By Dan Levine

May 7 (Reuters) - A U.S. appeals court has blocked the sale of Novartis AG's recently approved "biosimilar" form of Neupogen, Amgen Inc's blockbuster drug used to prevent infections in cancer patients.

A lower court judge rejected Amgen's request for an injunction. The U.S. Court of Appeals for the Federal Circuit ruled on Tuesday, however, that the injunction could take effect while Amgen's appeal is pending.

In a statement, Amgen said it is pleased with the ruling. A Novartis representative could not immediately be reached for comment on Thursday.

The Novartis drug, Zarxio, contains the same active ingredient as Amgen's $1.2 billion-a-year Neupogen, and once launched, would become the first biosimilar in the United States.

Because biosimilars are made in living cells, they are not considered exact duplicates of original brands. Insurers are hoping that biosimilars will be sold for discounts of 40 to 50 percent from the cost of original brands in the United States, but Novartis has not yet disclosed the intended U.S. price for Zarxio. Biosimilars have been on the market since 2006 in Europe.

The U.S. Food and Drug Administration in March approved Zarxio for the same five conditions for which Neupogen is used - among cancer patients undergoing various treatments.

(Reporting by Dan Levine; Editing by Grant McCool)