Oct 28 (Reuters) - A federal court in Massachusetts issued a preliminary injunction on Friday barring Amphastar Pharmaceuticals Inc. and two others from launching their generic version of blood thinner Lovenox until it reaches a decision on a patent challenge by Momenta and Sandoz.

Momenta and Sandoz launched a generic version of Sanofi-Aventis' blockbuster Lovenox in June last year. They claim that the defendants' generic version infringes a process over which they have a patent.

The court found that the plaintiffs met the four burdens they were required to demonstrate in order for the court to issue an injunction. In particular, the court found that Momenta and Sandoz had demonstrated that their patent challenge was likely to succeed on the merits.

The case is Momenta Pharmaceuticals Inc. and Sandoz Inc. v. Amphastar Pharmaceuticals Inc., International Medication Systems Ltd. and Watson Pharmaceuticals Inc. in U.S. District Court, District of Massachusetts, No. 11-11681

For the plaintiffs: Not immediately available.

For the defendants: Not immediately available.

(Reporting by Anand Basu; additional reporting by Rebecca Hailton)

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