Fluorouracil

Fluorouracil is also known as FU or 5FU and is one of the most commonly used drugs to treat cancer. It is used to treat many types of cancer including, breast cancer, head and neck cancers, anal cancer, stomach cancer, colon cancer and some skin cancers.

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 cells working properly. They stop cells making and repairing DNA. Cancer cells need to make and repair DNA so that they can grow and multiply. Anti metabolites also stop normal cells working properly. This is why you get side effects.

You can have fluorouracil as an injection or drip (infusion) into a vein (intravenously). It can also be used as an ointment called Efudix for skin cancer.

You can have fluorouracil intravenously through a thin, short tube (a cannula) put into a vein in your arm each time you have treatment. Or you may have it through a central line, a portacath or a PICC line. These are long, plastic tubes that give the drugs directly into a large vein in your chest. You have the tube put in just before your course of treatment starts and it stays in place as long as you need it. 

You usually have intravenous fluorouracil as part of a course of several cycles of treatment. The exact treatment plan depends on which type of cancer you have. To find out more about the way chemotherapy treatment is planned look at our planning chemotherapy page. You may have the fluorouracil over several days through a drip or using a small pump that you carry around.

Some other medicines can stop fluorouracil working so well. Or the fluorouracil can change how some other medicines work. You should tell your doctor if you are taking the anti epileptic drug phenytoin or the blood thinning drug warfarin. The fluorouracil can interfere with how your body absorbs these drugs.

The side effects associated with intravenous fluorouracil are listed below. You can use the links (underlined) to find out more about each side effect. Where there is no link, please see our cancer drugs side effects section or use the search box at the top of the page.

More than 10 in every 100 people have one or more of the side effects listed below.

Temporary drop in the number of blood cells made by the bone marrow, causing

• Increased risk of getting an infection from a drop in white blood cells – it is harder to fight infections and you can become very ill. You may have headaches, aching muscles, a cough, sore throat, pain passing urine or feel cold and shivery
• Tiredness and breathlessness due to a drop in red blood cells (anaemia) – you may need a blood transfusion
• Bruising more easily due to a drop in platelets – you may have nosebleeds, bleeding gums after brushing your teeth, or lots of tiny red spots or bruises on your arms or legs (known as petechia)

Some of these side effects can be life threatening, particularly infections. You should contact your doctor if you have any of these side effects. Your doctor will check your blood counts regularly to see how well your bone marrow is working.

Other common side effects include

• Tiredness (fatigue) during and after treatment – most people find their energy levels are back to normal from 6 months to a year after their treatment finishes
• Feeling or being sick, which is usually mild
• Mouth sores and ulcers
• Diarrhoea – you need to drink plenty of fluids. If the diarrhoea becomes severe or continues you could get dehydrated so tell your doctor or nurse
• Heart problems, such as angina, heart failure or a heart attack – let your doctor or nurse know if you have any chest pain
• This drug may have a harmful effect on a baby developing in the womb. It is not advisable to become pregnant or father a child while having chemotherapy. It is important to talk to your doctor or nurse about contraception before having the treatment

Between 1 and 10 in every 100 people have one or more of these.

• Hair thinning
• Brittle, chipped and ridged nails
• Sensitivity of the skin to sunlight – you should not use sunbeds or sit in the sun if having fluorouracil. Cover up or use a sun block
• Rashes, which may be itchy
• Watery eyes from increased production of tears
• Gritty eyes and blurred vision
• Loss of appetite
• Brown marking on the skin following the line of the vein where fluorouracil has been injected
• Continuous infusion of fluorouracil can occasionally cause soreness, redness and peeling on the palms of the hands and soles of the feet (palmar – plantar syndrome) which may cause tingling, numbness, pain and dryness

Fewer than 1 in 100 people have these.

• Total hair loss
• Darkened skin
• Confusion or unsteadiness
• Women may stop having periods (amenorrhoea) but this may only be temporary
• Loss of fertility – you may not be able to get pregnant or father a child after treatment with this drug. It is important to talk to your doctor about your fertility before starting treatment

The side effects above may be mild or more severe. A side effect may get better or worse through your course of treatment, or more side effects may develop as the course goes on. This depends on

• How many times you've had the drug before
• Your general health
• The amount of the drug you have (the dose)
• Other drugs you are having

Talk to your doctor, pharmacist or nurse about all your side effects so that they can help you manage them. Your chemotherapy nurse will give you a contact number. You can ring if you have any questions or problems. They can give you advice or reassure you. If in doubt, call them.

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and other over the counter remedies – some drugs can react together.

You should not have immunisations with live vaccines while you are having this treatment or for at least 6 months afterwards. In the UK, live vaccines include rubella, mumps, measles (usually given together as MMR), BCG and yellow fever. You can have other vaccines, but they may not give you as much protection as usual until your immune system has fully recovered.

It is safe for you to be in contact with other people who've had live vaccines as injections. There can be problems with oral vaccines, but not many people in the UK have oral vaccines now. So there is usually no problem in being with any baby or child who has recently had any vaccination in the UK. You might need to make sure that you aren't in contact with anyone who has had oral polio, cholera or typhoid vaccination recently, particularly if you live abroad.