AstraZeneca is looking to get approval for the extended-release version of its blockbuster antipsychotic Seroquel from US regulators as a treatment for depression.

The Anglo-Swedish drugmaker has submitted a supplemental New Drug Application to the US Food and Drug Administration for its once-daily Seroquel XR (quetiapine fumarate) to be approved for the treatment of major depressive disorder. The firm is looking to get the green light for the drug to be used as monotherapy, adjunct therapy, and maintenance therapy in adults and the submission is based on seven Phase III studies involving over 4,900 patients.

Seroquel XR is already on the market in the USA and 18 other countries for schizophrenia and last month AstraZeneca announced the submission of two separate sNDAs seeking approval for the treatment of manic and depressive episodes associated with bipolar disorder. In addition to the MDD submission, AstraZeneca hopes to file the drug for generalised anxiety disorder.

The firm noted that MDD affects 15 million American adults - between 5%-8% of the population each year – and studies have shown that at least one-third of patients treated with antidepressants fail to achieve a satisfactory response. It added that American Psychiatric Association guidelines recommend switching to a medication in another class when two drugs from the same class have proven ineffective.

Given this scenario, AstraZeneca feels that Seroquel XR could fill a gap in the lucrative antidepressant market. The firm is also keen to expand its Seroquel franchise as the original drug is facing the threat of generic competition. Seroquel sales last year rose 15% to over $4 billion in 2007, but a copycat version could soon be launched by Teva.