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Therapeutic drug monitoring (TDM) of quetiapine
Quetiapine is a novel atypical antipsychotic with so far unknown therapeutic serum concentrations. The present investigation analyzed data of 59 patients with either schizophrenia or schizoaffective disorder who were treated with quetiapine. Drug serum concentrations were measured under steady state conditions, and therapeutic effects were monitored by the clinical global impressions (CGI) scale. Antidepressants, mood stabilizers, or other medication except antipsychotics besides quetiapine were allowed. Quetiapine doses and serum levels were significantly correlated (N=140, rs=0,34, P<0,0005). Male and female patients received a comparable mean daily quetiapine dose (women 582±275mg, men 603±284mg). The mean quetiapine serum level, however, differed significantly between women and men (91 and 131ng/ml, respectively, P=0,0005). Clinical improvement was significantly better in patients with quetiapine serum levels above 77ng/ml than in patients with lower levels. TDM seems thus to be useful to optimize the therapeutic outcome of patients taking quetiapine.