Simultaneous determination of rufloxacin and theophylline by high-performance liquid chromatography in human plasma

A sensitive, specific and rapid liquid chromatographic procedure to monitor rufloxacin and theophylline selectively in human plasma has been developed and validated. Plasma samples were extracted with a mixture of dichloromethane-diethyl ether. The organic layer was evaporated to dryness, reconstituted with mobile phase, and the analytes were separated and quantified by LC on an octadecylsilane column with acetonitrile-0.1 mol dm-3 phosphate buffer (pH3) as mobile phase and UV detection at 280 nm. The procedure was linear from 0.05 to 5.0 micrograms cm-3, with a detection limit of 0.03 micrograms cm-3 for rufloxacin, and from 0.5 to 30 micrograms cm-3, with a detection limit of 0.02 micrograms cm-3 for theophylline. The accuracy of the method was defined by relative errors of 4.2, 5.0 and 1.6% for human plasma containing 0.1, 1.0 and 5.0 micrograms cm-3 of rufloxacin and 2.4, 2.0 and 2.7% at the concentrations of 1.0, 5.0 and 20 micrograms cm-3 for theophylline. The corresponding relative standard deviations were 3.4, 2.8 and 1.7% for rufloxacin and 2.1, 3.7 and 3.8% for theophylline at the same concentrations, respectively. The assay has been successfully applied to pharmacology, toxicology and pharmacokinetics studies in humans.