Improved Procedure forDetermination ofFlucytosine inHuman BloodPlasma byHigh-Pressure Liquid Chromatography

columnwitha mobile phase containing aqueousammoniumphosphate, phosphoric acid, methanol, andacetonitrile. Detection wasat254nm.Theassaywasshowntobelinear inthe10to200-,Ig/ mldrug-concentration range.Forty other drugs weretested forpotential interference withtheassay,andnone was found. Forroutine use,asingle-point working standard containing 75,ugofflucytosine permlwasused, giving intraassay coefficients ofvariation at50and150,ug/ml of1.8and2.3%respectively, whereas theday-todaycoefficient ofvariation at50p,g/ml was 10.0%. Advantages oftheprocedure include thesmallsample size, theuseofaconvenient andreliable internal standard, speed, andsimplicity. Theassayishighly suitable for routine clinical drug-analysis laboratories.