Which medication serves as an antidote for warfarin?

Phytonadione, also known as Vitamin K, is the medication that serves as an antidote for warfarin. Warfarin is an anticoagulant medication that functions by inhibiting vitamin K-dependent clotting factors, which are essential in the blood coagulation process. When there's a need to reverse the anticoagulant effects of warfarin, for instance in cases of excessive bleeding or before surgical procedures, phytonadione is administered. This supplement provides the necessary vitamin K that is required for the synthesis of clotting factors, effectively restoring the body's ability to form clots and reducing the risk of bleeding complications.

The other options listed do not have this specific antidotal effect in relation to warfarin. Each has its own indications and mechanisms of action, which do not pertain to reversing the effects of anticoagulants.