In the treatment of MDD, insufficient treatment outcome and the delayed onset of action still remain major problems.

Measuring plasma concentrations, i.e. TDM is a possible option to improve therapeutic outcomes.

The aim of this prospective and naturalistic study was to evaluate the economic and clinical benefit of TDM for depressed inpatients treated with citalopram.

Inpatients with MDD according to ICD-10 were included and treated with citalopram. Psychopathology was assessed by the 17-item Hamilton Depression (HAMD-17) rating scale in weekly intervals for five weeks. In parallel, serum concentrations of citalopram were measured.

55 patients were included (27f). 84% of the patients with citalopram plasma concentrations below 50 ng/ml (n = 36) were non-responders in week five. Among patients who achieved plasma concentrations ≥50 ng/ml (n = 19) on day 7, 47% became responder at week five (p = 0.025). Patients with plasma levels ≥50 ng/ml had a significantly shorter duration of hospitalization (49 ± 20) than patients below 50 ng/ml (72 ± 37; p = 0.033).

Our results show that citalopram plasma levels above 50 ng/ml are predictive for later treatment outcome and that TDM is cost effective due to reduced duration of hospitalization.