Platelet serotonin uptake inhibition as a basis for monitoring antidepressant drug treatment.

A quantitative method for measuring serotonin uptake inhibition in fresh platelets incubated in diluted plasma (stored frozen until analyzed) from patients treated with tricyclic and related antidepressants is described. The method was used in a clinical trial comparing the specific serotonin uptake inhibitor zimelidine with the mixed serotonin-norepinephrine uptake inhibitor desipramine in patients with endogenous depression, and correlating this with plasma drug concentration assessment. The bioassay, based on the use of one single, low concentration of serotonin, was found to be very sensitive and to have a high reliability (coefficient of variation about 2% as calculated from duplicate samples), and to correlate highly with log plasma concentration of zimelidine, norzimelidine, and of desipramine. This bioassay may have some advantages in relation to plasma drug concentration assessment, but only future studies can show whether it provides a better basis for antidepressant drug monitoring.