Fluorouracil (5FU)

Fluorouracil is a type of chemotherapy. It is also called 5FU. It is used to treat many different types of cancer.

It is best to read this information with our general information about chemotherapy and the type of cancer you have.

Your cancer team will talk to you about this treatment and its possible side effects before you agree (consent) to have treatment.

This information is correct at time of publishing. But sometimes the types of cancer this treatment is used for, or treatment side effects, may change between revision dates.

You can talk to your cancer team if you want more detailed information about this treatment. Or visit the electronic Medicines Compendium (eMC) website, which has patient information leaflets (PIL) for individual drugs.

You usually have 5FU in a chemotherapy day unit or clinic as an outpatient. Or you may have it during a stay in hospital. You may have it with other cancer drugs.

During your course of treatment, you will meet with someone from your cancer team, such as a:

• cancer doctor
• chemotherapy nurse or specialist nurse
• specialist pharmacist.

This is who we mean when we mention doctor, nurse or pharmacist in this information.

Before or on the day of each treatment, you will have a blood test. This is to check that it is safe for you to have chemotherapy.

You will meet with a doctor, nurse or pharmacist before you have chemotherapy. They will talk to you about your blood results and ask how you have been feeling. If your blood results are okay, the pharmacy team will prepare your chemotherapy.

Your nurse will usually give you anti-sickness drugs before chemotherapy. You will have your chemotherapy through 1 of the following:

• a cannula – a short, thin tube the nurse puts into a vein in your arm or hand
• a central line – a fine tube that goes under the skin of your chest and into a vein close by
• a PICC line – a fine tube that is put into a vein in your arm and goes up into a vein in your chest
• an implantable port (portacath) – a disc that is put under the skin on your chest or arm and goes into a vein in your chest.

Your nurse may give you 5FU as an injection into a vein, or as a drip into the vein (infusion).

5FU may also be given over a few days as a continuous infusion. This is usually given through a small portable pump connected to either a central line or a PICC line. The pump can be carried on a belt or in a bag. You can go home with the pump. The nurse will tell you how to look after it.

5FU can also be given as a cream to treat some types of skin cancer. If you have 5FU as a cream the side effects are different to having it into a vein. Your doctor, nurse or pharmacist will tell you more about it.

This information is about 5FU that is given into a vein (intravenously).

Your cancer team may also give you anti-sickness drugs and other medicines to take home. Take all your capsules or tablets exactly as they tell you to.

You usually have a course of several cycles of treatment over a few months. Your cancer team will discuss your treatment plan with you.

This treatment can reduce the number of white blood cells in your blood. These cells fight infection. If your white blood cell count is low, you may be more likely to get an infection. A low white blood cell count is called neutropenia.

An infection can be very serious when the number of white blood cells is low. It is important to get any infection treated as soon as possible. If you have any of the following symptoms, contact the hospital straight away on the 24-hour number:

• a temperature above 37.5°C  
• a temperature below 36°C 
• you feel unwell, even with a normal temperature
• you have symptoms of an infection.

Symptoms of an infection include:

• feeling shivery and shaking
• a sore throat
• a cough 
• breathlessness
• diarrhoea
• needing to pass urine (pee) often, or discomfort when you pass urine.

It is important to follow any specific advice your cancer treatment team gives you.

Your white blood cell count will usually return to normal before your next treatment. You will have a blood test before having more treatment. If your white blood cell count is low, your doctor may delay your treatment for a short time, until your cell count increases.

This treatment can reduce the number of platelets in your blood. Platelets are cells that help the blood to clot.

If the number of platelets is low, you may bruise or bleed easily. You may have:

• nosebleeds
• bleeding gums
• heavy periods
• blood in your urine (pee) or stools (poo)
• tiny red, brown or purple spots that may look like a rash – these spots can be harder to see if you have black or brown skin. 

If you have any unexplained bruising or bleeding, contact the hospital straight away on the 24-hour number. You may need a drip to give you extra platelets. This is called a platelet transfusion.

This treatment can reduce the number of red blood cells in your blood. Red blood cells carry oxygen around the body. If the number of red blood cells is low, this is called anaemia. You may feel:

• very low in energy
• breathless 
• dizzy and light-headed. 

If you have these symptoms, contact the hospital straight away on the 24-hour number. You may need treatment for anaemia. If you are very anaemic, you may need a drip to give you extra red blood cells. This is called a blood transfusion.

Your doctor, nurse or pharmacist will prescribe anti-sickness drugs to help prevent or control sickness. Take the drugs exactly as they tell you to, even if you do not feel sick. It is easier to prevent sickness than to treat it after it has started.

If you feel sick, take small sips of fluid often and eat small amounts regularly. It is important to drink enough fluids. If you continue to feel sick, or if you are sick (vomit) 1 to 2 times in 24 hours, contact the hospital on the 24-hour number as soon as possible. They will give you advice. They may change your anti-sickness treatment. Let them know if you still feel sick.

This treatment may cause severe diarrhoea. Diarrhoea means passing more stools (poo) than is normal for you, or having watery or loose stools. If you have a stoma, it will be more active than usual. 

Your doctor, nurse or pharmacist may give you anti-diarrhoea drugs to take at home. 

If you have diarrhoea or a mild increase in stoma activity, follow their advice about: 

• taking anti-diarrhoea drugs 
• how much and what type of fluids to drink 
• any changes to your diet that might help. 

Contact the hospital straight away on the 24-hour number if:

• you have diarrhoea at night 
• you have uncomfortable stomach cramps
• you have diarrhoea 4 or more times in a day 
• you have a moderate increase in stoma activity 
• the anti-diarrhoea drugs do not work within 24 hours.

