Ancobon (flucytosine)

Because prolonged serum flucytosine concentrations exceeding 100 mcg/mL may be associated with an increased risk of toxicity (e.g., adverse hematologic, GI, and hepatic effects), flucytosine dosage usually should be adjusted to ensure that peak serum concentrations of the drug remain below 100 mcg/mL. However, optimal target serum concentrations have not been identified, and a variety of target ranges have been recommended. The American Academy of Pediatrics (AAP), US Centers for Disease Control and Prevention (CDC), National Institutes of Health (NIH), Infectious Diseases Society of America (IDSA), and others generally recommend target serum flucytosine concentrations of 30-80 mcg/mL.

Some clinicians suggest that serum flucytosine concentrations should be measured beginning 3-5 days after initiation of the drug (or beginning after 3-5 doses) and then once or twice weekly during treatment and whenever there is evidence of toxicity or a change in renal function. Peak serum concentrations usually are measured using blood samples taken 2 hours after an oral dose.

In patients with impaired renal function, doses and/or frequency of administration of flucytosine must be modified in response to the degree of impairment and serum concentrations of the drug. Several methods of calculating flucytosine dosage for patients with impaired renal function have been proposed; however, for greater accuracy, dosage in these patients should be based on actual serum concentrations of the drug. Precise dosing is limited, since flucytosine is commercially available only as 250- and 500-mg capsules.

Some clinicians recommend that adults with creatinine clearances of 20-40 mL/minute receive 25 mg/kg of flucytosine every 12 hours and that those with creatinine clearances of 10-20 mL/minute receive 25 mg/kg once daily. In those with creatinine clearances less than 10 mL/minute, these clinicians recommend a flucytosine dosage of 25 mg/kg once every 48 hours.

Other clinicians recommend that the usual individual dose of flucytosine (12.5-37.5 mg/kg) be administered every 12 hours in patients with creatinine clearances of 20-40 mL/minute, every 24 hours in those with creatinine clearances of 10-20 mL/minute, and every 24-48 hours or longer (as determined by serum drug concentrations) in those with creatinine clearances less than 10 mL/minute. Alternatively, other clinicians have recommended that flucytosine doses of 12-35 mg/kg be administered at intervals equal to twice the half-life of the drug.

In patients undergoing hemodialysis, some clinicians recommend that flucytosine doses of 20-50 mg/kg be given once every 48-72 hours and that the doses be administered after dialysis.

Flucytosine is administered orally. The manufacturer suggests that nausea and vomiting associated with oral flucytosine may be reduced or avoided if each dose is administered by ingesting the capsules a few at a time over a 15-minute period.

Flucytosine has been administered IV; however, a parenteral dosage form of the drug is not commercially available in the US. Flucytosine also has been administered topically as a cream, but topical preparations of the drug are not commercially available in the US.

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There is no enhanced messaging for this drug.

There are no contraindication interactions for this drug.

There are no severe interactions for this drug.

There are no moderate interactions for this drug.

There is no enhanced messaging for this drug.

There are no contraindication contraindications for this drug.

There are no severe contraindications for this drug.

There are no moderate contraindications for this drug.

There is no enhanced messaging for this drug.

There are no severe adverse reactions for this drug.

There are no less severe adverse reactions for this drug.

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No enhanced messaging available.

Flucytosine was shown to be teratogenic in rats. When flucytosine was given to rats in a dosage of 40 mg/kg daily (0.051 times the human dosage) on days 7-13 of gestation, vertebral fusions occurred; at a dosage of 700 mg/kg daily (0.89 times the human dosage) on days 9-12 of gestation, cleft lip and palate and micrognathia were reported. In mice, flucytosine dosage of 400 mg/kg daily (0.236 times the human dosage) on days 7-13 of gestation was associated with a low incidence of cleft palate that was not statistically significant. Flucytosine was not teratogenic in rabbits when given in dosages up to 100 mg/kg daily (0.243 times the human dosage) on days 6-18 of gestation.

There are no adequate or controlled studies to date using flucytosine in pregnant women, and the drug should be used during pregnancy only when potential benefits justify possible risks to the fetus.

It is not known whether flucytosine is distributed into human milk.

Because many drugs are distributed into human milk and because of the potential for serious adverse effects in nursing infants, a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the mother.

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