Clozapine and neutrophil response in patients of African descent: A six-month, multinational, prospective, open-label clinical trial.

Introduction: Clozapine is the most effective antipsychotic for treatment-resistant schizophrenia, but it is markedly underutilized, particularly in the US Black population, partly because of concern over clozapine-associated low absolute neutrophil count (ANC). People of African descent have a lower normative ANC range than the White population, which is associated with a specific "ACKR1-null" ("Duffy null") CC genotype (SNP rs2814778) on the ACKR1 gene, termed benign ethnic neutropenia (BEN). The range of ANC variability and safety of clozapine have not been established in people with BEN or examined prospectively in people of African descent.
Methods: We completed a multisite, 6-month, prospective, open-label clinical trial of clozapine treatment in people of African descent with schizophrenia spectrum disorders for whom clozapine was clinically indicated, with or without the ACKR1-null genotype. We examined clozapine safety and weekly ANC during clozapine treatment and evaluated ANC variability by ACKR1-null genotype, sex, study site, and clozapine dosing using repeated measures analysis of covariance. Genotype was assayed using TaqMan® technology.
Results: We enrolled 274 participants, of whom 227 (82.8 %) completed 6 months of clozapine treatment. There was one case of severe neutropenia (<500 cells/mm ³ ) (0.36 %) over 1467.6 person-months of clozapine exposure. This participant recovered without sequelae after discontinuation of clozapine. Of the 249 participants with known genotypes, 199 (79.9 %) had the ACKR1-null genotype. Neutropenia (<1500 cells/mm ³ ) occurred significantly more often in the ACKR1-null group (33 % [65/199]) than in those with the T allele (6 % (3/50); p < 0.001). Fourteen (5 %) patients discontinued due to adverse events. Rates of infection and fever were low and sialorrhea was the commonest side effect (N = 187, 68 %).
Conclusion: To our knowledge, this is the largest prospective clozapine trial in people of African descent. Severe neutropenia was rare, despite the high prevalence (80 %) of the ACKR1-null genotype. Our findings suggest that clozapine can be used safely in Black patients including those with BEN.
Competing Interests: Declaration of competing interest Dr. Deanna Kelly serves on an advisory board for Alkermes, Teva, and Janssen. Dr. Richard Adebayo has served on the advisory boards of Janssen and a consultant for Invega product. Dr. Raymond Loves serves as a consultant for the Maryland Department of Health and the SMI Advisor, American Psychiatric Association. Dr. Sophie Lanzkron has served as an advisor for Bluebird bio, Novo Nordisk, Pfizer, Novartis and Magenta. She has research funding from Imana, Novartis, GBT, Takeda, CSL-Behring, HRSA, PCORI, MD CHRC. Dr. Robert Buchanan has served on the advisory board for Acadia, Merck and Neurocranial, is a consultant for Boehringer-Ingelheim, and is on DSMB for Merck, Negron, and Roche. All other authors have no conflicts to disclose.
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