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Overview: Flucytosine is used to treat certain fungal infections. Common side effects include nausea and vomiting. Serious side effects are less likely but can include allergic reactions, liver damage, and blood disorders. Notify your health care provider right away if you feel unusually weak or tired or have any trouble breathing.

Uses

What is flucytosine used for?

Flucytosine is an antifungal medicine commonly used to treat certain fungal infections, including the following. 

  • Candida infections (candidiasis) 
  • Cryptococcus infections (cryptococcosis)

Flucytosine may not be right for some of the infections listed above, depending on which germs are causing the infection. Fungi in some locations may have developed resistance to flucytosine, which will make it not work as well.

Flucytosine may also be used for other conditions as determined by your health care provider.

How does flucytosine work (mechanism of action)?

Flucytosine stops certain types of fungi from making proteins they need to grow and multiply.

How is flucytosine supplied (dosage forms)?

Brands and other names

  • Ancobon

Dosage forms and strengths

  • 250 mg oral capsules
  • 500 mg oral capsules

How should I store flucytosine?

Flucytosine should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting it. Store protected from light, in a cool, dry place.

Side Effects

What are the most common side effects of flucytosine?

The most common side effects of flucytosine are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Nausea, vomiting, diarrhea, or stomach pain
  • Chest pain or shortness of breath
  • Rash or itching
  • Loss of appetite
  • Dry mouth
  • Headache
  • Drowsiness or tiredness
  • Confusion
  • Low potassium levels

There may be other side effects of flucytosine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of flucytosine?

While less common, the most serious side effects of flucytosine are described below, along with what to do if they happen.

Severe Allergic Reactions. Flucytosine may cause allergic reactions, which can be serious. Stop taking flucytosine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking flucytosine. Keep all appointments, including those for lab work, while you are taking flucytosine. Call your health care provider right away if you have any of the following symptoms of liver damage.

  • Nausea or vomiting
  • Stomach or belly pain
  • Fever
  • Weakness or unusual tiredness
  • Itching
  • Loss of appetite
  • Light-colored poop
  • Dark-colored urine (pee)
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Blood Disorders. Flucytosine can cause blood disorders, such as agranulocytosis, aplastic anemia, low platelet levels (thrombocytopenia), and low white blood cell levels (leukopenia). Stop taking flucytosine and get help right away if you have any of the following symptoms of blood disorders.

  • Fever
  • Shortness of breath
  • Pale or yellowish skin
  • Easy bruising or bleeding
  • Frequent infection
  • Unusual weakness or tiredness
  • Dizziness, lightheadedness, or feeling like you are about to pass out
  • Headache
  • Fast or abnormal heartbeat

Warnings & Precautions

Who should not use flucytosine?

Allergies to Ingredients. People who are allergic to any of the following should not take flucytosine.

  • Ancobon
  • Flucytosine
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific flucytosine products they stock.

Dihydropyrimidine Dehydrogenase Deficiency. People with a genetic disorder known as dihydropyrimidine dehydrogenase (DPD) deficiency should not take flucytosine. Flucytosine is more likely to cause severe side effects in people with DPD deficiency.

What should I know about flucytosine before using it?

Do not take flucytosine unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share flucytosine with other people, even if they have the same condition as you. It may harm them.

Keep flucytosine out of the reach of children.

Flucytosine can make your skin more sensitive to light from the sun, sunlamps, and tanning beds. This is called photosensitivity. Exposure to this light can cause severe sunburns, blisters, and swelling. If you need to be in sunlight, wear sunscreen, a hat, and clothing that covers your skin.

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

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if flucytosine is right for you.

In particular, make sure that you discuss any of the following.

Other Medicines and Supplements. Flucytosine may interact with other medicines and supplements. Before taking flucytosine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Kidney problems
  • Blood disorders
  • Bone marrow problems, including if you are receiving or were previously treated with chemotherapy or radiation treatment

Pregnancy. It is not known if or how flucytosine could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. It is not known if flucytosine passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should stop breastfeeding or stop flucytosine.

Interactions

Does flucytosine interact with foods or drinks?

There are no known interactions between flucytosine and foods or drinks.

It is unknown if drinking alcohol will affect flucytosine, but heavy drinking can slow your immune response and make it harder for your body to fight infection. 

Does flucytosine interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, before taking flucytosine, make sure that you discuss if you are using cytarabine, which is a chemotherapy drug used to treat certain cancers.

This may not be a complete list of medicines that can interact with flucytosine. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much flucytosine?

If you or someone else has used too much flucytosine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of flucytosine?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.