Can serotonin and fluoxetine levels in plasma and platelets predict clinical response in depression?

We describe the clinical response and the area under the concentration-time curve (AUC) of fluoxetine and serotonin levels in plasma and platelets in 10 depressive patients treated with 20 mg/day of fluoxetine for 30 days. Depression severity was assessed at baseline and after treatment by the Hamilton Rating Scale for Depression (HAM-D). "Good clinical response" was defined as a decrease of 50% or more of the total HAM-D score compared with baseline. Using this measure, patients were thus classified as "responders" or "nonresponders." For both groups we describe the AUC of fluoxetine and serotonin levels in plasma and platelets at baseline and after 30 days of treatment. We found different trends of biochemical parameters in the examined groups. In fact, after treatment responders showed, in comparison with nonresponders, higher levels of fluoxetine in platelets and lower levels in plasma; responders also showed lower concentrations of serotonin in platelets and higher concentrations in plasma.