Oral Corticosteroids and Warfarin

A study published in the December, 2006 Annals of Pharmacotherapy found oral corticosteroids to be a medication with significant interactions with patients taking long term warfarin therapy.

29 of the 32 (90%) patients evaluated experienced an increase in INR test results. Only 2 patients experienced a decrease in INR values during the study. The average increase was 1.24 (95% CI 0.86 to 1.62). The average INR change was seen 6.7 days after the first corticosteroid exposure. Half the patients experiencing an increase in test results required a change in their warfarin dosing. None of the study patients required hospitalization.

The study limitations included a lack of standardization of testing frequency.

"Due to the retrospective nature of the study, patients were not seen in the clinic at specific intervals. Therefore, the time at which an INR change was observed (ranging from 3 to 10 days) reflects an approximation of the onset of the interaction."

15% of patients experienced "extreme" INR elevations with INRs exceeding 5.0.¹ The mechanism of interaction between warfarin and oral corticosteroids remains unknown. Alteration of liver metabolism (CYP3A4 isoenzyme pathway) is thought to be the cause.

The University of Oklahoma Health ScienceCenter researchers recommended earlier (and more frequent) monitoring to prevent elevations in INR test results.

1. Harrison D, Hazlewood K, Fugate S. Effect of Oral Coricosteroids on Chronic Warfarin Theropy. The Annals of Pharmacotherapy. December 2006 vol 40 no. 12, 2101-2106.