Flucytosine
Pronunciation: floo-SYE-toe-seen.
- Generic name
- flucytosine
- Brand names
- Ancotil, Fungicil, Flucy, Ancobon
- Drug class
- Antifungal agent
Availability and supply rules vary by country
Trade names by country: United States
Australia: · Full directory
What flucytosine is and how it works
Uses, formulations, monitoring, and supply rules can differ by patient, product, and country. Follow the exact local product information and professional advice.
Mechanism of action: how flucytosine works
Flucytosine is a fluorinated pyrimidine analog. After entering susceptible fungal cells via cytosine permease, it is converted by cytosine deaminase to 5-fluorouracil (5-FU), which is further metabolized to 5-fluorodeoxyuridine monophosphate (FdUMP) and 5-fluorouridine triphosphate (FUTP). FdUMP inhibits thymidylate synthase, blocking DNA synthesis, while FUTP disrupts RNA synthesis. This dual action impairs fungal cell replication and protein production. (2)
What flucytosine is used for
Candidiasis
Candidiasis (2)
Cryptococcosis
Cryptococcosis (2)
Chromomycosis
Chromomycosis (2)
Before taking flucytosine
Do not take / not appropriate for
- Absolute contraindication: Known hypersensitivity to flucytosine or any excipients. (Contraindication) (2)
Tell your clinician about
(2)How to take flucytosine
- General Instructions: Take flucytosine exactly as prescribed by your doctor. Do not skip doses or stop early, even if you feel better.. Adult Dosing: Typical adult dose is 50–150 mg/kg/day divided into 4 equal doses every 6 hours. Dose may be adjusted based on kidney function and blood levels.. Pediatric Dosing: Children are usually dosed at 100–150 mg/kg/day divided into 4 doses, with adjustments for kidney function.. Administration: Take capsules with a full glass of water. If you have trouble swallowing, ask your pharmacist about a liquid formulation. Take at evenly spaced intervals.. When To Stop: Do not stop taking flucytosine without your doctor's advice, even if symptoms improve. Stopping early may cause the infection to return or worsen.. Storage: Store at room temperature, away from moisture and heat. Keep out of reach of children.
- This page does not provide a dose calculator. Dosing must follow the prescriber, pharmacist, or product label.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (2)
Missed dose
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 resume your regular schedule. Do not take an extra dose to make up for a missed dose.
Overdose
In case of overdose, seek emergency medical attention or call your local poison control center. Symptoms may include confusion, hallucinations, severe nausea, vomiting, diarrhea, or bone marrow suppression. (2)
Side effects
Side effects and their urgency vary; report severe, persistent, or concerning symptoms to a healthcare professional.
Bone marrow suppression
Incidence: Reported in the clinician-authored database; frequency not established
Nausea
Incidence: Reported in the clinician-authored database; frequency not established
Vomiting
Incidence: Reported in the clinician-authored database; frequency not established
Diarrhea
Incidence: Reported in the clinician-authored database; frequency not established
Rash
Incidence: Reported in the clinician-authored database; frequency not established
Hepatotoxicity
Incidence: Reported in the clinician-authored database; frequency not established
Anemia
Incidence: Reported in the clinician-authored database; frequency not established
Thrombocytopenia
Incidence: Reported in the clinician-authored database; frequency not established
Serious warnings
BOXED WARNING — serious
Symptoms: BOXED WARNING: use with extreme caution in patients with impaired renal function — flucytosine accumulates and toxicity risk rises as kidney function falls. Close monitoring of hematologic (blood cell), renal, and hepatic status is essential for all patients on this medicine.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (2)
Flucytosine can cause serious blood disorders, including low white blood cell or platelet counts — serious
Symptoms: Flucytosine can cause serious blood disorders, including low white blood cell or platelet counts. Regular blood tests are required to monitor for toxicity. May cause severe gastrointestinal side effects. Not recommended for use during pregnancy unless clearly needed.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (2)
Contraindications — serious
Symptoms: Contraindications: known hypersensitivity to flucytosine or any excipients; known complete dihydropyrimidine dehydrogenase (DPD) enzyme deficiency. Precautions: use with caution in patients with renal impairment (risk of accumulation and toxicity), hepatic impairment, or bone marrow suppression. Monitor closely in elderly patients and those receiving concomitant nephrotoxic or myelosuppressive agents.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (2)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Recorded interactions | Flucytosine may interact with other medications that affect the kidneys or bone marrow, such as amphotericin B (increases toxicity risk), cytarabine, or certain antivirals. Always inform your healthcare provider about all medicines and supplements you are taking. Dose adjustments may be necessary to avoid harmful effects. |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
Teratogenic effects were seen in rats at certain doses, and there are no adequate, well-controlled studies in pregnant women. Use during pregnancy only if the potential benefit justifies the potential risk to the fetus, as judged by the treating physician. (2)
Breastfeeding
It is not known whether flucytosine passes into human milk. The prescriber and mother should weigh whether to discontinue nursing or discontinue the medicine, taking into account the drug's importance to the mother. (2)
Children
Frequency: Not established for pediatric use.. Weight Based: Not established; dosing should be based on clinical judgment.. Max Daily Dose: Not established for pediatric use.. Max Single Dose: Not established for pediatric use.. Age Restrictions: Safety not established in children. (2)
Renal_impairment
No specific numeric renal-dose-adjustment table is published. General guidance: if BUN or serum creatinine is elevated, or other signs of renal impairment are present, the initial dose should be at the lower end of the usual range, with close monitoring of serum flucytosine levels and kidney function. Use with caution in hepatic impairment as well; all adjustments are made by the treating clinician. (2)
Hepatic_impairment
No specific numeric renal-dose-adjustment table is published. General guidance: if BUN or serum creatinine is elevated, or other signs of renal impairment are present, the initial dose should be at the lower end of the usual range, with close monitoring of serum flucytosine levels and kidney function. Use with caution in hepatic impairment as well; all adjustments are made by the treating clinician. (2)
Monitoring
(2)Storage
Store at 25C (77F), with excursions permitted between 15-30C (59-86F), away from moisture and heat. Keep out of reach of children.
