Atrial fibrillation patients not achieving long-term stability with warfarin therapy

By Liz Meszaros, MDLinx
Published August 15, 2016

Key Takeaways

Over the long-term, warfarin may not control blood clotting in patients with atrial fibrillation, even in patients who have been stable on the drug for long periods, according to researchers from the Duke Clinical Research Institute, who have published their results in the August 9, 2016 issue of the Journal of the American Medical Association (JAMA).

Historically, warfarin has been the only agent available for patients with atrial fibrillation to lower their heightened risk for blood clots and stroke. Since 2010, however, the non-vitamin K oral anticoagulants (NOACs) have been available, and these circumvent the negative side effects of warfarin, which can interact negatively with other drugs and food and requires regular monitoring of patients.

“For these reasons, the majority of patients who are newly-diagnosed with atrial fibrillation are prescribed NOACs,” said lead author Sean Pokorney, MD, electrophysiology fellow, Duke University School of Medicine, Durham, NC. “One of the challenges we face as a health-care community is that there are patients who have been on warfarin for years, and a big question is whether they should be switched to a NOAC,” he added.

Dr. Pokorney and colleagues conducted this 18-month study in 3,749 patients with atrial fibrillation treated with warfarin from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation, maintained by the Duke Clinical Research Institute.

They measured international normalized ratios (INR) monthly in warfarin-treated patients. Ideal levels range between 2 and 3, and patients were considered stable if 80% of their INR values ranged between 2 and 3.

In the first 6 months, only 26% of patients had most of their INR values (80%) fall within this 2 to 3 range, while 10% achieved this in 100% of INR values. In addition, researchers found that in the former group, only 34% of patients remained stable over the next 12 months; while in the latter group, only 30% did so. In addition, roughly one-third of patients from both groups had one or more INR values well out of the ideal range in the following year.

“What these results essentially tell us is that patients’ past performance on warfarin doesn’t predict their future performance,” said Dr. Pokorney. “Just because patients have done well on warfarin in the past doesn’t mean they will continue to do well, and so it does call into question whether it is appropriate to switch them to a NOAC.”

He added that the risk of clotting and stroke is increased most when INR values fall below 1.5, while the risk of neurologic bleeding increases significantly when these values rise above 4.

“It’s not appropriate for every patient to be treated with a NOAC, but this study shows that all patients eligible for a NOAC, even those who have done well on warfarin in the past, should have a shared decision-making conversation with their health-care provider about considering a change,” Dr. Pokorney concluded.

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