Are antidepressants less effective in the acute treatment of bipolar I compared to unipolar depression?

Background: Using our routine documentation system we evaluated the hypothesis that antidepressants may be less effective in the acute treatment of bipolar I depressed patients compared to unipolar depressed patients. Method: Based on the data from 2032 consecutively admitted inpatients with unipolar or bipolar I depression we compared the efficacy of antidepressants in both groups. The outcome was assessed by the Global assessment scale (GAS), the duration of hospitalisation and the Apathic-, Depressive- and Manic Syndrome subscales of the Association for Methodology and Documentation in Psychiatry system. Results: Cohorts were comparable in treatment regimens and severity of depression at admission. At discharge, there were no statistically significant differences between bipolar I and unipolar depression for the outcome criteria Depressive Syndrome scale, GAS score and days in hospital. Bipolar patients showed a slightly decreased score of the Apathic Syndrome scale at discharge, also reflected by a slightly elevated score of the Manic Syndrome scale. Limitations: This study did not check for differences in side effects such as switching or cycling commonly attributed to the use of tricyclic antidepressants in bipolar patients. Naturalistic data were obtained prospectively, analysis, however, was done retrospectively, thus limiting, but not completely excluding a possible selection bias. Conclusion: Evaluating different outcome criteria, our naturalistic data of a large cohort seem to reject the hypothesis that antidepressants may be less effective in the acute treatment of bipolar I compared to unipolar depressed patients.