 Warfarin is a Vitamin K antagonist. Gamma-carboxylation of vitamin K is crucial for coagulation factors II, VII, IX, and X to function properly, as well as antithrombotic endogenous Protein C and Protein S. Gamma-carboxylation of vitamin K allows these clotting proteins to bind calcium at phospholipid surfaces upon which coagulation occurs. Warfarin and other vitamin K antagonists interfere with vitamin K and cause the liver to synthesize nonfunctional coagulation factors. 