Extrapyramidal syndromes in nonhuman primates: typical and atypical neuroleptics

The traditional (typical) neuroleptic drugs produce acute extrapyramidal symptoms (EPS) in the majority of patients, whereas the atypical neuroleptics produce only minimal motor system side effects. Studies of acute dystonia in nonhuman primates with typical (haloperidol, fluphenazine), atypical (clozapine), and putative novel antipsychotic compounds with low EPS (remoxipride, melperone) were conducted across a wide dose range in double-blind, placebo-controlled trials. Haloperidol and fluphenazine caused dystonia, and clozapine did not. Remoxipride and melperone also produced dystonia, but remoxipride only did so at doses that were higher than needed for antipsychotic efficacy. Melperone produced dystonia in doses that are in the antipsychotic dose range. The clinical relevance of the findings is discussed.