Flucytosine

How it works

It is taken up by fungal cells and converted to 5-fluorouracil, which disrupts fungal RNA and DNA synthesis; it is given with another antifungal to enhance efficacy and limit resistance.

Prescribing in practice

• Dose-related bone marrow suppression (leucopenia and thrombocytopenia) is the principal toxicity, so blood counts and drug levels must be monitored closely.
• It is almost always combined with another antifungal because resistance develops rapidly when used alone.
• It is largely renally excreted, so renal impairment markedly increases the risk of toxicity and requires dose adjustment and level monitoring.

Monitoring

Monitor full blood count, renal and hepatic function, and plasma flucytosine concentrations to avoid toxic accumulation.

Counselling the patient

• Regular blood tests are needed to check your blood counts and drug levels.
• Report any signs of infection, unusual bruising or bleeding.
• This is given alongside another antifungal medicine as part of your treatment.

Evidence & guidelines

Flucytosine combined with amphotericin B is standard induction therapy for cryptococcal meningitis in UK and international guidance.