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Pharmacology of flucytosine (5-FC)

Richard H Drew, PharmD, MS, FCCP, FIDP
John R Perfect, MD
Section Editor
Carol A Kauffman, MD
Deputy Editor
Anna R Thorner, MD


Flucytosine (5-flucytosine, 5-FC, Ancobon) is an antifungal agent originally developed in 1957 as an antimetabolite. Although it has found no role as an anti-tumor agent, it is used for the treatment of certain fungal infections.

Due to a high incidence of primary and/or acquired resistance, use of flucytosine as monotherapy is significantly restricted. Combination therapy of 5-FC with amphotericin B is recommended for the initial management of severe cryptococcal pneumonia and meningoencephalitis. Less frequently, 5-FC is added to the treatment of select invasive candidal infections.

Hematologic and hepatic toxicities may occur with 5-FC administration but can be reduced by monitoring serum concentrations and by adjusting the dose empirically in patients with renal dysfunction. When serum concentration testing is not available, careful monitoring for cytopenias will be necessary.

High acquisition costs associated with 5-FC worldwide (including the United States) have limited its availability. This is most notable in select African and Asian countries despite the high incidence of cryptococcal diseases in these areas [1-3].

The pharmacology of flucytosine will be discussed here. The clinical use of flucytosine is discussed separately. (See "Treatment of Cryptococcus neoformans meningoencephalitis in HIV-infected patients" and "Cryptococcus neoformans: Treatment of meningoencephalitis and disseminated infection in HIV seronegative patients" and "Candida endocarditis and suppurative thrombophlebitis" and "Candida infections of the central nervous system".)

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Literature review current through: Nov 2017. | This topic last updated: Jan 05, 2016.
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