Warfarin

• related: Hematology, INR goals

Warfarin is an anticoagulant commonly used in the treatment of atrial fibrillation and venous thromboembolism. Effects arise from the inhibition of vitamin K recycling, which reduces circulating levels of vitamin K-dependent clotting factors II, VII, IX, and X. The major risk of therapy is bleeding-associated complications, particularly intracranial hemorrhage.

Patients on warfarin with intracranial hemorrhage require urgent warfarin reversal to prevent the propagation of hemorrhage; this is accomplished by administering the following:

• Prothrombin complex concentrate, which contains vitamin K-dependent clotting factors and normalizes INR <10 minutes after administration.

• Intravenous vitamin K, which results in sustained warfarin reversal but takes 12-24 hours for full effect. Because of this delayed effect, vitamin K is always used with clotting factor replacement (Choice D).

  Fresh frozen plasma is considered the second-line therapy for replacing vitamin K-dependent clotting factors due to the large volume (often >2 L) required and the delay for blood compatibility tests. Fresh frozen plasma is typically used when prothrombin complex concentrate is unavailable.

  Intravenous idarucizumab is a monoclonal antibody used to reverse the anticoagulant dabigatran, a direct thrombin inhibitor. This patient was on warfarin, not dabigatran; idarucizumab would be ineffective.

• Do not reverse for INR < 1.8