Low-dose oral vitamin K to normalize the international normalized ratio prior to surgery in patients who require temporary interruption of warfarin
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BACKGROUND: In patients who require warfarin interruption before surgery and have an elevated international normalized ratio (INR) before surgery, low-dose vitamin K may normalize the INR in time for surgery. PATIENTS AND METHODS: In a retrospective cohort study, we assessed the efficacy of 1 mg oral vitamin K to normalize the INR for surgery and whether resistance to re-anticoagulation occurs when warfarin is restarted after surgery. We studied a cohort of patients with an INR 1.4-1.9 on the day before surgery who received 1 mg oral vitamin K (vitamin K group), and a comparator group of patients with a normal INR (< or = 1.3) on the day before surgery who did not receive vitamin K (no vitamin K group). In both patient groups, we determined the proportion of patients with a normalized INR on the day of surgery and compared the mean INR after surgery when warfarin was resumed. RESULTS: Of 43 patients in the vitamin K group, the INR was normalized (< or = 1.3) in 33 patients (76.6; 95% confidence interval [CI]: 64.1-89.4), and the INR was normal or near-normal (< or = 1.4) in 39 patients (90.7; 95% CI: 82.0-99.4) on the day of surgery. The mean (standard deviation) INR in the vitamin K and no vitamin K group 4-8 days after surgery was 1.75 (0.34) and 1.59 (0.36), respectively (P = 0.56). CONCLUSIONS: In patients requiring interruption of warfarin for surgery, 1 mg oral vitamin K on the day before surgery can normalize the INR by the day of surgery and may not confer resistance to warfarin re-anticoagulation after surgery.
