title: Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin.
abstract: 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 mug 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.
authors.affiliation: School of Clinical and Laboratory Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Sconce
authors.forename: Peter
authors.initials: P
authors.lastname: Avery
authors.forename: Hilary
authors.initials: H
authors.lastname: Wynne
authors.forename: Farhad
authors.initials: F
authors.lastname: Kamali
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000494:pharmacology / Q000627:therapeutic use*; D001778:Blood Coagulation Disorders / Q000097:blood / Q000188:drug therapy*; D019587:Dietary Supplements; D004355:Drug Stability; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D014812:Vitamin K / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D014859:Warfarin / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D014812:Vitamin K; D014859:Warfarin