Which medication inhibits the coagulation cascade to prevent clot formation?

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

Answer: (A)

Understanding how anticoagulants affect the coagulation cascade is essential. Heparin directly enhances antithrombin III, which blocks key enzymes in the cascade, especially thrombin and factor Xa. With thrombin activity reduced, fibrin formation is prevented, stopping clot development at an early stage. Aspirin works mainly on platelets by inhibiting COX-1 and reducing thromboxane A2, so it prevents platelet clumping rather than the enzymatic cascade itself. TPA is a thrombolytic that activates plasmin to dissolve existing clots, not to stop their formation. Warfarin lowers the production of vitamin K–dependent clotting factors in the liver, gradually reducing the cascade’s ability to form clots, but it acts more indirectly and over a longer period compared to heparin.