Warfarin Dosing During Transition from Enoxaparin
Continue the current 5 mg daily dose of warfarin and recheck the INR in 1-2 days; do not give a booster dose or increase the daily maintenance dose at this early stage of therapy. 1
Rationale for Current Management
Your patient is only on day 2 of warfarin therapy with an unchanged INR of 1.9. This scenario does not warrant dose adjustment because:
Warfarin requires 5-7 days to reach steady-state anticoagulation due to its mechanism of depleting vitamin K-dependent clotting factors, which have varying half-lives (Factor II has a half-life of 60-72 hours). 2 An INR response on day 2 primarily reflects depletion of Factor VII (shortest half-life of 6 hours) and does not indicate the full anticoagulant effect.
The American College of Chest Physicians recommends continuing the same warfarin dose when a single out-of-range INR is 0.5 below therapeutic range, with INR retesting within 1-2 weeks. 1 Your patient's INR of 1.9 (target 2.0-3.0) falls within this guidance, as it is only 0.1 below the therapeutic threshold.
Daily INR monitoring is appropriate during warfarin initiation until the INR stabilizes in the therapeutic range, then intervals can be extended. 2
Bridging Anticoagulation
Continue enoxaparin (Lovenox) at full therapeutic dose until the INR is ≥2.0 for two consecutive days. 1, 3 This typically occurs on days 4-6 of warfarin therapy.
The American College of Chest Physicians recommends against routinely bridging with heparin for a single subtherapeutic INR in stable patients, but your patient is in the initiation phase, not maintenance therapy, so continued enoxaparin is essential until therapeutic anticoagulation with warfarin is achieved. 1
Discontinue enoxaparin only after achieving an INR ≥2.0 on two consecutive measurements to ensure adequate anticoagulation and prevent thrombotic complications during the transition. 1, 4
Why Not to Increase the Dose Now
Loading doses or early dose escalation increase bleeding risk without providing faster protection against thrombosis. 2 The FDA label explicitly states that "use of a large loading dose may increase the incidence of hemorrhagic and other complications, does not offer more rapid protection against thrombi formation, and is not recommended." 2
One study comparing 10 mg versus 5 mg loading doses showed the higher dose achieved therapeutic INR earlier but resulted in more patients with INR >3.0, requiring tighter monitoring. 5 This approach is not standard practice and increases bleeding risk without clear benefit in most patients.
Warfarin dosing should be based on steady-state INR response, which cannot be assessed until at least day 4-5 of therapy. 2
Monitoring Schedule
Check INR daily until it reaches the therapeutic range (2.0-3.0) for two consecutive days. 2
Once therapeutic and stable, extend monitoring intervals progressively: every 2-3 days initially, then weekly, then up to every 4 weeks once consistently stable. 1
After achieving therapeutic INR, recheck within 24-48 hours after discontinuing enoxaparin to confirm the INR remains stable without bridging therapy. 1
Common Pitfalls to Avoid
Do not prematurely discontinue enoxaparin before achieving therapeutic INR on warfarin, as this creates a period of inadequate anticoagulation and increased thrombotic risk. 1, 3
Avoid making dose adjustments based on INR values in the first 3-4 days of therapy, as these do not reflect steady-state anticoagulation. 2
Do not use booster doses (50-100% increases for a single day) during warfarin initiation—this strategy is only considered for patients on stable maintenance therapy with isolated subtherapeutic INRs. 1
Elderly patients, those with liver dysfunction, or patients with genetic variations in CYP2C9 or VKORC1 may require lower maintenance doses (often 2-5 mg daily rather than 5-10 mg). 2 Consider these factors if the INR rises rapidly after day 3-4.