INR Range of 2-3 for Pulmonary Embolism
Yes, an INR range of 2.0-3.0 with a target of 2.5 is the appropriate therapeutic range for warfarin treatment of pulmonary embolism. 1, 2
Recommended Therapeutic Range
- The American College of Chest Physicians specifically recommends maintaining an INR between 2.0 and 3.0 (target 2.5) throughout the treatment period for patients with pulmonary embolism on warfarin therapy. 2
- This range has been demonstrated to be superior to both lower and higher ranges for balancing efficacy against bleeding risk in PE patients. 2
- The Australasian Society of Thrombosis and Haemostasis consensus guidelines similarly recommend an INR of approximately 2.5 (desirable range 2.0-3.0) for venous thromboembolism including PE. 3
Critical Bridging Requirements
You must continue heparin (unfractionated or low molecular weight) for at least 5 days AND until the INR has been therapeutic (≥2.0) for at least 24-48 hours before discontinuing heparin. 1, 2
- Both conditions must be met—the 5-day minimum duration and the 24-48 hour therapeutic INR window—as warfarin initially creates a prothrombotic state before achieving anticoagulation. 2
- Start unfractionated heparin immediately with an 80 IU/kg IV bolus followed by 18 IU/kg/hour continuous infusion, targeting an aPTT of 1.5-2.5 times control. 2
- Low molecular weight heparin is an acceptable alternative with equal efficacy and easier administration. 2
Monitoring Strategy
- Initial INR monitoring should occur every 1-2 days until stable in the therapeutic range. 1, 2
- Once stable, monitoring frequency can be reduced but must remain regular to ensure maintenance within the therapeutic range. 1
Critical Pitfall: Subtherapeutic Anticoagulation
Subtherapeutic INR levels (<2.0) are associated with a more than three-fold increased risk of VTE recurrence (hazard ratio 3.37). 4
- In a study of breakthrough PE in anticoagulated patients, 42% had at least one subtherapeutic INR (<2.0) in the 14 days preceding their diagnostic visit, highlighting the importance of consistent therapeutic anticoagulation. 5
- The risk of VTE recurrence increases substantially when INR drops below 2.0, occurring at a rate of 3.2 events per 100 person-years in warfarin-treated patients. 4
Special Considerations
- Avoid warfarin initiation in patients with baseline hepatic dysfunction and elevated INR (>2.5), as this indicates impaired synthetic function and unpredictable warfarin response. 6
- Begin warfarin at 2-5 mg daily (or 5-10 mg for the first 2 days), avoiding large loading doses that can cause excessive anticoagulation. 1, 2
- The risk of bleeding increases exponentially once INR exceeds 5.0 and becomes clinically unacceptable at this level. 3