title: Prospective study of supplemental vitamin K therapy in patients on oral anticoagulants with unstable international normalized ratios.
abstract: BACKGROUND
  It is not known whether patients on oral vitamin K antagonists who have unstable INRs achieve more stable INRs with daily vitamin K supplementation. We sought to determine whether vitamin K supplementation may decrease INR variability in patients with a history of unstable INRs, how soon the INR decreases after vitamin K therapy is initiated, the time to reach a therapeutic INR after vitamin K initiation, and how much of an increase in oral anticoagulant dose is needed to maintain the INR in the desired range.
  
  
  METHODS
  This is a prospective open label crossover study of patients on warfarin with a history of fluctuating INRs. A 9 week observation phase was followed by an 8 week period with patients receiving 500 microg of oral vitamin K daily. INRs were determined once weekly with a home point of care monitoring instrument.
  
  
  RESULTS
  Vitamin K supplementation led to a decrease in INR variability in five of the nine patients studied (56%). INR decrease occurred 2-7 days after initiation of vitamin K. Therapeutic INRs were achieved 2-35 days after vitamin K therapy was initiated and an increase in warfarin dose of 6-95% was required to bring the INR back into the therapeutic range.
  
  
  CONCLUSIONS
  INR fluctuations may decrease in selected patients with unstable INRs who receive vitamin K supplementation. A study with a larger sample size and longer follow-up period is needed. The results of the present study can help design such a study.
authors.affiliation: Department of Pharmacy, University of North Carolina Hospitals, Chapel Hill, NC 27599, USA.
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Ford
authors.forename: Caron P
authors.initials: CP
authors.lastname: Misita
authors.forename: Betsy Bryant
authors.initials: BB
authors.lastname: Shilliday
authors.forename: Robert M
authors.initials: RM
authors.lastname: Malone
authors.forename: Charity G
authors.initials: CG
authors.lastname: Moore
authors.forename: Stephan
authors.initials: S
authors.lastname: Moll
mesh_terms: D000925:Anticoagulants / Q000008:administration & dosage / Q000627:therapeutic use*; D018592:Cross-Over Studies; D019587:Dietary Supplements; D006801:Humans; D019934:International Normalized Ratio; D011446:Prospective Studies; D015203:Reproducibility of Results; D014812:Vitamin K / Q000008:administration & dosage / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D014812:Vitamin K