Metabolism of [I-123]epidepride may affect brain dopamine D-2 receptor imaging with single-photon emission tomography

Iodine-123 labelled epidepride is a novel radiopharmaceutical for the study of cerebral dopamine D-2 receptors using single-photon emission tomography (SPET). A lipophilic labelled metabolite of [I-123]epidepride which may en ter the brain and hamper the quantitation of receptors has been observed in human plasma. In the present study, gradient high-performance Liquid chrom atography (HPLC) was used to investigate the plasma concentration of the li pophilic labelled metabolite and its correlation to SPET imaging of striata l dopamine D-2 receptors, A linear regression fit showed a negative correla tion between the amount of the lipophilic labelled metabolite and the stria tum to cerebellum ratio (n=16, R=-0.58, P<0.02), suggesting that plasma met abolite analysis is essential when imaging dopamine D-2 receptors with SPET using [I-123]epidepride.