Timing of onset of antidepressant response with fluoxetine treatment

Objective: The purpose of this study was to assess the time until onset of antidepressant response with fluoxetine treatment. Method: The authors evaluated 182 outpatients with major depression who had a sustained acute response to fluoxetine treatment. The outpatients received 8 weeks of treatment with 20 mg/day of fluoxetine and were assessed biweekly with the 17-item Hamilton Depression Rating Scale. The onset of response was defined as a 30% decrease in score on the Hamilton depression scale that persisted and led to a 50% decrease by week 8. The Kaplan-Meier product limit and Cox regression analysis were used to model the relationship between relevant variables and time until onset of response. Results: The authors found that at weeks 2, 4, and 6, the probabilities of having an onset of response (for responders) were 55.5%, 24.7%, and 9.3%, respectively. The cumulative probabilities of onset of response at each time point were 55.5%, 80.2%, and 89.5%. Neither demographics nor clinical characteristics of depression predicted time until initial response. Conclusions: These data suggest that more than half of eventual responders to fluoxetine treatment at 8 weeks start to respond by week 2; over 75% start to respond by week 4. Conversely, the lack of onset of response at 4-6 weeks was associated with about a 73%-88% chance that patients would not have an onset of response by 8 weeks.