What Is Filgrastim?

In patients undergoing chemotherapy and experiencing a resultant loss of neutrophils, filgrastim is used to increase the count of neutrophil white blood cells and is sometimes identified as granulocyte colony-stimulating factor (G-CSF). As it is a synthetic growth factor that imitates the body’s own special protein growth factor, filgrastim bolsters the body’s immune system, stimulating the bone marrow to produce, activate, and release these neutrophils. Filgrastim is also indicated for people undergoing bone marrow transplants and those having stem cells harvested for re-introduction into the body. The Food and Drug Administration (FDA) has approved filgrastim’s use in patients who are cancer-free yet have a chronic form of neutropenia. Administered by subcutaneous injection, as stomach acids would destroy it otherwise, filgrastim is categorized as a biological response modifier.

The low counts of neutrophils in chemotherapy patients leave these people wide open to a vast array of infections from viruses, bacteria, and fungi, and resultant fevers that could be life-threatening. Low counts of neutrophils also can cause chemotherapy to be delayed, which can lessen the chemo’s effectiveness. Filgrastim is the drug instrumental in harvesting cells out of the bone marrow for collection, storage, and re-introduction at a later date. As bone marrow transplant patients undergo chemotherapies that destroy their own bone marrow and new transplants begin to function, filgrastim kicks up heavy production to fight infections.

Treating a shortage of neutrophils is the same purpose for which filgrastim is given to patients with human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS) suffering a condition called severe neutropenia. Many of these patients have had their bone marrow damaged by the super-antibiotics, antiretrovirals, and interferon treatments they’ve taken. As an adjunct medication, they need G-CSF to produce as many white blood cells as possible to keep their incidences of infection to a minimum. As filgrastim does not interfere with their other medications, it is a safe avenue for treatment of symptoms and to boost the body’s immune responses.

G-CSF has undergone numerous clinical trials and been observed for side effects and contraindications. Though there is no way for a healthcare provider to know beforehand if any particular patient will experience side effects, it was discovered that there are some minor side effects to expect in some patients. The most often reported side effects are bone pain, nausea, nosebleeds, and vomiting, and some patients have also seen slight elevation in their blood pressure. Occasionally, a patient may suffer more serious side effects, such as severe pain in the upper abdomen radiating to the shoulder, which could be due to enlargement of the spleen, shortness of or difficulty breathing, which could be adult respiratory distress syndrome (ARD), or sudden skin rashes, swelling, redness, and itching, which could be an allergic reaction.

Some people cannot take filgrastim at all due to possible drug interactions with other drugs or herbal supplements they are taking. Those who have sickle-cell anemia, myelodisplasia — which is preleukemia — or chronic myeloid leukemia cannot consider taking G-CSF. Patients undergoing radiation treatments are advised not to take it until all possible effects have worn off. Filgrastim also should not be taken within a 24 hour window before or after a chemotherapy session.