Target INR for Warfarin in Pulmonary Embolism
For patients with pulmonary embolism treated with warfarin, the target INR should be maintained at 2.5 with a therapeutic range of 2.0 to 3.0 throughout the entire treatment period. 1, 2
Therapeutic Target
- The FDA-approved warfarin dosing for pulmonary embolism specifies a target INR of 2.5 (range 2.0-3.0) for all treatment durations, supported by the 7th ACCP guidelines 2
- This target range (2.0-3.0) is consistently recommended across major international guidelines including the European Society of Cardiology 3 and the American Heart Association 3
- The therapeutic range applies equally whether the PE is provoked or unprovoked, and regardless of treatment duration 2, 4
Initiation and Overlap with Heparin
- Warfarin should be started simultaneously with heparin (unfractionated or low molecular weight) on the same day as diagnosis 3, 5
- Initial warfarin dosing should be 5-10 mg daily, with 5 mg preferred in older patients (>60 years) or those at bleeding risk, and 10 mg acceptable in younger, otherwise healthy patients 3, 1
- Heparin must be continued for a minimum of 5 days AND until the INR has been in therapeutic range (2.0-3.0) for at least 24-48 consecutive hours 3, 1, 5, 2
Monitoring Schedule
- Initial INR monitoring should occur every 1-2 days until the INR stabilizes within the therapeutic range 1
- Once stable in the therapeutic range, monitoring frequency can be reduced but must remain regular to ensure maintenance between 2.0-3.0 1
- The INR must be checked on at least 2 consecutive days showing values between 2.0-3.0 before discontinuing heparin 3, 1
Critical Evidence on Subtherapeutic Anticoagulation
- Maintaining INR below 2.0 significantly increases the risk of recurrent VTE by more than 3-fold (hazard ratio 3.37,95% CI 2.16-5.27) 6
- This finding from a large retrospective cohort of 1,753 warfarin-treated VTE patients demonstrates that subtherapeutic anticoagulation carries substantial clinical risk 6
- Conversely, INR values above 3.0 increase bleeding risk exponentially, becoming clinically unacceptable once INR exceeds 5.0 7
Common Pitfalls to Avoid
- Never discontinue heparin before 5 days of therapy, even if INR reaches therapeutic range earlier - this is a critical safety measure 3, 5, 2
- Do not use lower INR targets (such as 1.5-2.0) for standard PE treatment - these lower targets are only appropriate for specific long-term prophylaxis scenarios after completion of standard therapy 8
- Avoid starting warfarin at doses higher than 10 mg, as this increases risk of excessive anticoagulation without improving time to therapeutic INR in most patients 3
- Ensure adequate overlap: heparin must continue until BOTH criteria are met: ≥5 days of therapy AND INR ≥2.0 for ≥24 hours 5, 2