Determination of a New 5-Lipoxygenase Inhibitor, Zileuton, and its Inactive N-Dehydroxylated Metabolite in Plasma by High Performance Liquid Chromatography

Summary

A rapid and sensitive assay was developed for the measurement of plasma concentrations of zileuton racemate, a potent inhibitor of 5-lipoxygenase. Zileuton and its inactive Af-dehydroxylated metabolite were extracted from human, monkey, and rat plasma by use of a solid-phase extraction column (Analytichem Bond Elut®). The compounds were then separated by reverse-phase high performance liquid chromatography (HPLC) on a Supelcosil LC-18 column and quantified on the basis of ultraviolet absorption at 260nm relative to an internal standard. The extraction recovery of zileuton, as determined by HPLC assay, was 77.9 ± 1.7%. Recovery of the metabolite was 85.8 ± 0.7%. Calibration curves for both compounds were linear over the zileuton concentration range 0.01 to 10.0 mg/L (correlation coefficients > 0.987), while the intra- and interassay coefficients of variation were < 15.6%. In practice, > 97% of blinded daily spiked control samples for zileuton and > 90% of those for the metabolite were within 10% of their target concentrations.