Blood, 15 March 2007, Vol. 109, No. 6, pp. 2419-2423.
Prepublished online as a Blood First Edition Paper on November 16, 2006; DOI 10.1182/blood-2006-09-049262.
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HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY
Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin
Elizabeth Sconce1,
Peter Avery2,
Hilary Wynne3, and
Farhad Kamali1
1 School of Clinical and Laboratory Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom;
2 School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne, United Kingdom;
3 Care of the Elderly, Royal Victoria Infirmary, Newcastle upon Tyne, United Kingdom
Patients receiving warfarin who have unstable control of anticoagulation have a significantly lower intake of dietary vitamin K compared with their stable counterparts. We hypothesized that supplementation with oral vitamin K would improve stability in patients with previously unstable control of anticoagulation. Seventy warfarin-treated patients with unstable anticoagulation control were randomly assigned in a double-blinded fashion to receive a daily amount of 150 µg oral vitamin K or placebo orally for 6 months. Measures of stability of anticoagulation control in the 6-month study period were compared with those in the 6 months immediately prior to it. Vitamin K supplementation resulted in a significantly greater decrease in standard deviation of international normalized ratio (INR) compared with placebo (–0.24 ± 0.14 vs –0.11 ± 0.18; P < .001) and a significantly greater increase in percentage time within target INR range (28% ± 20% vs 15% ± 20%; P < .01). Anticoagulation control improved in 33 of 35 patients receiving vitamin K supplementation; of these, 19 fulfilled our criteria for having stable control of anticoagulation. However, only 24 of 33 patients receiving placebo demonstrated some degree of improvement, with only 7 patients fulfilling the criteria for having stable control. Concomitant supplementation of vitamin K, perhaps through reducing the relative day-to-day variability in dietary vitamin K intake, can significantly improve anticoagulation control in patients with unexplained instability of response to warfarin.
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