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Flucytosine Side Effects

For the Consumer

Applies to flucytosine: oral capsule, oral tablet

Along with its needed effects, flucytosine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking flucytosine:

More Common

  • Skin rash, redness, or itching
  • sore throat and fever
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • yellow eyes or skin

Less Common

  • Confusion
  • hallucinations (seeing, hearing, or feeling things that are not there)
  • increased sensitivity of skin to sunlight

Some side effects of flucytosine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More Common

Less Common

For Healthcare Professionals

Applies to flucytosine: oral capsule


Gastrointestinal side effects have included nausea, emesis, abdominal pain, diarrhea, anorexia, dry mouth, duodenal ulcer, gastrointestinal hemorrhage, enterocolitis, and ulcerative colitis.[Ref]

Nausea is common at high doses, generally occurs in the first two weeks of therapy, and often resolves with time or temporary dose reduction. Diarrhea is often associated with cramps, occurs most frequently in the first two weeks of therapy, and frequently resolves with time or temporary dose reduction. One case has been reported of a patient on long-term therapy who developed diarrhea which did not resolve spontaneously. X-ray of the small bowel revealed ulceration and the ileocecal valve and distal ileum appeared edematous. Flucytosine was discontinued and the patient improved over the next two weeks.[Ref]


Some patients experience significant increases in liver function tests and may develop signs and symptoms of hepatitis. Liver function test abnormalities generally resolve after discontinuation of flucytosine.[Ref]

Hepatic side effects have included jaundice, hepatic dysfunction, bilirubin elevation, increased hepatic enzymes, and acute hepatic injury including hepatic necrosis with possible fatal outcome in debilitated patients.[Ref]


Hematologic side effects have included anemia, agranulocytosis, aplastic anemia, eosinophilia, leukopenia, pancytopenia, thrombocytopenia, and fatal cases of bone marrow suppression.[Ref]

Bone marrow suppression may range from isolated leukopenia or thrombocytopenia to pancytopenia. Often there is just mild leukopenia or thrombocytopenia which does not require discontinuation of the drug. In most cases the suppression is reversible following discontinuation of flucytosine therapy, but at least one case of fatal, irreversible marrow failure has occurred.[Ref]


Photosensitivity has been reported in one case of a patient receiving long-term flucytosine. The photosensitivity persisted for one year after completion of therapy.

A case of anaphylaxis has been reported. In that case, a patient who had hemophilia and AIDS was receiving flucytosine for oral candidiasis. Flucytosine therapy was started following 10 days of miconazole and the patient developed a fever, erythema, pruritus, tachycardia and hypotension requiring volume support. Rechallenge was attempted one week later with one tablet. The rechallenge resulted in the same signs and symptoms and ran a similar course.[Ref]

Hypersensitivity side effects have included allergic reactions. Rashes have been reported rarely. At least one case of photosensitivity has been reported, in addition to a case of anaphylaxis.[Ref]


Cardiovascular side effects have included cardiac arrest, myocardial toxicity, and ventricular dysfunction. Cardiac toxicity with ST elevation has been reported in a 34-year-old woman, with no previous history of heart disease, the day after completing a 2-day flucytosine therapy.[Ref]

A 34-year-old woman reported severe chest pain the day after completing a 2-day flucytosine therapy. Cardiac echography indicated septo-apico-lateral severe hypokinesia, with left ventricular ejection fraction less than 15%. Aggressive cardiac intensive care with positive inotropic agents, placement of an intra-aortic balloon pump counterpulsation, and milrinone along with continuous veno-venous hemodiafiltration were needed over the 2 weeks of hospitalization before restoration of her cardiovascular status. Patient has not shown further signs of heart problems during the 2 years since this event.[Ref]


Respiratory side effects have included dyspnea, chest pain, and respiratory arrest.[Ref]


Dermatologic side effects have included rash, pruritus, urticaria, photosensitivity, and Lyell's syndrome.[Ref]


Genitourinary side effects have included crystalluria.[Ref]


Renal side effects have included azotemia, creatinine and BUN elevation, and renal failure.[Ref]

Nervous system

Nervous system side effects have included ataxia, hearing loss, headache, paresthesia, parkinsonism, peripheral neuropathy, pyrexia, vertigo, sedation, and convulsions.[Ref]


Psychiatric side effects have included confusion, hallucinations, and psychosis.[Ref]


Metabolic side effects have included hypoglycemia.


Other side effects have included fatigue and weakness.[Ref]


1. Stamm AM, Diasio RB, Dismukes WE, et al "Toxicity of amphotericin B plus flucytosine in 194 patients with cryptococcal meningitis." Am J Med 83 (1987): 236-42

2. "Product Information. Ancobon (flucytosine)." Roche Laboratories, Nutley, NJ.

3. Thompson GR 3rd, Cadena J, Patterson TF "Overview of antifungal agents." Clin Chest Med 30 (2009): 203-15, v

4. Bennett JE, Dismukes WE, Duma RJ, et al "A comparison of amphotericin B alone and combined with flucytosine in the treatment of cryptococcal meningitis." N Engl J Med 301 (1979): 126-31

5. Harder EJ, Hermans PE "Treatment of fungal infections with flucytosine." Arch Intern Med 135 (1975): 231-7

6. White CA, Traube J "Ulcerating enteritis associated with flucytosine therapy." Gastroenterology 83 (1982): 1127-9

7. Record CO, Skinner JM, Sleight P, Speller DC "Candida endocarditis treated with 5-fluorocytosine." Br Med J 01/30/71 (1971): 262-4

8. Holdsworth SR, Atkins RC, Scott DF, Jackson R "Management of candida peritonitis by prolonged peritoneal lavage containing 5-fluorocytosine." Clin Nephrol 4 (1975): 157-9

9. Kauffman CA, Frame PT "Bone marrow toxicity associated with 5-fluorocytosine therapy." Antimicrob Agents Chemother 11 (1977): 244-7

10. Wise GJ, Goldberg P, Kozinn PJ, Nawabi IU "Agranulocytosis associated with flucytosine for urinary candidiasis." Urology 8 (1976): 490-1

11. Kotani S, Hirose S, Niiya K, et al "Anaphylaxis to flucytosine in a patient with AIDS." JAMA 260 (1988): 3275-6

12. Shelley WB, Sica PA Jr "Disseminate sporotrichosis of skin and bone cured with 5-fluorocytosine: photosensitivity as a complication." J Am Acad Dermatol 8 (1983): 229-35

13. Isetta C, Garaffo R, Bastian G, Jourdan J, Baudouy M, Milano G "Life-threatening 5-fluorouracil-like cardiac toxicity after treatment with 5-fluorocytosine." Clin Pharmacol Ther 67 (2000): 323-5

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.