5-Fluorocytosine (5-FC) Solution

5-Fluorocytosine (5-FC) Solution is a fluorinated cytosine analog that is used as an antifungal agent.

5-fluorocytosine (5-FC) also known as Flucytosine. 5-Fluorocytosinewas first synthesized in 1957 as anti-tumor drug. It is an antifungal medication which is used with amphotericin B against Candida infections and cryptococcosis. This drug is mainly taken by mouth and by injection into a vein.

Mechanism or Mode of Action of 5-Fluorocytosine

First Candida species take the 5-Fluorocytosine via the cytosine permease and once inside the cell, it is rapidly converted into 5-fluorouracil (5-FU). The 5-FU is toxic to mammalian cell, whereas 5-FC is quite safe.

This 5-FU can exert its toxic effect by adopting two different pathways inside the cell. In one pathway, 5-FU is converted into 5-Fluorodeoxyuridine monophosphate (FdUMP) which is proven to be a potential inhibitor of thymidylate synthase, an essential enzyme for biosynthesis of thymidine. As a result, DNA synthesis gets blocked in fungal cells and it is unable to go for cell division.

Another mechanism is through the conversion of 5-FU into 5-fluorouridine monophosphate and subsequently into 5-Fluorouridine triphosphate which is incorporated into RNA in place of normal uridine triphosphate. In turn, this inhibits the protein synthesis in fungal cell.

Application of 5-Fluorocytosine

• It is used for the treatment of infections caused by Candida or Cryptococcus neoformans.
• It also used for the treatment of chromomycosis (chromoblastomycosis).

Side effects of 5-Fluorocytosine

There are several side effects of 5-Fluorocytosine such as;

1. The treated patient can lead to bone marrow suppression, where the production of leukocytes and erythrocytes is decreased. It also termed as myelotoxicity or myelosuppression.
2. loss of appetite
3. It can cause diarrhea, and vomiting.
4. It can cause psychosis.
5. Sometimes it’s responsible for Anaphylaxis and other allergic reactions.

5-Fluorocytosine (5-FC) Solution Preparation

To prepare  1L of 5-Fluorocytosine (5-FC) Solution the following components are require;

Component	Amount	Concentration
5-FC (mw: 129.09 g/mol)	10 g	0.0775 M

Preparation Procedure

1. Prepare 800 mL of distilled water in a suitable container.
2. Add 10 g of 5-FC to the solution.
3. Add distilled water until volume is 1 L.
4. Vortex. Incubate for 2 h at 37°C, manually mixing the solution every 15 min until the 5-FC dissolves. Filter the solution and use it immediately. Alternatively, aliquot into sterile tubes and store at -20°C.

References

• “5-Fluorocytosine (5-FC) Solution Preparation.” AAT Bioquest, Inc, 30 Apr. 2021, https://www.aatbio.com/resources/buffer-preparations-and-recipes/5-fluorocytosine-5-fc-10-mg-ml.
• Candida Infections and Their Prevention – Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Schematic-diagram-of-the-effect-of-5-Fluorocytosine-5-FC-on-the-fungal-cell-Genes-for_fig1_258405099 [accessed 30 Apr, 2021]