Use and effectiveness of warfarin in Medicare beneficiaries with atrial fibrillation.
OBJECTIVE
More than 2 million Americans have atrial fibrillation, and without antithrombotic therapy, their stroke rate is increased 5-fold. In randomized controlled trials, warfarin prevented 65% of ischemic strokes (hazard ratio [HR], 0.35; 95% CI, 0.26 to 0.48) compared with no antithrombotic therapy. However, the effectiveness of warfarin therapy outside of clinical trials is unknown, especially in black and Hispanic populations. Our goal was to quantify use of warfarin therapy, frequency of International Normalized Ratio monitoring, and effectiveness for stroke prophylaxis in Medicare beneficiaries with atrial fibrillation.


METHODS
This was a cohort study of Medicare beneficiaries with atrial fibrillation who were hospitalized between March 1998 and April 1999 in all 50 US states. The primary outcome was incident hospitalizations for ischemic stroke based on validated International Classification of Diseases, 9th Revision, Clinical Modification codes.


RESULTS
Two thirds of ideal anticoagulation candidates were prescribed warfarin on hospital discharge. In unadjusted analyses, the stroke rates per 100 patient years of warfarin therapy were 5.2 in (non-Hispanic) white Medicare beneficiaries, 10.6 in black beneficiaries, and 12.2 in Hispanic beneficiaries. After adjusting for comorbid conditions, warfarin prescription was more frequent and monitoring more regular in white Medicare beneficiaries than in black or Hispanic beneficiaries (P<0.0001). Warfarin use was associated with 35% fewer ischemic strokes (HR, 0.65; 95% CI, 0.55 to 0.76) compared with no antithrombotic therapy but was less effective in black and Hispanic beneficiaries (P for interaction=0.048).


CONCLUSIONS
The use, monitoring, and effectiveness of warfarin therapy are suboptimal in Medicare beneficiaries, especially in black and Hispanic beneficiaries.
Birman-Deych
Elena
E
Washington University School of Medicine, St. Louis, MO 63110, USA.
Radford
Martha J
MJ
Nilasena
David S
DS
Gage
Brian F
BF
D000368:Aged; D000925:Anticoagulants / Q000627:therapeutic use*; D001281:Atrial Fibrillation / Q000188:drug therapy*; D044383:Black People / Q000706:statistics & numerical data; D002545:Brain Ischemia / Q000150:complications; D015331:Cohort Studies; D005260:Female; D006630:Hispanic or Latino / Q000706:statistics & numerical data; D006760:Hospitalization; D006801:Humans; D008297:Male; D006278:Medicare; D010359:Patient Readmission / Q000706:statistics & numerical data; D011159:Population Surveillance; D020521:Stroke / Q000208:ethnology / Q000209:etiology / Q000628:therapy; D016896:Treatment Outcome; D014859:Warfarin / Q000627:therapeutic use*
D000925:Anticoagulants; D014859:Warfarin