Studies have shown that there is some efficacy for a number of agents, most notably lithium, in treating bipolar depression. However, the studies also highlight the unfortunate reality that many patients fail to respond adequately to first-line therapies and that there is a need to identify additional options for patients and clinicians. The atypical antipsychotics clozapine, olanzapine, quetiapine, risperidone, ziprasidone, and aripiprazole, have been the focus of increased interest in the treatment of bipolar depression.

The use of antipsychotics in the treatment of depressive episodes is not a particularly novel idea. In 1982, Robertson and Trimble reviewed 34 studies examining the use of typical antipsychotics to augment an antidepressant and noticed modest but generally consistent benefits. More widespread use of these agents in the management of depression has been limited, however, because of concerns about the long-term risk of tardive dyskinesia and the induction of extrapyramidal symptoms that often mimic depressive symptoms.

Clozapine, the first of the atypicals, was applied initially in the treatment of schizophrenia and schizoaffective disorder, where antidepressant effects were noted during open treatment. Subsequent case series described some benefit in dysphoric manias in bipolar disorder as well.

Much of the inditect evidence for antidepressant effects of the atypicals came from studies in major depressive disorder (MDD). For example, a series of eight patients with MDD who failed treatment with a selective serotonin reuptake inhibitor (SSRI) achieved marked and rapid response when risperidone was added to the SSRI. All patients remitted within 1 week; Hamilton Rating Scale for Depression score in these patients declined from a mean of 20.5 to a mean of 2.4 (Slide 11). A subsequent series of 30 patients yielded similar results.