Granulocyte colony-stimulating factor plasma levels during clozapine- and olanzapine-induced granulocytopenia

Objective: Recent case studies suggest that impaired granulopoiesis, well-known to occur during clozapine treatment, may also be observed when olanzapine is administered. The underlying mechanisms are unknown, but haematopoietic cytokines such as granulocyte colony-stimulating factor (G-CSF) are likely to be involved. Method: We measured the plasma levels of G-CSF and of other cytokines longitudinally in a female patient who developed granulocytopenia twice, first during clozapine treatment and again when olanzapine was administered. Results: G-CSF levels, but not those of other cytokines, closely paralleled granulocyte counts, yielding a significant positive correlation. G-CSF was not detectable in plasma when granulocytopenia occurred. Granulocytopenia resolved spontaneously despite continuing treatment with olanzapine. Conclusion: The present case suggests that clozapine and olanzapine both are able to induce transient granulocytopenia through a similar or common mechanism that does not involve a compensatory increase in C-CSF levels.