A medicine that boosts white-cell production (G-CSF)
Filgrastim
A medicine that boosts the body's production of infection-fighting white cells, used after chemotherapy or in neutropenia.
What is Filgrastim?
Filgrastim is a granulocyte colony-stimulating factor, or G-CSF, a medicine that prompts the bone marrow to make more neutrophils, the white cells that fight infection. It is mainly used to raise white-cell counts after chemotherapy or in people whose counts are low for other reasons, lowering the risk of serious infection. It is given by injection under the skin or into a vein, under specialist care. The most common side effect is bone or muscle pain, and rare but important risks include enlargement or rupture of the spleen and lung problems.
Education and reference only. This is a plain-language guide to Filgrastim — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Filgrastim is a specialist medicine known as a granulocyte colony-stimulating factor, or G-CSF. It works like a natural signal in the body that tells the bone marrow to produce neutrophils, the white blood cells most important for fighting bacterial infection. It is used mainly to help people whose neutrophil counts are low, such as after chemotherapy, in certain bone-marrow conditions, or to prepare for and recover from some transplant procedures. It is given by injection, either under the skin or into a vein, and is prescribed and supervised by a specialist team.
How it works
Filgrastim acts on the bone marrow, the spongy tissue inside bones where blood cells are made, encouraging it to produce and release more neutrophils into the bloodstream. By raising the number of these infection-fighting white cells, it shortens the time a person spends with a dangerously low count and reduces the chance of serious infection. Because it works by stimulating the marrow, counts usually rise over a few days, which is why blood tests are used to guide treatment and decide when to stop. It is a supportive treatment given around chemotherapy or in specific conditions rather than a continuous, lifelong medicine.
Company & origin
Originated / developed by: Specialist manufacturers.
A specialist medicine used in the UK to raise white-cell counts, particularly after chemotherapy or in people with low neutrophils.
Practical use
How to take Filgrastim
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Have it given by injection under the skin or into a vein, as arranged or as your specialist team has trained you.
- Use it on the schedule the team sets around your chemotherapy or treatment cycle, rather than changing the timing yourself.
- Attend for the blood tests that are arranged, as these guide how long it is needed.
- Report bone or muscle pain, which is common; simple painkillers often help and your team can advise.
- Seek urgent help for pain in the upper-left tummy or shoulder tip, or for new breathlessness.
Weighing it up
Advantages & disadvantages of Filgrastim
Advantages
- Raises infection-fighting white-cell counts and lowers the risk of serious infection after chemotherapy.
- Can shorten the time spent with a dangerously low neutrophil count.
- Can often be given at home once a person or carer is trained in the injection.
Disadvantages
- Commonly causes bone or muscle pain because the bone marrow is working hard.
- Must be given by injection and needs regular blood tests to guide treatment.
- Rarely, can cause spleen enlargement or rupture and lung problems, which need urgent attention.
Practical use
Good to know
The most useful thing to understand about filgrastim is that it is a supportive medicine: it does not treat cancer itself but helps protect against infection by keeping white-cell counts up, especially around chemotherapy. The most common side effect is bone or muscle pain, often felt in the back, hips or long bones, because the marrow is working hard; simple painkillers usually help and the specialist team can advise. Two rare but important risks to be aware of are enlargement of the spleen, which can occasionally lead to a rupture causing pain in the upper-left tummy or shoulder tip, and lung problems causing breathlessness; both need urgent medical attention. Because it is given by injection, the team will either administer it or train the person or a carer to do so, and regular blood tests are used to guide how long it is needed.
Who should not take it / use with caution
- People who have had a serious allergic reaction to filgrastim or similar medicines should not use it.
- It is used with care in certain bone-marrow conditions, such as some types of sickle cell disease, under specialist judgement.
- It should only be used under specialist supervision, with blood-count monitoring.
Monitoring
- Regular blood tests to check white-cell and neutrophil counts and guide treatment.
- Watching for bone pain, and for rarer problems such as spleen or lung symptoms.
- Reviewing how counts respond to decide how long treatment is needed.
Side effects
- Bone or muscle pain, often in the back, hips or long bones, which is the most common effect.
- Headache, tiredness or a temporary rise in some blood-test markers.
- Rarely, enlargement or rupture of the spleen, causing upper-left tummy or shoulder-tip pain.
- Rarely, lung problems causing breathlessness, or serious allergic reactions, which need urgent care.
Key interactions
- Its timing around chemotherapy matters, so the specialist team plans when it is given.
- Tell your team about all your medicines, as some treatments affect the bone marrow too.
- It is used as part of a wider treatment plan, so changes should be made by the specialist team.
Available as: A solution for injection under the skin or into a vein.
Answers
Filgrastim: frequently asked questions
What is filgrastim used for?
It is a G-CSF used to raise the number of infection-fighting white cells, mainly after chemotherapy or in people whose neutrophil counts are low, to lower the risk of serious infection.
Why does it cause bone pain?
Bone or muscle pain is common because the medicine makes the bone marrow work hard to produce white cells; simple painkillers usually help and your team can advise.
Does it treat the cancer itself?
No. Filgrastim is a supportive medicine that helps protect against infection by keeping white-cell counts up; it does not treat cancer directly.
What are the serious warning signs?
Seek urgent help for pain in the upper-left tummy or the tip of the shoulder, which can signal a spleen problem, or for new breathlessness, which can signal a lung problem.
Can I have it at home?
Often yes; many people or their carers are trained to give the injection under the skin at home, with blood tests arranged to guide treatment.
The wider class
About Granulocyte colony-stimulating factor (G-CSF)
Filgrastim belongs to the granulocyte colony-stimulating factor (g-csf) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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