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J Nucl Med. 2008; 49 (Supplement 1):37P
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Neurosciences: Psychiatry

Dopamine Disorders and Treatment

Quetiapine has a D2/3 receptor binding profile similar to clozapine: A [18F]fallypride PET study in patients with schizophrenia

Gerhard Gründer1, Frank Rösch3, Wolfgang Schäfer2 and Ingo Vernaleken1

1 Psychiatry; 2 Nuclear Medicine, RWTH Aachen, Aachen, Germany; 3 Nuclear Chemistry, U Mainz, Mainz, Germany

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Objectives: Most antipsychotics exert their antipsychotic effects within a "therapeutic window" between 60-80% striatal D2/3 receptor occupancy. Clozapine and quetiapine (QUET) occupy striatal D2/3 receptors to a significantly lesser extent. To further characterize QUET’s striatal and extrastriatal binding characteristics, we performed [18F]fallypride (FP) PET studies in patients with schizophrenia.

Methods: D2/3 DA receptors were quantified with FP-PET in 26 patients with schizophrenia. 14 were treated with QUET, 12 age-matched medication-free patients served as controls. After varying time points after the last drug administration (range 3-18 h), subjects underwent dynamic PET scans (180 mins). Binding potentials (BP) were calculated with the simplified reference tissue model. Occupancy (OCC) was calculated as % reduction in BP of treated patients relative to controls. Plasma concentrations and OCC values were fit to a simple one-site ligand binding model by nonlinear regression.

Results: Preliminary data analysis in 8 subjects revealed relatively low D2/3 receptor OCC in all brain regions investigated, with significantly higher OCC in extrastriatal than striatal regions. Striatal OCC did not exceed 50% even at extremely high plasma concentrations (max. 814 ng/mL), while binding in temporal cortex ranged from 40-80%. OCC declined rapidly with increasing interval between last QUET administration and PET scan.

Conclusions: QUET similar to clozapine occupies a maximum of 30-50% of striatal D2/3 receptors even at extremely high plasma levels. Extrastriatal OCC is significantly markedly higher. Preferential extrastriatal binding seems to especially characterize compounds with low affinity for D2/3 receptors.





This Article
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Right arrow Email this article to a friend
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Right arrow Alert me to new issues of the journal
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Right arrow Articles by Gründer, G.
Right arrow Articles by Vernaleken, I.
PubMed
Right arrow Articles by Gründer, G.
Right arrow Articles by Vernaleken, I.