Positron emission tomographic analysis of central D1 and D2 dopamine receptor occupancy in patients treated with classical neuroleptics and clozapine. Relation to extrapyramidal side effects

Arch Gen Psychiatry. 1992 Jul;49(7):538-44. doi: 10.1001/archpsyc.1992.01820070032005.


Positron emission tomography and selective radioligands were used to determine D1 and D2 dopamine receptor occupancy induced by neuroleptics in the basal ganglia of drug-treated schizophrenic patients. In 22 patients treated with conventional dosages of classical neuroleptics, the D2 occupancy was 70% to 89%. Patients with acute extrapyramidal syndromes had a higher D2 occupancy than those without side effects. This finding indicates that neuroleptic-induced extrapyramidal syndromes are related to the degree of central D2 occupancy induced in the basal ganglia. In five patients treated with clozapine, the prototype atypical antipsychotic drug, a lower D2 occupancy of 38% to 63% was found. This finding demonstrates that clozapine is also "atypical" with respect to the central D2 occupancy in patients. During treatment with clozapine, there is a low frequency of extrapyramidal syndromes, which accordingly may reflect the comparatively low D2 occupancy induced by clinical doses of clozapine. Classical neuroleptics, like haloperidol or sulpiride, did not cause any evident D1 occupancy, but the thioxanthene flupentixol induced a 36% to 44% occupancy. In four patients treated with clozapine, the D1 occupancy was 38% to 52%. The D1 occupancy induced by clozapine and flupentixol may contribute to the antipsychotic effect of these drugs.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Antipsychotic Agents / adverse effects
  • Antipsychotic Agents / metabolism*
  • Antipsychotic Agents / therapeutic use
  • Basal Ganglia / drug effects
  • Basal Ganglia / metabolism
  • Basal Ganglia Diseases / chemically induced*
  • Basal Ganglia Diseases / metabolism
  • Basal Ganglia Diseases / physiopathology
  • Benzazepines / metabolism
  • Clozapine / adverse effects
  • Clozapine / metabolism*
  • Clozapine / therapeutic use
  • Dopamine Antagonists
  • Female
  • Humans
  • Iodine Radioisotopes / metabolism
  • Male
  • Putamen / drug effects
  • Putamen / metabolism
  • Raclopride
  • Receptors, Dopamine / drug effects
  • Receptors, Dopamine / metabolism*
  • Salicylamides / metabolism
  • Schizophrenia / drug therapy
  • Schizophrenia / metabolism
  • Tomography, Emission-Computed*


  • Antipsychotic Agents
  • Benzazepines
  • Dopamine Antagonists
  • Iodine Radioisotopes
  • Receptors, Dopamine
  • Salicylamides
  • Raclopride
  • Clozapine