New Blood Thinner a Promising Alternative to Warfarin

MONDAY Nov. 15, 2010 -- 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 superior.

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 last month.

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 companies.

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 explained.

"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 analysis.

There were also fewer heart attacks and fewer deaths with rivaroxaban, although these differences were not statistically significant.

More information

The American Heart Association has more on atrial fibrillation.

Posted: November 2010


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