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ANTICOAGULATION

Effect of Oral Corticosteroids on Chronic Warfarin Therapy

PharmD Student, College of Pharmacy, The University of Oklahoma Health Sciences Center, Oklahoma City, OK

Susan E Fugate, PharmD BCPS CACP

Associate Professor, Department of Pharmacy: Clinical and Administrative Sciences, College of Pharmacy, The University of Oklahoma Health Sciences Center

Donald L Harrison, PhD

Assistant Professor, Department of Pharmacy: Clinical and Administrative Sciences, College of Pharmacy, The University of Oklahoma Health Sciences Center

Reprints: Dr. Fugate, Department of Pharmacy: Clinical and Administrative Sciences, College of Pharmacy, The University of Oklahoma Health Sciences Center, 1110 N. Stonewall, PO Box 26901, Oklahoma City, OK 73190-5040, fax 405/271-6430, Susan-Fugate{at}ouhsc.edu

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.

Key Words: corticosteroids, methylprednisolone, prednisone, warfarin

Published Online, November 21, 2006. www.theannals.com, DOI 10.1345/aph.1H418

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