KARLSRUHE, Germany (Reuters) - Britain's AstraZeneca Plc (>> AstraZeneca plc) on Tuesday lost an appeal in Germany's Federal Court against generic drugmakers selling cheap copies of its anti-psychotic drug Seroquel XR.

In November 2012, the federal patent court in Germany ruled a key patent on Seroquel XR, the extended-release version of Seroquel, was invalid.

The British drugmaker appealed that decision in the higher Federal Court, claiming its patent on the drug for treatment of schizophrenia, bipolar disorder and depression was valid until 2017.

The German patent had been challenged by generic drugmakers Teva Pharmaceutical Industries (>> Teva Pharmaceutical Industries Limited), Novartis's (>> Novartis AG) Hexal unit and Accord Healthcare Ltd.

AstraZeneca confirmed in a statement on Tuesday it had lost the German case, adding it was disappointed with the court's decision.

According to the generic drugmakers' lawyers, existing copycat versions will now remain on the German market and more generic versions can be launched.

AstraZeneca posted global sales of $1.34 billion from both the standard release and extended release versions of Seroquel in 2013, down 12 percent from a year earlier, hurt by the loss of exclusivity in several major markets.

(Reporting by Norbert Demuth and Ben Hirschler; Writing by Ludwig Burger)