A Case of Significant Fluctuation of Prothrombin Time-international Normalized Ratio with Change, and Cancellation of the Transluminal Nutrient Preparation under Warfarin Administration

We report a patient in whom the prothrombin time-international normalized ratio (PT-INR) fluctuated greatly with changes in transluminal nutrient preparations. The patient began treatment with warfarin due to the onset of atrial fibrillation after mandibular bone transection plus plate/abdomen direct dermal flap reconstruction for radiation osteomyelitis of the left lower jaw. The patient was administered medication by feeding tube and nutrients intravenously and by feeding tube. The PT-INR remained mostly within the therapeutic range at a warfarin dose of 0.50 mg/day, but suddenly fell below the normal limit when the transluminal nutrient preparation was changed from inthrow® (800 kcal/day; vitamin K (VK) 4.8 μg) to CZ-Hi® (700 kcal/day; VK 56 μg). PT-INR then rapidly increased when CZ-Hi® was discontinued; this elevation was not due to either a drug-drug interaction or a change in clinical condition. The sudden change in VK intake, despite its small magnitude, suggested the possibility that the intubation nutrients interacted with warfarin, thus affecting the PT-INR. Our observations suggest that nutrient preparations may interact with drugs, even if the preparations are classified as foods. To promote interprofessional collaboration among medical staff, pharmacists should report all food and drug interactions to physicians and dietitians for safe and effective medication.