MONDAY, Nov. 15 (HealthDay News) -- A new blood thinner might be
a viable alternative to warfarin (Coumadin), the standard for
decades to treat patients with the dangerous heart rhythm disorder
known as atrial fibrillation.
In research presented Monday at the American Heart Association's
annual meeting in Chicago, researchers reported that rivaroxaban
(Xarelto) proved to be just as good as warfarin, and possibly
Rivaroxaban also reduced the risk of serious bleeding events,
which is the most troubling side effect of warfarin. Dabigatran
(Pradaxa), another newer-generation blood thinner, was approved by
the U.S. Food and Drug Administration to treat atrial fibrillation
This latest study was sponsored by Johnson & Johnson
Pharmaceutical Research & Development and Bayer Healthcare, the
makers of rivaroxaban.
Warfarin is the mainstay for the treatment of patients with
atrial fibrillation, which affects some 2.2 million Americans.
During atrial fibrillation, the heart's two small upper chambers --
called the atria -- quiver rather than beat methodically, raising
the risk of blood clots and eventually a stroke.
The drug is effective in reducing the risk of stroke, but it has
significant drawbacks, including the bleeding risk and difficulties
with dosing and monitoring.
"In October of 2006, the FDA [U.S. Food and Drug Administration] issued a black-box warning for warfarin due to a growing appreciation of its hazards in routine clinical practice," said Dr. Elaine Hylek, who spoke at a Monday news conference on the findings, although she was not involved with the mammoth study. "The requirement for monitoring has relegated millions of people to no therapy or ineffective therapy because of lack of access to monitoring and an intense search for an alternative with more predictable dose responses."
Hylek is an associate professor of medicine at Boston University
School of Medicine and reported ties with several pharmaceutical
The latest trial, which scientists said was the largest of its
kind, involved an international collaboration of researchers in 45
countries, 1,215 medical centers and 14,269 patients with atrial
fibrillation who had already had a stroke or who had risk factors
for a stroke.
"This was a very high-risk population, with multiple problems where a lot of bad stuff could happen," said study co-chair Dr. Robert M. Califf, vice chancellor for clinical research at Duke University School of Medicine and director of the Duke Translational Medicine Institute in Durham, N.C. "They're the patients we most need to protect because they're so vulnerable."
Participants, median age 73, were randomly assigned to receive
rivaroxaban or warfarin.
When only patients who actually finished the trial (those who
continued to take the drug) were analyzed, rivaroxaban showed a 21
percent reduced risk for stroke and non-CNS systemic embolism -- a
type of blood clot.
But in the so-called "intention-to-treat" analysis, which looks
at all participants, including those who stopped taking the drug,
rivaroxaban did not surpass warfarin in preventing stroke or blood
clots, raising questions as to how it would do in actual practice.
The intention-to-treat analysis is considered the gold standard for
demonstrating a drug's superiority over another drug, Califf
"In a [real-world] environment where patients are going to come on and off drugs, rivaroxaban didn't meet statistical significance for superiority [against warfarin]," said Hylek. "I think it would be a more iron-clad situation [in terms of demonstrating superiority] if the intention-to-treat analysis demonstrated superiority."
Hylek added that she was not "embracing the superiority of
rivaroxaban, but it's important that the new kid on the block is
saying, 'I'm not inferior to you,' given that so many people can't
take warfarin because of monitoring problems."
Califf said use of the new drug would be left to "clinical
judgment" and emphasized the superiority of the drug in the first
There were also fewer heart attacks and fewer deaths with
rivaroxaban, although these differences were not statistically
American Heart Association has more on atrial
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