5-Fluorocytosine also called Capecitabine Intermediate 1 is an orally active antifungal agent with a very narrow spectrum of activity. It is indicated only for the treatment of serious systemic infections caused by susceptible strains of Candida and Cryptococcus spp.

The mechanism of action of 5-fluorocytosine (5-FC)has been studied in detail. The drug enters the fungal cell by active transport onATPases that normally transport pyrimidines. Once insidethe cell, 5-fluorocytosine is deaminated in a reaction catalyzedby cytosine deaminase to yield 5-fluorouracil(5-FU). 5-Fluorouracil is the active metabolite of the drug.

Capecitabine is an oral prodrug of 5-fluorouracil (5-FU), which is widely used for adjuvant and neoadjuvant chemotherapy of different solid tumors, particularly breast and colorectal cancers.