title: Estimation of the time-course of dopamine D2 receptor occupancy in living human brain from plasma pharmacokinetics of antipsychotics.
abstract: Although the kinetic profile of antipsychotics at dopamine D2 receptor sites has been suggested to be important for antipsychotic action and dosing schedule, the kinetic profiles of the respective antipsychotic drugs in the brain have not yet been clearly defined. We aimed to estimate the time-course of dopamine D2 receptor occupancy from plasma pharmacokinetics and the apparent in-vivo affinity parameter (ED50; concentration required to induce 50% occupancy). Dopamine D2 receptor occupancies and plasma concentrations of risperidone were measured in five patients with schizophrenia using positron emission tomography with [11C]FLB 457. Measured dopamine D2 occupancies were compared with those estimated from plasma kinetics and in-vivo ED50. The time-course of dopamine D2 receptor occupancy was simulated with altered plasma kinetics or apparent in-vivo affinity parameters of the drug. Mean half-life of dopamine D2 receptor occupancy of risperidone was 80.2 h while that of the plasma concentration was 17.8 h. Dopamine D2 receptor occupancy estimated from plasma pharmacokinetics and in-vivo ED50 was within 1 S.D. of the mean measured occupancy. When the ED50 value was changed to one-tenth and 10-fold, the simulated half-life of receptor occupancy changed to 117.6 h and 27.3 h respectively. Using plasma pharmacokinetics and in-vivo ED50, the time-course of receptor occupancy could be calculated. Simulation of drug kinetics at receptors would provide useful information for the evaluation of antipsychotics.
authors.affiliation: Brain Imaging Project, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takano
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Suhara
authors.forename: Yoko
authors.initials: Y
authors.lastname: Ikoma
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Yasuno
authors.forename: Jun
authors.initials: J
authors.lastname: Maeda
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ichimiya
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Sudo
authors.forename: Makoto
authors.initials: M
authors.lastname: Inoue
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Okubo
mesh_terms: D000328:Adult; D000465:Algorithms; D014150:Antipsychotic Agents / Q000097:blood* / Q000493:pharmacokinetics*; D001921:Brain / Q000000981:diagnostic imaging; D001923:Brain Chemistry / Q000187:drug effects*; D003198:Computer Simulation; D018492:Dopamine Antagonists / Q000097:blood / Q000493:pharmacokinetics; D006207:Half-Life; D006801:Humans; D008297:Male; D008875:Middle Aged; D011759:Pyrrolidines / Q000493:pharmacokinetics; D011869:Radioligand Assay; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D017448:Receptors, Dopamine D2 / Q000187:drug effects / Q000378:metabolism*; D018967:Risperidone / Q000097:blood / Q000493:pharmacokinetics; D012457:Salicylamides / Q000493:pharmacokinetics; D012559:Schizophrenia / Q000378:metabolism; D014055:Tomography, Emission-Computed
chemical_list: D014150:Antipsychotic Agents; D018492:Dopamine Antagonists; D011759:Pyrrolidines; D019275:Radiopharmaceuticals; D017448:Receptors, Dopamine D2; D012457:Salicylamides; C065065:FLB 457; D018967:Risperidone