From the Guidelines
When transitioning a patient from warfarin to dabigatran, dabigatran should be started when the INR is below 2.0. This approach is based on the most recent and highest quality study available, which emphasizes the importance of minimizing the risk of excessive anticoagulation during the transition period 1. The reason for this recommendation is that dabigatran is a direct thrombin inhibitor that begins working immediately after administration, while warfarin has a longer half-life and affects multiple clotting factors. Overlapping these medications at higher INR levels could potentially increase bleeding risk. Some key points to consider when initiating dabigatran in patients on warfarin include:
- If the INR is less than 2.0, dabigatran can be initiated immediately.
- If the INR is between 2.0 and 3.0, wait 24 hours after discontinuing warfarin before starting dabigatran.
- For INR values greater than 3.0, check the INR daily and start dabigatran once it falls below 2.0. For most patients, dabigatran is dosed at 150 mg twice daily, though a reduced dose of 110 mg twice daily may be appropriate for elderly patients or those with renal impairment, as noted in the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1. It is essential to counsel patients that dabigatran requires strict adherence to the twice-daily regimen, as missed doses can significantly reduce anticoagulation protection. Additionally, renal function should be evaluated before initiation of dabigatran and reevaluated at least annually, as recommended in the 2019 AHA/ACC/HRS focused update of the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1.
From the FDA Drug Label
When converting patients from warfarin therapy to dabigatran etexilate capsules, discontinue warfarin and start dabigatran etexilate capsules when the INR is below 2.0.
Dabigatran (Pradaxa) should be initiated in a patient on Warfarin (Coumadin) when the INR is below 2.0 2.
From the Research
Dabigatran Initiation in Patients on Warfarin
- The International Normalized Ratio (INR) at which Dabigatran (Pradaxa) should be initiated in a patient on Warfarin (Coumadin) is not explicitly stated in the provided studies.
- However, a study 3 reports the use of dabigatran as bridging therapy during warfarin optimization for cardioembolic stroke, where dabigatran was started and stopped when the patient's INR exceeded 2.
- In two cases, dabigatran was started on day 1 or 2 of hospital admission and stopped on day 5 or 6 when the INR was almost 2 or exceeded 2, respectively.
- This suggests that dabigatran can be initiated in patients on warfarin when the INR is below the therapeutic range, and stopped when the INR reaches the therapeutic range of 2.0-3.0.
Comparison of Dabigatran and Warfarin
- Studies 4 and 5 compare the efficacy and safety of dabigatran and warfarin in patients with atrial fibrillation, but do not provide specific guidance on the INR at which dabigatran should be initiated.
- A study 6 compares the major bleeding risk among non-valvular atrial fibrillation patients initiated on apixaban, dabigatran, rivaroxaban, or warfarin, but does not address the question of INR at which dabigatran should be initiated.
Clinical Practice
- In clinical practice, the decision to initiate dabigatran in a patient on warfarin should be based on individual patient factors, such as the risk of thrombosis and bleeding, and the ability to maintain the INR within the therapeutic range.
- The studies provided suggest that dabigatran can be a useful alternative to warfarin in certain patients, but do not provide a specific INR threshold for initiation.