Drug information

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Other Names
5-flucytosine, 5-fluorocytosine, 5-FC, Ancobon
Drug Class
Antifungal (Nucleoside Analog)
What is flucytosine?What is flucytosine?

What is flucytosine?

Flucytosine is an antifungal prescription medicine approved by the U.S. Food and Drug Administration (FDA) for the treatment of serious infections caused by certain strains of two types of fungi: Candida and Cryptococcus. For example, flucytosine is used to treat cryptococcosis, which is an infection caused by Cryptococcus fungi.

Cryptococcosis can be an opportunistic infection (OI) of HIV. An OI is an infection that occurs more frequently or is more severe in people with weakened immune systems—such as people with HIV—than in people with healthy immune systems. To learn more about OIs, read the HIVinfo What is an Opportunistic Infection? fact sheet.

How is flucytosine used in people with HIV?How is flucytosine used in people with HIV?

How is flucytosine used in people with HIV?

The Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents includes recommendations on the use of flucytosine to treat cryptococcosis in people with HIV.

The recommended uses may not always be consistent with FDA-approved uses of flucytosine. See the guidelines for complete information on recommended uses of flucytosine in adults and adolescents with HIV. Flucytosine may have other recommended uses not listed above.

What should I tell my health care provider before taking flucytosine?What should I tell my health care provider before taking flucytosine?

What should I tell my health care provider before taking flucytosine?

Before taking flucytosine, tell your health care provider:

  • If you are allergic to flucytosine or any other medicines.
  • About any medical conditions you have or have had, including
    • kidney problems
    • bone marrow problems
    • blood disorders
    • electrolyte imbalance, especially low potassium
  • If you are receiving radiation treatment.
  • About anything that could affect your ability to take medicines, such as difficulty swallowing or remembering to take pills.
  • If you are pregnant or plan to become pregnant. Flucytosine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Talk to your health care provider about the risks and benefits of taking flucytosine during pregnancy.
  • If you are breastfeeding or plan to breastfeed. For women with HIV in the United States, the Guideline does not recommend breastfeeding. Before your baby is born, or if you are already breastfeeding, talk to your health care provider to discuss alternative options for feeding your baby.
  • About other prescription and nonprescription medicines, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Flucytosine may affect the way other medicines or products work, and other medicines or products may affect how flucytosine works. Ask your health care provider if there are interactions between flucytosine and the other medicines you take.
Ask your health care provider about possible side effects from flucytosine. Your health care provider will tell you what to do if you have side effects.
How should I take flucytosine?How should I take flucytosine?

How should I take flucytosine?

Take flucytosine according to your health care provider’s instructions. Your health care provider will tell you how much flucytosine to take and when to take it. Before you start flucytosine and each time you get a refill, read any printed information that comes with your medicine.

How should flucytosine be stored?How should flucytosine be stored?

How should flucytosine be stored?

  • Store flucytosine capsules at 77°F (25°C).
  • Keep flucytosine in the container that it came in and keep the container tightly closed.
  • Do not use flucytosine if the original seal over the container opening is broken or missing.
  • Throw away flucytosine that is no longer needed or expired (out of date). Follow FDA guidelines on how to safely dispose of unused medicine.
  • Keep flucytosine and all medicines out of reach of children.
Where can I find more information about flucytosine?Where can I find more information about flucytosine?

Where can I find more information about flucytosine?

More information about flucytosine is available:

The above Patient Version drug summary is based on the following FDA label(s): Capsule.


Last Reviewed: January 26, 2021