Elevated International Normalized Ratio from Vitamin K Supplement Discontinuation

ObjectiveTo report a case of a critically elevated international normalized ratio (INR) following discontinuation of a vitamin K supplement in a patient receiving warfarin.Case Summary:A 64-year-old man with atrial fibrillation received warfarin for primary stroke prevention. He was initialed on tow-dose vitamin K supplementation therapy secondary to a high level of INR variability. The patient was stabilized on this therapy for approximately 9 months with a mean INR of 2.02 and a warfarin dose ranging from 6.5 to 7.5 mg/week. At a visit with his primary care physician, the patient's INR was subtherapeutic at 1.5. He had not been taking his vitamin K supplement for nearly a week, but had not missed any doses of warfarin. The vitamin K supplement was discontinued and his warfarin dose was increased by 14.3%. Nearly 2 weeks later the patient presented with a critically elevated INR of 8.5, but no acute bleeding. No other factors affecting the INR could be determined. After a dose of 2.5 mg of vitamin K was ...