It's one thing to beat down your potential competitor, but it's another thing to do it again and again. That's exactly what's happening with Bayer and Johnson & Johnson's (NYSE:JNJ) thrashing of Sanofi-Aventis' (NYSE:SNY) Lovenox.

Then again, drug development isn't for the faint of heart.

In the latest trouncing, the duo presented data on Friday showing that their anticoagulant drug candidate, rivaroxaban, reduced the risk of blood clots by 31% compared to Lovenox in patients undergoing knee replacement surgery, while keeping the risk of major bleeding, the most worrisome side effect of anticoagulants, virtually the same.

This is the fourth time rivaroxaban has trumped Lovenox in a phase 3 trial, but it's the most important trial for the U.S. approval because it compared rivaroxaban to a twice-daily 30 milligram dosage of Lovenox -- the standard treatment in the United States. Johnson & Johnson has been waiting on this data to submit the marketing application with the FDA; Bayer has already submitted its European marketing application based on the previous trial results.

Lovenox will face even more competition in the future. Partners Bristol-Myers Squibb (NYSE:BMY) and Pfizer (NYSE:PFE) have a similar anticoagulant, apixaban, farther back in the development cycle.

Not only is the continued success of rivaroxaban and potentially apixaban a blow to Sanofi, but the launch of the drug may also hurt Teva Pharmaceuticals (NASDAQ:TEVA), Momenta Pharmaceuticals (NASDAQ:MNTA), and Novartis (NYSE:NVS), all of which are developing generic versions of Lovenox. Since Lovenox is a complex molecule, these companies have invested a lot more time and money in generic Lovenox than they would in knockoffs of the average pharmaceutical drug.

It looks like there's about to be bloodshed in the anticoagulant, and Lovenox isn't the drug to stop the bleeding -- literally or figuratively.

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