(Adds comment from Momenta, updates stock price)
BOSTON, July 21 (Reuters) - A federal jury handed Amphastar Pharmaceuticals Inc a big win on Friday after it was accused of infringing on a patent held by Momenta Pharmaceuticals Inc through its production of a generic version of the blood-thinner Lovenox.
The verdict by the jury in Boston came in a lawsuit by Cambridge, Massachusetts-based biotechnology company Momenta and its partner, Novartis AG's Sandoz unit, that sought nearly $940 million in damages.
The jury found that while Rancho Cucamonga, California-based Amphastar had infringed Momenta's patent, it was invalid and unenforceable.
"We're extremely pleased with the jury verdict and that Amphastar is finally out from under this baseless lawsuit," said Michael Sommer, a lawyer for Amphastar.
Momenta Chief Executive Craig Wheeler in a statement said the company was disappointed and was considering its options, including a potential appeal.
"We continue to believe in the importance of investing in innovative techniques for bringing products to market and protecting those innovations from unauthorized use," he said.
Following the verdict, Amphastar's stock price rose 2.29 percent to $18.33 while Momenta's fell 2.32 percent to $16.85 on the NASDAQ stock exchange.
Sandoz did not respond to requests for comment.
Momenta and Sandoz filed the lawsuit in 2011 after the U.S. Food and Drug Administration approved Amphastar's generic version of Sanofi SA's blockbuster Lovenox, an anticoagulant used to treat and prevent blood clots.
Momenta claimed Amphastar infringed its patent covering a method used to confirm the structural signature of Lovenox, known generically as enoxaparin.
Momenta, whose generic version Lovenox was the first to receive FDA approval in 2010, claimed Amphastar's infringement and subsequent sales of its own generic caused it to suffer a significant loss of profits.
Momenta and Sandoz sought damages of $938 million. Sommer, Amphastar's lawyer, told jurors on Thursday during closing arguments that such an award would "wipe out Amphastar altogether."
Amphastar argued Momenta's goal was to avoid further competition for generic versions of Lovenox, which earned Sanofi $2.9 billion in sales in 2009, the year before Momenta's version was approved.
Before the trial, the case reached the U.S. Federal Circuit Court of Appeals twice, leading to reversals of an injunction against Amphastar in 2012 and a later ruling granting judgment in Amphastar's favor in 2015.
When they obtained the injunction, Momenta and Sandoz were required to post a $100.1 million bond, which Amphastar has said that it plans to try to collect should it prevail in the case.
The case is Momenta Pharmaceuticals, Inc. et al v. Amphastar Pharmaceuticals, Inc. et al, U.S. District Court, District of Massachusetts, No. 11-cv-11681. (Reporting by Nate Raymond in Boston; editing by Grant McCool and Tom Brown)