Where in the clotting cascade does warfarin exert its effect?

c. Warfarin acts as a vitamin K antagonist and so affects the synthesis of active factors II, VII, IX, X, protein C and protein S. The therapeutic goal is to cause a partial inhibition of clotting factor synthesis, to prolong prothrombin time 2-to 4-fold. Once administered warfarin does not exert its effect for 2–3 days and therefore during this lag period alternative anticoagulation should be used. This anticoagulation is usually in the form of a low molecular weight heparin, its anticoagulation action is via factor Xa and is much more rapid in its onset.