Atypical antipsychotics in Parkinson-sensitive populations.

Drug-induced iatrogenic hallucinations and psychosis occur in about 30% of Parkinson's disease (PD) patients and are the single most important precipitant for nursing home placement, which carries a grave prognosis. In addition, parkinsonism is a frequent accompaniment to the more common dementing syndromes, Alzheimer's disease (AD), vascular dementia, and dementia with Lewy bodies (DLB). The five most recent antipsychotic drugs approved by the Food and Drug Administration in the United States have been marketed as "atypical" antipsychotics (AA) due to their relative freedom from extrapyramidal symptoms when used in schizophrenia patients. The use of these newer antipsychotic drugs in PD and other parkinson-sensitive populations represents the most stringent test to their freedom from motor side effects. To date, clozapine, risperidone, olanzapine, and quetiapine have been studied in parkinson-vulnerable populations. This article reviews the data and highlights the differences that these four drugs have on motor function. It also emphasizes the challenges in evaluating the available data on the motor effects of AA, especially on the non-PD elderly and cognitively impaired population. Suggestions are made for future research to improve the interpretability of these studies.