Key result
Adding leflunomide to long-term warfarin therapy in a 61-year-old woman caused an elevated INR, requiring a 22% decrease in weekly warfarin dose to maintain therapeutic anticoagulation.
Why the study?
Does the addition of leflunomide to warfarin therapy cause a drug interaction that elevates INR?
Case Report (n=1)
Does the addition of leflunomide to warfarin therapy cause a drug interaction that elevates INR?
Adding leflunomide to warfarin may cause a clinically significant drug interaction leading to elevated INR, necessitating increased monitoring and potential warfarin dose reduction.
May indicate leflunomide-warfarin interaction elevating INR; single case leaves open need for confirmatory studies.
A 61-year-old Caucasian woman receiving long-term anticoagulation with warfarin for recurrent thromboembolism and atrial fibrillation was found to have an elevated international normalized ratio (INR) after she started leflunomide therapy for rheumatoid arthritis. Her INR had been stable for 4 months before this event. The patient required an overall decrease of 22% in her weekly warfarin dose to maintain a therapeutic INR within the goal range of 2.0-3.0 after adding leflunomide therapy. A comprehensive PubMed/MEDLINE search was conducted to identify literature addressing the potential interaction between warfarin and leflunomide. Evidence describing the interaction and its potential mechanism was limited to one published case report and to in vitro data, respectively. Our case report provides additional support that such an interaction exists and that it was at least partly responsible for the subsequent increase in the patient's INR. Therefore, continued evaluation and documentation of this potential drug interaction is imperative. To reduce the risk of adverse effects related to excessive anticoagulation with the start of leflunomide in patients taking warfarin, clinicians should increase their frequency of INR monitoring and adjust the warfarin dosage accordingly to maintain therapeutic anticoagulation.
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Chonlahan et al. (2006) conducted a case report in Rheumatoid arthritis and atrial fibrillation/recurrent thromboembolism on warfarin (n=1). Leflunomide was evaluated on Change in INR and warfarin dose requirement. Adding leflunomide to long-term warfarin therapy in a 61-year-old woman caused an elevated INR, requiring a 22% decrease in weekly warfarin dose to maintain therapeutic anticoagulation.
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