WEDNESDAY, May 23 (HealthDay News) -- An advisory panel to the U.S. Food and Drug Administration on Wednesday voted against a new use of a new blood thinner, Xarelto, to cut the risk of potentially lethal clots in people with acute coronary syndrome.

The panel of experts voted 6-to-4, with one member abstaining, against using the drug in these high-risk patients. Panel members said there wasn't enough data in company studies to definitively assess the medication's benefit at this time, the Associated Press reported.

The decision came as something of a surprise, since FDA briefing documents filed Monday in advance of the panel meeting looked more favorably on the drug.

A final decision from the FDA is expected June 29. The FDA is not required to follow the advice of its advisory panels, but it typically does.

Xarelto (rivaroxaban) is one of a new class of blood thinners that has been developed to overcome some of the problems that exist with the standard treatment, warfarin (Coumadin), which requires constant dose monitoring. Warfarin's effectiveness also can be altered by certain foods and other medications. Xarelto is already approved for use by those with atrial fibrillation (irregular heartbeat) and by people who are having hip- or knee-replacement surgery.

In the FDA briefing documents released Monday, an agency reviewer recommended approving the drug for treatment of acute coronary syndrome, mostly because trial data showed there was a reduction in cardiovascular death, even though there was also an increased risk of potentially fatal bleeding.

But the panel on Wednesday expressed concerns about a lack of data on potential side effects.

"What is not reflected in the sponsor's analysis are minor bleeding events," FDA reviewer Dr. Karen Hicks wrote in the briefing documents. "While it is true that these bleeding events typically do not lead to death or irreversible harm, these events may represent the biggest problem for both patients and health care providers if rivaroxaban is approved.

"While reductions in [cardiovascular] death still trump these bleeding events, if rivaroxaban is approved, we should expect a number of bleeding events that will require medical attention," Hicks wrote. "Carefully selecting patients for rivaroxaban therapy will be necessary to mitigate these bleeding risks."

In research presented at the American Stroke Association's International Stroke Conference in New Orleans in February, Australian doctors followed more than 14,000 people who took either Xarelto or warfarin for a median of two years. Of those patients, 136 had bleeding in the brain.

People who took Xarelto -- and suffered from the most common type of atrial fibrillation and didn't have heart valve damage -- were about one-third less likely to experience bleeding in the brain than those who took warfarin, the investigators found.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about stroke.