Momenta Pharmaceuticals (Nasdaq: MNTA) has won a spot on the U.S. market for its first drug. The Cambridge, MA-based biotech company said today that the FDA has approved a generic version of a common anti-clotting drug developed by Momenta and Sandoz, a unit of Novartis. The news sent Momenta stock rocketing up 77 percent by noon Eastern Time.

The FDA said M-enoxaparin, a drug designed to have the same anti-clotting effect as Sanofi-Aventis' (NYSE: SNY) enoxaparin, had passed the necessary studies to be sold in the U.S. The market is potentially huge, as Lovenox generated $4.1 billion in sales for Sanofi last year, making it the Paris-based company's second-biggest seller. It's the first time Momenta has proven it can make therapeutic equivalents to complex mixture drugs, which are harder to copy than conventional small molecule pills.

"We are extremely pleased," said Craig Wheeler, Momenta's CEO, in a statement.

Of course, this being the generics business, Momenta isn't the only company eyeing this market. Last August, the Wall Street Journal reported that a competitor made an ethics complaint about the FDA handling of Momenta's application for M-enoxaparin. Amphastar Pharmaceuticals, of Rancho Cucamonga, CA, alleged that Momenta had special access to Janet Woodcock, a top FDA official, while both firms were seeking approval for generic versions of enoxaparin. The complaint said Woodcock was a co-author with Momenta scientists on two scientific papers published in 2008.

Momenta made a brief nod toward Amphastar, and another rival, Teva Pharmaceuticals, in today's statement. "The company is aware that other ANDAs for enoxaparin sodium injection have been filed. These other applicants may receive approval at a later date," Momenta said.

Shares of Momenta climbed 77 percent to $21.10 at noon Eastern Time today. Momenta is hosting a conference call at 1 pm ET to discuss the news in greater detail.

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Luke Timmerman is the National Biotech Editor of Xconomy, and the Editor of Xconomy Seattle. You can e-mail him at [email protected], or follow him at twitter.com/ldtimmerman.