Medically reviewed on March 25, 2018
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Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Ancobon: 250 mg, 500 mg
Generic: 250 mg, 500 mg
Brand Names: U.S.
- Antifungal Agent, Oral
Penetrates fungal cells and is converted to fluorouracil which competes with uracil interfering with fungal RNA and protein synthesis
Rapid; serum concentrations are highly variable in neonates; monitor closely (Pasqualotto, 2007); serum concentrations tended to be higher in children <12 years of age; monitor closely (Soltani, 2006)
Into CSF, aqueous humor, joints, peritoneal fluid; Vd: 0.6 L/kg
Minimally hepatic; deaminated both in yeasts and possibly via gut bacteria to 5-fluorouracil
Urine (>90% as unchanged drug)
Time to Peak
Serum: Neonates: 2.5 ± 1.3 hours; Adults: ~1 to 2 hours
Neonates: 4 to 34 hours (Baley, 1990); Infants: 7.4 hours; Adults: 2 to 5 hours; Anuria: 85 hours (range: 30 to 250); End-stage renal disease (ESRD): 75 to 200 hours
3% to 4%
Special Populations: Renal Function Impairment
Prolonged half-life (29.9 to 250 hours in anuric or nephrectomized patients).
Use: Labeled Indications
Candida/Cryptococcus infections: Adjunctive treatment of systemic fungal infections (eg, septicemia, endocarditis, UTI, meningitis, or pulmonary) caused by susceptible strains of Candida or Cryptococcus
Off Label Uses
Aspergillosis, endocarditis treatment (pediatric)
Based on the American Heart Association (AHA) Scientific Statement for Infective Endocarditis in Childhood, flucytosine, in combination with amphotericin B, may be considered for the treatment of infective endocarditis due to Aspergillus or Candida in children or adolescents.
Hypersensitivity to flucytosine or any component of the formulation
Usual dosage ranges: Oral: 50 to 150 mg/kg/day in divided doses every 6 hours
Candidiasis (off-label dose) (IDSA [Pappas 2016]): Oral:
Central nervous system (eg, meningitis): 25 mg/kg/dose 4 times daily (with amphotericin B [liposomal]) until step-down therapy is clinically appropriate.
Cystitis, symptomatic: Fluconazole-resistant C. glabrata: 25 mg/kg/dose 4 times daily for 7 to 10 days as monotherapy.
Endocarditis (native or prosthetic valve) or infected implantable cardiac devices (eg, pacemaker, ICD, VAD): 25 mg/kg/dose 4 times daily (with an amphotericin B lipid formulation); for native or prosthetic valve endocarditis, therapy should continue for at least 6 weeks after valve replacement surgery (longer durations in patients with abscesses or other complications); for patients with implantable cardiac devices, therapy should continue for 4 to 6 weeks after surgery (4 weeks for infections limited to generator pockets and at least 6 weeks for infections involving the wires). Note: May transition to fluconazole if patient clinically stable with fluconazole-susceptible isolates in whom Candida has cleared from the bloodstream.
Endophthalmitis (with or without vitritis): Fluconazole- or voriconazole-resistant isolates: 25 mg/kg/dose 4 times daily (with amphotericin B [liposomal]) for at least 4 to 6 weeks until examination indicates resolution; for patients with vitritis or with macular involvement (with or without vitritis), an intravitreal injection with voriconazole or amphotericin B deoxycholate is also recommended.
Pyelonephritis, symptomatic: Fluconazole-resistant C. glabrata: 25 mg/kg/dose 4 times daily in combination with amphotericin B deoxycholate for 1 to 7 days or as monotherapy for 14 days.
Cryptococcal meningitis, treatment: Oral:
Non-HIV-infected, non-transplant: Induction: 25 mg/kg/dose (with amphotericin B) every 6 hours for at least 4 weeks; if clinical and microbiological improvement, may discontinue both amphotericin and flucytosine and follow with an extended course of fluconazole (IDSA [Perfect 2010]).
