SEROQUEL XL, AstraZeneca Plc’s schizophrenia drug was approved by the Food and Drug Administration on Friday to treat bipolar disorder.

The approval follows results of a trial of SEROQUEL XR, which involved 316 patients with bipolar mania or mixed episodes with or without psychotic features. Meanwhile, the bipolar depression submission was supported by a clinical study in 280 patients diagnosed with bipolar depression.

Seroquel (Quetiapine Fumarate Extended-Release Tablets) brought the company revenues of $4 billion in 2007, and the profit is expected to increase after its usage extension. The FDA approval makes the drug the first medication cleared in the US for the once-daily acute treatment of both depressive and manic episodes associated with bipolar disorder.

The psychological condition bipolar disorder, formerly known as Manic-depressive Illness, is characterized by episodes of significant disturbance in mood and the individuals affected are cycling between manic and depressive episodes. Bipolar disorder also carries a high risk of suicide.

In the long term, people suffering from bipolar disorder “experience depressive symptoms three times longer than manic symptoms," according to Dr. Trisha Suppes, Professor of Psychiatry and Behavioral Sciences, Stanford University Medical Center and VA Palo Alto Health Care System.

It’s still unclear what causes the disease but genetic factors are definitely playing a major role, as the disease was found to run in families. Other than a family history of psychotic disorders, few risk factors for the condition have been identified. People diagnosed with bipolar disorder receive medication such as mood stabilizers, anti-psychotic and antidepressants.

Bipolar disorder affects an estimated 8 million adults in the United States.