Low-dose Vitamin K to Augment Anticoagulation Control

Study Objectives: To determine the effect of daily low-dose oral vitamin K supplementation on reducing variations in the international normalized ratios (INRs) in patients taking warfarin.

Design: Retrospective analysis.

Setting: Anticoagulation clinic in a large, private-practice hematology group.

Patients: Eight motivated patients (three men, five women), aged 45-79 years, receiving anticoagulant therapy with warfarin, whose INRs had been fluctuating for reasons not associated with identifiable changes in diet, warfarin dosage, activity level, illness, or changes in drug therapy.

Intervention: Daily supplementation with oral vitamin K, starting with 100 microg/day

Measurements And Main Results: Anticoagulation providers monitored INR responses; all documented INR values were included in the analysis, even those intentionally allowed outside the therapeutic range when dosages were adjusted for procedures. After dietary vitamin K supplementation, INR fluctuations diminished in nearly all patients. Overall, a significant decrease was noted in the INR standard deviation (p<0.05), and more INRs were in the therapeutic range after the start of supplementation. Allowing for small fluctuations on either side of the target range, the number of INRs within 0.2 units of the target range increased from 32% to 57% (relative increase 76%). Time in range also increased by a similar degree.

Conclusion: Supplementation with daily low-dose oral vitamin K significantly increased the number of INRs in range as well as the time in range, and decreased INR fluctuation in this small series of selected patients.