Fluorouracil is also known as FU or 5FU and is one of the most commonly used drugs to treat cancer. It is most often used in combination with other cancer drugs to treat many types of cancer including:
- breast cancer
- head and neck cancers
- anal cancer
- stomach cancer
- colon cancer
- some skin cancers (as a cream)
How fluorouracil works
Fluorouracil is part of a group of chemotherapy drugs known as anti metabolites. Anti metabolites are similar to normal body molecules but they have a slightly different structure.
These differences mean that anti metabolites stop cancer cells working properly. They stop the cells making and repairing DNA. Cancer cells need to make and repair DNA so that they can grow and multiply.
How you have fluorouracil
You have fluorouracil into your bloodstream. You may have fluorouracil through a drip or using a small pump that you carry around for several days.
Fluorouracil is also available as an ointment for skin cancer. When used as an ointment it does not cause the usual side effects but it can cause temporary irritation and inflammation in the treated areas of skin
Into your bloodstream
You might have treatment through a long plastic tube that goes into a large vein in your chest. The tube stays in place throughout the course of treatment. This can be a:
- central line
- PICC line
When you have fluorouracil
You usually have fluorouracil as part of a course of several cycles of treatment. You generally have up to 6 cycles of treatment. Each cycle lasts 2, 3 or 4 weeks.
You have continuous treatment through a small portable pump. The nurse attaches it to your central line. This means you can go home with it. You go back to hospital regularly for the nurse to change your pump, and to see how you’re doing.
You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.
How often and how severe the side effects are can vary from person to person. They also depend on what other treatments you're having. For example, your side effects could be worse if you're also having other drugs or radiotherapy.
When to contact your team
Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:
- you have severe side effects
- your side effects aren’t getting any better
- your side effects are getting worse
Early treatment can help manage side effects better.
We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.
Common side effects
These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:
Increased risk of getting an infection
Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell. You might have other symptoms depending on where the infection is.
Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection.
Looking pale and breathlessness
You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.
Increased risk of bleeding and bruising
This is due to a drop in the number of platelets in your blood. These blood cells help the blood to clot when we cut ourselves. You may have nosebleeds or bleeding gums after brushing your teeth. Or you may have lots of tiny red spots or bruises on your arms or legs (known as petechiae).
Contact your advice line if you have diarrhoea, such as if you've had 4 or more loose watery poos (stools) in 24 hours. Or if you can't drink to replace the lost fluid. Or if it carries on for more than 3 days.
Your doctor may give you anti diarrhoea medicine to take home with you after treatment. Eat less fibre, avoid raw fruits, fruit juice, cereals and vegetables, and drink plenty to replace the fluid lost.
Feeling or being sick
Feeling or being sick is usually well controlled with anti sickness medicines. Avoiding fatty or fried foods, eating small meals and snacks, drinking plenty of water, and relaxation techniques can all help.
It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treating it once it has started.
You might have a sudden feeling of tightness in your chest, difficulty catching your breath, wheezing and a cough. This is caused by spasms in the muscles of your airways. Contact your healthcare advice line or tell your doctor.
An increase of in the level of uric acid in your blood
This can cause stiff, painful joints. You have regular blood tests during treatment to check for this.
Heart problems include changes to how your heart works. This can cause changes to your heart rhythm and your ankles can swell.
Tell your doctor or nurse straight away if you have any chest pain.
Your doctor might ask you to have tests to check your heart, such as a heart trace (ECG).
Sore inflamed mouth and throat
It may be painful to swallow drinks or food. Painkillers and mouth washes can help to reduce the soreness and keep your mouth healthy.
Loss of appetite
You might lose your appetite for various reasons when you are having cancer treatment. Sickness, taste changes or tiredness can put you off food and drinks.
You could lose all your hair. This includes your eyelashes, eyebrows, underarm, leg and sometimes pubic hair. Your hair will usually grow back once treatment has finished but it is likely to be softer. It may grow back a different colour or be curlier than before.
Tiredness and feeling weak (fatigue)
You might feel very tired and as though you lack energy.
Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.
Soreness, redness and peeling of palms and soles (hand foot syndrome)
The skin on your hands and feet may become sore, red, or may peel. You may also have tingling, numbness, pain and dryness. This is called hand-foot syndrome or palmar plantar syndrome.
Moisturise your skin regularly. Your healthcare team will tell you what moisturiser to use.
Rare side effects
This side effects happens in fewer than 1 in 100 people (fewer than 1%). You might have one or more of them. They include:
- feeling happy and excited
- eye problems including rapid eye movement, inflammation, blocked tear ducts, blurred vision, eyelid turning outwards, watery eyes and double vision
- headaches and dizziness
- shaking and trembling, stiffness and slow movement (symptoms of Parkinson's disease)
- an increase in the muscle tone of your legs and feet causing them to be stiff
- difficulty getting to sleep and sleeping
- low blood pressure
- liver damage - you have regular blood tests to check for this
- skin problems including rash, dry skin, increased sensitivity to sunlight, hives, darkening of the skin
- nail problems including thickening, pain, changes in colour of the nail and nail bed
Coping with side effects
We have more information about side effects and tips on how to cope with them.
What else do I need to know
Other medicines, food and drink
Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.
Loss of fertility
You may not be able to become pregnant or father a child after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.
Men might be able to store sperm before starting treatment. And women might be able to store eggs or ovarian tissue. But these services are not available in every hospital, so you would need to ask your doctor about this.
Contraception and pregnancy
This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for at least 6 months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.
Don’t breastfeed during this treatment because the drug may come through into your breast milk.
Treatment for other conditions
Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment if you need treatment for anything else, including teeth problems.
Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having. Ask your doctor or pharmacist how long you should avoid live vaccinations.
In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and one of the shingles vaccines called Zostavax.
You can have:
- other vaccines, but they might not give you as much protection as usual
- the flu vaccine (as an injection)
- the coronavirus (COVID-19) vaccine - talk to your doctor or pharmacist about the best time to have it in relation to your cancer treatment
Members of your household who are aged 5 years or over are also able to have the COVID-19 vaccine. This is to help lower your risk of getting COVID-19 while having cancer treatment and until your
Contact with others who have had immunisations - You can be in contact with other people who have had live vaccines as injections. Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as the oral typhoid vaccine.
If your immune system is severely weakened, you should avoid contact with children who have had the flu vaccine as a nasal spray as this is a live vaccine. This is for 2 weeks following their vaccination.
Babies have the live rotavirus vaccine. The virus is in the baby’s poo for about 2 weeks and could make you ill if your immunity is low. Get someone else to change their nappies during this time if you can. If this isn't possible, wash your hands well after changing their nappy.
Slow wound healing
Fluorouracil can cause slow wound healing. If you need to have an operation your doctor will normally advise you to stop having fluorouracil for a while beforehand.
They will let you know when you can start taking it again.
Between 2 and 8 out of 100 people (2 to 8%) have low levels of an enzyme called dihydropyrimidine dehydrogenase (DPD) in their bodies. A lack of DPD can mean you’re more likely to have severe side effects from capecitabine or fluorouracil. It might take you a bit longer to recover from the chemotherapy. These side effects can rarely be life threatening.
Before starting treatment with capecitabine or fluorouracil you have a blood test to check levels of DPD. So you may start treatment with a lower amount (dose) of the drug or have a different treatment. Your doctor or nurse will talk to you about this.
More information about this treatment
We haven't listed all the very rare side effects of this treatment. For further information see the electronic Medicines Compendium (eMC) website.
You can report any side effect you have that isn’t listed here to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.
This page is due for review. We will update this as soon as possible.