Flucytosine: uses, dosing, side effects & brands
Flucytosine is a nucleoside analog antifungal sold in the U.S. under one brand, for aspergillosis, candidiasis and chromoblastomycosis. Below: what the FDA label says, every product that contains it, what the pills look like, and its recall record.
Key facts
- Drug class
- Nucleoside Analog Antifungal
- Treats
- Aspergillosis, Candidiasis and Chromoblastomycosis
- Available as
- Capsule
- Sold as
- Ancobon
- Prescription?
- Prescription only
- Generic available?
- Not in our catalog
- Boxed warning
- Boxed warning
How flucytosine is dosed
From the FDA label for Ancobon (application NDA017001). Other flucytosine products — different forms, different strengths — are dosed differently. Follow the label for the one you were prescribed.
The usual dosage of ANCOBON is 50 to 150 mg/kg/day administered in divided doses at 6-hour intervals. Nausea or vomiting may be reduced or avoided if the capsules are given a few at a time over a 15-minute period. If the BUN or the serum creatinine is elevated, or if there are other signs of renal impairment, the initial dose should be at the lower level (see WARNINGS ). ANCOBON should be used in combination with amphotericin B for the treatment of systemic candidiasis and cryptococcosis because of the emergence of resistance to ANCOBON (see MICROBIOLOGY ).
Flucytosine side effects
The adverse reactions which have occurred during treatment with ANCOBON are grouped according to organ system affected. Cardiovascular: Cardiac arrest, myocardial toxicity, ventricular dysfunction. Respiratory: Respiratory arrest, chest pain, dyspnea. Dermatologic: Rash, pruritus, urticaria, photosensitivity. Gastrointestinal: Nausea, emesis, abdominal pain, diarrhea, anorexia, dry mouth, duodenal ulcer, gastrointestinal hemorrhage, acute hepatic injury including hepatic necrosis with possible fatal outcome in debilitated patients, hepatic dysfunction, jaundice, ulcerative colitis, enterocolitis, bilirubin elevation, increased hepatic enzymes. Genitourinary: Azotemia, creatinine and BUN elevation, crystalluria, renal failure. Hematologic: Anemia, agranulocytosis, aplastic anemia, eosinophilia, leukopenia, pancytopenia, thrombocytopenia, and fatal cases of bone marrow aplasia. Neurologic: Ataxia, hearing loss, headache, paresthesia, parkinsonism, peripheral neuropathy, pyrexia, vertigo, sedation, convulsions. Psychiatric: Confusion, hallucinations, psychosis. Miscellaneous: Fatigue, hypoglycemia, hypokalemia, weakness, allergic reactions, Lyell’s syndrome. To report SUSPECTED ADVERSE REACTIONS, contact Bausch Health US, LLC at 1-800-321-4576 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch .
Who shouldn’t take flucytosine
ANCOBON is contraindicated in patients with a known hypersensitivity to the drug. ANCOBON is contraindicated in patients with known complete dihydropyrimidine dehydrogenase (DPD) enzyme deficiency (see WARNINGS ).
Flucytosine drug interactions
Cytosine arabinoside, a cytostatic agent, has been reported to inactivate the antifungal activity of ANCOBON by competitive inhibition. Drugs which impair glomerular filtration may prolong the biological half-life of flucytosine.
Every flucytosine product we track (1)
Same active ingredient — different manufacturer, form, price and FDA recall record. That last one is what our independent score measures.
Only one: Ancobon.
What flucytosine pills look like
Imprint codes, colour and shape from the FDA’s labelling data. Match the imprint on your pill — or search any imprint.
| Imprint | Strength | Colour | Shape | Maker |
|---|---|---|---|---|
| 250;NL771 | 250 mg | gray, blue | capsule | — |
| 500;NL770 | 500 mg | white, gray | capsule | — |
| 250;NL771 | 250 mg | gray, blue | capsule | — |
| 500;NL770 | 500 mg | white, gray | capsule | — |
| FLU;250 | 250 mg | green, gray | capsule | — |
| FLU;500 | 500 mg | gray, white | capsule | — |
| 250;NL771 | 250 mg | gray, blue | capsule | — |
| 500;NL770 | 500 mg | white, gray | capsule | — |
| LL250 | 250 mg | green | capsule | — |
| LL500 | 500 mg | gray | capsule | — |
How long flucytosine keeps
No flucytosine label we read sets a separate limit for after opening, but they do specify how it must be stored — and the stability behind any date assumes those conditions.
Does flucytosine expire? The in-use limits and storage rules from its labelsWhat people report to the FDA about flucytosine
The FDA Adverse Event Reporting System (FAERS) collects reports from patients and clinicians. It holds 1,373 reports naming flucytosine, and the FDA flagged 96% of those reports as serious. The effects reported most often — leaving out reports about overdose, misuse or the condition being treated, which dominate the raw list for common medicines:
- immune reconstitution inflammatory syndrome107 reports
- meningitis cryptococcal96 reports
- acute kidney injury89 reports
- renal impairment78 reports
- cryptococcosis70 reports
- pyrexia63 reports
- disseminated cryptococcosis61 reports
- headache61 reports
Read these as a signal, not a rate. A report does not mean flucytosine caused the effect — anyone can file one, and many describe people taking several medicines for several conditions. Crucially there is no denominator: FAERS does not record how many people took the drug, so these counts cannot be turned into “X% of patients” — a bigger number often just means a more widely used or more talked-about drug. Duplicates exist, and publicity drives reporting. For what is actually established, read the FDA label section above.
Source: openFDA drug/event (FAERS), retrieved July 25, 2026.
Related calculators
Frequently asked questions
What is flucytosine?
ANCOBON (flucytosine), an antifungal agent, is available as 250 mg and 500 mg capsules for oral administration. In addition to the active ingredient of flucytosine, each capsule contains corn starch, lactose and talc. The 250 mg capsule shell contains black iron oxide, D&C Yellow No. 10, FD&C Blue No. 1, FD&C Yellow No. 6, gelatin and titanium dioxide. The 500 mg capsule shell contains black iron oxide, gelatin and titanium dioxide.
What kind of drug is flucytosine?
The FDA classifies flucytosine as a nucleoside analog antifungal. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.
Can you take flucytosine with other medicines?
It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run flucytosine against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.
What forms does flucytosine come in?
Across the brands we track, flucytosine is currently marketed as capsule, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.
Is there a generic flucytosine?
We do not currently list a generic-labelled flucytosine product. That does not always mean none exists — it means none appears under a generic name in the FDA data we track. Ask your pharmacist.
Cite this page
- APA
- pharmaranks. (2026, July 24). Flucytosine: uses, dosing, side effects & brands. https://pharmaranks.com/drugs/flucytosine
- MLA
- “Flucytosine: uses, dosing, side effects & brands.” pharmaranks, 24 July 2026, https://pharmaranks.com/drugs/flucytosine.
We summarise public FDA and NIH sources — for a clinical claim, cite the primary source we link to as well.
Sources: FDA openFDA drug label, National Drug Code Directory, and Enforcement (recall) database. This page reproduces public FDA data and is not medical advice. Dosing is set by your prescriber.
Read the full FDA label for flucytosine on DailyMed (NIH) ↗ — including its boxed warning in full.