What Is Fluorouracil, and How Is It Used to Treat Cancer?

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Fluoro-what? Fluorouracil may not be easy to pronounce, but it’s a common medication used for many different medical conditions. And it’s been used for more than a half-century, after its FDA approval in 1962. 

Fluorouracil is often given as an intravenous (IV) treatment for cancer. But it’s also available in topical forms (Efudex, Carac, Tolak) that can be applied to the skin. And capecitabine (Xeloda) is an oral medication that turns into fluorouracil once it’s absorbed by your body. 

Read on below to learn about fluorouracil and how it’s used for cancer treatment.

What is fluorouracil, and how does it work?

Fluorouracil and capecitabine are options in a type of cancer treatment called chemotherapy. Fluorouracil is commonly known as 5-fluorouracil, or “5-FU” for short. It comes as an IV injection and a topical cream and solution. And capecitabine is an oral prodrug that turns into fluorouracil in the body.

Chemotherapy medications including fluorouracil work by killing fast-growing cells, such as cancer cells. There are many types of chemotherapy. They differ based on where in the “cell cycle” they work. The cell cycle is the set of steps that all cells, including cancer cells, go through to grow and divide.

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Fluorouracil is a type of chemotherapy medication called an antimetabolite. To understand how antimetabolites work, it’s important to know that cancer develops when cells have a change in their DNA. This change causes them to replicate faster than normal. Antimetabolites work by preventing DNA from replicating, which stops cancer cells from multiplying and growing. 

What is fluorouracil used for?

Different forms of fluorouracil are FDA-approved for different uses. IV fluorouracil and capecitabine primarily treat a type of cancer called adenocarcinomas. These are solid tumor cancers that start in mucus-producing glands, such as the gut or prostate. Often, fluorouracil and capecitabine are used with other chemotherapy medications or radiation therapy.

In some cases, they can be used in the early stage of cancers, when a tumor is only found in one tissue or area. They can also be used in tumors that have come back (recurred) or spread to other parts of the body (metastasized). Your oncologist (cancer specialist) will determine what treatment regimen is best.

IV fluorouracil

IV fluorouracil is FDA-approved to treat adenocarcinomas of the:

• Gut

• Pancreas

• Skin

• Breast

Depending on which condition you’re treating, IV fluorouracil can be used on its own or in combination with other chemotherapies. It’s most commonly used with other chemotherapies because this is how it’s most effective. For example, IV fluorouracil is a first-choice option for advanced pancreatic cancer when combined with other medications in a regimen called FOLFIRINOX. This includes:

• Leucovorin: also called folinic acid, this is the “FOL”

• Fluorouracil: the “F” in the regimen name

• Irinotecan: abbreviated as “IRIN”

• Oxaliplatin: abbreviated as “OX” for advanced pancreatic cancer

Oral capecitabine

Oral capecitabine is approved to treat these cancers:

• Colorectal 

• Breast 

• Stomach 

• Esophageal 

• Pancreatic 

Capecitabine is most commonly reserved for advanced or metastatic cancers. It’s commonly used with other chemotherapy medications.

Topical fluorouracil

Topical fluorouracil is approved to treat certain skin conditions:

• Actinic keratosis

• Basal cell carcinoma (when fluorouracil 5% product is used)

Actinic keratosis (sometimes also called solar keratosis) is a type of precancerous skin condition. This means it has the potential to become cancerous but isn’t growing fast enough to be called cancer yet.

Basal cell carcinoma (BCC) is a skin cancer. It can present as a sore, scar, or rough patch of skin. Anyone can develop BCC, but it’s more likely in people with lighter skin and hair, because they tend to get sunburned easily. Sun exposure is a risk factor for developing BCC. 

How is fluorouracil administered?

As discussed, fluorouracil can be given several ways. It’s available as an IV injection, oral tablet, and topical cream and solution.

IV infusion

Fluorouracil can be given as an infusion into the vein. Sometimes it’s also given together with another non-chemotherapy medication called leucovorin to improve its cancer-killing effect. When given via IV, fluorouracil is processed by the body quickly. So, it’s typically given through a pump over 24 to 46 hours.

Oral tablet

Fluorouracil itself isn’t available in oral form. But the oral tablet capecitabine gets processed into fluorouracil once it's in your body. Capecitabine can also be used alone, in combination with other chemotherapy medications, or with radiation therapy.

Capecitabine tablets are usually taken twice daily. They should be swallowed whole and taken with a glass of water. Capecitabine is best taken within 30 minutes after a meal, at the same time each day (about 12 hours apart).

If you throw up after taking capecitabine, don’t take another tablet. Just continue with your next scheduled dose.

Topical cream and solution

Fluorouracil can also be given as a cream or topical solution to be used on the skin. It’s applied as a thin layer over the affected area. It’s usually applied twice a day. Depending on what type of skin cancer you’re treating, you may use this for 2 to 12 weeks.

What are the side effects of fluorouracil?

IV fluorouracil and oral capecitabine share a lot of the same side effects. The severity of side effects can vary depending on your specific regimen, but a few common fluorouracil side effects include:

• Diarrhea

• Nausea

• Vomiting

• Stomach pain

• Mouth sores

• Lack of energy 

• Tiredness

• Skin issues, such as swelling, irritation, and hand-foot syndrome

• Lowered appetite

• Weight loss

• Hair loss

Topical fluorouracil’s side effects are mostly skin-related. That’s because killing abnormal skin cells can cause irritation. But your skin will typically heal after treatment. Common skin effects include:

• Redness

• Burning

• Crusting

• Itching

• Blistering

Does fluorouracil have any serious side effects?

There are also several serious side effects that can happen when taking fluorouracil. Examples include:

• Heart problems

• Altered mental status 

• Severe diarrhea

• Fever and severe infection

• Lowered amount of certain blood cells

Your oncologist will monitor you closely in case treatment needs to be paused or stopped. Tell them immediately if you experience any severe side effects. They may need to make changes to your treatment. Or you may need emergency care. Call 911 or seek immediate medical attention if you have chest pain that won’t go away, shortness of breath, or confusion.

Who should avoid fluorouracil? [

If you’re pregnant or breastfeeding, you should avoid fluorouracil or capecitabine. If you’re able to become pregnant, use contraception during treatment with IV fluorouracil or oral capecitabine, and continue using it for 6 months after your last dose. If you are sexually active with a partner who can become pregnant, use contraception during treatment with IV fluorouracil or capecitabine and for 3 months after your last dose.

You should also avoid fluorouracil or capecitabine if you lack dihydropyrimidine dehydrogenase (DPD) activity. This is a genetic mutation. DPD is the enzyme (protein) that breaks down and removes fluorouracil. People with this mutation are at higher risk of experiencing severe and life-threatening side effects. Tell your oncologist if you know that you have a DPD mutation.

If you take warfarin (Coumadin, Jantoven), fluorouracil or capecitabine may increase your risk of bleeding. Your healthcare provider will monitor this possible interaction more closely. But you don’t necessarily have to avoid taking these medications together.

Why trust our experts?

Written by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Reviewed by:

John Strickler, MD

John Strickler, MD, joined the Duke University faculty in 2011 and is now an associate professor of medicine in the division of medical oncology. His research focuses on precision cancer medicine: identification of genomic biomarkers that predict sensitivity or resistance to targeted therapies and immunotherapy.

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