Drugs giant AstraZeneca has filed a lawsuit against US regulators to overturn last week's denial of petitions with regard to generic versions of its SEROQUEL and SEROQUEL XR tablets.The tablets, also know as 'quetiapine fumarate', are an antispsychotic drug used in the treatment of schizophrenia, bipolar disorder and depression.On March 7th, Astra filed a 'citizens petition' to raise issues regarding labelling requirements for generic copies of "innovative medicines" as well as data exclusivity rights. This was denied by the Food and Drug Administration (FDA).The company is attempting to delay the release onto the market of the generics."AstraZeneca seeks an injunction barring the FDA from granting final marketing approval of generic quetiapine until December 2nd 2012 when regulatory exclusivity expires on important clinical trial data, or, alternatively, at least until a federal court has a meaningful opportunity to review imminent FDA action regarding the pending generic marketing applications," the firm said on Tuesday morning."AstraZeneca will vigorously defend its legal rights."BC