title: Time course of dopamine D2 receptor occupancy by clozapine with medium and high plasma concentrations.
abstract: Most antipsychotics were thought to induce antipsychotic action at an excess of 70% striatal dopamine D2 receptor occupancy, while the clinical dose of clozapine was reported to show less than 60% occupancy. High-dose clozapine could occupy as high as 80% of striatal dopamine D2 receptor in monkey PET studies. Although the time course of dopamine D2 receptor occupancy is an important property of antipsychotics, that by clozapine has not been investigated in a clinical setting. We measured the time course of extrastriatal dopamine D2 receptor occupancy with different doses of clozapine and evaluated whether the measured occupancies fitted the binding theory. Three consecutive PET scans with [11C]FLB 457 were performed for two patients with schizophrenia, chronically taking 600 mg/day and 200 mg/day of clozapine, respectively. Series of occupancies were also measured in combination with fluvoxamine or paroxetine in one patient. Dopamine D2 receptor occupancies were also simulated using individual clozapine plasma data and previously determined in vivo ED50 value. The occupancy of one patient with high plasma concentration (1207 ng/ml at peak time) was around 75% at peak and around 60% after 26 h. Another patient with medium plasma concentration (649 ng/ml at peak time) showed less than 50% occupancy at peak, decreasing to 15% after 25 h. The measured occupancy values fitted well with the simulated occupancy values. At high plasma concentration, clozapine can induce high extrastriatal dopamine D2 receptor occupancy in the human brain, and this finding fitted well with the theoretical estimation.
authors.affiliation: Brain Imaging Project, National Institute of Radiological Sciences, 9-1-4-chome, Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takano
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Suhara
authors.forename: Ichiro
authors.initials: I
authors.lastname: Kusumi
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Asai
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Yasuno
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ichimiya
authors.forename: Makoto
authors.initials: M
authors.lastname: Inoue
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Sudo
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Koyama
mesh_terms: D000328:Adult; D014150:Antipsychotic Agents / Q000097:blood* / Q000627:therapeutic use; D002247:Carbon Isotopes / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003024:Clozapine / Q000097:blood* / Q000627:therapeutic use; D003198:Computer Simulation; D018492:Dopamine Antagonists / Q000493:pharmacokinetics; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004563:Electrochemistry / Q000379:methods; D016666:Fluvoxamine / Q000494:pharmacology; D006801:Humans; D008297:Male; D017374:Paroxetine / Q000494:pharmacology; D049268:Positron-Emission Tomography / Q000379:methods; D011759:Pyrrolidines / Q000493:pharmacokinetics; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D012457:Salicylamides / Q000493:pharmacokinetics; D012559:Schizophrenia / Q000097:blood* / Q000188:drug therapy; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D013997:Time Factors
chemical_list: D014150:Antipsychotic Agents; D002247:Carbon Isotopes; D003024:Clozapine; D018492:Dopamine Antagonists; D016666:Fluvoxamine; D017374:Paroxetine; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2; D012457:Salicylamides; D017367:Selective Serotonin Reuptake Inhibitors; C065065:FLB 457