Effects on warfarin dosage requirements after anticoagulation therapy with dabigatran

Purpose: This study measured the difference between the weekly warfarin dosage requirements for patients who were previously treated with warfarin, then treated with dabigatran before resuming warfarin therapy.

Methods: An existing quality assurance database of patients who had their anticoagulation therapy monitored at an outpatient anticoagulation clinic located in a cardiology and electrophysiology office was reviewed. Patients selected had been previously treated with warfarin, and then treated with dabigatran before resuming warfarin therapy. Previous and current weekly warfarin dose requirements and previous and current INR values were collected and compared using a 2- tailed paired t-test for 11 patients.  

Results: The average weekly warfarin dosage requirements post-dabigatran was higher in 8 of the 11 patients: previous dose (32.15mg/week ± 9), current dose (36.96mg/week ± 15.8) with a difference of -4.81mg ± 11.97 (p=0.212). The average INR was lower in 5 of the 8 patients who required a higher weekly warfarin dose: previous INR (2.35 ± 0.19), current INR (2.26 ± 0.32) with a difference of 0.09± 0.34 (p=0.404).

Conclusion: The increase in weekly warfarin dosage requirements had no statistical significance when each patient was compared to him/herself pre-dabigatran and post-dabigatran. Multiple factors can influence the dosage requirements of warfarin and should be evaluated in determining any changes in the warfarin dose. The formation of a consortium with other anticoagulation clinics would allow for further evaluation of the findings in this study.