The European Medicines Agency’s (EMA) Pharmacovigilance Risk Assessment Committee has recommended easing routine blood count monitoring for patients on clozapine, citing new data that show that the risk for severe neutropenia and agranulocytosis declines significantly after the first year of treatment.
Under the updated guidelines, monitoring for patients without a history of neutropenia can be reduced to once every 12 weeks after the first year, and to once annually after 2 years. In addition, absolute neutrophil count (ANC) will now be the sole parameter used for hematologic monitoring, replacing the previous requirement to also measure white blood cell count.
The revised recommendations are supported by a joint expert statement from the European Clozapine Task Force, published this year, which called for changes to the monitoring protocol due to the very low incidence of late-onset agranulocytosis.
Additional evidence comes from a large-scale study involving more than 26,000 patients, which found that clozapine-induced severe neutropenia peaked around week 9 (0.128% weekly incidence) and declined sharply after week 18, with rates becoming negligible — 0.001% per week — after 2 years of continuous use.
Mechanism and Risk Profile
Clozapine is an atypical antipsychotic indicated for treatment-resistant schizophrenia and for patients who cannot tolerate other antipsychotics due to neurologic side effects. It is also used to manage psychosis associated with Parkinson’s disease when standard treatments fail.
Clozapine works by antagonizing dopamine D2 and serotonin 5-HT2A receptors, contributing to its unique efficacy in refractory schizophrenia. However, it carries a known risk for drug-induced neutropenia and its most severe form, agranulocytosis.
Research suggests that a reactive metabolite of clozapine, the nitrenium ion, may bind to neutrophil proteins. This complex is then thought to act as a hapten, triggering an immune response that leads to the destruction of neutrophils, a process for which certain individuals may have a genetic predisposition.
All clozapine-containing products in the European Union will be updated to reflect the new ANC-based monitoring schedule and thresholds for treatment initiation and continuation. The direct healthcare professional communication will be distributed by the marketing authorization holders in coordination with national authorities, and published on EMA and national regulatory websites.
Clinicians are encouraged to review and update monitoring protocols accordingly and continue reporting suspected adverse events through established pharmacovigilance channels.