What is the primary effect of a platelet inhibitor?

• A. Increases bleeding time
• B. Prevents formation of thromboxane A2
• C. Promotes platelet aggregation
• D. Enhances clot stability

Answer: (B)

Platelet inhibitors mainly blunt the signals that cause platelets to activate and clump together. The key effect is to prevent the formation of thromboxane A2, a substance produced by activated platelets that promotes further activation and aggregation and causes vasoconstriction. By stopping thromboxane A2 production, these drugs reduce platelet aggregation and the formation of a platelet plug, which is why this is the best description of their primary action. As a consequence, bleeding time can be prolonged, but the defining action is inhibition of thromboxane A2 synthesis. They do not promote aggregation or strengthen clot stability; those would be opposite effects.