AstraZeneca today announced that its antipsychotic drug Seroquel has been approved in the USA for the treatment of patients with depressive episodes associated with bipolar I disorder.

Seroquel (quetiapine fumarate) is already approved as a twice-daily treatment for the treatment of acute manic episodes associated with bipolar disorder, as well as for schizophrenia, and is now the first and only single medication approved by the FDA to treat both depressive and manic episodes associated with this disease.

Sales of Seroquel reached $1.66 billion in the first half of 2006, a 27% rise year-on-year, and is AstraZeneca's second biggest-selling product behind gastrointestinal Nexium (esomeprazole). But the drug is facing a patent challenge from generic drugmaker Teva Pharmaceutical Industries, and AstraZeneca is hoping to win approval for a once-daily formulation, Seroquel SR, in order to defend the franchise.

Bipolar depression represents a substantial market in the USA with around 1.8 million adults suffering the more severe bipolar I disorder and an estimated 3% to 5% of the population suffering from bipolar II. Patients typically experience three times as many depressive as manic episodes, and bipolar depression is estimated to account for a third of all depressive illness in the USA.