CSF3 and neutropenia: Filgrastim (Neupogen®, Amgen, Thousand Oaks, CA) is the methionylated recombinant human granulocyte‐colony stimulating factor (G‐CSF) expressed in E. coli and is administered as a daily subcutaneous injection (or by intravenous infusion) in conjunction with myelosuppressive chemotherapy to increase the circulating levels of neutrophils and thereby reduce the duration of severe neutropenia 6.