Meta-analysis of 2001-2011 warfarin use shows decline in stroke rates compared with earlier studies
by Alexander R. Carbo, MD, SFHM, Jonathan T. Crocker, MD, Lauren Doctoroff, MD, FHM, Elizabeth Farrell, MD, Rebecca Newlin Hutchinson, MD, MPH, Hospital Medicine Program, Beth Israel Deaconess Medical Center, Boston
Clinical question: With the current use of warfarin for stroke prophylaxis in patients with nonvalvular atrial fibrillation, what do the most recent data show with regard to time spent in the therapeutic window, stroke risk, and bleeding risk?
Background: Historically, warfarin has been shown to decrease stroke risk in nonvalvular atrial fibrillation by 62% compared with placebo, balanced by a significant risk of bleeding. Despite the availability of multiple new antithrombotic agents, warfarin will likely continue to be widely used given its lower cost. As a result, physicians need an accurate estimate of warfarin’s efficacy and safety as currently used in practice.
Study design: Meta-analysis of randomized controlled trials (RCTs).
Setting: RCTs comparing warfarin to an alternative antithrombotic agent from 2001 to 2011.
Synopsis: Eight RCTs of nonvalvular atrial fibrillation were included, yielding data on 32,053 patients with a mean age range of 70 to 82 years and widely variable CHADS2 scores. The time spent at a therapeutic INR was found to be improved when compared to historical rates, ranging from 55% to 68%. The rate of stroke or non-central-nervous-system embolism ranged from 1.2% to 2.3% per year, with a pooled event rate of 1.66% per year, compared with 2.09% per year in earlier trials.
Major bleeding was defined differently across studies, with a reported incidence of 1.4% to 3.4% per year, a pooled event rate of intracranial hemorrhage of 0.61%, and a cumulative adverse event rate of 3.0% to 7.64%. Stroke rates were highest in patients older than 75 years, women, those with a history of transient ischemic attack or stroke, those new to warfarin, and those with higher CHADS2 scores.
Bottom line: Warfarin as currently used is associated with an annual rate of stroke or systemic embolism of 1.66% and an annual rate of major bleeding ranging from 1.4% to 3.4%.
Citation: Agarwal S, Hachamovitch R, Menon V. Current trial-associated outcomes with warfarin in prevention of stroke in patients with nonvalvular atrial fibrillation: a meta-analysis. Arch Intern Med. 2012;172:623-631.
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