Evaluation of Bivalirudin's Effect on International Normalized Ratio to Determine an Appropriate Strategy for Transitioning to Warfarin.

ABSTRACT

Background: Direct thrombin inhibitors are recommended in confirmed or suspected heparin-induced thrombocytopenia. False elevation of the international normalized ratio (INR) occurs with these agents making bridging to warfarin challenging. There is limited data regarding bivalirudin's effect on INR. Objective: To evaluate bivalirudin's effect on the INR and determine a strategy for transitioning to warfarin. Methods: This was a retrospective observational study. Included patients were >18 years old receiving primary bridging therapy with overlapping bivalirudin and warfarin for at least 72 hours. Patients with administration of alternate anticoagulants during the transition interval or active major bleeding within 48 hours prior to bivalirudin initiation were excluded. The primary endpoint was to determine the effect on INR at first therapeutic activated partial thromboplastin time after bivalirudin initiation and prior to warfarin initiation. Secondary endpoints included change in INR 12 and 24 hours after bivalirudin initiation, change in INR 4 hours after bivalirudin cessation, and incidence of major bleeding or new thrombotic events. Results: Thirty-four patients met study criteria. For the primary endpoint, the change in INR at first therapeutic activated partial thromboplastin time was 0.37 (range = 0.28-0.48), which occurred at 8.4 hours (range = 4.6-14.2; n = 14). INR increased at 12 and 24 hours by a median of 0.55 and 0.5 from baseline, respectively. Median change in INR 4 to 8 hours post-bivalirudin cessation was -0.48. Conclusion: Targeting an INR > 2.5 when bridging to warfarin will account for this false elevation and maintain an INR above 2.0 on bivalirudin discontinuation.