Methods. We searched our computer database for patients with PD currently on clozapine, olanzapine, risperidone, and quetiapine. All patients analyzed had two of three cardinal manifestations of PD (tremor, bradykinesia, or rigidity), although five also had some degree of autonomic failure. Clinical notes were reviewed for demographic information, dosage of dopaminergic therapy, and presence or absence of dementia. Dosage and duration of antipsychotic therapy, effectiveness of therapy, and reasons for switching from one drug to another were tabulated and analyzed.

Results. Out of 872 patients with a diagnosis of idiopathic PD, 99 (11.4%) were taking an atypical antipsychotic drug for symptoms of drug-induced psychosis (hallucinations or delusions). No patients were taking risperidone, six were taking olanzapine, 18 were taking clozapine, and 75 were taking quetiapine. Of the 84 patients who were known at one time to have been taking quetiapine, at the time of data analysis, 46 were still taking it (mean dose 86 mg/day for 10 months), nine had been switched to clozapine due to inadequate efficacy at a mean dose of 139 mg/day, and six had stopped taking the drug for various reasons. Inadequate follow-up was available on the remaining 23 patients, which was due to having recently started the drug (within 5 months of data analysis) in nine cases. Of the 61 patients with adequate follow-up, 40 remained on quetiapine with good control of hallucinations, yielding an overall favorable response rate of 66%.