Filgrastim is a recombinant human G-CSF (rhG-CSF) developed in the mid 1980s, and was approved by the United States (US) Food and Drug Administration (FDA) for use in chemotherapy induced neutropenia in 1991 under the trade name Neupogen®. Filgrastim was first approved in the EU in Germany in 2001 under the same trade name. Filgrastim is a non glycosylated protein, produced in E. coli bacteria transfected with rhG-CSF copy deoxyribonucleic acid (cDNA). Filgrastim differs from native human G CSF only in the addition of an N terminal methionine required for expression in a bacterial host. In 2002, a pegylated filgrastim with extended duration of action relative to the naked filgrastim was approved by the FDA and the EU Commission under the trade name Neulasta.