The short answer
Chemotherapy can reduce neutrophils, the white cells that fight infection. Filgrastim is given to decrease the chance of infection in people receiving chemotherapy for non-myeloid cancers. MedlinePlus says the first dose comes at least 24 hours after chemotherapy and continues daily for up to two weeks or until counts recover.
Filgrastim is a colony-stimulating factor sold under names including Neupogen, Granix, Nivestym, Releuko and Zarxio.
It is used to decrease the chance of infection in people with non-myeloid cancer receiving chemotherapy.
MedlinePlus says the first dose is given at least 24 hours after chemotherapy.
It is then given daily for up to two weeks, or until blood cell counts return to normal.
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The full explanation.
The problem the injection is solving.
Chemotherapy targets fast-dividing cells, and bone marrow is full of them. One thing that gets hit hard is the neutrophil — a white blood cell whose job is fighting infection. MedlinePlus states the link directly: doctors give filgrastim because chemotherapy can lower neutrophils.
Fewer neutrophils means weaker defense. So instead of just waiting for the marrow to catch up, an injection pushes production along faster. MedlinePlus describes filgrastim as a drug given to lower the chance of infection in people who have non-myeloid cancer and are getting chemotherapy.
You may know it by a brand name instead. MedlinePlus lists Neupogen, Granix, Nivestym, Releuko, and Zarxio among them.
The timing.
Two numbers from MedlinePlus matter before your cycle starts.
The first dose comes at least 24 hours after your chemotherapy. It does not happen alongside the infusion itself.
After that, MedlinePlus says you keep getting the medicine every day for up to two weeks, or until your blood counts return to normal. So the length of the course depends on your blood, not on a fixed calendar date.
This is why the injection schedule sits inside your chemo cycle instead of replacing part of it.
How it is given.
MedlinePlus describes filgrastim as a liquid that comes in vials and prefilled syringes. You get it as a shot under the skin, or through a vein. It is usually given once a day, though some people getting treatment for severe chronic neutropenia get it twice a day.
Some people get these shots at a clinic. Others learn to give the injection at home, or a family member does. If that applies to you, ask for a real demonstration, and get a phone number for when something feels wrong.
Other reasons it is used.
Filgrastim is not only a chemotherapy support drug. MedlinePlus also lists it for raising white blood cells in people with acute myeloid leukemia during treatment, in bone marrow transplant, and in severe chronic neutropenia. Neupogen is used for a different purpose after radiation: to increase the chance of survival in people exposed to harmful amounts of it.
Knowing that can be reassuring if you meet someone on the same injection for a completely different reason.
Side effects to mention.
Bone pain is the one people ask about most, and it is a known effect. MedlinePlus lists bone pain along with joint, back, arm, leg, mouth, throat, and muscle pain in its side effect list. It says to report these if they are severe or do not go away.
Two facts matter together here. The injection lowers your infection risk, but it does not erase it. Whatever infection warning signs your team gave you still apply while you are on these injections. NCI's general guidance during cancer treatment is blunt: infections can be life threatening and need urgent medical attention. Call your health care team if you have signs of one.
If you are not sure whether something counts, call anyway. Your team would rather field a call about aching legs than miss the start of an infection.
Planning around the injections.
Daily shots for up to two weeks is a real logistical task, not just a medical one. If a clinic is giving them, that means daily trips, which can be tiring on top of everything else treatment already demands. If you are giving them at home, keeping supplies stocked and storing the medicine correctly both matter.
Ask your pharmacy how the medicine should be stored between doses, since some formulations need refrigeration. Set a daily reminder so a dose is never missed by accident, especially on a day when you feel unwell and just want to rest.
When to get help sooner
MedlinePlus says to call your doctor immediately if any of these happen. It does not rank them, and neither should you.
- A rash, hives, itching, swelling of the face, eyes or mouth, wheezing, or shortness of breath.
- Fever, shortness of breath, trouble breathing, or fast breathing.
- Coughing up blood.
- Pain in the upper left part of the stomach, or at the tip of the left shoulder.
- Fever with abdominal pain, back pain, or feeling tired or unwell.
- Swelling of the stomach area, decreased urination, trouble breathing, dizziness or tiredness.
- Unusual bleeding or bruising, purple marks under the skin, or red skin.
- Decreased urination, dark or bloody urine, or swelling of the face or ankles.
- Painful, urgent or frequent urination.
If breathing is difficult, do not wait for a call back. That is an emergency, and the usual emergency number for your area is the right one to use.
Words to know
Tap any term to see what it means.
Common questions
Why not give the injection at the same time as chemotherapy?
MedlinePlus states that patients receive the first dose at least 24 hours after chemotherapy. The gap is part of how the medicine is scheduled. Your oncology team can explain the reasoning for your particular regimen.
What is it doing?
MedlinePlus explains that chemotherapy can reduce neutrophils, the infection-fighting blood cells, and that filgrastim is given because of this. It is also used to increase white blood cells in people with acute myeloid leukaemia during treatment, in bone marrow transplant, and in severe chronic neutropenia. MedlinePlus separately says Neupogen is used to increase the chance of survival in people exposed to harmful amounts of radiation.
How is it given?
MedlinePlus says it comes as a liquid in vials and prefilled syringes, injected under the skin or into a vein, usually once a day.
Is bone pain expected?
Bone pain appears in the MedlinePlus side effect list, along with joint, back, arm, leg, mouth, throat and muscle pain. It says to report these if they are severe or do not go away.
Questions to ask your doctor
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Your next step
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Sources last checked: 2026-08-11 what this meansLast updated: 2026-08-18Next planned review: 2027-08-11
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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