It is known as a hematopoietic growth factor or colony stimulating factorand is given by injection under the skin (subcutaneous) or in the vein (intravenous). Filgrastim is approved by the U.S. Food and Drug Administration (FDA) for use in cancer patients who are at risk of developing infection due to cancer treatment. It is also approved for treating other patients who have a very low white blood cell count. It is in a class of drugs called growth factors (cytokines).