Clinical and Theoretical Implications of 5-HT2 and D2 Receptor Occupancy of Clozapine, Risperidone, and Olanzapine in Schizophrenia

• Published in: The American journal of psychiatry Vol. 156; no. 2; pp. 286 - 293
• Main Authors: Kapur, Shitij, Zipursky, Robert B., Remington, Gary
• Format: Journal Article
• Language: English
• Published: Washington, DC American Psychiatric Publishing 01.02.1999; American Psychiatric Association
• Subjects: Adult; Antipsychotic Agents - metabolism; Antipsychotic Agents - pharmacology; Antipsychotic Agents - therapeutic use; Benzodiazepines; Biological and medical sciences; Carbon Radioisotopes; Clozapine - metabolism; Clozapine - pharmacology; Clozapine - therapeutic use; Drug Administration Schedule; Drug therapy; Female; Fluorine Radioisotopes; Humans; Male; Medical sciences; Mental disorders; Middle Aged; Neuropharmacology; Pharmacology. Drug treatments; Pirenzepine - analogs & derivatives; Pirenzepine - metabolism; Pirenzepine - pharmacology; Pirenzepine - therapeutic use; Psychiatry; Psycholeptics: tranquillizer, neuroleptic; Psychology. Psychoanalysis. Psychiatry; Psychopharmacology; Pyrimidinones; Raclopride; Receptors, Dopamine D2 - drug effects; Receptors, Dopamine D2 - metabolism; Receptors, Serotonin - drug effects; Receptors, Serotonin - metabolism; Risperidone - metabolism; Risperidone - pharmacology; Risperidone - therapeutic use; Salicylamides; Schizophrenia - diagnostic imaging; Schizophrenia - drug therapy; Schizophrenia - metabolism; Side effects; Tomography, Emission-Computed; Human; Olanzapine; Neuroleptic; Psychotropic; Schizophrenia; Clozapine; 5-HT2 Serotonine receptor; Psychosis; Chemotherapy; Biological fixation; D2 Dopamine receptor; Treatment; Atypical; Mechanism of action; Risperidone; Comparative study
• ISSN: 0002-953X; 1535-7228
• DOI: 10.1176/ajp.156.2.286

OBJECTIVE: Dopamine D2 receptor occupancy measurements provide a valid predictor of antipsychotic response, extrapyramidal side effects, and elevation of prolactin levels. The new antipsychotics clozapine, risperidone, and olanzapine obtain antipsychotic response with few extrapyramidal side effects and little prolactin elevation. The purpose of this study was to compare the D2 and serotonin 5-HT2 receptor occupancies of these drugs in patients receiving multiple-dose, steady-state regimens. METHOD: Forty-four patients with schizophrenia (16 taking risperidone, 2-12 mg day; 17 taking olanzapine, 5-60 mg day; and 11 taking clozapine, 75-900 mg day) had their D2 and 5-HT2 occupancies determined with the use of [11C]raclopride and [18F]setoperone, respectively, and positron emission tomography imaging. RESULTS: Clozapine showed a much lower D2 occupancy (16%-68%) than risperidone (63%-89%) and olanzapine (43%-89%). Risperidone and olanzapine gave equal D2 occupancies at doses of 5 and 20 mg day, respectively. All three drugs showed greater 5-HT2 than D2 occupancy at all doses, although the difference was greatest for clozapine. CONCLUSIONS: Clozapine, at doses known to be effective in routine clinical settings, showed a D2 occupancy clearly lower than that of typical antipsychotics, while risperidone and olanzapine at their usual clinical doses gave the same level of D2 occupancy as low-dose typical antipsychotics. The results also suggest that some previous clinical comparisons of antipsychotics may have been confounded by different levels of D2 occupancy. Clinical comparisons of these drugs, matching for D2 occupancy, may provide a better measure of their true "atypicality" and will help in understanding the contribution of non-D2 receptors to antipsychotic effects.