Lawsuits between branded drugmakers and their generic rivals happen almost every week it seems. Often it takes a lawsuit to figure out whether a patent is valid.

But the lawsuit filed by sanofi-aventis (NYSE: SNY) over a recently approved generic version of Lovenox is different. The French drugmaker is suing the U.S. Food and Drug Administration, asking the court to force the agency to take back the approval of the competing generic. Now that takes gumption.

Of course Lovenox, the drug in question, is a multibillion dollar franchise, and the complexity of the active ingredient makes Sanofi's argument somewhat reasonable. But still, claiming the FDA's decision will create "irreparable harm" is a slap in the face of the agency's scientific staff, a staff that Sanofi needs to approve the drugs currently in its pipeline. Wyeth sued the agency last year making a similar claim about generics, but the company was in the midst of disappearing into Pfizer (NYSE: PFE), so there was less risk of long-term repercussions.

Momenta Pharmaceuticals (Nasdaq: MNTA) fell 12% yesterday, which is a little surprising because the company said on Friday that they had expected the challenge from Sanofi. The company says the judge didn't invoke an injunction stopping its marketing partner, Novartis (NYSE: NVS), from selling the drug. A hearing is scheduled on August 17 to rule on a preliminary injunction.

Obviously anything can happen with the judge, but it's not like the FDA has taken this decision lightly, having taken many years to approve the generic. The agency has even passed over other applications -- so far -- from Teva Pharmaceuticals (Nasdaq: TEVA) and Amphastar Pharmaceuticals, so it's not a blanket endorsement that everyone has the capacity to make generic Lovenox.

Sure, there's some risk of Momenta losing its only product on the market, but that was theoretically true before Sanofi filed its lawsuit. If you're OK with that risk, Momenta is a little cheaper today than it was at the height of the post-approval euphoria.

Looking for more upcoming binary events? Jim Mueller highlights three to keep your eye on.