Pyrimidines

Among pyrimidine antifungal agents, only flucytosine (5-fluorocytosine) is approved by the US Food and Drug Administration (FDA) for use in children. Flucytosine has a limited spectrum of activity against fungi (Cryptococcus and Candida species) and has potential for toxicity and should be avoided in the setting of renal dysfunction. When flucytosine is used as a single agent, resistance often emerges rapidly. Flucytosine should be used in combination with amphotericin B for cryptococcal meningitis. It is important to monitor serum concentrations of flucytosine to avoid bone marrow toxicity. Flucytosine is only available in oral formulation in the United States.