Clozapine Rechallenge or Continuation Despite Neutropenia, an Extended Follow-up of a Consecutive Quebec Case Series

Clozapine for Quetiapine-Refractory Psychosis in Parkinson's Disease: A Long-Term Single-Center Retrospective Study

Background: Hallucinations and delusions are severe long-term complications of Parkinson's disease (PD). Clozapine is the only antipsychotic with proven efficacy in PD psychosis (PDPsy) available outside the United States but apprehensions about its adverse event profile result in a substantial underuse of clozapine. Objectives: To investigate the practical use and long-term efficacy of clozapine in severe psychotic disorders in PD. Methods: In this retrospective study, the author used data collected over a period of 20 years and included all PD patients under his care, who were treated with clozapine for psychotic disorders. Results: During the observation period, 41 PD patients (38 with PDPsy, 2 with psychotic depression, and one with schizoaffective disorder) were started on clozapine. They had responded poorly or only transiently to quetiapine. An overnight switch to clozapine was tolerated in most. Maximum clozapine doses ranged from 12.5 to 150 mg (72.9 ± 29.9 mg). A significant reduction in psychotic symptoms was achieved in 2 days to 6 months. Among the cases tolerating clozapine, 10 had a full, 25 had a good, 3 had a moderate, and 2 had a poor clinical response to clozapine. Treatment lasted up to 12 years. The long-term response was full or good in 23, moderate in 3, and poor in 2 patients. Conclusions: Clozapine is often effective in the treatment of psychotic disorders in PD including PDPsy poorly or only transiently responding to quetiapine. Side effects including agranulocytosis are manageable in the majority of cases. Clozapine treatment should not be delayed if other measures against PDPsy prove ineffective.

Clozapine rechallenge or continuation despite neutropenia or agranulocytosis using colony-stimulating factor: A systematic review

OBJECTIVES

Rechallenge/continuation of clozapine in association with colony-stimulating factors (CSFs) following neutropenia/agranulocytosis has been reported, but many questions remain unanswered about efficacy and safety. This systematic review aims to assess the efficacy and safety of rechallenging/continuing clozapine in patients following neutropenia/agranulocytosis using CSFs.

METHODS

MEDLINE, Embase, PsycInfo, and Web of Science databases were searched from inception date to July 31, 2022. Articles screening and data extraction were realized independently by two reviewers, according to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) 2020 systematic review guidance. Included articles had to report on at least one case where clozapine was rechallenged/continued using CSFs despite previous neutropenia/agranulocytosis.

RESULTS

Eight hundred forty articles were retrieved; 34 articles met the inclusion criteria, totaling 59 individual cases. Clozapine was successfully rechallenged/continued in 76% of patients for an average follow-up period of 1.9 years. There was a trend toward better efficacy reported in case reports/series, compared with consecutive case series (overall success rates of 84% and 60%, respectively, p-value = 0.065). Two administration strategies were identified, "as-needed" and prophylactic, both yielding similar success rates (81% and 80%, respectively). Only mild and transient adverse events were documented.

CONCLUSIONS

Although limited by the relatively small number of published cases, factors such as time of onset to first neutropenia and severity of the episode did not seem to impact the outcome of a subsequent clozapine rechallenge using CSFs. While the efficacy of this strategy remains to be further adequately evaluated in more rigorous study designs, its long-term innocuity warrants considering its use more proactively in the management of clozapine hematological adverse events as to maintain this treatment for as many individuals as possible.