What is Fluorouracil?

Fluorouracil, also known as 5-FU, is a prescription medication that falls into a class of cancer drugs known as pyrimidine antagonists. It may be used to treat several different types of cancer or precancerous conditions, including those of the digestive tract and skin. Depending on the exact condition, fluorouracil may be given intravenously or applied directly to the affected area. Health-care providers generally caution patients about a variety of potential side effects that may be caused by fluorouracil and warn against its use in certain people.

As a pyrimidine antagonist, fluorouracil works by interfering with the naturally occurring pyrimidines in the body. Pyrimidines are special molecules that help make up the genetic material in cells. When a person has cancer, certain cells in the body have undergone changes that are causing them to divide rapidly and take over the space occupied by normal, healthy cells. This process of division requires cells to make copies of genetic material. Fluorouracil works by tricking the body into thinking the drug is a natural pyrimidine, leading to its incorporation into the genetic code of the cell. There, fluorouracil typically stops the cell from making new copies of itself and can trigger a response that causes the cell to die.

Depending on the type of cancer or precancerous condition it is being used to treat, fluorouracil may either be given by IV (intravenous) therapy or applied to the skin. As a treatment for colon, stomach, pancreatic and/or breast cancer, it is likely to be given through an IV. For skin cancer or actinic keratosis, a type of precancerous skin condition, fluorouracil may be applied over the affected area in the form of a cream. The amount given and frequency of dosing generally depends on several factors, including a person’s weight, his or her exact condition, and how well he or she tolerates treatment.

Health-care providers generally caution patients to be alert for various side effects from this cancer drug, including nausea, vomiting, mouth sores, increased sun sensitivity and decreased blood cell counts, which can lead to an increased of infection and/or bleeding. Some of these side effects can be very serious, so experts generally recommend reporting any adverse reactions right away. In addition to helping identify potential problems early on, reporting side effects may allow health-care providers to make adjustments to the fluorouracil treatment to help reduce side effects that may be experienced with future doses.

Due to its mechanism of action and potential side effects, health-care providers often warn against the use of fluorouracil in certain people. This may include, for example, men and women who are trying or planning to conceive, as well as women who are already pregnant, as the cell-killing effects of the drug may extend to the reproductive cells and/or a developing fetus. It may also include people taking certain medications, such as leucovorin and aspirin, as well as certain supplements, such as vitamin E, as concurrent use of these can increase the risk of serious side effects.