Gender and age effects on quetiapine serum concentrations in patients with schizophrenia or schizoaffective disorders

The atypical antipsychotic quetiapine (QUE) yields a low risk for extrapyramidal symptoms (EPS) and prolactin elevation thus suggesting benefits in women and elderly with schizophrenia. We have analyzed gender and age effects on serum concentrations and clinical implications in a naturalistic therapeutic drug monitoring (TDM) study. 146 samples of 75 patients (63% females, age 36±14y) with schizophrenia or schizoaffekive disorder under monotherapy with quetiapine (25–1200mg/d) were included. Serum concentrations were determined under steady state conditions by HPLC, and clinical assessment comprised improvement (CGI) and side-effects (UKU) ratings. Mean daily doses and serum levels of QUE did not differ significantly between males and females (doses: 606±284 vs. 600±283mg; serum levels: 145±120 vs. 137±119ng/ml).Without significant gender differences, side-effects occured in 34.9% of patients (20.5% sedation, 4.8% EPS). 78.6% showed at least moderate clinical response; higher age was slightly associated with weaker response (P=0.012) and more side-effects (P=0.029). Good clinical response was more frequent (P=0.05) at QUE serum concentrations >50–100ng/ml in males and females; occurence of EPS was significantly associated (P<0.05) with higher concentrations (median 210ng/ml) only in females. According to these results, TDM of QUE seems useful in the treatment of schizophrenic patients, particularly in case of non-response or rarely occuring side-effects.