The relationship between response to fluoxetine, plasma drug levels, imipramine binding to platelet membranes and whole-blood 5-HT.

1. Thirty-four (34) out-patients with major depressive disorder as defined by Research Diagnostic Criteria were treated with fluoxetine in an open study. 2) All patients received 60 mg daily of the drug for between 18 and 21 days. 3) Of the 28 patients who completed the trial 21 showed improvement and 7 of these showed a marked change. 4) The 7 good responders had a higher fluoxetine:norfluoxetine ratio after three weeks treatment than the remaining patients; 6 of these patients were males. 5) All patients, irrespective of response, showed a decrease in imipramine binding and decrease in whole blood 5-hydroxytryptamine (5-HT) during the period of the study. 6) The response to the drug may be related to metabolism of fluoxetine.