Prospective evaluation of anticoagulant reversal with oral vitamin K1 while continuing warfarin therapy unchanged

Study objectives: To study the efficacy and safety of partially correcting therapeutic anticoagulation by administering oral vitamin K-1. Design: Prospective interventional trial. Setting: Outpatient anticoagulation clinic. Patients: Patients who required reversal of their normal or excessive therapy with oral anticoagulant drugs were recruited. Interventions: All patients received a single oral dose of vitamin K-1. The dose was calculated using a regression formula and was intended to decrease the international normalized ratio (INR) to a predetermined value. Patient follow-up continued for 8 weeks. We compared the actual change of the INR to the predicted change. Results: Sixty-five reversals of anticoagulant therapy were initiated in the study group. Sixty-four of the 65 reversals were successful. The mean (+/- SEM) initial INR was 2.6 +/- 0.1 for the preprocedure patients and 8.4 +/- 0.5 for the excessively anticoagulated patients. The predicted change in the INR correlated with the actual change (r = 0.92, p < 0.0001), There were no thromboembolic events and only one hemorrhagic complication. The mean (+/- SEM) dose of oral vitamin K-1 was 5.0 +/- 0.3 mg for the preprocedure patients and 10.0 +/- 1.0 mg for the excessively anticoagulated patients. Conclusions: The administration of a single oral dose of vitamin K-1 is a safe and effective method for partially reversing anticoagulant therapy without disrupting the daily maintenance dose of warfarin. A reliable regression formula was developed to predict the dose of vitamin K-1 needed to achieve the desired INR.