Objective: To review the demographic aspects, safety, and efficacy of Clozapine treatment for Parkinson’s Disease Psychosis (PDP) in a large patient cohort.

Background: The impact of PDP is highly distressing to patients and their support networks, requiring significant healthcare resource allocation for increased community care and hospital admissions. Clozapine is effective in the treatment of PDP. However, significant barriers to prescription include adverse effects such as agranulocytosis and the related intense blood monitoring requirements. The Sheffield (UK) Clozapine service for PD was established over 20 years ago.

Method: A review of all PD patients registered by Sheffield Teaching Hospitals (STH) to the Clozaril Patient Monitoring Service (CPMS) was performed (July 2001 to February 2022). The CPMS and STH pharmacy dispensing system were used to determine the following regarding Clozapine therapy: patient demographics; duration and maintenance dose of therapy; frequency of abnormal blood monitoring results; date and reason for discontinuation. The full clinical records of patients initiated on Clozapine from 2015-2022 were further scrutinised for details on clinical response and adverse effects.

Results: A total of 221 patients were identified. The mean (±standard deviation) age of therapy initiation was 69±8.9 yrs with a male: female ratio of 1.9:1 and an average age of death of 73±9.9 yrs. Median total daily maintenance dosage of Clozapine was 37.5mg (range: 12.5-187.5, n=175). Median duration of therapy was 30 months (range: 1-226 months, n=179). Severe neutropenia requiring therapy discontinuation (defined as neutrophil count less than 1.5×10⁹/L) was detected in 5 patients (2.9%, n=173). Mild neutropenia was detected in a further 32 patients (19.0%, n=168) requiring increased monitoring until resolution. No patients initiated on Clozapine during this >20yr period experienced adverse health effects due to neutropenia. Full clinical records were available for 32 patients initiated on Clozapine between 2015 and 2022. Psychotic symptoms completely resolved in 11/32 (34.3%) of patients and partially improved in 14/32 (43.8%). The remainder had no documentation of clinical response.

Conclusion: We provide further evidence that Clozapine is a safe and effective treatment for PDP. Neutropenia rates are similar to those seen in patients who are on Clozapine treatment for schizophrenia.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/clozapine-therapy-for-parkinsons-disease-psychosis-a-21-year-service-analysis/