Effect of oral corticosteroids on chronic warfarin therapy.

Background: A potential drug interaction exists between oral corticosteroids and warfarin, but there is limited documentation.

Objective: To evaluate the potential drug interaction between oral corticosteroids and long-term warfarin therapy.

Methods: A retrospective review was conducted of 387 medical records for active patients within an anticoagulation clinic. Inclusion criteria were stable anticoagulation therapy, short-term oral corticosteroid therapy, international normalized ratio (INR) recorded within 30 days prior to corticosteroid initiation (pre-INR), and INR recorded during corticosteroid therapy or within 14 days of discontinuation (post-INR). Patients were excluded if they had been started on any antibiotic or other drug with a probable interaction with warfarin at the same time as corticosteroid initiation. Thirty-two patient encounters met the predetermined inclusion and exclusion criteria. The primary outcome assessed was the difference between pre- and post-INR values. Secondary endpoints included bleeding events, emergency department (ED) visits, hospitalizations, and warfarin dose modifications.

Results: The mean difference between pre- and post-INR values was 1.24 (95% CI 0.86 to 1.62). Ninety-seven percent of the 32 patient encounters resulted in a change in their post-INR value, and 62.5% of patients had supratherapeutic INR values at the post-corticosteroid assessment. The majority of patients assessed had an elevation of their INR following concomitant use of warfarin and corticosteroids. The INR change was observed at a mean +/- SD of 6.7 +/- 3.3 days following the first dose of corticosteroid. Overall, 16 patients (50%) required a modification of their anticoagulation therapy during or following corticosteroid therapy. Only one adverse event of minor epistaxis was reported, and no ED visits or hospitalizations occurred as a consequence of the drug combination.

Conclusions: Use of oral corticosteroids in patients on long-term warfarin therapy may result in a clinically significant interaction, which requires close INR monitoring and possible warfarin dose reduction.