Simultaneous Determination of the 5-Lipoxygenase Inhibitor “Zileuton” and its N-Dehydroxylated Metabolite in Untreated Rat Urine by Micellar Liquid Chromatography

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Abstract
A specific and sensitive HPLC procedure for the quantitative determination of Zileuton, (N- (1- (benzo-[b]-thien-2-yl)ethyl)-N-hydroxyurea), and its N-dehydroxylated metabolite in an untreated urine sample was developed. Separation of these compounds is achieved with micellar liquid chromatography, using sodium dodecyl sulfate (SDS) as the mobile phase and a CN-bonded silica column with UV detection at 262 nm. Because of the dissolving power of the micellar phase, urine samples were injected into the system without time-consuming protein precipitation and/or drug extraction steps. Changes in mobile phase variables such as SDS concentration, pH and/or organic modifier concentration profoundly affected both chromatographic selectivity and drug retention. Linear calibration curves of the relative peak heights versus concentrations were obtained from 0.10 – 5.0 ppm for Zileuton and its metabolite. The minimum quantifiable concentration using this column was 0.08 – 0.10 ppm.