Patients with bipolar I disorder represent a well characterised clinical population. In contrast, bipolar II disorder has not been studied to the same extent. Bipolar II disorder is associated with a high degree of psychosocial impairment and an elevated risk of suicide compared with bipolar I disorder, necessitating early and effective treatment.
Few treatment guidelines for bipolar disorder offer specific guidance for the management of bipolar II disorder. Pharmacological treatment options that are included are mood stabilisers (lithium), antidepressants (fluoxetine, venlafaxine), anticonvulsants (lamotrigine, divalproex) and atypical antipsychotics; however, there is a paucity of clinical trial data to support their use in these patients. Open-label studies provide evidence for the use of lithium and divalproex in patients with acute bipolar II depression and lamotrigine has demonstrated modest efficacy in randomised trials against depressive symptoms in these patients. In addition, the use of antidepressant monotherapy in patients with bipolar II depression remains controversial.
Quetiapine monotherapy has recently been recommended as a first-line treatment for bipolar II depression.1 This is as a consequence of four double-blind, placebo-controlled studies in patients with bipolar I and II disorder (BOLDER I and II [8-week] 2,3 and EMBOLDEN I and II [8-week acute/26-52-week continuation phase]). The results of these studies demonstrated that quetiapine significantly improved depressive symptoms compared with placebo in the bipolar II subpopulation. Similar results have been reported with once-daily, extended release quetiapine fumarate (quetiapine XR). Further studies are required to evaluate treatments for bipolar II disorder, particularly in the long-term management of the illness.

References
1. Yatham LN et al. Bipolar Disord 2009; 11: 225-255.
2. Calabrese JR et al. Am J Psychiatry 2005; 162: 1351-1360.
3. Thase ME et al. J Clin Psychopharmacol 2006; 26: 600-609.