Broker says Astra's Crestor may face patent threat

LONDON, Aug 31 (Reuters) - Five generic firms have recently filed manufacturing applications with the U.S. Food and Drug Administration to make a form of AstraZeneca's (AZN.L) cholesterol drug Crestor, suggesting a patent challenge could be imminent, according to Citigroup analysts.

The submission of so-called Drug Master Files with the FDA often precedes an application to market a generic drug.

The main U.S. patent for Crestor does not expire until 2016 and it was recently extended by four years under the provisions of the patent term restoration act.

But generic companies who believe they have found a loophole in the company's patent can mount a challenge well ahead of that time, which would cast uncertainty over the future of the Anglo-Swedish company's key growth product in the United States.

Citigroup said in a note there was typically a delay of a month or two after the filing of a Drug Master File before the notification of a patent challenge appears on the FDA website.

The five-year exclusivity for Crestor expires on Aug. 12, 2008, meaning generics may file challenges one year prior to this date.

Drug Master Files for Crestor, known generically as rosuvastatin, were made in June and July by India's Glenmark Pharmaceuticals (GLEN.BO), Aurobindo Pharma (ARBN.BO) and MSN Laboratories; Israel's Teva Pharmaceutical Industries (TEVA.O); and China's Changzhou Pharmaceutical Factory, Citigroup said.

((Reporting by Ben Hirschler, editing by David Holmes; email: ben.hirschler@reuters.com; Reuters Messaging: ben.hirschler.reuters.com@reuters.net; +44 20 7542 5082)) Keywords: ASTRAZENECA CRESTOR/

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