Pegfilgrastim injection products are used to reduce the chance of infection in people who have certain types of cancer and are receiving chemotherapy medications that may decrease the number of neutrophils (a type of blood cell needed to fight infection). Pegfilgrastim injection (Neulasta) is also used to increase the chance of survival in people who have been exposed to harmful amounts of radiation, which can cause severe and life-threatening damage to bone marrow. Pegfilgrastim is in a class of medications called colony stimulating factors.