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Fluorouracil Side Effects

For the Consumer

Applies to fluorouracil: injectable, solution

In addition to its needed effects, some unwanted effects may be caused by fluorouracil. In the event that any of these side effects do occur, they may require medical attention.

Also, because of the way these medicines act on the body, there is a chance that they might cause other unwanted effects that may not occur until months or years after the medicine is used. These delayed effects may include certain types of cancer, such as leukemia. Discuss these possible effects with your doctor.

Major Side Effects

You should check with your doctor immediately if any of these side effects occur when taking fluorouracil:

More common:
  • Diarrhea
  • heartburn
  • sores in mouth and on lips
Less common:
  • Black, tarry stools
  • cough or hoarseness, accompanied by fever or chills
  • fever or chills
  • lower back or side pain, accompanied by fever or chills
  • nausea and vomiting (severe)
  • painful or difficult urination, accompanied by fever or chills
  • stomach cramps
  • Blood in urine or stools
  • pinpoint red spots on skin
  • unusual bleeding or bruising

Severity: Moderate

If any of the following side effects occur while taking fluorouracil, check with your doctor or nurse as soon as possible:

  • Chest pain
  • cough
  • shortness of breath
  • tingling of hands and feet, followed by pain, redness, and swelling
  • trouble with balance

Minor Side Effects

Some of the side effects that can occur with fluorouracil may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common:
  • Loss of appetite
  • nausea and vomiting
  • skin rash and itching
  • weakness
Less common:
  • Dry or cracked skin

This medicine often causes a temporary loss of hair. After treatment with fluorouracil has ended, normal hair growth should return.

Side Effects: Post Treatment

After you stop taking this drug, it is possible that you may still experience side effects that need medical attention. If you notice any of the following side effects check with your doctor immediately:

  • Black, tarry stools
  • blood in urine or stools
  • cough or hoarseness, accompanied by fever or chills
  • fever or chills
  • lower back or side pain, accompanied by fever or chills
  • painful or difficult urination, accompanied by fever or chills
  • pinpoint red spots on skin
  • unusual bleeding or bruising

For Healthcare Professionals

Applies to fluorouracil: compounding powder, intravenous solution


Gastrointestinal side effects can be severe and life-threatening with fluorouracil. Stomatitis and esophagopharyngitis, diarrhea, anorexia, nausea and emesis are commonly seen during therapy. The mucositis and diarrhea are dose-limiting and occur with both bolus and continuous infusion schedules. Mucositis may be preceded by a sensation of dryness, followed by erythema and formation of white, patchy membrane, ulceration, and necrosis. Lesions may occur anywhere in the gastrointestinal tract and result in dysphagia, retrosternal burning, watery diarrhea and proctitis. The diarrhea may be bloody. Profuse nausea, vomiting and diarrhea can lead to dehydration and hypotension. If diarrhea occurs, supportive care and aggressive hydration should be instituted.[Ref]

Patients should be examined prior to each dose of fluorouracil and questioned about mouth soreness and/or watery stools. Treatment should be withheld in the face of ongoing mucositis or diarrhea. Antidiarrheal agents may provide symptomatic relief from mild diarrhea; however, be less effective in the setting of moderate to severe diarrhea. Octreotide has been shown to be more effective than loperamide for the treatment of fluorouracil-induced diarrhea.

An oral hygiene program is often instituted to help reduce the severity of mucositis, and topical anesthetics can provide local pain relief. Allopurinol mouthwashes have shown little benefit in the amelioration of fluorouracil-induced mucositis. Mouth cooling (oral cryotherapy) with ice chips or popsicles for 30 minutes prior to bolus infusions of fluorouracil has been shown to reduce the severity of mucositis.[Ref]


Hematologic side effects including leukopenia have been reported. Leukopenia usually follows every course of fluorouracil; however, it may be less severe with continuous infusion therapy. The lowest white blood cell counts are seen between the 9th and 14th days after the first course of treatment. Pancytopenia, thrombocytopenia, agranulocytosis and anemia are also seen with fluorouracil therapy.[Ref]


Palmar-plantar erythrodysesthesia syndrome consists of a dysesthesia affecting the hands and feet followed 3 to 4 days later by symmetrical swelling of the palms and soles of the feet in combination with erythema and tenderness of the distal phalanges. The swelling and erythema progress with continued therapy with the development of a central pallor over the tufts of the distal phalanges. Sometimes the face may also be involved. Patients with an underlying skin disorder may be more prone to such toxicity. This condition resolves after 7 days of discontinuation of therapy and recurs upon reinstitution of treatment. Pyridoxine may provide remission of this complication and allow continuation of fluorouracil treatment.

