Determination of Tosufloxacin in Plasma by High-Performance Liquid Chromatography with Column Switching

A high-performance liquid chromatography (HPLC) assay was developed for the determination of tosufloxacin in plasma. The plasma samples were directly introduced onto a HPLC precolumn, or after filtering through a Molcut (R) membrane filter, which prolonged the life time of the precolumn resulting from the removal high molecular proteins. The tosufloxacin and sparfloxacin as an internal standard in plasma or filtrate were separated from any interfering substances and then were concentrated on a pre-column using as ODS stationary phase and then were introduced to an analytical column with an ODS stationary phase by column switching. To-. sufloxacin and sparfloxacin were detected by ultraviolet absorption at 269 nm. The determination of tosufloxacin was possible over the concentration range of 50-1500 ng/mL ; and the limit of detection was 20 ng/mL. The recovery of tosufloxacin added to plasma was 96.2-99.5% with a coefficient of variation of less than 1.9%. This method is applicable to drug level monitoring in the plasma of patients being treated with tosufloxacin and in healthy volunteers participating in a scientific investigation to analyze the pharmacokinetics of drug-drug interaction of tosufloxacin.