(CBS/AP) Scientists have been looking for alternatives to the anticoagulant warfarin for preventing strokes in patients with the heart rhythm disorder atria fibrillation. Last October, the FDA approved one new anticoagulant called Pradaxa (dabigatran), but the agency seems unlikely to approve another drug called Xarelto (rivaroxaban).
In a new report, the FDA said data from the ROCKET study of more than 14,000 patients didn't clearly show how safe Xarelto was, or whether it's as effective as the popular blood thinner warfarin.
"ROCKET does not show convincingly that rivaroxaban is as effective as warfarin when the latter is used skillfully," concluded the 388-page report.
The daily pill - developed by Johnson & Johnson and Germany's Bayer Healthcare -works by blocking a clotting protein called "factor Xa." Older blood thinners, including warfarin, work by preventing blood platelets from sticking together.
A final decision will be made once an outside panel reviews the FDA report, in addition to data from the drugmakers, this Thursday. The advisers will then vote whether to recommend that the FDA approves Xarelto for this use. FDA officials often follow advisers' recommendations, but aren't obligated to do so.
"We're confident in the effectiveness of rivaroxaban in preventing strokes in patients with atrial fibrillation and look forward to presenting our data to address the FDA's questions on Thursday," said J&J spokesman Ernie Kniewitz. "In our book, we've laid out a lot of points that support the effectiveness of rivaroxaban."
Bayer already markets rivaroxaban in 110 countries.
Drugmakers have been looking for an alternative to the inexpensive warfarin, sold as Coumadin and other brands, because the drug also has its drawbacks. It's notoriously difficult to find the correct dose a patient needs, often requiring patients to get frequent blood tests. Too much warfarin causes dangerous internal bleeding.
The FDA report stated that the study used to approve Pradaxa showed it clearly was superior to warfarin in preventing stroke and dangerous blood clots, whereas ROCKET failed to show the same for Xarelto.
Atrial fibrillation significantly ups the risk for blood clots that can travel to the brain via the bloodstream to cause a stroke. Anticoagulant therapy can cut this stroke risk dramatically. More than 2.2 million Americans have atrial fibrillation.
The National Institute of Neurological Disorders and Stroke has more on atrial fibrillation and stroke.