Fluorouracil

Cancer Treatment

Fluorouracil injection is used to treat cancers affecting several parts of the body, including:

• Colon and rectum
• Breast
• Stomach
• Pancreas

Skin Conditions

When applied to the skin as a cream or solution, fluorouracil is used to treat:

• Actinic keratosis: These are scaly or crusty growths on the skin caused by years of exposure to the sun. They are considered precancerous because they can develop into skin cancer if left untreated.
• Superficial basal cell carcinoma: This is a common type of skin cancer. Fluorouracil is typically used for this condition when other types of treatment are not appropriate.

Mechanism of Action

Fluorouracil belongs to a class of medications known as antimetabolites. These drugs are designed to interfere with the normal metabolic processes of cells, specifically those involved in growth and reproduction.

The medication works by mimicking the natural building blocks that cells need to produce DNA and RNA. When cells attempt to use fluorouracil instead of these natural substances, it disrupts their ability to create the genetic material required for cell division. This interference prevents the cells from multiplying and eventually leads to their destruction.

Fluorouracil is particularly effective against certain types of cells because of how it targets them:

• Targeting rapid growth: Cancer cells and abnormal skin cells typically grow and divide much faster than healthy cells. Because these cells are more active, they are more likely to absorb the medication, making them more vulnerable to its effects.
• Systemic and local action: When administered by injection, the drug travels through the bloodstream to slow or stop the growth of cancer cells throughout the body. When applied topically to the skin, it works locally to destroy abnormal cells in the treated area.

Common Side Effects

Side effects vary based on whether the medication is applied to the skin or given by injection.

When used topically on the skin, common side effects include:

• Redness, dryness, or scaling
• Burning or stinging sensations
• Itching or skin irritation
• Swelling or tenderness at the application site
• Temporary changes in skin color

When given by injection, common side effects include:

• Nausea and vomiting
• Loss of appetite
• Diarrhea
• Mouth sores or inflammation
• Temporary hair loss
• Nail changes or skin darkening

Serious Side Effects

Contact a healthcare provider immediately if you experience any of the following:

• Signs of infection, such as fever, chills, or sore throat
• Severe or bloody diarrhea
• Severe stomach pain or persistent vomiting
• Unusual bruising or bleeding
• Chest pain or shortness of breath
• Confusion, loss of balance, or coordination problems
• Hand-foot syndrome, which involves redness, swelling, or pain on the palms of the hands or soles of the feet

Serious Toxicity and Supervision

Fluorouracil injection is typically administered under the supervision of a physician experienced in cancer chemotherapy. Because of the potential for severe reactions, hospitalization is often recommended during the initial course of treatment. Topical forms should be used exactly as directed to avoid excessive systemic absorption and severe local reactions.

DPD Deficiency

Patients with a deficiency of the enzyme dihydropyrimidine dehydrogenase (DPD) are at a significantly higher risk for life-threatening or fatal toxicity. This enzyme is responsible for breaking down the drug; without it, fluorouracil can build up to dangerous levels, causing severe mouth sores, diarrhea, low white blood cell counts, and neurological problems.

Blood and Immune System Risks

This medication can cause severe bone marrow suppression, leading to low levels of white blood cells and platelets. This increases the risk of serious infections and bleeding. Healthcare providers monitor blood counts closely during treatment to determine if the dosage needs to be adjusted or paused.

Gastrointestinal and Cardiac Warnings

Treatment is usually discontinued if signs of severe gastrointestinal toxicity occur, such as frequent bowel movements, watery stools, or sores in the mouth and throat. Additionally, fluorouracil has been associated with cardiotoxicity, including chest pain, heart rhythm changes, and heart attack. Patients should seek immediate medical attention if they experience chest pain during treatment.

Topical Use and Pet Safety

When using topical fluorouracil, it is important to avoid contact with the eyes, nose, and mouth. The treated area will be highly sensitive to sunlight, and sun exposure should be minimized. According to the FDA, topical fluorouracil is extremely toxic to pets; even a small amount ingested by a dog or cat (such as by licking the user's skin) can be fatal.

