX-2 inhibition to reduce inflammation, increasing platelet production to aid healing, or blocking ADP receptors on platelets—don’t describe aspirin’s primary mechanism in preventing thrombus formation; ADP receptor antagonists are a different class of antiplatelet drugs.