Warfarin is an antagonist of which vitamin?

Warfarin acts as an antagonist of vitamin K, which plays a crucial role in the synthesis of several clotting factors in the liver, including factors II (prothrombin), VII, IX, and X. Vitamin K is essential for the post-translational modification of these factors through a process called gamma-carboxylation, which is necessary for their functionality in the coagulation cascade.

Warfarin inhibits the enzyme vitamin K epoxide reductase, which is involved in the recycling of vitamin K from its epoxide form back to its active form. By decreasing the availability of active vitamin K, warfarin effectively diminishes the synthesis of functional clotting factors, leading to its anticoagulant effect. This mechanism is critical in the management of conditions such as thrombosis and pulmonary embolism, where reducing blood clot formation is necessary.

The other vitamins listed do not play a direct role in the blood coagulation process that warfarin targets. As such, vitamin K is specifically the one that warfarin antagonizes in order to exert its desired therapeutic effects.