Fluorouracil
1 medicine
Fluorouracil (5-FU) is a chemotherapy medicine that stops cancer cells building DNA; it also treats some skin lesions as a cream. People with a deficiency in the enzyme DPD can develop severe, sometimes fatal, toxicity from standard doses, so testing before treatment is recommended.
Key facts
- Fluorouracil (5-FU) is a cytotoxic antimetabolite. It is given by injection or infusion for cancer, or applied as a cream or solution for certain skin lesions.
- A small proportion of people lack enough of the enzyme DPD (dihydropyrimidine dehydrogenase), which normally breaks fluorouracil down. In these people even standard doses can cause severe, sometimes fatal, toxicity, so many cancer centres test DPD activity before the first systemic dose.
- Fluorouracil suppresses bone marrow, lowering white blood cells, red blood cells and platelets; blood counts are checked regularly during treatment.
- Seek urgent care for fever, signs of infection, severe or bloody diarrhoea, mouth ulcers that stop you eating or drinking, or unusual bleeding or bruising.
What fluorouracil treats
By injection or infusion, fluorouracil treats colorectal, breast, stomach, pancreatic and head-and-neck cancers, usually combined with other chemotherapy drugs. As a topical cream or solution, it treats actinic keratosis (sun-damaged skin patches) and some superficial basal cell skin cancers.
How fluorouracil works
Cells copy their DNA before they divide. Fluorouracil is disguised as a normal DNA building block, so dividing cells take it up and their DNA copying stalls. Cancer cells and the abnormal skin cells in actinic keratosis divide faster than most normal cells, making them more sensitive to this effect, though normal fast-dividing tissue such as bone marrow and the gut lining is also affected.
Before you take it
- Tell your treatment team if you or a close relative has ever had severe, unexpected toxicity from fluorouracil or capecitabine (a related tablet medicine); this can suggest DPD deficiency.
- Fluorouracil is not used in pregnancy: it can seriously harm a developing baby. Effective contraception is needed during treatment and for a period afterward, for both women and men.
- Tell your team about liver or kidney problems, low blood counts, or heart disease, since fluorouracil can occasionally cause chest pain or heart rhythm changes.
- For the topical form, avoid sun exposure on treated skin and tell your prescriber about other skin products you use.
Side effects
Common effects include nausea, diarrhoea, mouth soreness, and skin or nail changes; topical use causes redness, crusting and irritation where it is applied.
Stop and seek urgent medical care for any of these:
- Fever, chills, or other signs of infection (a possible sign of very low white cell counts).
- Severe or bloody diarrhoea, or mouth ulcers preventing you from eating or drinking.
- Unusual bruising or bleeding.
- Chest pain, breathlessness, or an irregular heartbeat.
Safety essentials
- DPD deficiency is the single biggest risk with fluorouracil: it can turn a standard dose into a severe or fatal one. Report any personal or family history of serious reactions to fluorouracil or capecitabine before treatment starts.
- Blood counts are monitored throughout treatment because of the risk of myelosuppression; doses are adjusted or delayed if counts fall too low.
- Tell your team immediately about mouth sores, diarrhoea or hand-foot skin reactions, since these can signal that the dose needs adjusting before they become severe.
This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.