UPDATE 1-AstraZeneca gets generic challenge to Crestor drug

(Adds details, sales, background)

LONDON, Nov 1 (Reuters) - Anglo-Swedish drugmaker AstraZeneca Plc (AZN.L) said on Thursday that Canada's Cobalt Pharmaceuticals was seeking U.S. regulatory permission to sell a generic version of its anti-cholesterol pill Crestor.

Cobalt believes it has found a legal loophole that would allow it to market a cheap copy of the medicine before AstraZeneca's patents expire. Crestor is covered by three key patents valid until 2016, 2020 and 2021.

"AstraZeneca is evaluating Cobalt's allegations and certifications," AstraZeneca said in a statement. "AstraZeneca has full confidence in its intellectual property portfolio protecting Crestor."

The news is a further blow to Britain's second-biggest drugmaker, which is already fighting generic threats to its two biggest revenue generators -- Nexium, for stomach acid, and Seroquel, for schizophrenia and bipolar disorder.

Crestor, a newer drug that AstraZeneca originally licensed from Japan's Shionogi & Co Ltd (4507.T), had sales in the second quarter of $678 million, out of total group sales of $7.27 billion.

AstraZeneca views Crestor as a key growth driver for the business in the years ahead and has been running a major clinical trials programme to try to prove its superiority to other similar statin drugs.

The British-based company is due to report third-quarter results at 1100 GMT.

((Reporting by Ben Hirschler and Mark Potter; editing by Paul Bolding; email: ben.hirschler@reuters.com; Reuters Messaging: ben.hirschler.reuters.com@reuters.net; +44 20 7542 5082)) Keywords: ASTRAZENECA CRESTOR/

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