Clozapine rechallenge following neutropenia using granulocyte colony-stimulating factor: A Quebec case series.

Abstract:

<p><b>BACKGROUND: </b>Clozapine has a unique efficacy profile among individuals suffering from treatment-resistant schizophrenia, but is associated with hematological side effects. The use of granulocyte colony-stimulating factors (G-CSF) to allow clozapine continuation or rechallenge has emerged as a promising option, but evidence is still scarce.</p><p><b>AIM: </b>To describe the largest case series so far published regarding this practice.</p><p><b>METHOD: </b>A national clozapine hematological monitoring database was consulted to identify all patients who had had neutrophil count <1.5 × 10/L since 2004 in Quebec and was cross-referenced with hospital pharmacy software to identify patients who had received at least one dose of G-CSF, such as filgrastim, while being exposed to clozapine. All data were collected retrospectively, using patients' medical files, from January to July 2019.</p><p><b>RESULTS: </b>Using G-CSF, three out of eight patients could maintain clozapine despite neutropenia episodes that otherwise would have required treatment discontinuation. The only side effect reported was mild short-lived back pain, over a mean 3-year follow-up period. In all but one case, filgrastim was used on an "as-needed" basis at doses of 300 mcg administered subcutaneously.</p><p><b>CONCLUSION: </b>These results suggest that the "as-needed" use of G-CSF is well-tolerated and may allow clozapine rechallenge in some well-selected patients, adding to the paucity of data regarding long-term safety and efficacy of this strategy. More research may help to better define potential candidates and optimal regimen of such practice.</p>