A 65-year-old woman developed hyperpigmentation of the hands and feet, desquamating erythema of the palms and slight pitting of the nails while receiving continuous infusion fluorouracil. After application of a 7 mg nicotine patch one hour prior to drug infusion, the desquamation, erythema, and hyperpigmentation resolved even with continued chemotherapy. This improvement may be due to the vasoconstricting properties of the nicotine patch.[Ref]

Dermatologic side effects occur with both bolus and continuous infusion schedules. Loss of hair, which may progress to total alopecia, nail changes (onycholysis and pigmentation), dermatitis, and increased pigmentation and atrophy of the skin may occur. Fluorouracil is capable of enhancing the cutaneous toxicity of radiation which typically occurs within 7 days of radiation and presents as erythema followed by dry desquamation or in severe cases, erythema. Increased reactions with ultraviolet light may occur with exaggerated sunburn reactions. Photosensitivity may also occur along with pigmentation over the veins into which fluorouracil was administered. Actinic keratoses may develop an erythematous inflammatory reaction following systemic administration of fluorouracil. With continuous infusion and high dose bolus fluorouracil, palmar-plantar erythrodysesthesia ("hand-foot syndrome") is particularly common.[Ref]


The mechanism of cardiac toxicity with fluorouracil is unknown but proposed mechanisms include direct toxicity to the myocardium, coronary vasospasm, autoimmune phenomena, and thrombogenic effects. Another theory has suggested an impurity, fluoroacetaldehyde, generated in the alkaline solution of fluorouracil vials during storage which may be converted to a cardiotoxic substance, fluoroacetate.

Most arrhythmias caused by fluorouracil are treatable. Ischemic symptoms, such as chest pain and ECG changes, usually disappear when the fluorouracil infusion is stopped. If the symptoms respond to nitrate therapy, the infusion may be continued cautiously. The use of calcium-channel blockers or steroids has not been shown to protect against cardiotoxicity.

Risk factors for fluorouracil-related cardiotoxicity include advanced age, a history of cardiac disease, continuous infusion regimens, high doses, combination chemotherapy, or concomitant irradiation of the mediastinum. Sex and concomitant use of leucovorin were not shown to be risk factors for fluorouracil toxicity.[Ref]

Cardiac side effects associated with fluorouracil therapy are characterized by chest pain, arrhythmia, and electrocardiogram (ECG) changes. ECG changes consisted of diffuse ST segment elevations (or depression), tall peaked T waves, T-wave inversions, and sinus tachycardia. Other changes seen include prolongation of the QT interval, atrial fibrillation, ventricular extrasystoles, sustained and nonsustained ventricular tachycardia, and ventricular fibrillation. In some patients, chest pain was accompanied by ECG and serum enzyme changes suggestive of myocardial ischemia. Studies suggest the incidence of cardiac toxicity to be less than 10%. Cardiac toxicity has been observed with both the bolus and infusional schedules; however, is more common with the continuous infusion. A case of late-onset severe cardiotoxicity from fluorouracil therapy resulting in death has been reported.[Ref]

Nervous system

Nervous system side effects including somnolence, cerebellar ataxia, and upper motor neuron signs have rarely been reported. These symptoms are more common with intracarotid arterial infusions, high doses or intensive daily schedules and usually reverse upon discontinuation of the drug.[Ref]

A cerebellar syndrome has also been reported with a variety of treatment schedules and doses of fluorouracil, however, the incidence increases with higher weekly doses or after intensive daily treatment regimens. This syndrome may present with gross dysmetria, slurred speech, ataxia of the trunk or extremities, and dizziness. The cerebellar dysfunction appears to be reversible with symptoms abating after discontinuation of therapy, decreasing the fluorouracil dose or increasing the interval between treatment courses.

Neurotoxicity with fluorouracil can also present as an acute encephalopathy or a multifocal leukoencephalopathy. Features of the latter include white-matter lesions on MRI and symptoms such as mental decline, memory loss, motor signs, seizures, speech disturbances, and ataxia. Cessation of chemotherapy and treatment with steroids may be beneficial.

The cause of fluorouracil neurotoxicity is not known but may be associated with the formation of metabolites (fluoroacetate or fluorocitrate) that inhibit the Krebs cycle in the cerebellum, concurrent administration of levamisole, thiamine deficiency, or dihydropyrimidine dehydrogenase deficiency.[Ref]


Ocular side effect including excessive lacrimation (most common), epiphora, blepharitis, conjunctivitis, cicatricial ectropion, tear duct stenosis, blurred vision, keratitis, and punctal stenosis have been reported. Excessive lacrimation usually improves with dose reduction of fluorouracil and conjunctivitis is reversible with discontinuation of therapy at an early point. Surgical correction of dacrystenosis and ectropion, however, may be required.[Ref]

A small pilot study has suggested that ocular ice pack therapy may lessen fluorouracil-induced toxicity to a moderate degree when applied 5 minutes prior to chemotherapy.[Ref]


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Not all side effects for fluorouracil may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

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