title: Warfarin doses for anticoagulation therapy in elderly patients with chronic atrial fibrillation.
abstract: OBJECTIVE
  Anticoagulation is a challenge for the prophylaxis of thromboembolic events in elderly patients with chronic atrial fibrillation. Stable anticoagulation is defined as the time within >70% of the therapeutic range. However, the dosage required to achieve stable anticoagulation remains unknown. The aim of this study was to analyze the warfarin dose necessary for the maintenance of stable oral anticoagulation therapy in elderly patients.
  
  
  METHODS
  We analyzed 112 consecutive outpatients with atrial fibrillation who were >65 years of age, had received anticoagulation therapy with warfarin for more than 1 year and had a stable international normalized ratio between 2.0 and 3.0 for >6 months. The international normalized ratio was measured in the central laboratory using the traditional method.
  
  
  RESULTS
  The patients were stratified according to the following age groups: <75 or >75 years and <80 or >80 years. The mean daily doses of warfarin were similar for patients <75 or >75 years (3.34+1.71 versus 3.26 +1.27 mg/ day, p = 0.794) and <80 or >80 years (3.36+ 1.49 versus 3.15 + 1.23 mg/day, p = 0.433). In 88 (79%) patients, the daily warfarin dose was between 2 and 5 mg/day; in 13 (11%) patients, the daily warfarin dose was <2.0 mg/day; and in 11 (10%) patients, the daily warfarin dose was >5.0 mg/day. The correlation between the daily warfarin dose and the international normalized ratio was 0.22 (p = 0.012).
  
  
  CONCLUSIONS
  Stable anticoagulation was achieved in 80% of patients who received doses of 2 to 5 mg/day of warfarin, and the mean daily dose was similar across the age groups analyzed.
authors: Heart Institute, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP, Brazil. corantonio@incor.usp.br
authors: Antonio de Padua
authors: Ade P
authors: Mansur
authors: Julio Yoshio
authors: JY
authors: Takada
authors: Solange Desiree
authors: SD
authors: Avakian
authors: Celia M C
authors: CM
authors: Strunz
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage*; D001281:Atrial Fibrillation / Q000097:blood*; D016009:Chi-Square Distribution; D002908:Chronic Disease; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D012016:Reference Values; D013997:Time Factors; D016896:Treatment Outcome; D014859:Warfarin / Q000008:administration & dosage*
chemical_list: D000925:Anticoagulants; D014859:Warfarin