Interpretative Information

Normal peak serum concentration for 5-fluorocytosine is 30-45 µg/mL with a 2 g PO dose or 60-80 µg/mL with a 100 mg/kg/day PO dose. Trough serum concentration is not well established. Toxicity may be seen with sustained levels greater than 100 µg/mL.

For bioassay measurements, the presence of other antimicrobial agents may interfere with the assay. Other factors that may influence antimicrobial levels include inherent differences among patients and their underlying physical conditions as well as the dose and route of administration of the antimicrobial agent.