Pharmacopsychiatry 2005; 38 - 23
DOI: 10.1055/s-2005-862636

Serum Concentrations of Quetiapine and Clinical Effects

A Dragicevic 1, J Sachse 1, S Härtter 1, C Hiemke 1, MJ Müller 1
  • 1Department of Psychiatry, University of Mainz, Germany

Quetiapine is a novel second generation antipsychotic used mainly for the treatment of patients with schizophrenia. Therapeutic serum concentrations are so far unclear. This investigation analyzed data of patients treated with quetiapine and correlated serum concentrations of quetiapine with therapeutic effects and side effects.

The study included 59 patients who were treated with only quetiapine as antipsychotic medication. The use of antidepressants, mood stabilizers and other medication was allowed.

Blood was taken for drug determination under steady state. Drug concentrations were measured by high performance liquid chromatography with on line extraction using column switching and subsequent separation and ultraviolet detection. Therapeutic effects were monitored by the clinical global impressions (CGI) scale and side effects by the UKU scale.

The mean dose of quetiapine was 591mg (range 50 to 1200mg). The mean serum level was 120 ng/ml. Quetiapine doses and serum levels were significantly correlated (N=140, rs=0,34, P<0.0005). Patients receiving other medication showed higher serum levels of quetiapine than patients without comedication (122±84 ng/ml vs. 95±92 ng/ml; P=0.023). Male and female patients received similar mean quetiapine doses (women 582±275mg/day, men 603±284mg/day). The mean quetiapine serum level, however, was significantly lower in women than in men (91 and 131ng/ml, respectively, P=0.0005). A significant correlation was found between quetiapine serum levels and clinical improvement (rs=-0,26, P=0.005) which indicated that clinical improvement correlated with quetiapine serum levels. Correlations between side effects and quetiapine serum levels were not found (P>0.05). Receiver operator characteristics (ROC) analyses, which may be used to determine a quetiapine serum level to distinguish between responders and non-responders, revealed that clinical improvement was significantly better in patients with quetiapine serum levels above 77ng/ml than in patients with lower blood levels. Quetiapine serum levels showed significant differences between the group of non-responders and responders and also between responders and very good responders.

TDM of quetiapine seems to be useful to optimize the therapeutic outcome of patients taking quetiapine. A dose is recommended leading to trough blood levels of quetiapine above 77 ng/ml under steady state conditions.