A drug used to treat neutropenia (a condition in which there is a lower-than-normal number of white blood cells) caused by some types of chemotherapy. It is used to help prevent infection in patients with certain types of cancer. Pegfilgrastim is also used to help prevent damage to the bone marrow in patients who were exposed to high doses of certain types of radiation. Pegfilgrastim helps the bone marrow make more white blood cells. It is a form of filgrastim and is able to stay in the body longer. Pegfilgrastim is a type of colony-stimulating factor. Also called filgrastim-SD/01 and Neulasta.