Filgrastim

Definition

Filgrastim is a medicine used to increase the white blood cell count in the body, which will help prevent infection. Filgrastim is known by the brand name Neupogen.

Purpose

Filgrastim is a drug approved by the Food and Drug Administration (FDA) to increase white blood cell counts. If a patient has a lower than normal white blood cell count it is referred to as neutropenia.

Filgrastim can be used to treat neutropenia caused by cancer chemotherapy treatment. In these patients the filgrastim increases the recovery of white blood cells after chemotherapy. Filgrastim can also be used to treat patients who have a neutropenia not related to chemotherapy. In both cases, the filgrastim decreases the risk of fever and infection.

Filgrastim is not usually used in leukemia patients. However, in patients with the disease known as acute myelocytic leukemia, it is approved for use after chemotherapy. Filgrastim can increase the recovery of the white blood cell count thereby decreasing the length of time a patient may have a fever associated with a low white count.

Filgrastim can also be used after bone marrow transplantation. Once the new healthy bone marrow has been given back to a patient, filgrastim can be administered to help increase the white blood cell count and decrease the risk of fever and infection.

Filgrastim can be used for patients who will receive a peripheral blood stem cell transplant. Patients will receive the filgrastim before the transplant. The filgrastim in these patients causes young, non-developed blood cells, known as stem or progenitor cells, to move from the bone marrow to the blood where they will then be removed from a patient by the process of apheresis. These blood cells are stored until after the patient receives larges doses of chemotherapy that destroy the bone marrow and the cancer. The patient then receives these stored cells back by an intravenous infusion. The stored cells repopulate the bone marrow and develop into the many types of functioning blood cells.

Description

Filgrastim has been available to cancer patients since the 1990s, and is highly effective at decreasing neutropenia. Filgrastim may be referred to as G-CSF, granulocyte colony stimulating factor, colony stimulating factor. This compound is manufactured by recombinant DNA methods using E. coli as the host organism. Chemotherapy destroys white blood cells temporarily. These white blood cells will grow again, but during the time that the levels are low, patients are at an increased risk of developing fevers and infection. Filgrastim acts to stimulate the bone marrow to make more white blood cells, which can either prevent the white count from dropping below normal or decrease the time that the level is low. By effectively avoiding fevers and infections, patients are able to receive their next doses of chemotherapy without delay.

Recommended dosage

Filgrastim is a clear colorless liquid that is dosed on body weight in kilograms. It is kept refrigerated until ready to use, and it is administered to patients as a subcutaneous injection (directly underneath the skin) It is usually administered in the back of the arms, upper legs, or stomach area. Filgrastim can also be given to patients as a short intravenous infusion into a vein over 15 to 30 minutes.

Chemotherapy-caused neutropenia

The starting dose for patients who have just finished chemotherapy is 5 micrograms per kilogram of body weight per day. This is given as a subcutaneous injection under the skin daily for up to 14 consecutive days, and sometimes longer. The doctor will inform the patient when it is time to stop the filgrastim.

Bone marrow transplants

The recommended dose is 10 micrograms per kilogram per day. This can be administered as a 4- to 24-hour infusion intravenously, or as a 24-hour subcutaneous infusion.

Peripheral blood stem cell transplant

The recommended dose is 10 micrograms per kilogram per day. This can be given either as a under the skin injection, intravenously, or as a continuous infusion over 24 hours. This dosing should begin four days before the first apheresis collection process and continue until the last day of collection.

Other neutropenia

The dose recommendation is variable based on the reason for neutropenia. The range of filgrastim doses has been from 5 micrograms per kilogram per day up to 100 microgram per kilogram per day. Doctors may increase the filgrastim dose based on how the white blood cell count responds to the treatment. Other factors that play a role in filgrastim dosing include how low the white blood cell count is and the length of time the white blood cell count remains low.

Precautions

Filgrastim should not be received by a patient in the 24-hour time frame before or after receiving chemotherapy or reinfusion of bone marrow or stem cells.

Blood counts will be monitored while on the drug filgrastim. This allows the doctor to determine if the drug is working and when to stop the drug.

It is not recommended to give filgrastim to patients who have certain types of leukemias.

Patients with a known previous allergic reaction to filgrastim or to any other substance derived from the bacteria E. coli should not take filgrastim.

Patients who may be pregnant, or trying to become pregnant, should tell their doctor before receiving filgrastim.

Side effects

The most common side effect from filgrastim is bone pain. The filgrastim causes the bone marrow to produce more white blood cells, and, as a result, patients may experience pain in their bones. Tylenol, an over-the-counter pain reliever, can usually control mild to moderate pain that occurs with standard dosed filgrastim. Larger doses of filgrastim, like those given for bone marrow transplant patients, can cause severe bone pain that may need a prescription pain reliever to ease the pain.

Another common side effect due to filgrastim administration is pain or burning at the site of the injection. This can be decreased by bringing the filgrastim to room temperature before administering the injection, icing the area of injection to numb it before receiving the injection, and moving the site of the injection with each dose.

Patients who have received filgrastim after cancer chemotherapy have reported fever, nausea and vomiting, muscle pain, diarrhea, hair loss (alopecia), mouth sores, fatigue, shortness of breath, weakness, headache, cough, rash, constipation, and pain. These side effects may be due to the chemotherapy administration.

Interactions

Filgrastim should not be given at the same time as chemotherapy or radiation therapy. Dosing should begin at least 24 hours after the last dose of treatment.

Patients on the drug lithium should tell their doctor before starting filgrastim therapy.

Filgrastim use for delayed myelosuppression has not been studied after the use of the chemotherapy agents mitomycin-C, and nitrosoureas, or after the drug fluorouracil.

KEY TERMS

Food and Drug Administration (FDA)

A government agency that oversees public safety in relation to drugs and medical devices. The FDA gives the approval to pharmaceutical companies for commercial marketing of their products.

Chemotherapy

Specific drugs used to treat cancer.

Subcutaneous

Underneath the initial layer of skin.

Intravenous

To enter the body through a vein.

Reinfusion

The transfer through a vein of healthy stem cells or bone marrow to a patient that had received larges doses of chemotherapy used to destroy cancer cells.

Neutropenia

Low white blood cell count.

Recovery

Blood counts that are returning back to normal levels.

Apheresis

The process of removing and collecting specific cells from the blood through a machine.

Peripheral blood stem cell transplant

A procedure that collects and stores healthy young and non-developed blood stem cells. These are then given back to a patient to help them recovery from high doses of chemotherapy that they received to destroy their cancer.

Bone marrow transplant

A procedure that destroys all of a patients' diseased bone marrow and replaces it with healthy bone marrow.