5-FU (5-Fluorouracil), Topical - Health Tips

Get practical tips regarding 5-FU (5-Fluorouracil), Topical to help you prepare for your appointments and manage your care from home.

Thoughts on 5-FU (5-Fluorouracil), Topical by Dr. Matt Zirwas, MD, FAAD
February 2021

Note: 5-fluorouracil (5-FU) is very poisonous when ingested by dogs or cats. Even tiny amounts can be very toxic, resulting in acute gastrointestinal signs (e.g., vomiting, diarrhea), central nervous system signs (e.g., severe tremors, seizures, etc.), bone marrow suppression, and possible death. Care should be taken to prevent ingestion of this medication by pets.

Thoughts on 5-FU (5-Fluorouracil), Topical by Dr. Joel Siegel, MD
December 2020

5-Fluorouracil (5-FU) is a medication applied to the skin for the treatment of actinic keratoses.

5-FU is a topical chemotherapy that kills sun-damaged skin cells. It can also damage normal skin cells and result in significant skin irritation.

Using 5-FU usually results in a mild to a severe burning sensation. After 5-10 days of treatment, the sun-damaged parts of treated skin become red and irritated. Sores and crusts may appear with ongoing use. If you have severe sun-damage, you may have severe crusting -- YOUR SKIN MAY LOOK HORRIBLE!! Don't get alarmed - this reaction means that the medication is working. These raw areas result from the destruction of defective skin cells.  If you are not experiencing discomfort, tenderness, or itching, continue applying the medication. If you do have discomfort, discontinue the medication and make a note of the date you stopped it.

DIRECTIONS FOR APPLICATION:

  • Wash the area to be treated with plain water.
  • Apply a small amount of the medication on the skin with your fingertip. It is important to apply the medication to the entire area, not just to the lesions which are visible to the naked eye.
  • After applying, wash hands.
  • Apply sunscreen with an SPF of 30 or higher. This medication will make you very sensitive to sunlight.