5-FU chemotherapy
Fluorouracil
A widely used chemotherapy medicine, usually given by infusion under cancer-team care, for many cancers; also a skin cream for sunspots.
What is Fluorouracil?
Fluorouracil, often called 5-FU, is a chemotherapy medicine usually given by drip (infusion) in hospital by a cancer team, used for many cancers including bowel, breast and stomach. There is also a skin cream version used to treat sunspots and some early skin cancers. The common side effects of the infusion are mouth soreness, diarrhoea and low blood counts, which raise the risk of infection. As with all chemotherapy, a fever or feeling suddenly unwell is an emergency and must be reported to your team straight away. Some people lack an enzyme called DPD and are tested before treatment, because they are at risk of severe side effects.
Education and reference only. This is a plain-language guide to Fluorouracil — 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
Fluorouracil (5-FU) is one of the oldest and most widely used cytotoxic chemotherapy medicines, given by injection or drip in hospital for a long list of cancers, including those of the bowel, stomach, breast and head and neck. It is often combined with other chemotherapy medicines and sometimes with radiotherapy. The same active ingredient is also made into a skin cream (such as Efudix) used to treat sun-damaged skin and some early, surface skin cancers, which works in a more local way. The infusion form is always planned and supervised by an oncology team and given in cycles.
How it works
Fluorouracil blocks an enzyme that cancer cells need to make the building blocks of DNA, so the cells cannot copy themselves properly and many die. Because it targets fast-dividing cells, it also affects healthy fast-growing tissues such as the lining of the mouth and gut and the bone marrow, which is why mouth soreness, diarrhoea and low blood counts are common. The capecitabine tablet is in fact turned into fluorouracil inside the body, so the two are closely related. An enzyme called DPD breaks fluorouracil down; people with very little of it clear the medicine too slowly and can have severe toxicity, which is why they are tested first. The skin cream works by acting on abnormal skin cells where it is applied.
Company & origin
Originated / developed by: Generic (long-established).
A long-established chemotherapy medicine used in the UK, under specialist care, for many cancers and as a skin cream for sun damage.
Practical use
How to take Fluorouracil
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- The infusion is given in hospital by your cancer team, on a planned schedule of cycles with rest periods to recover.
- Look after your mouth with gentle, regular care and tell your team early if it becomes sore or ulcerated.
- Report diarrhoea promptly, drink fluids, and contact your team if it is severe, as it can cause dehydration.
- Contact your cancer team's emergency line straight away if you get a fever, shivering or feel suddenly unwell.
- If you are using the skin cream, apply it exactly as directed, expect the area to redden and crust, and protect it from sunlight.
Weighing it up
Advantages & disadvantages of Fluorouracil
Advantages
- A long-established, effective treatment used across many different cancers, often as part of combination therapy.
- Flexible: available as an infusion for internal cancers and as a cream for sun-damaged skin and surface skin cancers.
- Decades of experience mean its effects and how to manage them are very well understood.
Disadvantages
- Commonly causes mouth soreness, diarrhoea and low blood counts, with a real risk of serious infection.
- The infusion usually needs hospital visits or a pump, and can cause hand-foot syndrome and eye irritation.
- People with DPD enzyme deficiency are at risk of severe toxicity, so testing and close supervision are essential.
Practical use
Good to know
With the infusion, mouth soreness (mucositis) and diarrhoea are common and should be reported early, as good mouth care and prompt treatment of diarrhoea make a real difference and prevent dehydration. As with all chemotherapy, it lowers your white cells, red cells and platelets, so a temperature, shivering, sore throat or feeling suddenly very unwell is a medical emergency (possible neutropenic sepsis) — ring your cancer team's emergency line immediately. Before starting, many people are tested for DPD enzyme deficiency, because those who lack it can suffer severe, even life-threatening, side effects. Sore, red palms and soles (hand-foot syndrome) and eye watering or sensitivity can also occur. Pregnancy must be avoided during treatment, contraception is advised, and fertility can be affected, so discuss this beforehand. Live vaccines should be avoided. The skin cream causes the treated area to become red, sore and crusted before it heals, which is an expected part of how it works; follow the instructions and protect the area from sun. Feeling anxious is completely normal — your team is there to support you, so do contact them with any worry.
Who should not take it / use with caution
- People with a complete DPD enzyme deficiency should not receive it, as toxicity can be severe or life-threatening.
- It is avoided in pregnancy and breastfeeding because it can harm a developing baby.
- It is used with great caution, or avoided, in people who are very unwell, malnourished or have severe organ problems, as judged by the cancer team.
Monitoring
- Regular blood tests to check blood counts and kidney and liver function during treatment.
- DPD enzyme status is usually checked before treatment to identify those at risk of severe toxicity.
- Reviewing mouth soreness, diarrhoea and other side effects at each cycle, with dose adjustments as needed.
Side effects
- Mouth soreness and ulcers, diarrhoea, nausea, tiredness and hand-foot syndrome are common with the infusion.
- Low blood counts can cause infections, bruising, bleeding and anaemia — a fever or feeling very unwell needs urgent care.
- The skin cream causes expected redness, soreness and crusting of the treated area; rarely, serious heart or severe DPD-related toxicity occurs.
Key interactions
- It can increase the effect of warfarin, raising bleeding risk, so blood-clotting (INR) is monitored closely.
- It must not be combined with brivudine and similar antivirals, which dangerously increase its toxicity.
- Live vaccines are avoided during treatment, and your team will review all your other medicines before starting.
Available as: Injection or infusion given in hospital, and a skin cream; all prescribed and supervised by a specialist.
Answers
Fluorouracil: frequently asked questions
What is 5-FU?
5-FU is the common name for fluorouracil, a long-established chemotherapy medicine usually given by drip for many cancers, and also available as a skin cream for sun-damaged skin.
Why is my skin cream making the area red and sore?
With the fluorouracil cream, the treated area becoming red, sore and crusted is an expected part of how it works as it clears abnormal cells, and it heals afterwards; follow your instructions and protect it from sun.
What should I do if I get a temperature during treatment?
Treat it as an emergency. A fever or feeling suddenly unwell can signal a serious infection (neutropenic sepsis), so ring your cancer team's emergency line straight away.
Why am I being tested before treatment?
Many people are tested for DPD enzyme deficiency, because those who lack this enzyme cannot break the medicine down properly and are at risk of severe side effects.
Can I have it if I might become pregnant?
No. It can harm a developing baby, so pregnancy must be avoided and contraception used; discuss fertility and family plans with your team before starting.
The wider class
About Chemotherapy (antimetabolite)
Fluorouracil belongs to the chemotherapy (antimetabolite) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF
- NICE CKS
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.