You may need to give a stool sample, or go to hospital to have fluids through a drip or antibiotics.

This treatment may cause a sore mouth and throat. You may also get mouth ulcers. This can make you more likely to get a mouth or throat infection. Use a soft toothbrush to clean your teeth or dentures in the morning, at night and after meals.

Contact the hospital straight away on the 24-hour number, if:

• a sore mouth or throat affects how much you can drink or eat 
• your mouth, tongue, throat or lips have any blisters, ulcers or white patches. 

They can give you advice, and mouthwash or medicines to help with the pain or to treat any infection. Follow their advice and make sure you:

• drink plenty of fluids
• avoid alcohol and tobacco
• avoid food or drinks that irritate your mouth and throat.

This treatment can affect the palms of your hands and the soles of your feet. This is called palmar-plantar or hand-foot syndrome. 

If you have white skin these areas may become red. If you have black or brown skin, these areas might get darker. 

The skin on the palms of your hands and the soles of your feet may:

• be sore
• be painful, tingle, or swell
• peel, crack or blister. 

If you have any of these symptoms, contact the hospital straight away on the 24-hour number. They can give you advice. This is especially important if you have any broken skin or if walking is difficult. They can prescribe creams and painkillers to help.

You can care for your hands and feet by: 

• keeping your hands and feet cool by washing in cool water
• gently moisturising your hands and feet regularly
• wearing gloves to protect your hands and nails when working in the house or garden
• wearing loose cotton socks and avoiding tight-fitting shoes and gloves.

This treatment can affect your appetite. Don’t worry if you do not eat much for 1 or 2 days. But if your appetite does not come back after a few days, or if you are losing weight, tell your doctor, nurse or pharmacist. They can give you advice. They may give you food or drink supplements. Or they may suggest changes to your diet or eating habits to help.

Feeling tired is a common side effect of this treatment. It is often worse towards the end of treatment and for some weeks after it ends. Try to pace yourself and plan your day so you have time to rest. Gentle exercise, like short walks, can help you feel less tired. 

If you feel sleepy, do not drive or use machinery.

5FU can affect how the heart works. You may have tests to check how well your heart is working. These may be done before, during and after treatment. 

You may develop heart problems even if these test results are normal. Very rarely, 5FU causes heart failure or a heart attack. The risk of this happening is very low. It happens to less than 1 in 100 (1%) of people who have 5FU. But it is important that you know about it. 

Contact the hospital straight away on the 24-hour number if you have any of these symptoms during or after treatment:

• breathlessness
• dizziness
• changes to your heartbeat
• swollen feet and ankles.

Always call 999 if you have:

• chest pain, pressure, heaviness, tightness or squeezing across the chest
• difficulty breathing.

5FU can cause sudden tightness (spasm) in the muscles in your chest for a short time. Contact the hospital straight away on the 24-hour number if you have any of these symptoms during treatment:

• breathlessness
• a cough that does not go away
• wheezing.

Always call 999 if you have difficulty breathing.

If you feel sick, have blurred vision or notice any effects on your nervous system, do not drive or use machines. Your doctor can tell you more about this.

Cancer and some cancer treatments can increase the risk of a blood clot. Contact the hospital straight away on the 24-hour number if you have any of these symptoms during or after treatment:

• throbbing pain or swelling in a leg or arm
• reddening of the skin in the area – if you have black or brown skin, this can be harder to notice, but the skin might become darker
• suddenly feeling breathless or coughing.

Always call 999 if you have:

• chest pain
• difficulty breathing.

A blood clot is serious, but it can be treated with drugs called anticoagulants. These thin the blood. Your doctor, nurse or pharmacist can give you more information about preventing and treating blood clots.

Some medicines can affect how this treatment works or be harmful while you are having it. Always tell your cancer doctor, nurse or pharmacist about any drugs you are taking or planning to take, such as: 

• medicines you have been prescribed
• medicines you buy in a shop, pharmacy or online
• vitamins or supplements 
• herbal drugs and complementary or homeopathic therapies
• recreational drugs – for example, cannabis.

Doctors usually recommend that people with cancer have vaccinations for flu and for coronavirus (covid). These help reduce your risk of serious illness from these infections. Most people can have these vaccines, including people with weak immune systems.

If your immune system is weak, you should not have live vaccinations. Live vaccines can make you unwell because they contain a very weak version of the illness they will protect you against. Live vaccines include Zostavax^®, which is a shingles vaccine, and the yellow fever vaccine.

It is important to ask your doctor, nurse or pharmacist for advice about having vaccinations. They can explain what vaccines are right for you and when it is best to have them.

Your doctor, nurse or pharmacist will advise you not to get pregnant or make someone pregnant while having this treatment and for some time afterwards. The drugs may harm a developing baby. It is important to use contraception to prevent pregnancy. Follow their advice about:

• what types of contraception to use 
• how long after treatment you should continue to use contraception. 

It is possible that small amounts of chemotherapy may be passed on through vaginal fluids or semen. If you have sex in the first few days after treatment, your cancer team will usually advise using condoms or a dental dam to protect your partner.

Some cancer drugs can affect whether you can get pregnant or make someone pregnant. If you are worried about this, it is important to talk with your doctor before you start treatment.

You are advised not to breastfeed while having this treatment, or for some time after treatment ends. This is because the drugs could be passed to the baby through breast milk. 

Your doctor, nurse or pharmacist can give you more information.

If you need medical treatment for any reason other than cancer, always tell the healthcare professional that you are having cancer treatment. Give them the contact details for your cancer doctor or cancer team so they can ask for advice.

If you have appointments with a dentist, always tell them you are having cancer treatment. Talk to your cancer team before you have any dental treatment.