AstraZeneca has been given the thumbs-up by US regulators to market its antipsychotic Seroquel as a treatment for bipolar disorder.

Specifically the US Food and Drug Administration has approved Seroquel (quetiapine fumarate) for the maintenance treatment of patients with bipolar I disorder, as an adjunct to lithium or divalproex. The drug is currently available as a treatment of schizophrenia, plus depressive and acute manic episodes.

First-quarter sales of Seroquel increased 10% to $1.05 billion, AstraZeneca's second-best-selling product, but analysts believe that this latest approval may not do much to boost that figure as it is already prescribed off-label for the new indication. What will be more significant is the patent infringement trial that the Anglo-Swedish drugmaker will be involved in to stop generic competition for Seroquel starting August 11.

That day, the US District Court in New Jersey will starting hearing the case against Teva Pharmaceutical Industries and Novartis’ Sandoz unit who have filed Abbreviated New Drug Applications in the USA where the patent on Seroquel expires in 2011. AstraZeneca is looking to extend the franchise through extended-release versions of the antipsychotic, called Seroquel XR.

It is also looking to get approval for the latter from the FDA as a treatment for depression and for both manic and depressive episodes associated with bipolar disorder.