A new stroke preventer from Bayer and Johnson & Johnson moved one step closer to U.S. approval, but questions remained about restrictions on labeling and the need for more studies.

A Food and Drug Administration advisory panel voted 9-2 on Thursday to recommend approval of the once-a-day anti-clotting pill, called Xarelto.

Xarelto is one of several promising entrants angling to replace warfarin for people with dangerously irregular heart rhythms, called atrial fibrillation (AF).

Warfarin is a problematic decades-old clot preventer originally developed as rat poison.

"I've seen the problems many patients face with warfarin," said Dr. Philip Sager, a panel member and executive committee member of the Cardiac Safety Research Consortium in San Francisco.

"I think there's a tremendous unmet medical need for new therapies," Sager said.

Analysts estimate the stroke-fighting market could top $10 billion annually.

AF patients' irregular heartbeats can cause blood to pool, increasing their risk of blood clots and strokes. But many are unwilling to take warfarin, which requires regular blood tests, or are unable to tolerate it.

Panelists were divided on whether Xarelto was as effective as warfarin.

In clinical trials that compared Xarelto to warfarin, panelists and the FDA said the older drug was not always given in the proper dosing, making it more difficult to determine if Xarelto was just as good.

Earlier this week, FDA reviewers said for conditions such as stroke, which can cause irreversible harm, new drugs must be shown to be at least as effective as older treatments.

They also focused on risks for patients when they come off the drug. When patients stopped taking Xarelto and resumed warfarin at the end of the main clinical trial, higher risk of stroke was seen, a so-called "rebound" effect.

"Additional data probably should be obtained regarding how to transition (off of Xarelto) prior to approval," said Dr. Michael Lincoff, chair of the panel and professor of medicine at the Cleveland Clinic.

The FDA is set to make the final decision on Xarelto in early November, Johnson & Johnson said.

The drug is approved in the United States and Europe for anti-clotting in patients after knee and hip surgery, a much smaller market than stroke prevention for AF patients.