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Fluorouracil (5-FU)

Fluorouracil (5-FU) is an option for people with locally advanced and advanced pancreatic cancer who don’t cope well with gemcitabine.

5-FU is one of the drugs used in FOLFIRINOX, which is a combination of several drugs for pancreatic cancer, and is very rarely given on its own. 5-FU is also combined with leucovorin (folinic acid) and oxaliplatin in FOLFOX, a second-line treatment for advanced pancreatic cancer

How is 5-FU given? 

You will have your chemotherapy as an outpatient in the chemotherapy unit at the hospital, which means you will go in for treatment, but won’t need to stay overnight.

5-FU is given as an injection into the vein or through a special pump (infusion). If given as part of FOLFIRINOX you will usually have an injection of 5-FU (called a bolus) followed by an infusion of 5-FU lasting 46 hours. Read more about how 5-FU is given as part of FOLFIRINOX.

If given as part of FOLFOX you will have an injection of the 5-FU, followed by an infusion of 5-FU, which lasts 46 hours. Read about how 5-FU is given if taken as part of FOLFOX.

If 5-FU is given on its own you will have an infusion or injection.

The exact number of cycles you have will depend on your treatment plan and how well you respond to it. Your nurse or doctor will tell you more about this.

5-FU may be given as an injection through a fine plastic tube (a cannula) which is put into a vein in your arm or hand each time you have treatment. Or you may have it  through a central line, such as a PICC line, Hickmann line or a portacath. These are tubes that deliver drugs directly into a large vein in your chest, and stay in place for as long as your course of chemotherapy lasts.

If you are having 5-FU through a central line as an infusion, it may be given over 46 or 48 hours through a small portable pump attached to a belt, so that you can go home. When it’s finished the pump is usually disconnected at the hospital, or at home by a nurse. You will then have a break from chemotherapy for the next 12 days. 

Oxaliplatin with 5-FU and folinic acid (FOLFOX) chemotherapy cycle

Folfirinox Chemotherapy Cycle


What are the side effects of 5-FU? 

5-FU can cause side effects but these can affect everyone differently. Your doctor or nurse should give you information about side effects. Make sure you read this, and ask them any questions you may have about the possible side effects, and how to manage them. Knowing what to expect can help you to deal with any side effects.

Common side effects

  • Increased risk of infection. 5-FU can increase your risk of getting an infection, because it can cause a drop in the number of your white blood cells. This means your body is less able to fight infection. Signs of an infection include a high temperature, headaches, aching muscles, a cough, sore throat, or feeling shivery and cold.
  • Anaemia (low level of red blood cells). 5-FU can lower the number of red blood cells in your blood (anaemia). This can make you feel tired, faint and short of breath. If you are very anaemic, you may need to be given extra red blood cells in a drip (blood transfusion).
  • Nosebleeds. 5-FU can sometimes cause nosebleeds when you blow your nose. If you have a nosebleed that doesn’t stop after five minutes call your doctor or nurse who will be able to help.
  • Sore mouth or mouth ulcers. This can be mild or severe, making eating and drinking difficult. Try to drink lots of fluids, clean your teeth regularly with a soft toothbrush and avoid spicy or citrus foods that might sting your mouth. Your doctor or nurse can give you an anti-bacterial mouthwash which should help. Using painkillers such as paracetamol or ibuprofen can also help. 
  • Feeling or being sick (nausea or vomiting). This is a common side effect of 5-FU but can be controlled with anti-sickness medication. You will usually be given medication before your chemotherapy starts to help control or prevent sickness. If it doesn’t work, tell your doctor or nurse – you should be able to change the medication. Read more about coping with feeling and being sick.
  • Loose watery poo (diarrhoea). If you have diarrhoea, make sure you drink plenty of fluids. If you have diarrhoea more than four times a day, tell your doctor or nurse. They may give you medication to control it, or reduce the dose of your chemotherapy drug in future cycles.
  • Loss of appetite. During your treatment you may not feel like eating. Try to eat small meals often. If your appetite doesn’t improve after a few days, let your doctor or dietitian know. Read more about loss of appetite
  • Fatigue (extreme tiredness). Fatigue is a common side effect of 5-FU. There are ways to deal with fatigue. People can feel tired or exhausted for much of the time during treatment. You might want to keep a fatigue diary, so you can see when you have more energy to do things. This may help you to plan activities on the days that you are feeling better, and rest on days when you’re more tired than normal.
  • Sore hands and feet. 5-FU can cause soreness, redness and peeling on the palms of your hands and soles of your feet. Or your skin might look shiny, feel tight and crack around the fingertips. Your doctor or nurse may prescribe a vitamin or creams before starting chemotherapy to help with this. Keeping your hands and feet cool can also help. The soreness usually gets better after your chemotherapy ends.
  • Hair loss. 5-FU may cause your hair to thin. It should grow back gradually once treatment stops. Your nurse can give you advice on dealing with thinning hair.

Less common side effects

  • Heart problems. 5-FU can cause chest pain, palpitations or a fluttering heart. If you have any of these symptoms let the medical team know immediately on the emergency number you should have been given. They may prescribe medication. These symptoms usually end after treatment.
  • Eye problems. 5-FU may cause sore or watery eyes.Tell your nurse or doctor if this happens, as you may need antibiotic eye drops.
  • Skin changes. Your skin may darken or be more sensitive to the sun. Use a high factor sun cream if you’re going outside. Let your doctor or nurse know about any skin changes.
  • Risk of a blood clot. 5-FU can increase the risk of a blood clot forming in a vein (thrombosis), although this is very rare. If you have pain or swelling in one of your legs or arm, or are very short of breath, phone an ambulance or the emergency contact number that you will have been given immediately. A blood clot needs to be treated straight away.
  • Allergic reactions. 5-FU may cause an allergic reaction while it’s being given, but this is very rare. Signs of this can include a rash, feeling dizzy, or swelling of the face and hands. If this happens tell your nurse or doctor immediately as any allergic reaction will need to be treated straight away.

We haven’t listed every possible side effect of Fluorouracil (5-FU). Speak to your doctor or nurse for more information if you experience anything unusual. If you are unable to contact your doctor or nurse, contact the medical team on the emergency number that you should have been given.

If you have any questions about 5-FU or side effects, you can also call our specialist nurses free on our Support Line.  

More chemotherapy information

Published May 2017 

Review date May 2019

Information Standard