Snapshot A 55-year-old man with non-Hodgkin lymphoma undergoing chemotherapy is about to get his first dose of filgrastim, a granulocyte-colony stimulating factor, for his chemotherapy-induced neutropenia. A few minutes after the dose, he starts feeling pruritus, and it was noted by the nurse that he developed urticaria over his trunk. He did not experience swelling of his lips, tongue, or throat. He is given a dose of diphenhydramine and monitored for the next few hours. His urticaria subsides, and he continues to deny any difficulty breathing or throat swelling. Introduction Drugs filgrastim recombinant human granulocyte-colony stimulating factor (G-CSF) pegfilgrastim recombinant PEG-conjugated human G-CSF sargramostim recombinant granulocyte macrophage CSF (GM-CSF) Mechanism of action G-CSF stimulates production of neutrophils GM-CSF stimulates production of neutrophils, dendritic cells, and monocytes/macrophages Clinical use neutropenia myelosuppressive chemotherapy aplastic anemia congenital neutropenia stem cell transplantation Adverse effects nausea and vomiting bone pain cutaneous vasculitis allergic reaction angioedema urticaria anaphylaxis thrombocytopenia capillary leak syndrome leukocytosis