Double-blind olanzapine vs. haloperidol D2 dopamine receptor blockade in schizophrenic patients: A baseline-endpoint [¹²³I]IBZM SPECT study.

The aim of this study was to compare in vivo striatal D2 dopamine receptor occupancy induced by olanzapine and haloperidol in schizophrenic patients using a baseline-endpoint [¹²³I]IBZM single photon emission computerized tomography (SPECT) design. The relationships of striatal D2 receptor occupancy with clinical efficacy and extrapyramidal symptoms (EPS) were also assessed. 27 inpatients with schizophrenia or schizophreniform disorder (19–44 yrs old) were included in a 4-week prospective, randomized, double-blind, parallel and comparative clinical trial. 13 patients were treated with haloperidol (10 mg/day) and 14 with olanzapine (10 mg/day). Ratings of clinical status and EPS were obtained weekly. The percentage of D2 receptor occupancy was estimated by using basal ganglia (striatum)/frontal cortex IBZM uptake ratios obtained from each patient before and after 4 weeks of maintained antipsychotic treatment. Olanzapine led to a mean striatal D2 receptor occupancy of 49% (range 28-69%), which was significantly lower than that induced by haloperidol (mean 64%, range 46-90%). The baseline-endpoint SPECT design used in this study revealed lower antipsychotic D2 occupancy percentage values than those reported in the literature, using other approaches. (PsycInfo Database Record (c) 2021 APA, all rights reserved)