Neutropenia and Agranulocytosis in Patients Receiving Clozapine in the UK and Ireland

Clozapine can cause reversible agranulocytosis and neutropenia. This study documents the occurrence of blood dyscrasias and identifies predisposing risk factors. An analysis was made of the haematological, demographic, and dosage data from a central database on 6316 patients receiving clozapine over four and a half years in the UK and Ireland. During the study period, 2.9% of the patients developed neutropenia and 0.8% developed agranulocytosis. The peak incidence of both disorders was in the first 6-18 weeks of treatment. Fatal agranulocytosis occurred in 0.03% of patients. After the first year of treatment, the incidence of agranulocytosis significantly decreased to the order noted with some phenothiazines. The use of a patient monitoring service kept the haematological risks associated with using clozapine within acceptable limits, particularly in view of the benefits of this medication in treatment-resistant schizophrenia.