Which anticoagulant requires INR monitoring and has vitamin K as its antidote?

• A. INR monitoring with vitamin K antidote
• B. PTT monitoring with protamine
• C. No monitoring and no antidote
• D. Immediate reversal with platelets

Answer: (A)

Warfarin is a vitamin K antagonist whose effect varies with diet, other drugs, and liver function, so therapy is monitored with the INR to keep the level in the target range. The antidote is vitamin K, which reverses its effect by allowing the liver to synthesize the vitamin K–dependent clotting factors II, VII, IX, and X. In urgent reversal, vitamin K is given along with fresh frozen plasma or prothrombin complex concentrates to rapidly restore clotting factor levels. Other anticoagulants are monitored differently (for example, heparin with the aPTT) or have different reversal strategies, not vitamin K.