Possible Enhancement of the Effect of Warfarin Secondary to Oral Prednisone Therapy

Abstract

Alarge number of medications have been reported to either increase or decrease the effect of warfarin on the international normalized ratio (INR).1 Therefore, knowledge of medications that may interact with warfarin is essential to ensure safe and effective use of this drug. Patients taking warfarin should undergo more frequent testing of INR upon introduction of new medications that may interact with warfarin. In a recent systematic review of medications and foods that may interact with warfarin, oral corticosteroids were not listed as having clinically significant interactions. 1 In fact, interactions between methylprednisolone and warfarin were described as “highly improbable”.1 We report here a clinically significant increase in INR associated with the initiation of oral prednisone therapy in a patient whose condition had previously been stabilized with warfarin therapy.*