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Well-managed warfarin therapy may lower complication rates
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If patients assigned warfarin had adequate time in therapeutic range, the drug was associated with a low rate of complications, according to the results of a registry study.
Researchers conducted a retrospective cohort study based on Swedish registries of 40,449 patients (mean age, 72 years; 40% women; mean CHA2DS2-VASc score at baseline, 3.3) with atrial fibrillation commencing warfarin therapy for stroke prevention between 2006 and 2011. Follow-up was until death, cessation of warfarin therapy or Nov. 15, 2015, whichever came first.
Patients were stratified by whether they also were taking aspirin. The outcomes of interest were annual complication incidence associated with individual time in therapeutic range, variability of INR, aspirin use and factors related to intracranial bleeding.
Mortality, major bleeding low
Fredrik Björck, MD, and colleagues found that in the study cohort, the annual incidence of mortality was 2.19% (95% CI, 2.07-2.31) and the annual incidence of intracranial bleeding was 0.44% (95% CI, 0.39-0.49).
Patients also taking aspirin experienced any major bleeding at an annual rate of 3.07% (95% CI, 2.7-3.44) and experienced thromboembolism at an annual rate of 4.9% (95% CI, 4.43-5.37), Björck, from the department of public health and clinical medicine at Umeå University, Sundsvall, Sweden, and colleagues wrote.
The researchers also found that patients with renal failure had elevated risk for intracranial bleeding compared with patients without renal failure (HR = 2.25; 95% CI, 1.32-3.82).
In patients with individual time in therapeutic range less than 70%, the annual rate of any major bleeding was 3.81% (95% CI, 3.51-4.11) and the annual rate of any thromboembolism was 4.41% (95% CI, 4.09-4.73), according to the researchers.
In patients with high variability in INR, the annual rate of any major bleeding was 3.04% (95% CI, 2.85-3.24) and the annual rate of any thromboembolism was 3.48% (95% CI, 3.27-3.69), Björck and colleagues wrote.
The researchers determined that in patients with individual time in therapeutic range more than 70%, level of variability in INR had no effect on event rates.
“Well-managed warfarin treatment is a valid alternative in patients with AF who require anticoagulant treatments, with relatively low complication rates and low all-cause mortality,” Björck and colleagues wrote. “Therapy should be closely monitored in those with renal failure, concomitant aspirin use, and an [individual time in therapeutic range] less than 70% or a high [international normalized ratio] variability. The [individual time in therapeutic range] is a strong indicator of probability for both bleeding and thromboembolic events and should be maintained at 70% or greater.”
Caution on extrapolation
In a related editorial, John H. Alexander, MD, MHS, and Laine E. Thomas, PhD, both from Duke Clinical Research Institute, Duke Health, wrote that the analysis of the effect of INR on outcomes “is not designed in a way that can be used to inform patient prognosis nor treatment decisions regarding anticoagulation for patients with AF.”
“The real danger is that physicians and patients will use these findings to guide treatment decisions among warfarin-experienced or, worse, warfarin-naive patients,” Alexander and Thomas wrote. “It would be easy to inappropriately extrapolate these data because the results are consistent with the expectation that INR control matters and because other sources of information related to INR control ... are commonly available.” – by Erik Swain
Disclosure: Björck reports no relevant financial disclosures. See the full study for a list of the other researchers’ relevant financial disclosures. Alexander reports financial ties with Bristol-Myers Squibb, CSL Behring, Daiichi Sankyo, GlaxoSmithKline, Janssen, Pfizer, Portola, Sohmalution, Regado Biosciences, Sanofi, Tenax, Vivus and Xoma. Thomas reports financial ties with Bristol-Myers Squibb, Janssen Scientific Affairs and Pfizer.
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