title: Dietary vitamin K intake and stability of anticoagulation with coumarins: evidence derived from a clinical trial.
abstract: BACKGROUND
  Dietary vitamin K intake has been considered a major factor that influences stability of oral anticoagulation (OA) with coumarins. Few studies have evaluated the relationship between amounts of dietary vitamin K intake and stability of anticoagulation.
  
  
  OBJECTIVE
  To assess whether high dietary vitamin K intake is associated to stability of International Normalized Ratio (INR) of the prothrombin time.
  
  
  METHODS
  We performed a sub-analysis of a randomized clinical trial involving outpatients from the anticoagulation clinic of a university hospital. INR and vitamin K intake were prospectively collected at baseline, 15, 30, 60 and 90 days after randomization. Patients were considered with a stable anticoagulation when their INR coefficient of variation was less than 10%. Dietary vitamin K intake was assessed by a food frequency questionnair and a score of intake was derived.
  
  
  RESULTS
  We studied 132 patients on chronic OA (57 ± 13 years; 55% males); 23 patients (17%) were achieved stable anticoagulation. Stable and unstable patients had no significant differences in baseline characteristics. The dietary vitamin K score over the entire follow-up for stable patients was significantly lower than that for unstable patients (p = 0.012).
  
  
  CONCLUSIONS
  Our findings suggest that INR stability could be achieved with relatively low amounts of dietary vitamin K.
authors.affiliation: Medical School, Federal University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: P
authors.initials: P
authors.lastname: Zuchinali
authors.forename: G C
authors.initials: GC
authors.lastname: Souza
authors.forename: M C S
authors.initials: MC
authors.lastname: de Assis
authors.forename: E R
authors.initials: ER
authors.lastname: Rabelo
authors.forename: L E
authors.initials: LE
authors.lastname: Rohde
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000494:pharmacology*; D002908:Chronic Disease; D003374:Coumarins / Q000494:pharmacology*; D004032:Diet; D005260:Female; D018565:Food-Drug Interactions; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D014812:Vitamin K / Q000008:administration & dosage*
chemical_list: D000925:Anticoagulants; D003374:Coumarins; D014812:Vitamin K