Which anticoagulant is considered a Vitamin K antagonist?

The correct answer is Warfarin, which is a well-known anticoagulant that functions as a Vitamin K antagonist. It achieves its anticoagulant effect by inhibiting the synthesis of Vitamin K-dependent clotting factors, specifically factors II, VII, IX, and X, in the liver. These factors are essential for the normal functioning of the coagulation cascade, and by blocking their production, Warfarin effectively reduces the blood's ability to clot.

In contrast, the other options listed in the question represent different classes of anticoagulants. Dabigatran is a direct thrombin inhibitor, while Rivaroxaban and Apixaban are direct factor Xa inhibitors. None of them have the same mechanism of action as Warfarin as they do not interfere with Vitamin K metabolism or the synthesis of Vitamin K-dependent proteins. Therefore, Warfarin stands out as the only anticoagulant among the choices that specifically acts as a Vitamin K antagonist.