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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Submitted September 26, 2006
Accepted November 6, 2006
Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin
Elizabeth Sconce, Peter Avery, Hilary Wynne, and Farhad Kamali*
Schools of Clinical & Laboratory Sciences and Mathematics & Statistics, Newcastle University, Newcastle upon Tyne, United Kingdom
Care of the Elderly, Royal Victoria Infirmary, Newcastle upon Tyne, United Kingdom
* Corresponding author; email: farhad.kamali{at}ncl.ac.uk.
Patients receiving warfarin with unstable control of anticoagulation have a significantly lower intake of dietary vitamin K compared to their stable counterparts. We hypothesised that supplementation with oral vitamin K would improve stability in patients with previously unstable control of anticoagulation. 70 warfarin treated patients with unstable anticoagulant control were randomly assigned in a double-blinded fashion to receive a daily amount of 150 µ g oral vitamin K or placebo p.o. for six months. Measures of stability of anticoagulation control in the 6 month study period were compared to those in the 6 months immediately prior to it. Vitamin K supplementation resulted in a significantly greater decrease in standard deviation of INR compared to placebo (-0.24 ± 0.14 vs. -0.11 ± 0.18; p<0.001) and a significantly greater increase in percentage time within target INR range (28 ± 20% vs. 15 ± 20%; p<0.01). Anticoagulation control improved in 33/35 patients receiving vitamin K supplementation and, of these, 19 fulfilled our criteria for having stable control of anticoagulation. However, only 24/33 patients receiving placebo demonstrated some degree of improvement with only 7 of these 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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