In vivo 123I IBZM SPECT imaging of striatal dopamine 2 receptor occupancy in schizophrenic patients

Rationale: Single photon emission computed tomography (SPECT) using I-123 iodobenzamide (IBZM) as tracer substance has been shown to be a useful tool to visualize dopamine 2 (D2) receptor occupancy. Objectives: We investigated the striatal D2 receptor occupancy of zotepine which is referred to the class of atypical antipsychotic drugs. Methods: I-123 IBZM and SPECT were used to visualize striatal dopamine 2 (D2) receptor occupancy in zotepine-treated schizophrenic patients. Two groups of schizophrenic patients receiving either 150 mg/day zotepine (n=6) or 300 mg/day (n=6) underwent examination. For the quantification of striatal D2 receptor occupancy, striatal IBZM binding in patients treated with antipsychotics was compared to untreated healthy controls (n=8) reported earlier. Results: Zotepine led to a mean overall striatal D2 receptor occupancy of 73%. Patients with 150 mg daily showed a significantly lower occupancy (65.8%, SD=6.2) than patients with 300 mg/day (77.8%, SD=10.7; P <0.05). No clinically relevant extrapyramidal side effects occurred during treatment with zotepine. Conclusions: There was no correlation between the degree of striatal D2 receptor occupancy and clinical improvement.