Anticoagulation (Warfarin and DOACs)
Warfarin and the direct oral anticoagulants interrupt the clotting cascade at different points (vitamin K recycling versus a single activated factor), and that mechanistic difference dictates monitoring, dosing and how bleeding is reversed.
First principles
Warfarin blocks the recycling of vitamin K, not clotting itself
Factors II, VII, IX and X need a vitamin K-dependent carboxylation step to become functional, and this requires vitamin K to be continually regenerated by the enzyme vitamin K epoxide reductase (VKORC1). Warfarin inhibits VKORC1, so existing functional factors are not destroyed but new ones cannot be made; anticoagulation only develops as the existing factors clear from plasma, and factor VII (shortest half-life) falls first, which is why the INR rises before the anticoagulant effect is complete and why warfarin has a slow, unpredictable onset requiring monitoring.
Educational content pending clinical review. Not medical advice.