Abstract

Brief reversal of oral anticoagulant therapy is frequently necessary prior to minor surgery or invasive procedures. We sought to determine the effect of an oral dose of 2.0 mg of vitamin K(1) on the international normalized ratio (INR) among patients with a stable therapeutic INR who were maintained on their daily dose of warfarin. We prospectively studied a convenience cohort of patients attending an anticoagulation clinic who had either just completed treatment for venous thromboembolism or were receiving prophylaxis for atrial fibrillation, cardiomyopathy, or peripheral vascular disease. Each patient received an oral dose of 2.0 mg of aqueous vitamin K(1). Serial INR measurements were taken over 1 week. There was wide variation in the INR response between patients, from no change to complete reversal of anticoagulation. The effect also varied widely over time. There was a significant inverse correlation between the fall in logarithm of the INR and the daily warfarin dose required to achieve an INR value of 2.5 (r=-0.52, p=0.011). Use of a 2.0 mg oral dose of vitamin K(1) does not reliably reverse (correct) a therapeutic INR in patients maintained on their daily dose of warfarin.