Utilization of dietary vitamin K supplementation to aid in INR stabilization for patients on chronic oral anticoagulant therapy: a series of case reports

Abstract

Warfarin is a narrow therapeutic range medication with numerous potential factors affecting its' metabolism with consequent fluctuation of the International Normalized Ratio (INR) outside of the therapeutic range. Identifying factors that can be managed by the patient to aid in stabilization of the INR is a key goal of anticoagulation management. In patients who report stable medication usage (both prescription and over-the-counter), dietary intake of vitamin K rich foods, alcohol intake, and stable use of vitamin and herbal preparation supplementation, but who continue to have unstable INRs, the use of vitamin K supplementation has been shown to afford some stabilization of INRs. In each of our practices, from three different settings (a university hospital, a large health maintenance organization and a small rural hospital anticoagulation management service), dietary grade vitamin K supplementation, in doses ranging from 100 to 300 micrograms daily, has been instituted in a small cohort of patients in an effort to achieve INR stabilization. Each patient is on chronic anticoagulation with warfarin and other possibilities of INR fluctuations (co-morbidities, medication changes, compliance, dietary changes, and alcohol ingestion) have been explored as possible contributing factors for unstable INRs. Upon initiation of dietary vitamin K, improvement in INR stabilization did not occur in most cases. Increases in warfarin dose requirements occurred in most cases. Further studies in the use of dietary vitamin K to aid in INR stabilization are required before such adjunct therapy can be broadly recommended.