Relationship between parameters of serotonin transport and antidepressant plasma levels or therapeutic response in depressive patients treated with paroxetine and amitriptyline

In a double-blind clinical study, antidepressant plasma levels, parameters of platelet serotonin (5-HT) transport (Km, Vmax and basal platelet 5-HT content) and therapeutic response were measured in depressive patients treated with either paroxetine (30 mg/day) or amitriptyline (150 mg/day) for 6 weeks. No correlation could be found between paroxetine plasma levels and therapeutic outcome after 2, 4 and 6 weeks of treatment. In contrast to the amitriptyline group, a marked increase in Km from baseline to week 2 was determined in paroxetine-treated patients, with Km increase being correlated with paroxetine plasma levels at week 2. However, no significant relationship could be found between 5-HT transport parameters and any of the outcome measures in either treatment group.