AstraZeneca has filed for US approval to market its antipsychotic drug Seroquel (quetiapine fumarate) for the treatment of depression in patients with bipolar disorder.

Seroquel is already approved for the treatment of patients with schizophrenia and manic episodes in bipolar disorder – also known as manic depression. If the US Food and Drug Administration approves the latest filing, Seroquel would be the only drug on the market cleared to tackle both major symptom types in bipolar patients, which could make it the drug of choice for the disorder.

At present bipolar patients tend to be treated with a mood stabilizer such as lithium or valproic acid, with antipsychotics added in to tackle mania and antidepressants used for depressive episodes. Studies suggest that Seroquel could do both jobs and potentially reduce the number of medications some bipolar patients need to take.

On average, bipolar patients spend around two-thirds of the time in a depressive phase, according to AstraZeneca. In two clinical trials carried out in support of the application, BOLDER I and BOLDER II, more than half of the Seroquel-treated patients met the criteria for remission from depression.

Up to 50% of patients with bipolar depression attempt suicide, and approximately 10%-15% kill themselves.

Approval in bipolar depression could boost Seroquel's sales, as the condition affects approximately 3%-4% of the adult population and is the sixth leading cause of disability in the world. Seroquel is one of AstraZeneca’s biggest sellers, bringing in just over $2 billion in the first nine months of 2005. The drug has patent protection until 2011, although this is being challenged by generic company Teva.