Heparin + Warfarin

Why do we give heparin before starting long-term warfarin? Warfarin knocks out Vitamin K epoxide reductase in the liver. This decreases factors 2, 7, 9 and 10. It also decreases protein C and S, which inactivate the coagulation cascade. Although synthesis is stopped, there are still pre-existing factors within the blood. The first ones to decrease are protein C and S. Uh oh...that means you still have coagulation factors floating around and nothing to stop them. This hypercoagulable state could result in skin necrosis! Not to worry. This is why we give heparin to transition the patient onto warfarin therapy. What does heparin do? It binds to antithrombin 3 which inhibits factors 2 and 10.