Fluorouracil, which is also called 5FU, is a chemotherapy drug usually given to treat bowel, breast, skin, stomach, and gullet (oesophagus) cancer. This information should ideally be read with our general information about chemotherapy and your type of cancer.
5FU is available as:
a colourless fluid
a cream (Efudix®), which is used to treat certain types of skin cancer.
5FU may be given in one of the following ways:
as an injection through a fine tube (cannula) inserted into a vein (intravenously), usually in the back of your hand
through a fine, plastic tube inserted under the skin and into a vein near your collarbone (central line)
into a fine tube inserted into a vein in the crook of your arm (PICC line)
as a cream applied directly to the skin.
This information is mainly about 5FU when given as an injection into a vein. Your doctor, nurse or pharmacist will give you specific information if you use 5FU as a cream.
Chemotherapy is usually given as a course of several sessions (or cycles) of treatment over a few months. The length of your treatment and the number of cycles you have will depend on the type of cancer you're being treated for. Your nurse or doctor will discuss your treatment plan with you.
Each person’s reaction to chemotherapy is different. Some people have very few side effects while others may experience more. The side effects described here won't affect everyone who has 5FU and may be different if you're having more than one type of chemotherapy drug. The side effects of 5FU as a cream are generally very mild.
We have outlined the most common side effects but haven't included those that are rare and unlikely to affect you. If you notice any effects that aren't listed here, discuss them with your doctor, chemotherapy nurse or pharmacist.
Your mouth may become sore or dry, or you may notice small ulcers during this treatment. Drinking plenty of fluids, and cleaning your teeth regularly and gently with a soft toothbrush, can help reduce the risk of this happening. Some people may find sucking on ice soothing. Tell your nurse or doctor if you have any of these problems, as they can prescribe mouthwashes and medicine to prevent or clear mouth infections.
You may notice that food tastes different. Normal taste usually comes back after treatment finishes. A dietitian or specialist nurse at your hospital can give you advice about ways of coping with this side effect.
5FU can cause diarrhoea. This can usually be easily controlled with medicine, but tell your doctor if it's severe or continues. It's important to drink plenty of fluids if you have diarrhoea.
5FU may cause an inflammation of the lining of the eyelids (conjunctiva) that makes your eyes feel sore, red and itchy. Let your doctor know so they can prescribe soothing eye drops if necessary. Less commonly, you may also have an increased production of tears.
Rarely, your skin may darken. If it does, it usually goes back to normal a few months after the treatment has finished. During treatment and for several months afterwards, you'll be more sensitive to the sun, and your skin may burn more easily than normal. You can still go out in the sun but should wear a suncream with a high sun protection factor (SPF) and cover up with clothing and a hat.
Sometimes areas of skin that have been treated with radiotherapy may become red and sore. Tell your doctor if this happens.
Risk of infection
5FU can reduce the number of white blood cells, which help fight infection. White blood cells are produced by the bone marrow. If the number of your white blood cells is low you'll be more prone to infections. A low white cell count is called neutropenia.
Neutropenia begins seven days after treatment, and your resistance to infection is usually at its lowest 10–14 days after chemotherapy. The number of your white blood cells will then increase steadily and usually return to normal before your next cycle of chemotherapy is due.
Contact your doctor or the hospital straight away if:
your temperature goes above 38ºC (100.4ºF)
you suddenly feel unwell even with a normal temperature.
You'll have a blood test before having more chemotherapy to check the number of white blood cells. Occasionally, your treatment may need to be delayed if the number of your blood cells (blood count) is still low.
Bruising or bleeding
5FU can reduce the production of platelets, which help the blood to clot. Tell your doctor if you have any unexplained bruising or bleeding, such as nosebleeds, bleeding gums, blood spots or rashes on the skin. You may need to have a platelet transfusion if your platelet count is low.
5FU can reduce the number of red blood cells, which carry oxygen around the body. A low red blood cell count is called anaemia. This may make you feel tired and breathless. Tell your doctor or nurse if you have these symptoms. You may need to have a blood transfusion if the number of red blood cells becomes too low.
Feeling tired is a common side effect of chemotherapy, especially towards the end of treatment and for some weeks after it’s over. It’s important to try to pace yourself and get as much rest as you need. Try to balance this with some gentle exercise, such as short walks, which will help. If tiredness is making you feel sleepy, don’t drive or operate machinery.
