Dopamine D₂ Receptor Occupancy in Olanzapine-Treated Schizophrenics

Several studies have shown that conventional antipsychotics are associated with high degrees of D₂ dopamine receptor occupancy in the corpus striatum. Less is known about D₂ levels with atypical antipsychotic drugs, although studies on clozapine indicate low to moderate D₂ occupancy and high rates of 5HT₂ occupancy. This study used [¹²³I]IBZM-SPECT imaging to assess D₂ receptor occupancy in 10 schizophrenic patients treated with both low-dose (5 mg/day) and high-dose (20 mg/day) olanzapine. Dosages were maintained for at least two weeks before each SPECT scan.

D₂ receptor occupancy was 60% with low-dose olanzapine and 83% with the higher dose, a highly significant difference. There were no differences in clinical efficacy between high and lo…