TOPLINE

Serious neutropenia requiring clozapine cessation was uncommon, with the risk concentrated in the initial 15 weeks of treatment, a nationwide Taiwanese study showed. Older age and low baseline white blood cell (WBC) count strongly predicted neutropenia across all severity levels.

METHODOLOGY

• Researchers conducted a nationwide population-based cohort study using linked health insurance claims and laboratory data from Taiwan's National Health Insurance database between 2014 and 2023.
• The study included 12,810 new clozapine users and 4850 individuals who restarted clozapine after a treatment gap of at least 42 days (6153 re-initiation episodes).
• Neutropenia was classified into three categories: isolated minor neutropenia (absolute neutrophil count [ANC], 1000-1500/µL or WBC 2500-3000/µL), serious neutropenia with clozapine cessation within 6 weeks (ANC < 1000/µL or WBC < 2500/µL), and serious neutropenia without cessation.
• Researchers assessed inflection points over time in the weekly incidence of neutropenia and potential risk factors including age, sex, baseline WBC, psychiatric diagnosis, and concomitant medications.
• Participants were followed up from clozapine initiation or re-initiation until a neutropenic event, treatment discontinuation, or the last available WBC test.

TAKEAWAY

• Among new users, the occurrence rates of isolated minor neutropenia, serious neutropenia with cessation, and serious neutropenia without cessation were 10.5, 1.7, and 2.9 per 1000 person-years, respectively; rates among re-initiators were similar (12.5, 2.2, and 3.4 per 1000 person-years respectively). Risk inflection points varied by severity: week 6 for serious neutropenia without cessation, week 14 for isolated minor neutropenia, week 15 for serious neutropenia leading to cessation, after which the incidence of neutropenia declined substantially and remained low throughout continued treatment. 
• Compared with new users younger than 35 years, those aged 55 years or older had significantly higher risks for isolated minor neutropenia (adjusted hazard ratio [aHR], 3.11; 95% CI, 2.31-4.20), serious neutropenia leading to cessation (aHR, 6.41; 95% CI, 2.59-15.90), and serious neutropenia without cessation (aHR, 2.76; 95% CI, 1.55-4.93).
• Baseline WBC count < 4000 cells/µL was associated with increased risks compared with WBC count ≥ 8000 cells/µL: isolated minor neutropenia (aHR, 13.29; 95% CI, 9.63-18.36), serious neutropenia leading to cessation (aHR, 11.42; 95% CI, 5.54-23.53), and serious neutropenia without cessation (aHR, 9.90; 95% CI, 5.78-16.97).
• Concomitant use of valproic acid (aHR, 2.06), benzodiazepines (aHR, 1.68), non-clozapine antipsychotics (aHR, 1.49), or diuretics (aHR, 1.80) was associated with an increased risk for isolated minor neutropenia. Concomitant use of valproic acid (aHR, 1.81) or carbamazepine (aHR, 3.32) was associated with an increased risk for serious neutropenia leading to cessation. Concomitant use of carbamazepine (aHR, 2.77) or diuretics (aHR, 2.24) was associated with an increased risk for serious neutropenia without cessation. Corticosteroid use was associated with an increased risk across all three neutropenia categories.

IN PRACTICE

"Our findings, combined with existing evidence, suggest that the risk of clozapine associated neutropenia is highly time-dependent and strongly stratified by individual baseline [hematologic] status and age," the authors wrote.

"Intensified monitoring during the initial 15 weeks, particularly for high-risk subgroups, could optimize patient safety while potentially reducing the long-term monitoring burden and improving clozapine accessibility for patients with treatment resistant schizophrenia," they added.

SOURCE

The study was led by Chi-Shin Wu, National Center for Geriatrics and Welfare Research, National Health Research Institutes, Miaoli, Taiwan. It was published online on August 22 in The Lancet Regional Health: Western Pacific.

LIMITATIONS

The study was conducted within a single national health-care system, potentially limiting its generalizability. The study excluded patients lacking at least two recorded WBC or ANC measurements, potentially limiting generalizability to off-label clozapine use. Neutropenia was defined using WBC thresholds when ANC was unavailable, which may have led to misclassification of outcomes and modest underestimation of absolute incidence rates. Medication exposure was based on prescription records rather than confirmed adherence, and residual confounding by unmeasured factors could not be excluded. Lastly, the study did not assess downstream clinical outcomes associated with neutropenia detection or treatment interruption.

DISCLOSURES

The study was funded by the National Health Research Institutes, Taiwan. Several authors reported having financial or other ties with various organizations. Details are provided in the original article.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.