Less common side effects
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Feeling sick (nausea) or being sick (vomiting)
This may begin soon after the treatment is given and can last for a few days. Your doctor can prescribe very effective anti-sickness (anti-emetic) drugs to prevent or greatly reduce nausea and vomiting. If the sickness isn't controlled, or if it continues, tell your doctor; they can prescribe other anti-sickness drugs that may be more effective.
Some anti-sickness drugs can cause constipation. Let your doctor or nurse know if this is a problem.
This is rare, but your hair may thin or occasionally fall out completely. If this happens, it usually begins about 3–4 weeks after starting treatment, although it may occur earlier. This is temporary and your hair will start to grow back once the treatment has finished. Your hair may grow back straighter, curlier, finer or a slightly different colour than it was before. Your nurse can give you advice about coping with hair loss.
Your nails may become brittle, chipped and ridged. These changes usually grow out slowly over a few months once the treatment has ended.
During treatment with 5FU and for several months afterwards, you'll be more sensitive to the sun, and your skin may burn more easily than normal. You can still go out in the sun but should wear a suncream with a high sun protection factor (SPF) and cover up with clothing and a hat.
5FU can cause a rash or dry skin, which may be itchy. Your doctor can prescribe medicine to help with this.
Soreness and redness of the palms of the hands and soles of the feet
This is sometimes known as palmar plantar or hand-foot syndrome. It can happen when 5FU is given. It's usually temporary and improves when the treatment is finished.
Your doctor may prescribe creams or a vitamin called pyridoxine (vitamin B6), which some people find helpful. It can also help to keep your hands and feet cool and to avoid tight-fitting clothing, such as socks, shoes and gloves.
Changes in the way your heart works
5FU may affect the way your heart works. Some people can experience chest pain and tightening across the centre of the chest while taking it. Chest pain can be caused by many different things other than chemotherapy. If you develop any of these symptoms, contact your doctor immediately.
It’s important to let your doctor know straight away if you feel unwell or have any severe side effects, even if they’re not mentioned above.
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Risk of developing a blood clot
Cancer can increase the risk of developing a blood clot (thrombosis), and chemotherapy may increase this risk further.
A blood clot may cause symptoms such as pain, redness and swelling in a leg, or breathlessness and chest pain. Blood clots can be very serious, so it’s important to tell your doctor straight away if you notice any of these symptoms. Most clots can be treated with drugs that thin the blood. The doctor or nurse can give you more information.
Some medicines, including those you can buy in a shop or chemist, can be harmful to take when you're having chemotherapy. Tell your doctor about any medicines you're taking, including over-the-counter drugs, complementary therapies and herbal drugs.
Your ability to become pregnant or father a child may be affected by having this treatment. It's important to discuss fertility with your doctor before starting treatment.
It's not advisable to become pregnant or father a child while having 5FU as it may harm the developing baby. It’s important to use effective contraception while having this drug and for at least a few months afterwards. You can discuss this with your doctor or nurse.
It’s not known whether chemotherapy drugs can be present in semen or vaginal fluids. To protect your partner, it’s safest to either avoid sex or use a barrier form of contraception for about 48 hours after chemotherapy.
There's a potential risk that chemotherapy drugs may be present in breast milk. Women are advised not to breastfeed during chemotherapy and for a few months afterwards.
If you’re admitted to hospital for a reason not related to the cancer, it’s important to tell the doctors and nurses looking after you that you're having chemotherapy treatment. You should tell them the name of your cancer specialist so that they can ask for advice.
It’s a good idea to know who you should contact if you have any problems or troublesome side effects when you’re at home. Your chemotherapy nurse or doctor will give you details of who to contact for advice. This should include ‘out-of hours’ contact details if you need to call someone at evenings, overnight or at the weekend.
This section is based on our fluorouracil fact sheet, which has been compiled using information from a number of reliable sources, including:
Sweetman, et al. Martindale: The Complete Drug Reference. 37th edition. 2011. Pharmaceutical Press.
British National Formulary. 62nd edition. 2011. British Medical Association and Royal Pharmaceutical Society of Great Britain.
electronic Medicines Compendium. (accessed October 2011).
Perry MC. The Chemotherapy Source Book. 4th edition. 2007. Lippincott Williams and Wilkins.