Fluorouracil (pronounced floo-ro-you-ro-sill), which is also called 5FU, is a chemotherapy drug that is given as a treatment for some types of cancer, including bowel, breast, stomach, and gullet (oesophagus) cancer. This information describes 5FU, how it is given and some of its possible side effects. It should ideally be read with our general information about chemotherapy and about your type of cancer, which give further information and advice.

If you have any further questions you can ask your doctor or nurse at the hospital where you are having your treatment, or speak to one of our cancer support service nurses.

5FU is available as:

• a colourless fluid
• a cream (Efudix®).

5FU may be given as:

• an injection into a vein (intravenously) through a fine tube (cannula) inserted into the vein
• a drip (infusion) into the vein through a cannula. It may be given through a central line, which is inserted under the skin into a vein near the collarbone, or into a PICC line inserted into a vein in the crook of the arm
• cream applied directly to the skin.

Each person's reaction to chemotherapy is different. Some people have very few side effects, while others may experience more. The side effects described in this information will not affect everyone who is given 5FU, and may be different if you are having more than one chemotherapy drug.

We have outlined the most common and less common side effects, so that you can be aware of them if they occur. However, we have not included those which are very rare and therefore extremely unlikely to affect you. If you notice any effects which you think may be due to the drug, but which are not listed in this information, please discuss them with your doctor or chemotherapy nurse.

Sore mouth and ulcers Your mouth may become sore, or you may notice small ulcers during this treatment. Sucking ice chips whilst the chemotherapy is being given may help to reduce the chance of this occurring. Drinking plenty of fluids and cleaning your teeth regularly and gently with a soft toothbrush can also help. Tell your nurse or doctor if you do have any of these problems, as special mouthwashes and medicines to prevent or clear any mouth infection can be prescribed. You may also notice that your food tastes different.

Taste changes You may notice that your food tastes different. Normal taste will usually come back after the treatment finishes.

Diarrhoea This can usually be easily controlled with medicine but let your doctor know if it is severe or if it continues. It is important to drink plenty of fluids if you have diarrhoea.

Gritty eyes and blurred vision If this happens it is important that you tell your doctor, who can prescribe soothing eye drops.

Skin changes Your skin may darken, due to excess production of pigment. This will slowly return to normal a few months after the treatment has finished. The skin over the vein used for the injection may become discoloured, but this is only temporary.

Lowered resistance to infection 5FU can reduce the production of white blood cells by the bone marrow, making you more prone to infection. This effect can begin seven days after treatment has been given, and your resistance to infection usually reaches its lowest point 10–14 days after chemotherapy. Your blood cells will then increase steadily, and will usually have returned to normal levels within 21 days.

Contact your doctor or the hospital straightaway if:

• Your temperature goes above 38ºC (100.5ºF)
• You suddenly feel unwell (even with a normal temperature).

You will have a blood test before having more chemotherapy, to make sure that your cells have recovered. Occasionally it may be necessary to delay your treatment if the number of blood cells (the blood count) is still low.

Bruising or bleeding 5FU can reduce the production of platelets (which help the blood to clot). Let your doctor know if you have any unexplained bruising or bleeding.

Anaemia (low number of red blood cells) While having treatment with 5FU you may become anaemic. This may make you feel tired and breathless. Let your doctor or nurse know if these are a problem.

Tiredness feeling weak You may feel very tired. It is important to allow yourself plenty of time to rest.

Feeling sick (nausea) and vomiting If this happens it may begin after the treatment is given and last for a few days. Your doctor can now prescribe very effective anti-sickness (anti-emetic) drugs to prevent or greatly reduce nausea and vomiting. If the sickness is not controlled, or continues, tell your doctor, who can prescribe other anti-sickness drugs that may be more effective.

Hair loss This is rare, but hair may thin, or occasionally be lost completely. If hair loss happens, it usually begins about 3–4 weeks after starting treatment, although it may occur earlier. Hair loss is temporary, and the hair will regrow once the treatment ends.

Changes to nails Your nails may become brittle, chipped and ridged. These changes grow out slowly over a few months once the treatment has ended.

Sensitivity of the skin to sunlight During treatment with 5FU, and for several months afterwards, you will be more sensitive to the sun, and your skin may burn more easily than normal. You can still go out in the sun, but always wear a high protection factor suncream and protective clothing.

Rashes 5FU can cause a rash, which may be itchy. Your doctor can prescribe treatment to help reduce this.

Soreness and redness of the palms of the hands and soles of the feet (Sometimes known as palmar planter or hand and foot syndrome). This can happen when 5FU is given continuously or over a long time. It is temporary and improves when the treatment is finished. You may be prescribed vitamin B6 (pyridoxine), which can help to reduce this.

Increased production of tears This may sometimes be caused by 5FU. This is a temporary side effect, although the tears can sometimes irritate the front of the eye (conjunctiva). If this happens your doctor can give you soothing eye drops.

Other medicines Some medicines can be harmful to take when you are having chemotherapy. Let your doctor know about any medications you are taking, including non-prescribed drugs such as complementary therapies and herbal drugs.

Fertility Your ability to become pregnant or father a child may be affected by taking this drug. It is important to discuss fertility with your doctor before starting treatment.

Contraception It is not advisable to become pregnant or father a child while taking 5FU, as the developing foetus may be harmed. It is important to use effective contraception while taking this drug, and for at least a few months afterwards. Again, discuss this with your doctor.

This section is based on our Fluorouracil factsheet which has been compiled using information from a number of reliable sources, including:

• Martindale: The Complete Drug Reference (35th edition). Eds. Sweetman et al. Pharmaceutical Press, 2006.
• British National Formulary (52nd edition). British Medical Association and Royal Pharmaceutical Society of Great Britain, September 2006.
• The Chemotherapy Source Book (3rd edition). Ed. Perry. Lippincott, Williams and Wilkins, 2001.

For further references, please see general bibliography.