Quetiapine as add-on treatment for bipolar I disorder: efficacy in preventing relapse of depressive episodes.

Objective: To assess the long-term response to add-on quetiapine therapy in patients with bipolar I disorder who were not adequately responding to standard medications.
Methods: Outpatients with bipolar I disorder (DSM-IV-TR) responding inadequately to standard treatment were observed before and after the addition of quetiapine. Symptom severity was evaluated using the Clinical Global Impressions scale for Bipolar Disorder (CGI-BP) each month. Relapses included hospitalization, treatment in a day hospital or clinic, scores >/= 1 point higher than previous CGI-BP scores and/or upward titration of quetiapine or other medications.
Results: Sixty-one patients (age range of 18-68 years) were observed prospectively for an average of 7.5 months (range 3-18 months) prior to addition of quetiapine and subsequently followed for an average of 15.7 months (range 6-42 months). The final mean quetiapine dose was 537.1 +/- 91.7 mg/d. Prior to quetiapine addition, an annual relapse rate of 2.09 episodes was recorded, relating to 0.94 depressive and 1.15 manic or mixed episodes. Following quetiapine addition, annual relapse rates were reduced to 0.61 episodes, representing 0.14 depressive and 0.46 manic or mixed episodes. Compared with the period of add-on quetiapine treatment, the relative risk of relapse prior to quetiapine therapy was 3.4 for all episodes (chi2 = 24.8, P < 0.001), 6.7 for depressive episodes (chi2 = 24.7, P < 0.001), and 2.5 for manic or mixed episodes (chi2 = 9.0, P < 0.05).
Conclusion: This naturalistic follow-up study provides preliminary evidence for the efficacy of long-term add-on quetiapine treatment in the prevention of relapses of manic or mixed and depressive episodes of bipolar I disorder, and particularly in the prevention of depressive episodes.