Flucytosine (5-FC)

Flucytosine, also known as 5-fluorocytosine (5-FC), is a synthetic fluorinated pyrimidine analog used as an antifungal medication (StatPearls, 2024). It acts as a prodrug that is selectively converted into the active antimetabolite 5-fluorouracil (5-FU) within fungal cells by the enzyme cytosine deaminase, which is absent in human cells (NIH, 2024). This conversion leads to the inhibition of both DNA and RNA synthesis, effectively halting fungal growth and replication (Wikipedia, 2024). Flucytosine is primarily indicated for serious systemic infections caused by Candida and Cryptococcus species, often in combination with amphotericin B to prevent the rapid development of resistance (DrugBank, 2024). Its clinical use requires careful monitoring of renal function and serum drug levels to avoid dose-related toxicities such as bone marrow suppression and hepatotoxicity (StatPearls, 2024).

Other names

5-fluorocytosine5-FCAncobonAncotil4-amino-5-fluoro-1,2-dihydropyrimidin-2-one

Flucytosine is a prodrug that enters fungal cells via cytosine permease and is converted by cytosine deaminase into 5-fluorouracil (5-FU). 5-FU is further metabolized into 5-fluorodeoxyuridine monophosphate (FdUMP), which inhibits thymidylate synthase to block DNA synthesis, and 5-fluorouridine triphosphate (FUTP), which is incorporated into RNA, disrupting protein synthesis (StatPearls, 2024; NIH, 2024).