Some good news at last for AstraZeneca's Seroquel franchise has come after a US court ruled that the formulation patent for its extended-release version of the antipsychotic blockbuster is valid and has been been infringed by generics companies.

The district court in New Jersey has found the formulation patent protecting Seroquel XR (quetiapine fumarate) extended-release tablets to be valid and ruled that four firms - Anchen Pharmaceuticals, Osmotica Pharmaceutical Corp, Torrent and Mylan have infringed it. The formulation patent expires in November 2017.

AstraZeneca reached a settlement with the USA's Handa Pharmaceuticals in September which prevents the latter from selling a generic form of Seroquel XR until November 2016.

The US decision comes a week after the UK High Court declared that the patent on Seroquel is invalid, following a challenge by Accord Healthcare, Intas Pharmaceuticals, Novartis' Hexal and Sandoz generics units and Teva. The UK court was 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.

The Seroquel XR ruling in the USA is very welcome for AstraZeneca which has seen several firms launch their generic versions of the instant-release form of the drug on both sides of the Atlantic this week. The firm has been trying to get injunctions stopping copycat forms of the drug and sued the US Food and Drug Administration but the lawsuit has been thrown out and  requests for injunctions have been dismissed.