[Three patients with Parkinson's disease whose therapeutic levels were successfully improved after administration of quetiapine for suppression of psychosis].

Psychosis characterized by hallucination or delusion, which occurs during drug therapy of parkinsonian patients, is one of the limiting factors for the control of motor symptoms or complications. In the present study, we encountered three patients with Parkinson's disease (PD) at advanced stages; all three patients had severe psychosis and severe wearing-off phenomenon and one had severe orthostatic hypotension. Their psychotic symptoms were successfully treated by administration of quetiapine, resulting in the favorable control of motor fluctuations and elevation of therapeutic levels unless any aggravation of parkinsonism occurs. Although the measure against drug-induced psychosis is principally a reduction of the doses or withdrawal of causative drugs, the effective use of antipsychotic drugs, such as quetiapine, is helpful to suppress psychosis and allow the patient to adjust to antiparkinsonian drugs for the control of symptoms other than psychosis.