HIV-infected or solid organ transplant recipients: Induction: 25 mg/kg/dose (with amphotericin B) every 6 hours for at least 2 weeks; if clinical and microbiological improvement, may discontinue both amphotericin and flucytosine and follow with an extended course of fluconazole (HHS [OI adult 2017]; IDSA [Perfect 2010]).
Cerebral cryptococcomas: Induction: 25 mg/kg/dose (with amphotericin B and corticosteroids) every 6 hours for at least 6 weeks, followed with an extended course of fluconazole (IDSA [Perfect 2010])
Refer to adult dosing.
General dosing, susceptible infections: Infants, Children, and Adolescents (off-label population): Oral: 50 to 150 mg/kg/day in divided doses every 6 hours (Red Book [AAP 2015])
Aspergillosis, endocarditis (off-label use): Limited data available: Children and Adolescents: Oral: 37.5 mg/kg/dose every 6 hours in combination with amphotericin B (AHA [Baltimore 2015])
Candidiasis, endocarditis (off-label): Children and Adolescents: Oral: 37.5 mg/kg/dose every 6 hours in combination with amphotericin B (AHA [Baltimore 2015])
Cryptococcal meningitis, treatment:
Non-HIV-infected: Children (off-label population): Oral: Induction: 25 mg/kg/dose (with amphotericin B) every 6 hours for at least 4 weeks; if clinical improvement, may discontinue both amphotericin and flucytosine and follow with an extended course of fluconazole (Perfect 2010).
HIV-infected: Adolescents (off-label population): Refer to adult dosing.
Dosing: Renal Impairment
Adults: The manufacturer recommends dose reduction for elevated BUN or serum creatinine (or other signs of renal impairment); however, no specific dosage adjustments are provided. The following adjustments have been recommended (based on a usual dose of 25 mg/kg/dose every 6 hours):
CrCl >40 mL/minute: No dosage adjustment necessary (HHS [OI adult 2017]; IDSA [Perfect 2010])
CrCl 20 to 40 mL/minute: 25 mg/kg/dose every 12 hours (HHS [OI adult 2017])
CrCl 10 to 20 mL/minute: 25 mg/kg/dose every 24 hours (HHS [OI adult 2017])
CrCl <10 mL/minute: 25 mg/kg/dose every 48 hours (HHS [OI adult 2017])
ESRD on intermittent hemodialysis (IHD): 25 to 50 mg/kg/dose every 48 to 72 hours; administer dose after hemodialysis (Drew 1999; HHS [OI adult 2017])
Infants, Children, and Adolescents: The following adjustments have been recommended:
Aronoff 2007: Infants, Children, and non-HIV-exposed/positive Adolescents (based on a usual dose of 100 to 150 mg/kg/day divided every 6 hours):
GFR >50 mL/minute/1.73 m2: No dosage adjustment necessary.
GFR 30 to 50 mL/minute/1.73 m2: 25 to 37.5 mg/kg/dose every 8 hours
GFR 10 to 29 mL/minute/1.73 m2: 25 to 37.5 mg/kg/dose every 12 hours
GFR <10 mL/minute/1.73 m2: 25 to 37.5 mg/kg/dose every 24 hours
Hemodialysis: 25 to 37.5 mg/kg/dose every 24 hours
Peritoneal dialysis: 25 to 37.5 mg/kg/dose every 24 hours
Continuous renal replacement therapy: 25 to 37.5 mg/kg/dose every 8 hours (monitor serum concentrations)
HHS [OI pediatric] 2016: HIV-exposed/-positive: Children: Severe renal impairment: Avoid use.
HHS [OI adult] 2017: HIV-exposed/-positive: Adolescents (based on a usual dose of 25 mg/kg/dose every 6 hours):
CrCl >40 mL/minute: No dosage adjustment necessary.
