AstraZeneca has submitted its extended-release version of its schizophrenia blockbuster Seroquel for European approval as a treatment for generalised anxiety disorder.

If approved, Seroquel XR (quetiapine fumarate) would be the first atypical antipsychotic to be given the go-ahead in Europe for the treatment of GAD. The filing follows a similar submission to the US Food and Drug Administration in May.

The filing is based on what AstraZeneca describes as “a robust clinical development programme” involving more than 3,500 patients in five Phase III studies. The data shows that significantly greater symptom improvements were seen in patients treated with quetiapine XR compared to those treated with placebo in short-term treatment. The studies also demonstrated that the drug had a fast onset of action with improvement observed as early as day four, an improvement which was upheld during maintenance therapy.

The submission represents AstraZeneca’s latest bid to extend the lucrative Seroquel franchise, which currently brings in over $4 billion to the firm’s coffers. The non-extended release formulation faces patent expiries in 2011 and the new version is key to offsetting loss of sales.

Seroquel XR is already on the market in 39 countries for schizophrenia and earlier this month was given the go-ahead by the FDA for the acute treatment of the depressive episodes associated with bipolar disorder. A filing using the drug for the treatment of major depressive disorder was made in the USA in February and in June for Europe.