ABSTRACT
Flucytosine (5 fluorocytosine, 5FC) is an oral antifungal with activity in vitro against most Candida spp. (with the exception of C. krusei). Primary resistance rates for Cryptococcus neoformans range between 1%-24.5%. Use as a monotherapy is limited to select cases of candidal cystitis/pyelonephritis due to concerns for the rapid development of both primary and secondary resistance. In contrast, combination therapy of flucytosine with amphotericin B has been proven to improve treatment outcomes in patients with cryptococcal meningitis when used as the initial part of therapy. Combination therapy (usually with amphotericin B) is also used in select cases of invasive candida infections. In addition to concerns regarding resistance, flucytosine use is also limited by its toxicities (primarily hematologic), lack of a parenteral preparation in the US, widespread availability worldwide, and cost. Serum concentration monitoring and dose adjustment in patients with renal insufficiency should be employed in an attempt to achieve target serum concentrations while reducing the potential for serum concentration-related side effects.
