Risk of neutropenia-related hospitalisation among clozapine initiators

BACKGROUND: Clozapine is highly effective for treatment-resistant schizophrenia but has been associated with an increased risk of agranulocytosis. As a result, until 2025, the Food and Drug Administration required patients receiving clozapine to undergo regular blood testing to monitor for neutropenia as part of a Risk Evaluation and Mitigation Strategy (REMS) programme. OBJECTIVE: This study sought to compare the risk of neutropenia-related hospitalisations between clozapine and olanzapine initiators. METHODS: The study cohort was nested in claims data from Medicaid and two commercial health insurance databases and consisted of adults initiating clozapine or olanzapine who had a recorded diagnosis of schizophrenia or schizoaffective disorder and ≥1 dispensing of a different antipsychotic in the 6 months before initiation. Propensity score matching (1:1) was used to mitigate confounding. The primary outcome was hospitalisation with a neutropenia diagnosis in the primary position. Both as-treated and intention-to-treat analyses were implemented. FINDINGS: After propensity score matching, there were 16 873 initiators in each group. At 6 months postinitiation, there were 12 neutropenia-related hospitalisations among the clozapine cohort (incidence rate: 2.21 per 1000 person-years; 95% CI 1.25 to 3.89) and