CrCl 20 to 40 mL/minute: 25 mg/kg/dose every 12 hours
CrCl 10 to 20 mL/minute: 25 mg/kg/dose every 24 hours
CrCl <10 mL/minute: 25 mg/kg/dose every 48 hours
ESRD on hemodialysis: 25 to 50 mg/kg/dose every 48 to 72 hours; administer dose after hemodialysis
Dosing: Hepatic Impairment
There are no dosage adjustments provided in the manufacturer's labeling; use with caution.
50 mg/mL Oral Suspension (ASHP standard concentration) (ASHP 2017)
A 50 mg/mL oral suspension may be made with capsules and OraPlus and OraSweet. Mix 30 mL of OraPlus and 30 mL of OraSweet together in a separate container. Empty the contents of six 500 mg capsules in a mortar; add 15 mL portion of the vehicle mixture and triturate. Transfer mixture to a 60 mL (2 ounce) amber prescription bottle. Rinse the mortar with an additional 15 mL of vehicle mixture and pour into the amber bottle. Repeat rinsing procedure until a final bottle volume of 60 mL is achieved. Label the bottle "shake well." Stable for 90 days at 3°C to 5°C (37°F to 41°F) or 23°C to 25°C (73°F to 77°F).VandenBussche HL, Johnson CE, Yun J, et al. Stability of flucytosine 50 mg/mL in extemporaneous oral liquid formulations. Am J Health Syst Pharm. 2002;93(19):1853-1855.12374070
10 mg/mL Oral Suspension
A 10 mg/mL oral suspension may be made with capsules and distilled water. Empty the contents of ten 500 mg capsules in a mortar; add small portions of distilled water and mix to a uniform paste. Mix while adding distilled water in incremental proportions to almost 500 mL; transfer to a 500 mL volumetric flask, rinse mortar several times with distilled water, and add sufficient quantity of distilled water to make 500 mL. Store in glass or plastic prescription bottles and label "shake well". Stable for 70 days refrigerated and 14 days at room temperature.Wintermeyer SM and Nahata MC. Stability of Flucytosine in an Extemporaneously Compounded Oral Liquid. Am J Health Syst Pharm. 1996;53(4):407-409.8673661
Administer around-the-clock to promote less variation in peak and trough serum levels. To reduce or avoid nausea and vomiting, administer a few capsules at a time over 15 minutes until full dose is taken.
Store at room temperature of 25°C (77°F); excursions permitted to 15°C to 30°C (59°F to 86°F).
Amphotericin B: May enhance the adverse/toxic effect of Flucytosine. This may be related to the adverse effects of amphotericin B on renal function. Monitor therapy
BCG (Intravesical): Myelosuppressive Agents may diminish the therapeutic effect of BCG (Intravesical). Avoid combination
Chloramphenicol (Ophthalmic): May enhance the adverse/toxic effect of Myelosuppressive Agents. Monitor therapy
CloZAPine: Myelosuppressive Agents may enhance the adverse/toxic effect of CloZAPine. Specifically, the risk for neutropenia may be increased. Monitor therapy
Cytarabine (Conventional): May diminish the therapeutic effect of Flucytosine. Consider therapy modification
Deferiprone: Myelosuppressive Agents may enhance the neutropenic effect of Deferiprone. Avoid combination
Dipyrone: May enhance the adverse/toxic effect of Myelosuppressive Agents. Specifically, the risk for agranulocytosis and pancytopenia may be increased Avoid combination
Gimeracil: May increase serum concentrations of the active metabolite(s) of Flucytosine. Specifically, gimeracil may increase concentrations of fluorouracil. Avoid combination
Promazine: May enhance the myelosuppressive effect of Myelosuppressive Agents. Monitor therapy
Saccharomyces boulardii: Antifungal Agents (Systemic, Oral) may diminish the therapeutic effect of Saccharomyces boulardii. Avoid combination
Flucytosine causes markedly false elevations in serum creatinine values when the Ektachem® analyzer is used. The Jaffé reaction is recommended for determining serum creatinine.
