Determination of zafirlukast, a selective leukotriene antagonist, human plasma by normal-phase high-performance liquid chromatography with fluorescence detection.

A high-performance liquid chromatographic (HPLC) method was developed for the determination of zafirlukast, a selective peptide leukotriene receptor antagonist, in human plasma. Zafirlukast and the internal standard, ICI 198 707, were extracted from deproteinated plasma samples using large reservoir C18 solid-phase extraction columns and analyzed by normal-phase liquid chromatography with fluorescence detection. The method had a lower limit of quantitation of 0.75 ng/ml and a linear calibration curve in the range of 0.75 to 200 ng/ml. The absolute recovery of zafirlukast was > 90%, and the within-day and between-day relative standard deviations were < 9%. The utility of the method in the characterization of the plasma concentration-time profiles of zafirlukast in clinical studies was demonstrated.