Diagnosis at the first episode to differentiate antidepressant treatment responses in patients with mood and anxiety disorders.

Rationale: Co-morbidity of mood and anxiety disorders is often ignored in pharmacotreatment outcome studies and this complicates the interpretation of treatment response. The clinical trials are usually based on single categories from the Diagnostic and Statistical Manual of Mental Disorders (DSM).

Objectives: The present study is a first attempt to differentiate the responses to antidepressants using a design that differs from that used in previous clinical trials. To avoid bias due to co-morbidity, we included patients with any DSM-III-R diagnosis of mood or anxiety disorder for which antidepressant treatment was indicated. We also explored the role of the diagnosis at the first episode in the efficacy of the different antidepressants.

Methods: A total of 92 outpatients with a mood and/or anxiety disorder were randomly assigned to treatment with imipramine or fluvoxamine in a 6-week study. The diagnosis at the first episode--or primary diagnosis--was available for 78 patients, 40 with a primary depression and 38 with a primary anxiety disorder.

Results: Analyses using the MIXED procedure for repeated measures showed no general differences between treatment with imipramine and treatment with fluvoxamine. When the primary diagnoses were taken into consideration, differentiation occurred. Patients with primary depression showed better responses to imipramine than to fluvoxamine. The assumption that patients with primary anxiety disorder would respond better to fluvoxamine than imipramine was observed for only the Clinical Global Impression.

Conclusions: The results suggest that the nature of the first illness episode may be more valuable than the DSM categories of mood or anxiety disorders, which may lend support to the concept of primary versus secondary depression for purposes of differentiating treatment responses. Given the exploratory nature of the study, however, replication of our finding is needed.