Fluorouracil (5-FU) is a type of chemotherapy that has an anti-cancer effect by preventing the production of DNA in the cell. This blockage of DNA production prevents the cancer cell from reproducing and making vital proteins, which leads to death of the cell.

Topical fluorouracil is used to treat actinic keratosis and superficial basal and squamous cell skin cancers. The medication destroys sun-damaged skin cells, but can also damage normal skin and cause skin irritation.

How to Use Topical Fluorouracil

Topical fluorouracil (5-FU) comes as a topical cream, available in 2 strengths. Your healthcare provider will determine which strength is right for your condition and tell you how often to use the cream (typically 1-2 times a day). Most patients will use the cream for 2-12 weeks, depending on the condition being treated and the response to treatment.

To apply the cream:

Wash the area to be treated with plain water and dry. Wait 10 minutes.
Wear a glove when applying the medication or use a non-metal applicator to apply.
If your hands come into contact with the 5-FU, wash them right away.
Use an amount sufficient to cover the lesions being treated.
If you need to cover the area, use only porous gauze dressing that allows the area to "breathe".
Do not apply in the eye, into the vagina, or to mucous membranes.

Possible Side Effects of Topical Fluorouracil

There are a number of things you can do to manage the side effects of topical fluorouracil. Talk to your care team about these recommendations. They can help you decide what will work best for you. These are some of the most common side or important effects:

Skin Changes

The treatment area will typically cause a burning feeling and, after a few days of treatment, will become red and crusted. The area will look worse than before treatment, which will likely continue for a few weeks after treatment stops. You may have any of the following in the treated area: darkening of skin color, pain, irritation, redness, itching, scarring, rash, and skin ulcerations (blisters).

Sun Sensitivity

This medication can make your skin more sensitive to the sun, which can result in severe sunburn or rash. Sun sensitivity can last even after chemotherapy is completed. Avoid the sun between 10-2 pm, when it is strongest. Wear sunscreen (at least SPF 30 with UVA/UVB protection) every day and reapply when in the sun for extended periods of time); wear sunglasses with UVA/UVB protection, a hat, and long sleeves/pants to protect your skin and seek out shade whenever possible.

Other Side Effects

The amount of medication that is absorbed into your blood is limited with topical use, but some people have a deficiency of the enzyme DPD which is needed to break down 5-FU. These patients can develop serious toxicity. If you experience diarrhea, stomach pain, fever, chills, vomiting, or sores in your mouth, report this to your healthcare provider right away or if you have a known or family history of DPD deficiency.

Reproductive Concerns

Exposure of an unborn child to this medication could cause birth defects, so you should not become pregnant or father a child while on this medication. Effective birth control is necessary during treatment. Even if your menstrual cycle stops or you believe you are not producing sperm, you could still be fertile and conceive. You should not breastfeed while receiving this medication.