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A3516 - Warfarin Failure: A Case Report
Author Block: A. Amin, D. Shahi, I. Apostolis, S. Kwatra; Internal Medicine, Western Reserve Health Education, Youngstown, OH, United States.
Introduction:
Warfarin failure is defined as recurrent VTE, despite an apparently stable therapeutic INR between 2.0 and 3.0 and such an event suggests that this degree of anticoagulation was insufficient to neutralize the sum of hypercoagulable stimuli in a given individual.[1]. We present a case of such failure in an individual who has had recurrent DVTs despite compliance with warfarin therapy and achievement of a therapeutic INR.
Case Presentation:
68 year old male with PMH of recent bilateral DVTs, hypertension presented with right leg pain and swelling. He's been on Warfarin therapy for the past 5 months. US imaging revealed a nonocclusive thrombus involving the right common femoral vein. Patient insisted on compliance with medication, which was verified by therapeutic INR of 2.6. After comparing older images it was confirmed that this was an acute thrombus. Coagulation panel was found to be unremarkable. Thereafter, patient was admitted and succesful placement of IVC filter.
Discussion:
When approaching a case of Warfarin failure, it's important to distinguish Warfarin resistance from Warfarin inefficacy. Warfarin resistance implies the inability to achieve/maintain a therapeutic INR goal between 2.0 and 3.0 despite higher doses of Warfarin. Meanwhile, Warfarin inefficacy indicates an inability of adequate anticoagulation to prevent recurrent thrombosis. This should always prompt a clinician to search for other risk factors such as malignancy [2]. Ultimately, one must consider the options for treatment in patients who experience Warfarin inefficacy. One study discussed that a modest increase in the target therapeutic INR range could be considered. [3] In another study, patients were either treated with an escalation dose of LWMH versus eventually switching from Warfarin to LMWH. Investigators found that dose escalation seemed to be safe and prevented recurrent events in a short follow-up.[4]. Lastly, IVC filter insertion should always be considered in subjects in whom anticoagulant therapy is ineffective or contraindicated as was in the patient presented in this case.
Conclusions:
Warfarin failure due to inefficacy is a rare occurrence. Clinical practitioners must balance the risk of bleeding with preventing thrombosis when titrating Warfarin doses for each individual patient. [5] As always, there should be a high suspicion for malignancy in the setting of recurrent VTE despite a therapeutic INR. Recent studies suggest higher target therapeutic INR ranges or dose escalation of LMWH as management options for patient who experience Warfarin inefficacy. However, IVF filter should always be considered as an option these patient in particular.