Pregnancy and Breastfeeding

Fluorouracil can cause fetal harm when administered to pregnant women. Effective contraception is necessary for both men and women during treatment and for a specified period after the last dose. Breastfeeding is generally not recommended while using this medication due to the potential for serious adverse reactions in the infant.

Pregnancy

Fluorouracil can cause fetal harm, including birth defects or pregnancy loss, when administered to a pregnant person. This risk applies to both the injectable form and the topical preparations, as the medication can be absorbed through the skin into the bloodstream. It is important to use effective birth control to prevent pregnancy during treatment and for a period of time after the last dose. If you become pregnant or think you might be pregnant while using this medication, notify a healthcare professional immediately.

Breastfeeding

It is not known whether fluorouracil passes into breast milk. Because of the potential for serious adverse reactions in a nursing infant, breastfeeding is generally not recommended during treatment and for a specific duration after the final dose. Patients should discuss the risks and benefits of breastfeeding with their healthcare provider to determine the safest course of action.

Topical Forms

Fluorouracil is applied directly to the skin to treat certain conditions. It is available in the following topical preparations:

• Cream: A topical formulation for application to the skin.
• Solution: A liquid formulation for application to the skin.

Injectable Forms

For systemic treatment, fluorouracil is provided as a solution for administration by a healthcare professional. These forms include:

• Injection: A solution administered into a vein, which may be given as a rapid injection or as a slow infusion over a period of time.

FDA Approval and Indications

Fluorouracil has been approved by the U.S. Food and Drug Administration (FDA) for several decades. Its approved uses vary significantly based on the route of administration:

• Topical Formulations: Approved for the treatment of actinic or solar keratoses (precancerous skin growths) and superficial basal cell carcinoma when traditional surgical methods are not feasible.
• Injectable Formulations: Approved for the palliative management of certain types of cancer, including colon, rectal, breast, stomach, and pancreatic carcinomas.

Boxed Warning

The injectable form of fluorouracil carries an FDA boxed warning. Due to the risk of severe toxicity, the FDA recommends that patients be hospitalized during their initial course of therapy. This medication must be administered under the supervision of a physician experienced in the use of cancer chemotherapy agents.

Safety Communications

The FDA has issued specific safety alerts regarding topical fluorouracil and pet safety. The medication is highly toxic to dogs and cats; even a small amount ingested from a person's skin or a discarded tube can be fatal to animals. The FDA advises patients to store the medication away from pets and ensure that animals do not lick treated areas of skin.

Regulatory Status

Fluorouracil is classified as a prescription medication and is not available over-the-counter. It is subject to strict regulatory oversight regarding its manufacturing, labeling, and distribution to ensure patient safety and drug efficacy.

Uses of Fluorouracil Cream

Fluorouracil cream is primarily prescribed to treat actinic or solar keratoses, which are scaly, crusty growths caused by damage from years of sun exposure. It is also used to treat superficial basal cell carcinoma, a type of skin cancer, when other treatments like surgery are not suitable.

Application Instructions

The cream is typically applied to the affected skin once or twice daily for several weeks. Users should follow these general guidelines:

• Clean and dry the area before application.
• Apply enough cream to cover the entire lesion with a thin film.
• Wash hands immediately after application unless a glove or applicator was used.
• Do not cover the treated area with tight bandages or dressings unless instructed by a doctor.

Skin Reactions

The medication works by targeting and destroying abnormal cells, which often causes significant skin irritation. Common reactions include redness, dryness, burning, pain, and crusting. The skin may look worse during treatment before it begins to heal. This process is expected and indicates the medication is active.

Important Safety Information

Treated skin will be highly sensitive to ultraviolet light. It is necessary to avoid sun exposure and artificial UV light sources like tanning beds. Additionally, fluorouracil cream should not be used by individuals who are pregnant or planning to become pregnant, as it can cause serious birth defects.