Striatal and extra-striatal D2/D3 dopamine receptor occupancy by quetiapine in vivo: [123I]-epidepride single photon emission tomography (SPET) study.

Background Selective action at limbic cortical dopamine D2-like receptors could mediate atypical antipsychotic efficacy with few extrapyramidal side-effects. Aims To test the hypothesis that quetiapine has ‘limbic selective’ D₂/D₃ receptor occupancy in vivo. Method The high-affinity D₂/D₃ ligand [¹²³I]-epidepride and single photon emission tomography were used to estimate D₂/D₃ specific binding and an index of relative percentage D₂/D₃ occupancy in striatal and temporal cortical regions for quetiapine-treated patients (n=6). Quetiapine-, and previously studied typical-antipsychotic- and clozapine-treated patients were compared. Results Mean (s.d.) relative percentage D₂/D₃ receptor occupancy by quetiapine was 32.0% (14.6) in striatum and 60.1% (17.2) in temporal cortex (mean daily dose 450 mg: range 300-700 mg/day). Quetiapine treatment resulted in limbic selective D₂/D₃ blockade similar to clozapine and significantly higher than typical antipsychotics. Conclusions Preliminary data suggest that limbic selective D₂/D₃ receptor blockade is important for atypical drug action. [ABSTRACT FROM AUTHOR]