How often should International Normalized Ratio (INR) be checked when bridging from Lovenox (enoxaparin) to Warfarin (coumarin)?

INR Monitoring Frequency During Lovenox-to-Warfarin Bridging

When bridging from enoxaparin (Lovenox) to warfarin, check INR daily until it reaches the therapeutic range for 2 consecutive days, then continue LMWH until the INR is therapeutic on 2 separate measurements before discontinuing the enoxaparin. 1, 2

Initial Bridging Phase: Daily Monitoring

• Check INR daily starting from day 1 of warfarin initiation until the INR reaches therapeutic range (typically 2.0-3.0) and remains there for 2 consecutive days 1, 2
• The FDA warfarin label explicitly states that "PT should be determined daily after the administration of the initial dose until PT/INR results stabilize in the therapeutic range" 2
• Continue full-dose enoxaparin therapy overlapped with warfarin for 4-5 days minimum, until warfarin produces the desired therapeutic INR response 2

Timing of LMWH Discontinuation

• Do not discontinue enoxaparin until the INR is within therapeutic range on 2 consecutive measurements 3
• LMWH or UFH should be continued until the INR returns to therapeutic levels 3
• For high-risk patients (mechanical heart valves, recent VTE), therapeutic-dose LMWH at 1 mg/kg twice daily or 1.5 mg/kg once daily should be maintained throughout the bridging period 3

Post-Therapeutic Monitoring Schedule

Once therapeutic INR is achieved and LMWH discontinued:

• Check INR 2-3 times weekly for the first 1-2 weeks 1
• Then reduce to weekly monitoring for approximately 1 month 1
• After stability is confirmed, extend to at least monthly monitoring (can be up to every 4-12 weeks for consistently stable patients) 1

Critical Timing Considerations for Blood Draws

When both heparin and warfarin are being administered concurrently, proper timing of INR measurement is essential to avoid interference:

• Draw blood for INR at least 5 hours after the last IV bolus dose of heparin 2
• Wait at least 4 hours after cessation of continuous IV heparin infusion 2
• Wait 24 hours after the last subcutaneous heparin/LMWH injection 2

Common Pitfalls to Avoid

• Never discontinue LMWH based on a single therapeutic INR—this is the most common error and leaves patients unprotected, as warfarin's full anticoagulant effect is delayed 3, 2
• Avoid checking INR too soon after LMWH administration, as it can falsely elevate the INR reading and lead to premature discontinuation of bridging therapy 2
• Do not use loading doses of warfarin during bridging, as this increases hemorrhagic complications without providing faster protection; start with 5 mg daily (or 2-4 mg in elderly patients) 2, 4
• Failing to continue daily INR monitoring until stability is achieved—the FDA label emphasizes this is necessary to prevent both thrombotic and hemorrhagic complications 2
• In patients with mechanical prosthetic heart valves, be especially vigilant as the evidence for LMWH is less robust than for UFH, and the FDA has strengthened warnings about Lovenox use in this population 3

Special Populations Requiring Closer Monitoring

• Elderly patients, those with congestive heart failure, active cancer, or requiring low maintenance warfarin doses (<3 mg/day) have prolonged INR normalization times and require more frequent monitoring 5
• Patients with renal insufficiency (creatinine clearance <30 mL/min) may require dose adjustments of LMWH and closer INR monitoring 3
• Cancer patients should be monitored particularly closely, as they have higher rates of both thrombotic and bleeding complications during bridging 3