AstraZeneca's bid to protect its blockbuster Seroquel franchise has been hurt by a ruling from the UK High Court which states that the patent on the extended-release version of the antipsychotic is invalid.

The patent on Seroquel XR (quetiapine fumarate) prolonged-release tablets had been challenged by Accord Healthcare, Intas Pharmaceuticals, Novartis' Hexal and Sandoz generics units and Teva. The Anglo-Swedish firm noted that the UK court is the first to rule the patent invalid, in contrast to a decision on March 7 by the District Court in The Hague, Netherlands in support of its validity.

Noting that the decision is limited to the UK, AstraZeneca said it is engaged in "numerous other proceedings regarding Seroquel XR-related patents and regulatory exclusivity". Trials have concluded in the USA and in Spain, with decisions pending, and the company notes that it remains committed to defending its intellectual property protecting the drug.

Last week, AstraZeneca sued the US Food and Drug Administration after the agency denied the firm's Citizen Petitions requesting that the regulator withhold finally approving any generic with labelling that omits warnings required for branded versions of Seroquel (quetiapine) and Seroquel XR. In the USA, the patent covering instant-release quetiapine ran out in September 2011, and paediatric exclusivity will expire on March 26.