How is warfarin therapy used in the treatment of acute pulmonary embolism (PE)?

Updated: Sep 18, 2020
  • Author: Daniel R Ouellette, MD, FCCP; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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A vitamin K antagonist such as warfarin should be started on the same day as anticoagulant therapy in patients with acute PE. [5] Parenteral anticoagulation and warfarin should be continued together for a minimum of at least five days and until the INR is 2.0.

The anticoagulant effect of warfarin is mediated by the inhibition of vitamin K–dependent factors, which are II, VII, IX, and X. The peak effect does not occur until 36-72 hours after drug administration, and the dosage is difficult to titrate.

A prothrombin time ratio is expressed as an INR and is monitored to assess the adequacy of warfarin therapy. The recommended therapeutic range for venous thromboembolism is an INR of 2-3. This level of anticoagulation markedly reduces the risk of bleeding without the loss of effectiveness. Initially, INR measurements are performed on a daily basis; once the patient is stabilized on a specific dose of warfarin, the INR determinations may be performed every 1-2 weeks or at longer intervals.

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