An Unlikely Culprit of Hospital-Acquired Warfarin Resistance: A Case Report and Review of Literature.

Purpose: Warfarin is an anticoagulant medication used to prevent thromboembolic events in many conditions, but therapeutic monitoring requires close attention to prevent serious side effects. Resistance to warfarin can be acquired or hereditary, and many foods and medical conditions have been implicated in acquired warfarin resistance, such as supplemental nutrition shakes in this case presentation. Case Summary: A 65-year-old woman with a prior mechanical aortic valve replacement presented for an elective non-cardiac surgery. She was chronically stable at an international normalized ratio (INR) goal of 2.5-3.5. Surgery was performed without complication, and postoperative INRs were persistently low at 1.5-1.8, despite escalating warfarin doses up to 15 mg warfarin daily at day 12. After a thorough medication and dietary review, the culprit was identified as Boost Plus Nutritional Drinks, a significant source of vitamin K, that she had consumed only while hospitalized postoperatively. Her INR normalized after stopping the shake consumption. Discussion: This is the first known case of a hospitalized patient who developed acquired warfarin resistance from nutritional shakes. Hospitalized patients routinely require supplemental nutrition, and hospitals have a variety of nutritional shakes available, all of which have varying amounts of vitamin K. A review of available supplemental nutrition shakes revealed MightyShakes as the only brand without a significant amount of vitamin K, but other brands also have relatively small quantities of Vitamin K. Conclusion: Supplement administration requires close attention in hospitalized patients on warfarin. Certain brands of nutritional shakes, like MightyShakes, can be safely utilized in such patients if caution is exercised.