AstraZeneca has suffered another setback in its bid to hold back generic competition to its Seroquel franchise after a lawsuit against the US Food and Drug Administration concerning its stance on copies of the antipsychotic was thrown out of a US court.

Earlier this month, the Anglo-Swedish drugmaker sued the regulator after the latter denied its Citizen Petitions requesting that the agency withhold finally approving any generic with labelling that omits warnings required for branded versions of Seroquel (quetiapine) and Seroquel XR. Those warnings relate to hyperglycaemia and suicidal thoughts.

AstraZeneca was seeking an injunction barring the granting final marketing approval of copycat forms of the drug until December 2 or "at least until a federal court has a meaningful opportunity to review imminent FDA action regarding the pending generic marketing applications". However, a court for the District of Columbia has denied the company’s request for a preliminary injunction and dismissed the lawsuit without prejudice.

The firm says it "continues to believe strongly in the merits of its position and is evaluating its options". In the USA, the patent covering instant-release quetiapine ran out in September 2011, and paediatric exclusivity will expire on March 26.

Last week, the UK High Court states that the patent on Seroquel XR is invalid.