The effect of changing from simvastatin to rosuvastatin on the international normalized ratio of patients taking warfarin

Purpose:   This study evaluated the effect of rosuvastatin on the INR of patients taking warfarin in patients who were previously taking simvastatin.  The goal of this study is to develop a clinical practice guideline for management of this interaction in our medical facility’s anticoagulation service. 

Methods:  A retrospective chart review of patients taking warfarin who were switched from simvastatin to rosuvastatin during January 1, 2010 to December 31, 2011 was conducted at the Durham VA Medical Center.  This study included patients who maintained a stable INR defined as remaining within +/-0.3 of the recommended range for the past two clinic visits.  Charts were reviewed to determine changes in INR values, warfarin dosage adjustments made within 2 months of their statin switch date and the incidence of any bleeding events.   

Results:   Thirty-two patients were converted from simvastatin to rosuvastatin while taking warfarin during the designated study period.  Comparison of mean INR pre- and post- statin switch revealed that no clinically significant change in INR occurred after conversion (2.39 to 2.37).  In the 28% of patients who required dose modification, 67% required an increase in warfarin weekly dose to maintain INR goal.  No major adverse events were noted. 

Conclusion:   Patients taking warfarin were safely converted from simvastatin to rosuvastatin without clinically significant impact on their INR.  In our study population, we found variability in warfarin dose requirements associated with this therapy change.  Further analysis is required to develop a practice guideline for our facility.