Flucytosine (5-FC)

Absorption: No PO absorption, IV only.

 

Distribution: Wide – small water soluble molecule.

 

Elimination: Renal – converted to 5-FU inside fungal cells, therefore inhibitory to DNA synthesis. Rapid development of resistance, so add in ampho-B or fluconazole. Resistance occurs due to a change in the enzyme that 5-FC→5-FU.

 

Spectrum of Action: Yeasts (Cryptococcus & candida), moulds (aspergillus). No activity against zygomycetes.

 

Toxicity & S/E: Nausea, vomiting, diarrhoea, ↑LFTs & reversible bone marrow suppression. Monitor levels!

 

Clinical Use: Add to amp-B for cryptococcal meningitis, candidaemia & refractory aspergillosis.