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

Objective: Recent case studies suggest that impaired granulopoiesis, well-k nown to occur during clozapine treatment, may also be observed when olanzap ine is administered. The underlying mechanisms are unknown, but haematopoie tic cytokines such as granulocyte colony-stimulating factor (G-CSF) are lik ely to be involved. Method: We measured the plasma levels of G-CSF and of other cytokines longi tudinally in a female patient who developed granulocytopenia twice, first d uring 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 ar e able to induce transient granulocytopenia through a similar or common mec hanism that does not involve a compensatory increase in C-CSF levels.