Most patients with the condition take a blood thinner to reduce the risk of stroke. Although these drugs help prevent stroke, they can also cause uncontrollable bleeding, which can be fatal, the researchers said.
Two newer drugs -- Xarelto (rivaroxaban) and Pradaxa (dabigatran) -- are replacing the older drug warfarin, a medication that is notoriously difficult to monitor. Which of these newer drugs is safer, however, hasn't been proven, said the U.S. Food and Drug Administration researchers behind the new study.
"There are now several new oral anticoagulants and we don't have a lot of studies that compare one to the other," said Dr. Rita Redberg. A professor of cardiology at the University of California, San Francisco, she had no role in the study.
"As a patient, you are making a decision with your doctor on how these compare with warfarin, and which one is right for you," she said.
In this study, Xarelto seemed to have a "slight increased risk of bleeding," Redberg said.
The study findings were published online Oct. 3 in the journal JAMA Internal Medicine.
The advantage of these new drugs is that, unlike warfarin, these drugs don't require frequent blood tests to ensure patients are getting the proper dose, Redberg explained.
On the downside, until recently there was no antidote for these drugs should major bleeding occur, Redberg said. "There have been deaths reported of people who have had trauma and were on one of these new anticoagulants, and they were not able to be reversed," she said.
But, a drug that reverses the effect of Pradaxa was approved recently, said Redberg, who co-wrote a journal editorial that accompanied the study.
Knowing which drug option is best is complicated, Redberg said. Patients should discuss the risks and benefits of each of these drugs with their doctor, she stressed.
For the study, researchers led by Dr. David Graham, associate director of science at the FDA's Center for Drug Evaluation and Research, collected data on nearly 119,000 Medicare patients with atrial fibrillation treated with either Xarelto or Pradaxa from November 2011 through June 2014.
The researchers found little difference in stroke risk among patients taking either Pradaxa or Xarelto. But, there was a small yet statistically significant increase in risk of bleeding in the brain and stomach of patients taking Xarelto. And among certain patients 75 and older, Xarelto was associated with a small but statistically significant increased risk of death.
However, the study did not prove that Xarelto caused bleeding or death, just that there was an association.
Sarah Freeman, a spokeswoman for Janssen Pharmaceuticals, which makes Xarelto, said the company has reported all safety data to the FDA and denies "the central premise of the [new] report."
"With more than 23 million patients prescribed Xarelto worldwide, real-world evidence continues to confirm the positive benefit-risk profile of Xarelto," she said.
"Xarelto, too, has been thoroughly evaluated across its approved indications in real-world research following the medicine's approval, and study after study confirm that Xarelto is performing as expected," Freeman said.
A cardiologist not connected to the study said the FDA researchers' findings need to be replicated in a randomized trial before they can be taken as gospel.
"Randomized trials have shown that Pradaxa and Xarelto are better or as good as warfarin in preventing stroke in patients with atrial fibrillation," said Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles.
"These studies have also shown that the newer agents significantly reduce the risk of intracranial hemorrhage compared with warfarin," Fonarow added.
But because this new study looked at patients already taking these newer drugs and wasn't a trial that randomly assigned patients to one drug or the other, it wasn't a real head-to-head comparison, Fonarow said. So the "validity and clinical implications of these findings are uncertain," he said.
"Addressing the comparative effectiveness and safety of these drugs will require randomized clinical trials," Fonarow added.
Visit the American Heart Association for more on atrial fibrillation.
Copyright © 2016 HealthDay. All rights reserved.