Warfarin (Coumafene) is a vitamin K antagonist, and it works by blocking the action of vitamin K, which is necessary for the synthesis of clotting factors in the liver. Warfarin blocks the action of vitamin K by inhibiting the enzyme gamma-glutamyl carboxylase, which is responsible for the carboxylation of glutamate residues in the clotting factors. This prevents the production of functional clotting factors, leading to an anticoagulant effect.