Bayer AG's experimental pill rivaroxaban is significantly more effective than standard injections of Lovenox in preventing blood clots after knee surgery, researchers said on Sunday.

The news confirms the German drugmaker's leadership in the multibillion-dollar race to bring a new class of oral anticoagulants to market.

Results of a large Phase III trial showed only 9.6 percent of patients given rivaroxaban experienced venous thromboembolism (VTE), or blood clots, following total knee replacement against 18.9 percent of those on Sanofi-Aventis SA's Lovenox.

Major life-threatening VTE occurred in 1 percent of rivaroxaban patients against 2.6 percent for the Lovenox group.

Lead investigator Dr. Michael Lassen, an orthopaedic surgeon at Hoersholm Hospital, University of Copenhagen, said it was exciting that a once-daily pill had proved better than the current gold standard injection therapy.

It's very important, he said in a telephone interview. Instead of having an injectable when a patient goes home, it is much more convenient with an oral drug and there is also no need for monitoring.

Lassen presented results from the 2,531-patient study at the International Society on Thrombosis and Haemostasis meeting in Geneva.

Bayer and rivals have been seeking new anticoagulants since Exanta, a once-promising medicine from AstraZeneca Plc, failed to win U.S. Food and Drug Administration approval in 2004 after being associated with liver toxicity.

Lassen told Reuters there was no signal whatsoever of similar problems with rivaroxaban.

Rates of major bleeds -- always a risk with anticoagulants -- were similarly low with both rivaroxaban and Lovenox at 0.6 and 0.5 percent respectively. There were no indications of cardiovascular problems, with two heart attacks seen in both arms of the trial, Lassen added.


Bayer, which is co-developing rivaroxaban with Johnson & Johnson (JNJ.N: Quote, Profile, Research), aims to submit the drug for approval as a treatment to stop clots after surgery later this year in Europe and in 2008 in the United States.

But the lion's share of eventual sales, which Bayer believes could exceed 2 billion euros ($2.7 billion) a year, are expected to come from its use as a chronic therapy to prevent stroke in patients with atrial fibrillation, a common heart arrhythmia.

In this setting, it would replace warfarin, sold by Bristol-Myers Squibb Co. under the name Coumadin but also widely available as a generic. Warfarin is notoriously difficult to tolerate because of its interactions with food and other medicines, necessitating constant blood tests.

Bayer expects rivaroxaban to be filed for use in stroke prevention in 2010.

Rivaroxaban works by blocking a protein called Factor Xa, which plays an early role in the chemical process leading to blood clots.

Bayer is not alone in targeting Factor Xa. Bristol-Myers, working with Pfizer Inc., has a similar product called apixaban less than a year behind in development. Others in the race include Eli Lilly Co.

Bayer believes it has an edge over apixaban because rivaroxaban is given just once-daily while apixaban must be taken twice. But some industry analysts believe a once-daily dose could be a gamble if it proves less effective in the ongoing stroke trials.