Frequency not defined.
Cardiovascular: Cardiotoxicity, chest pain, ventricular dysfunction
Central nervous system: Ataxia, confusion, fatigue, hallucination, headache, paresthesia, parkinsonian-like syndrome, peripheral neuropathy, psychosis, sedation, seizure, vertigo
Dermatologic: Pruritus, skin photosensitivity, skin rash, toxic epidermal necrolysis, urticaria
Endocrine & metabolic: Hypoglycemia, hypokalemia
Gastrointestinal: Abdominal pain, anorexia, diarrhea, duodenal ulcer, enterocolitis, gastrointestinal hemorrhage, nausea, ulcerative colitis, vomiting, xerostomia
Genitourinary: Azotemia, crystalluria
Hematologic & oncologic: Agranulocytosis, anemia, aplastic anemia, bone marrow aplasia, eosinophilia, leukopenia, pancytopenia, thrombocytopenia
Hepatic: Hepatic injury (acute), hepatic insufficiency, hepatic necrosis, increased liver enzymes, increased serum bilirubin, jaundice
Hypersensitivity: Hypersensitivity reaction
Neuromuscular & skeletal: Weakness
Otic: Hearing loss
Renal: Increased blood urea nitrogen, increased serum creatinine, renal failure
• Hematologic disease: Use with caution in patients with bone marrow depression, hematologic disease or who have been treated with radiation or drugs that suppress the bone marrow; bone marrow toxicity may be irreversible.
• Hepatic impairment: Use with caution in patients with hepatic impairment; hepatotoxicity may occur.
• Renal impairment: [US Boxed Warning]: Use with extreme caution in patients with renal dysfunction; dosage adjustment required.
• Monitoring: [US Boxed Warning]: Closely monitor hematologic, renal, and hepatic status. Hepatotoxicity and bone marrow toxicity appear to be dose related; monitor levels closely and adjust dose accordingly.
• Monotherapy: Avoid use as monotherapy; resistance rapidly develops.
Pretreatment: Electrolytes (especially potassium), CBC with differential, BUN, renal function, blood culture
During treatment: CBC with differential and LFTs (eg, alkaline phosphatase, AST/ALT) frequently; serum flucytosine concentrations (2 hours after administration of a dose) after the initial 3 to 5 days of treatment (HHS [OI adult 2017]; IDSA [Perfect 2010]) and as clinically indicated; renal function
Adverse events have been observed in some animal reproduction studies. Flucytosine is metabolized to fluorouracil which may cause adverse events if administered during pregnancy; refer to the Fluorouracil (Systemic) monograph for additional information.
• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)
• Patient may experience fatigue, dry mouth, nausea, headache, vomiting, diarrhea, or lack of appetite. Have patient report immediately to prescriber signs of infection, signs of kidney problems (urinary retention, blood in urine, change in amount of urine passed, weight gain), signs of low potassium (muscle pain or weakness, muscle cramps, or an abnormal heartbeat), signs of bleeding (vomiting blood or vomit that looks like coffee grounds; coughing up blood; blood in the urine; black, red, or tarry stools; bleeding from the gums; abnormal vaginal bleeding; bruises without a reason or that get bigger; or any bleeding that is very bad or that will not stop), signs of low blood sugar (dizziness, headache, fatigue, feeling weak, shaking, a fast heartbeat, confusion, hunger, or sweating), signs of liver problems (dark urine, feeling tired, lack of appetite, nausea, severe abdominal pain, light-colored stools, vomiting, or yellow skin or eyes), severe abdominal pain, confusion, severe loss of strength and energy, swelling of arms or legs, tremors, difficulty moving, muscle rigidity, angina, seizures, mood changes, hearing impairment, change in balance, burning or numbness feeling, excessive weight gain, shortness of breath, or hallucinations (HCAHPS).
• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.
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- Drug class: miscellaneous antifungals
Other brands: Ancobon