Circadian rhythm of white blood cells during clozapine treatment

Rationale: The atypical antipsychotic clozapine is effective in the treatme nt of patients with refractory schizophrenia. It carries a well-known risk of neutropenia and agranulocytosis, which necessitates the immediate discon tinuation of clozapine. Objective: We report a patient who developed neutro penia on clozapine, but behind the cell count decrease showed to be a diurn al variation of the white blood cells (WBC). Methods: Due to the lack of ef ficacy of subsequent treatment of conventional and other atypical neurolept ics, treatment with clozapine was restarted after discontinuation. When the morning count of WBC began to fall, WBC count was repeated in the afternoo ns. Results: Careful blood cell monitoring showed a pronounced diurnal vari ation of WBC (2.9-4.2 x 10(9)/l in the morning and 3.6-7.1 x 10(9)/l in the afternoon) and granulocytes (0.8-1.4 x 10(9)/l and 2.9-5.5 x 10(9)/l, resp ectively). Conclusions: Some patients may thus have a spuriously low cell c ount and may be unnecessarily denied effective treatment.