Professional information
Clinician-facing context only. This section does not replace current product labeling.
General
Indication: Candidiasis
Dose summary: 25 mg/kg IV or orally every 6 hours, adjusted based on renal function.
Renal context: No specific numeric adjustment table is published; the initial dose should be at the lower end of the usual 50-150 mg/kg/day range if BUN/serum creatinine is elevated or other renal-impairment signs are present, with close monitoring of serum flucytosine levels. (2)
Frequently asked questions
What infections does flucytosine treat?
Flucytosine is used to treat serious fungal infections, especially those caused by Candida and Cryptococcus species, such as cryptococcal meningitis and systemic candidiasis.
Can flucytosine be used alone?
Flucytosine is rarely used alone due to the risk of resistance. It is most effective when combined with other antifungal medications, such as amphotericin B.
How long do I need to take flucytosine?
The duration of treatment depends on the type and severity of infection. Your doctor will determine the appropriate length of therapy, which may range from several weeks to months.
What monitoring is required during flucytosine therapy?
Regular blood tests are needed to monitor kidney function, liver function, and blood cell counts to detect any side effects early.
Is flucytosine safe in pregnancy or breastfeeding?
Flucytosine should only be used in pregnancy if the potential benefit justifies the risk. It is not recommended during breastfeeding as it may pass into breast milk.
What should I do if I develop severe side effects?
Contact your doctor immediately or seek emergency care if you experience symptoms such as severe rash, jaundice, unusual bleeding, or signs of infection.
Can I drink alcohol while taking flucytosine?
It is best to avoid alcohol while taking flucytosine, as it may increase the risk of liver problems.
What happens if I take too much Flucytosine?
Taking too much Flucytosine can lead to serious side effects, including bone marrow suppression, liver dysfunction, and gastrointestinal issues. If an overdose is suspected, it is crucial to seek immediate emergency medical attention. Overdose symptoms may vary, and prompt medical intervention is essential for proper management and to prevent severe complications.
Is Flucytosine safe during pregnancy?
Flucytosine's pregnancy category requires careful consideration. It is crucial to consult your doctor if you are pregnant, planning to become pregnant, or breastfeeding before starting or continuing Flucytosine. Your healthcare provider will assess the potential risks and benefits to both you and the baby, and determine the most appropriate course of treatment.
What is the mechanism of action of flucytosine?
Flucytosine is a fluorinated pyrimidine analog. After entering susceptible fungal cells via cytosine permease, it is converted by cytosine deaminase to 5-fluorouracil (5-FU), which is further metabolized to 5-fluorodeoxyuridine monophosphate (FdUMP) and 5-fluorouridine triphosphate (FUTP). FdUMP inhibits thymidylate synthase, blocking DNA synthesis, while FUTP disrupts RNA synthesis. This dual action impairs fungal cell replication and protein production. (2)
What is the generic name of Flucytosine?
The generic name is flucytosine. It is sold under brand names including Ancotil, Fungicil, Flucy, Ancobon.
What class of drug is flucytosine?
Flucytosine is classed as: Antifungal agent.
References
- MedGuideGlobal clinician-authored medicine record for flucytosineMedGuideGlobal · null · accessed 2026-08-06 · source 1
- ANCOBON (flucytosine) capsules — prescribing informationU.S. Food and Drug Administration (DailyMed) · United States · accessed 2026-08-06 · source 2
- FLUCYTOSINE CAPSULE [MAJOR PHARMACEUTICALS] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 3
- Flucytosine — FDA approval record (Drugs@FDA ANDA204652)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 4
- flucytosine — RxNorm normalized drug concept (RXCUI 4451)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 5
Brand names by country
Single-ingredient flucytosine names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- ANCOBON500 mg, 250 mg · bausch health us llc