title: Gas-chromatographic determination of 5-fluorocytosine in human serum.
abstract: We describe a sensitive and precise gas-chromatographic method, in which cytosine is used as the internal standard, for determination of an antifungal agent, 5-fluorocytosine, in serum. The trimethylsilyl derivative of this drug is well separated from the internal standard and from normal serum constituents. Amphotericin B does not interfere with the determination of 5-fluorocytosine. The lower limit of detection for 5-fluorocytosine is 1 mg/liter when 200 mul of serum is analyzed. Within-run precision (CV), established by analysis of 10 replicates, was 4.5% at a concentration of 19.9 mg/liter. Twenty-five serum samples were analyzed for 5-fluorocytosine by a microbiological assay and by the gas-chromatographic method. Mean value observed with the bioassay was 78.5 mg/liter and with our procedure was 69.4 mg/liter. When values for our assay were regressed against values for the bioassay, slope of the least-squares line was 0.85, intercept was 2.7 mg/liter, and r was 0.93.
mesh_terms: D002849:Chromatography, Gas / Q000379:methods; D003596:Cytosine / Q000031:analogs & derivatives*; D005437:Flucytosine / Q000097:blood*; D006801:Humans; D008832:Microchemistry
chemical_list: D003596:Cytosine; D005437:Flucytosine