Controlled efficacy study of fluoxetine in dysthymia

There have been very few controlled studies of antidepressants in dysthymia, particularly in samples diagnosed reliably and with an adequate length of follow-up. In this investigation, we measured the long-term outcome in a large group of patients meeting DSM-III-R criteria for dysthymia. This study was designed to investigate whether fluoxetine is effective in the treatment of dysthymia.

This randomised study including 140 patients, compared fluoxetine (91 patients) and placebo (49 patients) on a double-blind basis in two distinct phases: a short-term end-point (3 months with 20 mg/day fluoxetine) and a medium-term end-point (6 months) where the initial responders continued double-blind treatment unchanged and non-responders received an additional treatment of 20 mg/day fluoxetine.

After three months of treatment, response was seen more frequently in the fluoxetine group (42/72) than in the placebo group (14/39, P < 0.0001). Improved patients at 3 months were still improved at 6 months. Furthermore, 50% of the nonresponders at 3 months improved and rated as responders at 6 months, after fluoxetine was increased to 40 mg daily.

This study showed the significant and persistent action of fluoxetine on dysthymia. The finding that 50% of the non-responders at 3 months were improved at 6 months, after fluoxetine dosage was increased to 40 mg daily, argues in favour of treating dysthymic patients for at least 6 months, and with a higher dosage if the initial doses are ineffective.