Myocarditis monitoring during clozapine initiation: audit of practice in an NHS trust

Background: Clozapine is the most effective treatment for individuals with treatment-resistant schizophrenia, but concerns about adverse effects continue to limit its use. In contrast to haematological monitoring, which is governed by established protocols, there is no standardised framework for detection of clozapine-associated myocarditis. Clozapine-induced myocarditis is rare but potentially fatal and typically occurs within the first 4 weeks of treatment. As early symptoms such as fever and tachycardia overlap with common side-effects of clozapine, diagnosis is often delayed, and clozapine may be unnecessarily discontinued. Evidence suggests that routine monitoring of troponin and C-reactive protein (CRP), alongside assessment of vital signs and electrocardiography (ECG), can support earlier detection and safer treatment.

Aims: To evaluate cardiac monitoring practice in patients initiating clozapine treatment.

Method: We undertook a retrospective review of all patients registered to start clozapine at Kent and Medway Mental Health National Health Service (NHS) Trust between January 2021 and March 2024. Data were collected on baseline ECG completion, weekly troponin and CRP testing during the first 4 weeks, and documented cardiac symptoms.

Results: Of 219 patients, 180 had complete data. Baseline ECG was completed in 80% of cases. No routine troponin monitoring was identified, and CRP testing was infrequent. Tachycardia occurred in more than 40% of patients. Fifteen patients were referred to cardiology before initiation, as well as six in the first 4 weeks and five thereafter. Twelve patients (7%) discontinued clozapine early, mainly owing to tachycardia.

Conclusions: The findings indicate an absence of systematic myocarditis monitoring. Incorporating weekly troponin and CRP testing into existing mandatory blood testing could improve safety, guide appropriate cardiology referrals and reduce unnecessary discontinuation.