Background: The efficacy and safety of olanzapine monotherapy in bipolar depression has been evaluated in 2 placebo-controlled studies. Methods: We pooled data from 2 previously published studies examining olanzapine monotherapy in patients with bipolar I depression. Changes from baseline to 6 weeks in Montgomery-Åsberg Depression Rating Scale (MADRS) total score, MADRS-6 (included items: apparent sadness, reported sadness, inner tension, lassitude, inability to feel, and pessimistic thoughts) score, and individual MADRS item scores were assessed with an analysis of variance (ANOVA) model. Influence of patient baseline characteristics (age, gender, MADRS total score, age at onset of bipolar disorder, psychotic features, melancholic feature, mixed features [≥2 on ≥3 Young Mania Rating Scale items], and racial origin) on the efficacy of olanzapine monotherapy was examined with an ANOVA model for each factor and stepwise multiple regression analysis. Results: Included were a total of 690 olanzapine-group and 524 placebo-group patients. MADRS total, MADRS-6, and all individual MADRS item scores (except concentration difficulties and suicidal thoughts) showed significantly (P≤0.05) greater decreases from baseline to 6 weeks in olanzapine-treated patients than those on placebo. The only baseline characteristic associated with response to olanzapine was melancholic feature. Limitations: The study was limited by omission of patients with bipolar II disorder, post hoc analysis of data from only two clinical trials, and exclusion of suicidal patients. Conclusions: Olanzapine monotherapy improved core symptoms of depression in patients with bipolar I depression. Additionally, we identified melancholic feature as a baseline factor associated with improved treatment response to olanzapine.
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