Fluorouracil

What Is Fluorouracil?

Fluorouracil is a prescription medicine that belongs to a drug class called antimetabolites. More specifically, it is a pyrimidine analog. It interferes with the making of DNA in fast-growing cells, such as cancer cells and abnormal skin cells.

Approved Uses

Fluorouracil injection is FDA-approved to treat certain cancers, including adenocarcinoma of the:

• Colon and rectum
• Breast
• Stomach
• Pancreas

It is often given together with other cancer medicines as part of a treatment plan.

Fluorouracil topical (skin) products are FDA-approved to treat:

• Actinic keratoses (AKs), which are rough, scaly, precancerous patches caused by long-term sun exposure
• Superficial basal cell carcinoma (sBCC), a slow-growing type of skin cancer, when standard treatments are not practical (this use applies to certain strengths only)

Other Prescribed Uses

Specialists sometimes use fluorouracil for conditions that are not listed on the FDA label. These decisions are individual and are made by an experienced specialist. This guide does not recommend use for any condition that is not FDA-approved.

Available Formulations and Strengths

• Injection: a liquid given into a vein by a trained healthcare professional (50 mg per mL, in vials of different sizes)
• Topical cream: several strengths are available depending on the product, such as Fluorouracil Cream 1%-10g, Fluorouracil Cream 5%-10g
• Topical solution: 2% and 5%

Available products and strengths can vary. Your pharmacist can confirm which product you have.

What Is the Recommended Dosage of Fluorouracil?

There is no single dose that fits everyone. Your specialist decides the dose and schedule based on several factors.

For the Injection

• The type and stage of cancer
• The treatment plan, including which other medicines are given with it
• Body size (body surface area)
• Blood counts, liver function, and kidney function
• Genetic testing results. Some people have low activity of an enzyme called DPD (dihydropyrimidine dehydrogenase, made by the DPYD gene). They may have severe or life-threatening side effects, and testing may be recommended before treatment.
• How well you tolerate treatment. Doses are often lowered or delayed if side effects occur.

For Topical Products

• The condition and the area being treated
• The strength and form of the product
• The skin’s response, since some redness and irritation are expected

Available Dosage Forms

The injection is given in a clinic, infusion center, or hospital. Some treatment plans use a small portable pump that gives the medicine slowly over hours or days, so you may go home with the pump attached. Topical products are applied to the skin as directed.

Follow Your Specialist’s Instructions

Doses and schedules must be set by your specialist. Do not change how much you use, how often you use it, or how long you use it on your own. For topical products, more is not better and can cause harsh skin reactions.

How Fluorouracil Works

Cells need building blocks to make new DNA. Fluorouracil looks similar to one of those building blocks. Once inside the cell, it blocks an enzyme needed to make DNA and can also get into RNA. Fast-growing cells, such as cancer cells and abnormal skin cells, are more affected. Healthy fast-growing cells, such as those in the mouth, gut, hair, and bone marrow, can also be affected, which explains many side effects.

• In cancer treatment, it helps slow or stop the growth of cancer cells. It is usually part of a larger plan and may be combined with other medicines, surgery, or radiation.
• On the skin, it destroys abnormal skin cells. The skin often becomes red, sore, and crusted before it heals.

Fluorouracil treats or manages a condition. It does not work the same way for everyone, and it does not guarantee a cure.

Is a Prescription Required to Buy Fluorouracil Online?

Yes. Fluorouracil is a prescription-only medicine in both the injection and topical forms. It should be started and monitored by a licensed medical specialist, such as:

• An oncologist (for injection therapy)
• A dermatologist (for topical treatment of skin conditions)

The injection is a hazardous drug that is prepared and given by trained professionals. It is not something to be bought or given at home without a care team’s direction.

Buying Medicine Safely

• Use only licensed pharmacies that require a valid prescription.
• Be cautious of websites that sell fluorouracil without a prescription. Products from these sources may be counterfeit, expired, contaminated, or the wrong strength.
• Do not use veterinary products or products from unverified sellers.
• If you are unsure whether a pharmacy is legitimate, ask your specialist, your local pharmacist, or your country’s pharmacy regulator.

Side Effects of Fluorouracil

Not everyone has side effects, and they can differ by form. Tell your care team about any new symptoms.

