Drug treatment of panic disorder: early response to treatment as a predictor of final outcome.

One of the core problems in clinical research is the detection of early changes in target symptoms that predict future therapeutic outcome. To analyze potential predictors of outcome, data of a multicenter study on patients with panic disorder were used. A total of 1010 patients were randomly allocated either to alprazolam, imipramine or placebo treatment. Early improvement in the number of spontaneous panic attacks within the first week of treatment predicted outcome exclusively in the alprazolam group. In contrast, placebo responders and nonresponders were differentiated by early changes in anticipatory anxiety intensity. For tricyclic antidepressants such as imipramine an evaluation period of more than one week is required to allow conclusions about outcome.