Association Between Citalopram Serum Levels and Clinical Improvement of Patients With Major Depression

Imaging studies have shown that serum concentrations of the selective serotonin reuptake inhibitor citalopram correlate with serotonin transporter (5-HTT) occupancy in vivo. In patients with major depressive disorders treated with citalopram, 80% 5-HTT occupancy was considered to be necessary for maximal therapeutic effects, which requires citalopram serum concentrations of at least 50 ng/mL. The aim of this study was to compare treatment outcome in patients with citalopram serum concentrations greater than and less than 50 ng/mL after 7 days of treatment. This study included inpatients with acute major depressive disorder according to International Classification of Disease, 10th Revision who were treated with citalopram. In weekly intervals, the severity of depression was assessed with the 17-item Hamilton Depression Rating Scale (HAMD-17), and serum concentrations of citalopram were measured from baseline until week 5. Fifty-five patients were eligible for this analysis. After 7 days of treatment, 19 patients showed citalopram serum concentrations of 50 ng/mL or greater; 36 patients had lower concentrations. Patients at greater than the 50-ng/mL threshold had (i) lower mean HAMD-17 sum scores from day 7 to end point (P <= 0.018 for each analysis); (ii) a more pronounced HAMD-17 decrease (P <= 0.019 for each analysis), and (iii) 23 days' shorter duration of hospitalization (P = 0.033) than patients with levels of citalopram less than 50 ng/mL. As regards adverse effects, both patient groups were not significantly different. Despite therapeutic doses, a significant number of patients had serum concentrations less than 50 ng/mL, and these were associated with an unfavorable treatment outcome; therapeutic drug monitoring is recommended to optimize dosing citalopram in the early phase of treatment.