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Oral administration of vitamin k1 to correct excessive anticoagulation in patients receiving warfarin was reported to be effective decades ago but is virtually unused today in favor of parenteral vitamin K1 therapy. Weibert and colleagues performed an uncontrolled study of the efficacy of oral vitamin K1 in patients with an INR greater than five and without evidence of major bleeding complications. Eighty-one outpatients received 2.5 mg of oral vitamin K1 and were instructed to withhold their warfarin until their next visit. Fifty-eight patients held one dose of warfarin and were seen within 24 hours, while the remainder held two doses and were seen between 24-48 hours. The goal was to lower the INR to between two and five, at which time warfarin was restarted (provided any minor bleeding had stopped).
Excluding patients whose initial INR was greater than 10, 96% of patients had an INR of less than five at follow-up. Seventy-two percent of patients who were re-evaluated within 24 hours had reached the target INR, as did 74% of those seen at 24-48 hours. Seventeen percent of patients were "over-corrected," with an INR of less than 2.0. No patient developed thromboembolic or hemorrhagic complications, and no patient had warfarin resistance when anticoagulation therapy was resumed. Weibert et al conclude that oral vitamin K1 is safe and effective for the routine management of patients with warfarin-induced over-anticoagulation.
Weibert et al provide a strong case for considering oral vitamin K1 2.5 mg as an alternative to parenteral vitamin K1. It is important to bear in mind that this is not a controlled study. Weibert et al have made no attempt to compare oral with parenteral vitamin K1 therapy or to compare oral therapy with simply withholding warfarin. As a fat-soluble vitamin, oral vitamin K1 therapy may be inappropriate for patients with fat malabsorption. Furthermore, some clinicians may consider withholding warfarin to be safer than administering vitamin K1 in certain situations (e.g., when dropping the INR into the normal range, even briefly, would pose an unacceptable risk of thromboembolic complications). (Dr. Karras is Assistant Professor of Medicine, Temple University School of Medicine, Philadelphia, PA.)