Common Side Effects of the Injection

• Nausea and vomiting
• Diarrhea
• Mouth sores or sore throat
• Loss of appetite
• Tiredness
• Hair thinning
• Low blood cell counts
• Redness, swelling, or peeling of the palms and soles (hand-foot syndrome)
• Sensitivity to sunlight
• Watery or irritated eyes
• Nail changes or skin darkening

Common Side Effects of Topical Products

• Redness, dryness, and peeling
• Burning, stinging, or itching
• Crusting, scabbing, or open sores in the treated area
• Swelling or tenderness
• Skin color changes
• Increased sun sensitivity

These skin reactions are often expected as part of the treatment and usually improve after treatment ends, but severe reactions should be reported.

Serious Side Effects

• Severe diarrhea or dehydration
• Severe mouth sores that make eating or drinking hard
• Serious infections from low white blood cell counts
• Bleeding or bruising from low platelet counts
• Heart problems, including chest pain, irregular heartbeat, or, rarely, heart attack
• Nervous system problems, including confusion, trouble with balance or coordination, or seizures
• High ammonia levels in the blood (which can cause confusion or sleepiness)
• Severe skin reactions
• Severe allergic reactions
• Life-threatening reactions in people with low DPD enzyme activity

Serious reactions are much less common with topical products, but rare cases have been reported, especially in people with DPD deficiency.

When to Get Medical Help Right Away

Contact your specialist or seek emergency care if you have:

• Fever, chills, or signs of infection
• Chest pain, a racing or irregular heartbeat, or trouble breathing
• Severe or watery diarrhea, or vomiting that will not stop
• Mouth sores that prevent eating or drinking
• Confusion, severe dizziness, or trouble with balance or speech
• Unusual bleeding or bruising
• Widespread rash, blistering, or peeling skin
• Swelling of the face, lips, or throat
• Very severe symptoms soon after starting treatment, which can be a sign of DPD deficiency
• A problem with a portable pump, such as leaking or stopping

Drug Interactions

Fluorouracil can interact with other medicines. Some interactions can be dangerous.

Major Interaction Categories

• Warfarin (blood thinner): Fluorouracil can raise the effect of warfarin and increase bleeding risk. Blood clotting tests (INR) need close monitoring.
• Phenytoin (seizure medicine): Fluorouracil may raise phenytoin levels, so levels may need monitoring.
• Leucovorin or levoleucovorin: These are often given on purpose with fluorouracil to strengthen its effect, which can also increase side effects. Your care team manages this combination.
• Capecitabine: This is an oral medicine that the body turns into fluorouracil. It should not be combined with fluorouracil unless a specialist directs it.
• Certain antiviral medicines such as brivudine (not sold in the United States) can cause severe, potentially fatal reactions when combined with fluorouracil.
• Other cancer medicines and treatments that lower blood counts, including radiation, may raise the risk of side effects.
• Live vaccines: These are generally avoided during cancer treatment. Ask before any vaccination.
• Metronidazole and other medicines that may change how the body handles fluorouracil, depending on the situation

Over-the-Counter Medicines

Ask a pharmacist or specialist before using OTC products, including pain relievers such as aspirin and ibuprofen (which can raise bleeding risk when blood counts are low). For topical fluorouracil, avoid using other skin products on the treated area unless your specialist approves.

Supplements and Herbal Products

Vitamins, supplements, and herbal products may interact with cancer treatment or affect the liver or bleeding risk. Do not start them without checking first.

Share a Full Medication List

Give your licensed medical specialist a complete list of everything you take, including prescription medicines, OTC medicines, supplements, and herbal products. Update the list whenever anything changes.

Safety & Important Considerations

DPD Deficiency and Genetic Testing

Some people have little or no DPD enzyme activity. Without it, the body cannot break down fluorouracil properly, and severe or fatal side effects can occur. Testing for DPYD gene variants may be recommended before injection treatment. An emergency medicine to counter serious fluorouracil toxicity exists, but it must be given quickly and only by a healthcare team.

Liver and Kidney Precautions

People with liver or kidney problems may need closer monitoring or dose changes.

Heart Precautions

Chest pain during treatment can be a sign of heart problems. Tell your team if you have a history of heart disease, and report chest pain right away.

Pregnancy and Breastfeeding

• Fluorouracil can harm an unborn baby. Women who can become pregnant should have a pregnancy test before injection treatment and use effective birth control during treatment and for a period afterward. Men with partners who can become pregnant should also use effective birth control during and after treatment. Your specialist will give the exact timing.
• Topical fluorouracil is not recommended for use during pregnancy. Tell your specialist right away if you are pregnant, planning pregnancy, or become pregnant.
• Breastfeeding is generally not advised during treatment and for a period afterward. Discuss with your specialist.

Children and Older Adults

• Children: Safety and effectiveness of fluorouracil are not well established in children. Use in children must be directed by a specialist.
• Older adults: They may be more sensitive to side effects, such as diarrhea, mouth sores, and low blood counts, and may need closer monitoring.

