Onset of antidepressant action: a pharmacological question?

This study was conducted to analyse the onset of action of antidepressants in naturalistic conditions.

Multicenter, prospective, open-label, non-comparative naturalistic study among 582 depressed outpatients treated with mirtazapine. The patients were assessed at screening, and after 1, 2 and 4 weeks by the 17-item Hamilton depression rating scale (17-HAM-D) and clinical global impression (CGI). Onset of action was measured by traditional analyses based on the time to a persistent reduction of more than 50% from baseline on the 17-HAM-D. Patients were grouped into four groups: very fast responders, fast responders, traditional responders and partial or non-responders. The non-parametric Kruskall-Wallis test was used to assess differences between the groups and logistic regression to predict response after 1 week of treatment.

16% of patients had a very fast response, 42.1% a fast response, 26.5% a traditional response and 15.5% a partial or non-response. There were no significant differences between these groups with regard to dose of mirtazapine or sociodemographic characteristics. The baseline total 17-HAM-D was lower in the faster groups than in the slower groups. The evolution of 17-HAM-D items was similar in each responder group.

Time to response varied from early faster response to late slower response. The evolution of 17-HAM-D for each type of response was similar, but occurred at a different time in each group.