Filgrastim is used to decrease 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), in people who are undergoing bone marrow transplants, and in people who have severe chronic neutropenia (condition in which there are a low number of neutrophils in the blood). Filgrastim is also used to prepare the blood for leukapheresis (a treatment in which certain blood cells are removed from the body and then returned to the body following chemotherapy). Filgrastim is in a class of medications called colony-stimulating factors. It works by helping the body make more neutrophils.

Filgrastim comes as a solution (liquid) to inject under the skin or into a vein. It is usually given once a day, but may be given twice a day when it is used to treat severe chronic neutropenia. The length of your treatment depends on the condition that you have and how well your body responds to the medication. If you are using filgrastim to decrease the risk of infection during chemotherapy, you will receive your first dose of filgrastim at least 24 hours after you receive a dose of chemotherapy, and will continue to receive the medication every day for up to 2 weeks. If you are using filgrastim to decrease the risk of infection during a bone marrow transplant, you will receive the medication at least 24 hours after you receive chemotherapy and at least 24 hours after the bone marrow is infused. If you are using filgrastim to prepare your blood for leukapheresis, you will receive your first dose of filgrastim at least 4 days before the first leukapheresis and will continue to receive the medication until the last leukapheresis. If you are using filgrastim to treat severe chronic neutropenia, you may need to use the medication for a long period of time.