A rapid and sensitive LC-MS/MS method for determination of fluconazole in human plasma and its application in infants with Candida infections.

A rapid and sensitive LC-MS/MS method was developed to quantify fluconazole in human plasma. Seventy microliters of plasma were treated with protein precipitation procedures. Chromatographic separation was achieved on a C18 column using a gradient mobile phase of acetonitrile and water in 0.1% formic acid. Fluconazole and its deuterium-labeled internal standard were monitored in positive mode using electrospray ionization source. The method was fully validated over the range of 0.01 to 10 microg/mL. Intraday and interday precision ranged from 2.84% to 10.8% and 5.27% to 11.5%, respectively. The process recovery efficiency for fluconazole ranged from 98.6% to 104.4%. No carryover and minimal matrix effects were observed. Acceptable stability of fluconazole in blood at room temperature for up to 72 hours guaranteed that fluconazole concentrations in scavenged blood specimens were usable for infant PK analysis and model development. This method has been utilized for a fluconazole pharmacokinetic trial with 55 preterm and term infants younger than 90 days of age. The fast sample preparation cycle and lower limit of quantitation make this method a potential tool for therapeutic drug monitoring of fluconazole to optimize pediatric antifungal therapy. Optimal dose regimen of fluconazole in neonates and young infants might be achieved with application of TDM and pharmacometric approach designed to achieve AUC/MIC >50 for most Candida species with a MIC90 less than 8 microg/mL.