The Effect of Clozapine on Hematological Indices: A 1-Year Follow-Up Study

Jimmy Lee, Hiroyoshi Takeuchi, Gagan Fervaha, Valerie Powell, Amaal Bhaloo, Robert Bies, Gary Remington

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)


Clozapine is the antipsychotic of choice for treatment-resistant schizophrenia and is linked to a need for mandatory hematological monitoring. Besides agranulocytosis, other hematological aberrations have resulted in premature termination in some cases. Considering clozapine's role in immunomodulation, we proceeded to investigate the impact of clozapine on the following 3 main hematological cell lines: red blood cells, platelets, white blood cells (WBCs), and its differential counts. Data were extracted from patients initiated on clozapine between January 2009 and December 2010 at a single hospital. Patients with a preclozapine complete blood count, who were receiving clozapine during the 1-year follow-up period, were included in the present investigation. Counts of red blood cells, platelets, WBC, and its differential including neutrophils, lymphocytes, monocytes, eosinophils, and basophils were extracted and trajectories plotted. One hundred one patients were included in this study and 66 remained on clozapine at the end of 1 year. There was a synchronized but transient increase in WBC, neutrophils, monocytes, eosinophils, basophils, and platelets beginning as early as the first week of clozapine treatment. There were no cases of agranulocytosis reported in this sample, and five developed neutropenia. A spike in neutrophils immediately preceded the onset of neutropenia in three of the five. The cumulative incidence rates were 48.9% for neutrophilia, 5.9% for eosinophilia, and 3% each for thrombocytosis and thrombocytopenia. Early hematological aberrations are visible across a range of cell lines, primarily of the myeloid lineage. These disturbances are transient and are probably related to clozapine's immunomodulatory properties. We do not suggest discontinuing clozapine as a consequence of the observed aberrations.

Original languageEnglish
Pages (from-to)510-516
Number of pages7
JournalJournal of clinical psychopharmacology
Issue number5
Publication statusPublished - 2015 Oct 12


  • agranulocytosis
  • clozapine
  • eosinophilia
  • leukocytosis
  • schizophrenia
  • thrombocytosis

ASJC Scopus subject areas

  • Psychiatry and Mental health
  • Pharmacology (medical)


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