AstraZeneca, the Anglo-Swedish drugs giant, today won approval to lengthen the patent life of one of its best selling drugs for another five years.

America's Food and Drug Administration has granted AstraZeneca the right to market Seroquel XR, a new once-per-day version of its blockbuster schizophrenia drug.

Seroquel had global sales of $3.4 billion last year but its patent was due to expire in 2012. The new extended release version will have a patent until 2017 and is expected to generate billions of dollars in extra sales for Britain’s second largest pharmaceutical company.

AstraZeneca has suffered a string of bad news lately, including late-stage failures of drugs it was developing for stroke and heart disease and its share price has dived from £35 in the past six months. Today it was unchanged at 2745p

There are two million schizophrenia sufferers in the US alone. The existing version of Seroquel needs to be taken several times per day to control their symptoms.

The company said the extended release version would be launched in the US - easily the biggest market - in the second half of this year.

AstraZeneca is relying on revenues from its current range of drugs including Seroquel and stomach acid treatment Nexium to fund an acquisitions spree designed to rebuild its weak pipeline of new medicines.

The largest of these was the controversial $15.6 billion acquisition of US biotechnology group MedImmune announced last month.

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