The role of quetiapine extended release in the treatment of bipolar depression.

Bipolar disorder is a common, recurrent, and chronic condition associated with significant morbidity and reduced longevity mainly due to the depressive pole of the illness. Despite the great need for effective therapies, relatively few randomized controlled trials have been conducted and, to date, only two agents have been approved by the United States Food and Drug Administration for treatment of bipolar depression (olanzapine/fluoxetine combination and quetiapine). Quetiapine is the first approved monotherapy for treatment of bipolar depression, and an extended-release (XR) form of quetiapine is now available. This once-daily, bioequivalent formulation represents a useful alternative for patients who cannot tolerate twice-daily, immediate-release (IR) quetiapine. Here, we summarize the evidence supporting the efficacy of quetiapine for treatment of bipolar depression, and also review the similarities and differences between the two formulations. Additional research on longer-term use of quetiapine XR is needed to establish the durability of therapeutic effects and tolerability over months or years of therapy, both alone and in combination with other mood stabilizers. Studies on the potential utility of lower doses of quetiapine XR and head-to-head studies to evaluate relative efficacy and cost-effectiveness also are needed.