The timing and severity of clozapine-associated neutropenia in the US: Is the risk overstated?

BACKGROUND

Concern about clozapine-associated neutropenia contributes to clozapine's underutilization and racial disparities in access. People with African ancestry are more likely to have lower normative absolute neutrophil counts (ANC), associated with the Duffy null genetic polymorphism. Recent data on clozapine-associated neutropenia in the US are lacking.

METHODS

Patients prescribed clozapine in the Johns Hopkins Medicine electronic medical record (EMR) between 2013 and 2023 were identified. Duffy null Associated Neutrophil Count (DANC) was assigned if there were two ANC's < 2000 cells/μL, >30 days apart, before starting clozapine. Rates of neutropenia, timing of first neutropenia, and demographic differences were explored.

RESULTS

974 received clozapine and had ANC's available, with 63.9 % male, 51.1 % White, and 39 % Black. 287 were presumed to start clozapine during the study period, and were 62.4 % male, 46 % White, and 44.9 % Black. No patients developed severe neutropenia. 59 (6.1 %) developed mild or moderate neutropenia. 19 (6.6 %) new starts had presumed DANC, and none developed neutropenia. 11 of 16 presumed new starts who developed neutropenia did so within eight months. No demographic differences were found between groups for presumed new starts. For non-new starts, where DANC assignment was not possible, Black patients were more likely than White patients to develop neutropenia (OR 3.48, 95 % CI [1.65, 7.73]).

DISCUSSION

To our knowledge, this is the first observational study of clozapine-associated neutropenia in the US in the past decade, and it includes a substantial proportion of Black patients. ANC monitoring requirements may be too strict, contributing to clozapine underutilization.