Bayer drug's safety comparable to standard care-study

* Safety record keeps Xarelto on track in new drug race

* Attention turns to stroke prevention study in Nov

STOCKHOLM, Aug 31 (Reuters) - Bayer's (BAYGn.DE) anticoagulant Xarelto showed a similar safety profile compared with standard therapy in clinical trial results released on Tuesday, keeping it in the multibillion-dollar race to replace the old and troublesome drug warfarin.

Experts had been waiting to see details of the study, after the German drugmaker announced on Aug. 4 that Xarelto was as good at dissolving potentially deadly clots in the legs and preventing new ones as the standard treatment of injecting Sanofi-Aventis's (SASY.PA) Lovenox, followed by warfarin pills.

A key worry has been that Bayer's potent new oral medicine might cause excessive bleeding. In fact, the incidence of major and non-major clinically relevant bleeds was identical in both treatment groups, at 8.1 percent.

The number of major bleeds was, in fact, lower in the Xarelto arm of the 3,400-patient trial at 14 compared with 20 in the Lovenox plus warfarin arm, although the difference was not significantly different.

Overall net clinical benefit -- a measure of primary efficacy outcome plus major bleeding -- favoured Xarelto, with 2.9 percent of patients on Bayer's medicine having a negative outcome against 4.2 percent of those on standard care.

There was no signal of liver toxicity, an issue that has concerned doctors with new types of anticoagulants.

Bayer and its partner Johnson & Johnson (JNJ.N) are training their sights on an emerging warfarin-replacement market estimated at more than $10 billion a year. Bayer has said Xarelto, or rivaroxaban, could eventually generate more than 2 billion euros ($2.5 billion) in annual sales.

The big opportunity for new anticoagulants lies in preventing strokes in patients with irregular heartbeats. In that market, Bayer's unlisted German rival Boehringer Ingelheim is in the lead with a product called Pradaxa that will be reviewed by a U.S. regulatory panel next month.

Bristol-Myers Squibb (BMY.N) and Pfizer (PFE.N) also presented new data on their experimental apixaban in stroke prevention at the Stockholm conference.

Results of a second Xarelto study looking at Bayer's drug when given to significantly older patients as a stroke preventer will be presented at the American Heart Association annual meeting in November.

(Reporting by Ben Hirschler; Editing by Erica Billingham)