Monitoring flucytosine blood concentrations

Flucytosine plasma concentration monitoring is routinely recommended in patients with:

• central nervous system infection
• critical illness
• difficulties with medication compliance.

Measure flucytosine plasma concentration 3 to 5 days after starting therapy or dose adjustment. The flucytosine trough plasma concentration should be between 25 and 40 mg/L to prevent drug resistance. Haematological toxicity and hepatoxicity has been associated with a peak plasma concentration higher than 100 mg/L (2 hours after an oral dose or 30 minutes after an intravenous dose)Abdul-Aziz 2020Chau 2021John 2019Kauffman 1977Vermes 2000.

See Practical information on using flucytosine for information on clinical monitoring for flucytosine.

For information on flucytosine plasma concentration monitoring in haematology patients, see the Australian and New Zealand antifungal consensus guidelines.