Study: Warfarin May Not Stabilize Atrial Fibrillation Patients

Prescribing warfarin to prevent strokes may not consistently control blood clotting in atrial fibrillation patients, even those who have historically been stable on the drug, according to a new study.  

A team of researchers led by Sean D. Pokorney, MD, MBA, an electrophysiology fellow at Duke University School of Medicine, analyzed data from patients in the Duke Clinical Research Institute's Outcomes Registry for Better Informed Treatment of Atrial Fibrillation. Patients taking warfarin were eligible to participate in the study, for which the authors focused on the international normalized ratio (INR).
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INR is typically measured monthly for patients being administered warfarin and should fall between 2 and 3. Throughout the first 6 months of the study, 968 patients (26% of those taking warfarin) had 80% or more of their INR values within this range, while 376 patients (10% of warfarin patients) had 100% of their INR values in this range. Participants were monitored for an additional 12 months. During this time, patients were considered stable if 80% or more of their INR values fell between 2 and 3.

In evaluating patients in the 80% group, the authors found that 34% of these participants remained stable during the 12-month monitoring period, while 37% of those in the 100% group remained stable in that span. The researchers also noted that roughly one-third of patients in both the 80% and 100% groups had one or more INR values that were far from the ideal range during the subsequent year.

These results are "particularly important for primary care providers, as they are often the providers who are managing a patient's warfarin," Dr Pokorney said.

"There are a lot of atrial fibrillation patients who have been on warfarin for years, and they have not been switched to a non-vitamin K oral anticoagulant (NOAC), because there is a belief that NOACs are for patients who do not do well on warfarin and are not necessarily for patients who are doing well on warfarin," he continued.

This study "really challenges the idea of keeping those patients on warfarin," he said, "because even patients who have been very stable on warfarin are likely to become unstable at some point, putting those patients at increased risk of stroke or bleeding events."

Before this study's findings emerged, "it seemed reasonable to keep patients on warfarin, who had been stable on warfarin in the past, because we believed that they were likely to remain stable in the future," Dr Pokorney said. Unfortunately, "so many different things affect warfarin, [such as] illness, medication, and foods, that past performance on warfarin is not a good predictor of future performance," he said.

Therefore, Dr Pokorney said, primary care providers should engage all eligible patients on warfarin in shared decision-making to consider switching to a NOAC, even if they have been on warfarin for a long time and have done well on it in the past.

—Mark McGraw

Reference:
Pokorney SD, Simon DN, Thomas L, et al. Stability of international normalized ratios in patients taking long-term warfarin therapy. JAMA. 2016;316(6):661-663.