Supratherapeutic International Normalized Ratio Due to Reduced Vitamin K Intake Secondary to Prolonged Vomiting in a Patient on Warfarin

OBJECTIVE:To report a case of prolonged vomiting during warfarin therapy, leading to an elevated international normalized ratio (INR).CASE SUMMARY:A 32-year-old female with a history of cyclic vomiting syndrome since early childhood and bilateral pulmonary emboli diagnosed 4 months prior to this acute event presented to the clinic for routine monitoring of warfarin therapy. The warfarin dose had been maintained at 35 mg/wk for 3½ months (INR 2-3.5), but it was increased to 37.5 mg/wk because the INR had trended down to the low goal range over the preceding month. At presentation, the patient reported a 15-day history of vomiting with minimal oral intake that required intravenous fluids to prevent dehydration. The INR was 4.7; warfarin was withheld, and oral vitamin K 5 mg as well as subcutaneous vitamin K 10 mg was administered the following day. The INR then decreased to 1.3. Therapy was transitioned to subcutaneous enoxaparin 1 mg/kg every 12 hours for the duration of the patient's anticoagulation thera...