IBZM SPECT IMAGING OF STRIATAL DOPAMINE-2 RECEPTORS IN PSYCHOTIC-PATIENTS TREATED WITH THE NOVEL ANTIPSYCHOTIC SUBSTANCE QUETIAPINE IN COMPARISON TO CLOZAPINE AND HALOPERIDOL

We investigated the striatal dopamine-2 (D-2) receptor occupancy cause d by different antipsychotic substances in 18 psychotic patients (16 w ith schizophrenic and two with schizoaffective disorder according to D SM-TV) with single photon emission computed tomography (SPECT) using I -123-iodobenzamide (IBZM) as tracer substance. Four patients were trea ted with the novel antipsychotic compound quetiapine (300-700 mg/day), six with clozapine (300-600 mg/ day) and eight with haloperidol (10-2 0 mg/day). They were compared with eight healthy controls. Measurement of S/F ratios and consecutive calculation of D-2 receptor occupancy r evealed a significantly lower striatal D-2 occupancy rate with quetiap ine and clozapine in comparison to haloperidol. In correspondence with the low striatal D-2 receptor occupancy rates and again in contrast t o the haloperidol treatment group, there were no extrapyramidal motor side-effects (EPS) in the quetiapine and clozapine treatment groups. T herefore, the reported data support the position that quetiapine can b e considered to be an atypical antipsychotic substance due to its rela tively weak striatal D-2 receptor blocking property and therefore its low propensity to induce EPS.