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Introduction

Written by Sarah Lewis, PharmD
Medically reviewed by Victor Nguyen, PharmD, MBA
Updated on July 26, 2023

Fluorouracil (flure oh YOOR a sil) is a generic medication prescribed for certain kinds of cancer and precancerous skin conditions. Fluorouracil belongs to a group of drugs called antimetabolites.

The Food and Drug Administration (FDA) has approved fluorouracil to treat:

• colon or rectal cancer
• breast cancer
• stomach cancer
• pancreatic cancer
• basal cell carcinoma
• actinic keratoses

These approved uses differ based on the form of fluorouracil your doctor prescribes.

Side effects of fluorouracil

Fluorouracil may cause mild or serious side effects. More common mild side effects of fluorouracil and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about fluorouracil’s side effects, ask your doctor or pharmacist. You can also refer to the prescribing information for fluorouracil listed in the “Resources” section.

Mild side effects

More common mild side effects reported with some forms of fluorouracil are listed below. These side effects may differ based on the form of fluorouracil you’re prescribed.

This article doesn’t include all possible mild side effects of the drug. To learn more about fluorouracil’s side effects based on the form, refer to the prescribing information for fluorouracil listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Fluorouracil topical cream’s* mild side effects include:

• burning
• itchiness
• soreness
• ulcers (sores)
• mild allergic reaction†

Fluorouracil intravenous (IV) injection’s mild side effects include:

• dry skin
• headache
• mild diarrhea
• sensitivity to light or watery eyes
• mild allergic reaction†

* Topical drugs are applied to the skin.
† For details about this side effect, see the “Interactions and warnings for fluorouracil” section.

Serious side effects

Serious side effects of fluorouracil are listed below. These side effects may differ based on the form of fluorouracil you’re prescribed.

This article doesn’t include all possible serious side effects of the drug. To learn more about fluorouracil’s side effects based on the form, refer to the prescribing information for fluorouracil listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, fluorouracil’s serious side effects include:

• nervous system problems, such as:
  • confusion
  • vision problems
  • loss of coordination
• hand-foot syndrome (a skin reaction on the palm of the hands and soles of the feet)
• heart problems, such as:
  • irregular heartbeat
  • heart attack
  • heart failure
• low blood cell counts, which can be severe and possibly fatal
• mucositis (swelling, sores, and shedding of the lining of the mouth or esophagus)
• severe diarrhea
• severe allergic reaction*

For fluorouracil topical cream, the following serious side effects may also occur:

• skin blisters
• hair loss
• high white blood cell counts or changes in other blood cell counts
• irritation or reaction in the eyes, nose, or mouth

* For details about this side effect, see the “Interactions and warnings for fluorouracil” section.

Common questions about fluorouracil

Below you’ll find answers to a few commonly asked questions about fluorouracil.

When do you stop treatment with fluorouracil?

How long you need to use fluorouracil and when you stop treatment with it varies. In general, your doctor will likely recommend using the topical cream or topical solution for 2–6 weeks. (Topical drugs are applied to the skin.)

For the intravenous (IV) injection, your doctor will let you know how long you’ll need treatment. It can vary with the type of cancer you’re treating and the specific regimen your doctor prescribes. Your doctor will continue treatment based on how the cancer and your body responds. They may need to pause or adjust treatment if certain side effects occur. (For details about the drug’s side effects, see the “Side effects” section.)

Talk with your doctor to find out how long to expect treatment with fluorouracil.

How does fluorouracil work? And how long does it take to start working?

Fluorouracil works by blocking an enzyme (a type of protein) that cells need to multiply (make more cells) and grow. Cancer cells multiply and grow faster than healthy cells. So this action slows or stops the growth of cancer cells.

Fluorouracil will start working as soon as treatment begins. But it can take some time to get rid of the cancerous or precancerous cells.

If you’d like to know more about this, talk with your doctor or pharmacist.

Uses of fluorouracil

The Food and Drug Administration (FDA) approves prescription drugs such as fluorouracil for certain conditions. Approved uses for fluorouracil are described below. These uses differ based on the form of fluorouracil prescribed.

Use for certain skin conditions

Doctors may prescribe fluorouracil topical cream or topical solution for treating actinic keratoses and basal cell carcinoma. (Topical drugs are applied to the skin.) It’s used for this purpose in adults and is usually prescribed as a short-term treatment.

With actinic keratoses, skin cells have made precancerous changes. They appear as rough, scaly patches of skin. They commonly occur in areas of skin that are exposed to the sun. These include the face, ears, arms, and backs of the hands.

With basal cell carcinoma, skin cancer has developed. This is the most common form of skin cancer. It usually occurs on sun-exposed skin. It often looks like a waxy bump or dome-shaped growth.

Doctors may not prescribe fluorouracil topical cream or topical solution to certain people. This includes people with dihydropyrimidine dehydrogenase (DPD) enzyme deficiency. (With this condition, you have a low level of DPD enzyme, a type of protein.)

Use for certain cancers

Doctors may prescribe fluorouracil intravenous (IV) injection for treating certain kinds of cancer, including:

• colon or rectal cancer
• breast cancer
• stomach cancer
• pancreatic cancer

It’s used for this purpose in adults. The length of treatment varies with the type of cancer you have and the specific treatment regimen your doctor recommends.

With cancer, gene mutations (changes) allow cells to multiply (make more cells) and grow out of control. Sometimes, these gene mutations are inherited from a parent. But most of the time, the mutations happen due to small amounts of cell damage over a person’s lifetime. At a certain point, the damage causes the cells to become abnormal and grow uncontrollably. These cells are cancer.

Fluorouracil IV injection is usually prescribed together with other chemotherapy drugs or leucovorin.

Doctors may not prescribe fluorouracil IV injection for certain people. This includes people with DPD enzyme deficiency.

Interactions and warnings for fluorouracil

Below, you’ll find information about fluorouracil’s possible interactions and warnings.

Interactions of fluorouracil

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you use fluorouracil, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for fluorouracil” section below.

Warnings for fluorouracil

Some people should not use fluorouracil, and others should use it cautiously.

Fluorouracil could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether fluorouracil is a safe option for you. These warnings may differ based on the form of fluorouracil you’re prescribed.

Ask your doctor about specific warnings for fluorouracil, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Fluorouracil can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to fluorouracil or any of its ingredients, your doctor will likely not prescribe fluorouracil. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to fluorouracil, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of fluorouracil

If you apply fluorouracil, you should not apply more fluorouracil than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve applied too much fluorouracil, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and fluorouracil

Information about fluorouracil and pregnancy and breastfeeding is described below.

Fluorouracil and pregnancy

Fluorouracil should not be applied or given during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before having treatment with this medication. Your doctor may suggest birth control options to use during treatment with fluorouracil.

Fluorouracil and breastfeeding

Fluorouracil should not be applied or given while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before having treatment with this medication. Your doctor may recommend other ways to feed your child during treatment with fluorouracil.

What to ask your doctor

Let your doctor know if you have questions about fluorouracil or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• What’s the most important information I need to know about fluorouracil?
• How long should I expect to have fluorouracil treatment?
• How can I prevent or manage side effects of fluorouracil?

Resources

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Fluorouracil cream USP 5%. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/f75c4b87-3015-a938-e053-6394a90ac4cb/spl-doc
• Fluorouracil – fluorouracil injection, solution. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/d10f12a2-7b38-4351-93df-1e8444d2a9e4/spl-doc
• Fluorouracil topical solution, USP 2% and 5%. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/1b2f6145-b338-42ed-88a7-f4da65c59164/spl-doc

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.