Flucytosine (5FC)

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Chapter: Essential pharmacology : Antifungal Drugs

It is a pyrimidine antimetabolite which is inactive as such. It is taken up by fungal cells and converted into 5fluorouracil and then to 5fluorodeoxyuridylic acid which is an inhibitor of thymidylate synthesis. Thymidylic acid is a component of DNA.


FLUCYTOSINE  (5FC)

 

It is a pyrimidine antimetabolite which is inactive as such. It is taken up by fungal cells and converted into 5fluorouracil and then to 5fluorodeoxyuridylic acid which is an inhibitor of thymidylate synthesis. Thymidylic acid is a component of DNA. The fungal selectivity of 5FC depends on the fact that mammalian cells (except some marrow cells) have low capacity to convert 5FC into 5fluorouracil.

 

It is a narrow spectrum fungistatic, active against Cryptococcus neoformans, Torula, Chromoblastomyces; and a few strains of Candida. Other fungi and bacteria are insensitive.

 

Adverse Effects

 

Toxicity of 5FC is lower than that of AMB; consists of dose-dependent bone marrow depression and gastrointestinal disturbances, particularly enteritis and diarrhoea.

 

Liver dysfunction is mild and reversible.

 

Use

 

Flucytosine is not employed as the sole therapy except occasionally in chromoblastomycosis. Rapid development of resistance limits its utility in deep mycosis. In cryptococcosis (both meningeal and nonmeningeal) its synergistic action with AMB is utilized to reduce the total dose of the more toxic latter drug.


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