Flucytosine

ANCOBON

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Flucytosine ballicule: receptor binding, kinetics and half-life diagram — Mechanism of action: Flucytosine ballicule

Flucytosine ANCOBON mascot mnemonic cartoon — Visual mnemonic: Flucytosine mascot
**“Flew sight unseen (and co-pilot-bound)”**
With amphotericin "bee" as copilot

What it isAntifungal converted to 5-fluorouracil by fungal cytosine deaminase; cryptococcal meningitis with amphotericin.

Why this oneCombined with amphotericin it sterilizes CSF faster than amphotericin alone, improving survival.

What limits itMyelosuppression tracks blood levels, so monitoring is needed, and it is renally cleared. Never use alone — resistance emerges rapidly.

Flucytosine molecular structure (skeletal formula) — Molecular structure: Flucytosine

FDA-approved for

Serious Candida and Cryptococcus infections (1971)

FDA label

Read the full label on DailyMed ↗

BOXED WARNING Extreme caution in renal impairment; close hematologic, renal, and hepatic monitoring of all patients is essential.

FDA dosing	Population	Start	Target	Max
Systemic candidiasis & cryptococcosis (in combination with amphotericin B)	Adults	50 mg/kg/day divided q6h (QID)	50-150 mg/kg/day divided q6h	150 mg/kg/day

Renal Elevated BUN/creatinine or other signs of renal impairment: start at the lower dose level (50 mg/kg/day); extreme caution (boxed)

Hepatic Undefined

Instructions

Give capsules a few at a time over a 15-minute period to reduce nausea/vomiting
Use in combination with amphotericin B for systemic candidiasis and cryptococcosis (resistance emerges on monotherapy)

Available strengths

cap 250, 500 mg

Contraindications

Known complete dihydropyrimidine dehydrogenase (DPD) enzyme deficiency

Cautions

Use with extreme caution in impaired renal function (boxed)
Monitor hematologic, renal, and hepatic status closely in all patients (boxed)

Adverse reactions

Nausea, vomiting, diarrhea, anorexia, abdominal pain
Hepatic injury incl. necrosis (possibly fatal in debilitated patients), jaundice, enzyme elevations
Marrow toxicity: anemia, leukopenia, thrombocytopenia, agranulocytosis, pancytopenia, fatal bone marrow aplasia
Azotemia, BUN/creatinine elevation, crystalluria, renal failure
Cardiac arrest, myocardial toxicity, ventricular dysfunction
Confusion, hallucinations, psychosis, sedation, convulsions, ataxia, paresthesia, peripheral neuropathy, hearing loss
Rash, pruritus, urticaria, photosensitivity; Lyell's syndrome
Hypoglycemia, hypokalemia

Pregnancy Teratogenic in rats (vertebral fusions; cleft lip/palate at higher doses); no adequate human studies — use only if potential benefit justifies fetal risk.

Lactation Undefined

Cost

Flucytosine (ANCOBON)

Strength		#/mo	generic $/mo	CostPlus
250 mg	cap	120 QID		offered
500 mg	cap	120 QID		offered

NADAC is a voluntary CMS survey of what retail community pharmacies pay for the drugs they stock. Flucytosine is dispensed outside retail pharmacies, so it rarely appears on surveyed invoices.

⚠ BOXED WARNING

Use with extreme caution in renal impairment

Classes and tags

Clinical profile

Therapeutic safety burden4 / 4

Overdose danger2 / 4

Weight-gain liability0 / 4

Sedation liability1 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism0 / 4

Embryofetal risk2 / 4

Defining liabilityConcentration-dependent marrow suppression and hepatic toxicity

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