Warfarin interferes with prothrombin production, thereby altering the clotting mechanism during which process?

• A. Platelet aggregation
• B. Activation of thrombin
• C. Release of tissue thromboplastin
• D. Stimulation of factor activation complex

Answer: (B)

Warfarin reduces production of vitamin K–dependent clotting factors in the liver, especially prothrombin. With less prothrombin available, the conversion of prothrombin to thrombin by the prothrombinase complex is slowed, so thrombin generation is impaired. Since thrombin is the central enzyme that converts fibrinogen to fibrin and amplifies the coagulation cascade, this activation step is where warfarin’s effect is most evident. Platelet aggregation belongs to primary hemostasis and is not the main process affected by prothrombin levels. The release of tissue thromboplastin initiates the extrinsic pathway, but warfarin’s impact is on the production of vitamin K–dependent factors, not the trigger itself.