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Side Effects of Fluorouracil (Adrucil, Carac, Efudex, Fluoroplex)


Description: Fluorouracil (5-FU) is a chemotherapeutic agent used to treat certain cancers including breast and colorectal. Its brand names include Adrucil, Carac, Efudex, and Fluoroplex. Because severe toxic reactions are very common, it is recommended that patients be hospitalized during the initial course of therapy at the minimum.


Fluorouracil is a toxic drug with a slim margin of safety. Thus, patients should be supervised, as therapeutic response is unlikely to occur without some evidence of an adverse reaction. This includes: gastrointestinal hemorrhage, severe hematological toxicity and death, even in patients in relatively good condition. (Fluorouracil label as reported by the FDA, 2000).

Serious Side Effects of Fluorouracil

Therapy is to be discontinued immediately whenever one of the following signs of toxicity appears:

  • Vomiting, intractable
  • Stomatitis or esophago pharyngitis, at the first visible sign
  • Thrombocytopenia (platelets under 100,000)
  • Gastrointestinal ulceration and bleeding
  • Diarrhea, frequent bowel movements or watery stools
  • Hemorrhage from any site
  • Leukopenia (WBC under 3500) or a rapidly falling white blood count


Additionally, the administration of 5-fluorouracil has been linked to the occurrence of palmar-plantar erythrodysesthesia syndrome (hand-foot syndrome). In addition, stomatitis and esophago pharyngitis (which may lead to ulceration and sloughing), nausea, anorexia, emesis, and diarrhea is commonly seen during therapy. Leukopenia generally follows every course of therapy with fluorouracil. Alopecia and dermatitis may be seen in a large number of cases.
(Fluorouracil label as reported by the FDA, 2000).

Less Common Fluourouracil Side Effects

Other adverse reactions are:

  • Cardiovascular: Angina, arrhythmia, heart failure, MI (myocardial ischemia), vasospasm, ventricular ectopy
  • Hematologic: Agranulocytosis, anemia, leukopenia, pancytopenia, thrombocytopenia
  • Central nervous system: Acute cerebellar syndrome, euphoria, headache, nystagmus, confusion, disorientation, stroke
  • Gastrointestinal: Anorexia, esophago pharyngitis, mesenteric ischemia (acute), bleeding, diarrhea, nausea, sloughing, stomatitis, ulceration, vomiting
  • Dermatologic: Alopecia, dermatitis, dry skin, fissuring, nail changes (nail loss), palmar-plantar erythrodysesthesia syndrome (Hand-foot syndrome), pruritic maculopapular rash, photosensitivity, Stevens-Johnson syndrome, toxic epidermal necrolysis, vein pigmentation
  • Respiratory: Epistaxis
  • Local: Thrombophlebitis
  • Ocular: Lacrimation, lacrimal duct stenosis, photophobia, visual changes
  • Miscellaneous: Anaphylaxis, generalized allergic reactions

(Fluorouracil label as reported by the FDA, 2000).

Understand Your Risk for Side Effects with the Rxight® Genetic Test

Rxight® genetic testing allows patients and their physicians to know how a drug will affect them adversely even before they start taking the medication. Rxight® is based on the analysis of a panel of 18 genes and their alleles to determine how well the enzymes for which they encode are able to process medications in the body.


So-called “slow metabolizers” of fluorouracil are more likely to experience serious side effects from what is considered a normal dose, whereas “fast metabolizers” are generally unable to derive benefit from a standard dose. Rxight® tests for antimetabolites like fluorouracil along with over 200 other clinically relevant prescription and over-the-counter medications, providing patients and prescribers with a medication blueprint that they can use to determine safe and effective dosing with minimal side effects.


Contributors to this Article:
Michael Sapko, MD, PhD; Deborah Kallick, PhD, Medicinal Chemistry


Read more about Rxight® Drug Sensitivity Testing