Monitoring

For injection treatment, expect regular blood tests, including blood counts and liver and kidney tests, and checks for side effects. For topical treatment, your dermatologist will follow the skin’s response and confirm healing after treatment.

Sun Protection

Fluorouracil can make skin more sensitive to sunlight. Use sunscreen, wear protective clothing, and avoid tanning beds and long sun exposure during treatment.

Safe Use of Topical Products

• Wash your hands well after applying, or use gloves.
• Keep the medicine away from the eyes, nostrils, and mouth.
• Do not cover the treated area with airtight bandages unless told to.
• Do not use on broken or unaffected skin unless told to.
• Keep pets and children away from treated areas until the medicine dries or is washed off as directed.

Handling Body Fluids and Waste (Injection)

For a period after treatment, bodily fluids may contain some of the medicine. Follow your care team’s instructions on flushing, laundry, and glove use, especially for caregivers and anyone who is or could be pregnant.

Who This Medication Is For

Fluorouracil is prescribed for people who need treatment for a condition that a specialist has decided it can help manage.

• Injection (FDA-approved indications): Certain adenocarcinomas of the colon, rectum, breast, stomach, and pancreas.
• Topical (FDA-approved indications): Actinic keratoses, and, for certain strengths, superficial basal cell carcinoma.

Whether it is right for a particular person depends on their diagnosis, other health conditions, lab results, genetic test results, and other treatments.

Who Should Not Take Fluorouracil

Tell your specialist before starting if any of the following apply.

• Allergy: You have had a serious allergic reaction to fluorouracil or any ingredient in the product.
• Known DPD deficiency or a history of severe fluorouracil reactions: It may not be safe, or a different treatment or a much lower dose may be needed.
• Pregnancy: Fluorouracil can cause harm to an unborn baby. Topical use is generally avoided during pregnancy.
• Severe infection, very low blood counts, or poor nutrition: These may need to be addressed first, especially for injection treatment.
• Heart disease, including a history of chest pain or heart attack: Extra caution is needed.
• Taking warfarin, phenytoin, or brivudine: Interactions may require changes or avoiding certain combinations.
• Recent or planned live vaccines: Discuss timing with your specialist.

Your specialist will review the full list of precautions in the current FDA labeling for your product.

What to Do If You Miss a Dose

• For injection treatment: Doses are given by your care team on a set schedule. If you miss an appointment, contact your oncology team right away to reschedule. Do not try to make up a dose on your own. If a portable pump stops, leaks, or is disconnected, call your care team right away.
• For topical products: If you miss an application, apply it when you remember unless it is almost time for the next one. Then go back to your regular schedule.
• Never apply extra medicine to make up for a missed application, because this can cause severe skin irritation.
• If you are unsure what to do, contact your licensed medical specialist or pharmacist for guidance.

Related medications to Fluorouracil

The right alternative depends on the condition being treated. Examples of options that may be used in similar situations include:

• For cancers treated with the injection: Capecitabine (an oral medicine that the body turns into fluorouracil), trifluridine/tipiracil (another related medicine), and other chemotherapy, targeted, or immune therapies, depending on the cancer type and stage.
• For actinic keratoses: Freezing (cryotherapy), imiquimod cream, diclofenac gel, tirbanibulin ointment, and photodynamic therapy.
• For superficial basal cell carcinoma: Surgery, imiquimod cream, radiation, and other procedures.

These options differ in how they work, their side effects, and their monitoring needs. Do not switch or stop treatment on your own. Any change should be made only after talking with your licensed medical specialist.

Storage Instructions

• Temperature: Store topical products at room temperature, generally between 68°F and 77°F (20°C to 25°C), unless the label says otherwise. Do not freeze. Injection vials are stored and handled by pharmacy and clinic staff.
• Moisture and light: Keep topical products tightly closed, away from moisture (avoid bathrooms) and direct light and heat.
• Child safety: Keep all medicines locked or out of reach and sight of children and pets. Use child-resistant caps.
• Disposal: Do not throw away unused medicine or used supplies in household trash unless instructed. Ask your pharmacist about safe disposal, especially for pumps, used tubing, and any product that is a hazardous drug.

Disclaimer:

This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Patients must consult a licensed medical specialist, such as an oncologist (for cancer treatment) or a dermatologist (for skin conditions), before starting, changing, or stopping treatment. Treatment decisions must be based on a full clinical evaluation by a qualified specialist. If you think you are having a medical emergency, call your local emergency number right away.