Clozapine rechallenge following myocarditis: a systematic review of rechallenge cases

Introduction and objectives: Clozapine is the antipsychotic medication with the greatest efficacy in treatment-resistant schizophrenia (TRS). Unfortunately, clozapine is ceased in approximately 0.2% to 8.5% of people due to concerns about clozapine-associated myocarditis (CAM). The opportunity for clozapine rechallenge is important for people with TRS and CAM, due to limited alternative treatments. However, there is a lack of consensus regarding the optimal process, monitoring, and dose titration to achieve successful clozapine rechallenge. The study aimed to review the process, monitoring, and dose titration within cases of clozapine rechallenge after CAM, to identify features associated with successful rechallenge.

Methods: A systematic review of clozapine rechallenge cases following CAM was conducted. PubMed, EMBASE, Cinahl, and PsycINFO were searched for cases. Reference lists of retrieved articles and field experts were consulted to identify additional studies.

Results: Forty-five cases were identified that described clozapine rechallenge, 31 of which were successful. Successful rechallenge cases generally used a slower dose titration regime with more frequent monitoring than standard clozapine initiation protocols; however, this data was not always completely recorded within cases. Six cases referred to published rechallenge protocols to guide their rechallenge.

Conclusions: The process, monitoring, and dose titration of clozapine rechallenge are inconsistently reported in the literature. Despite this, 69% of case reports detailed a successful rechallenge post CAM; noting limitations associated with reliance on case data. Ensuring published clozapine rechallenge cases report standardised data, including titration speed and monitoring frequencies, is required to guide the development and validation of guidelines for clozapine rechallenge.