Rapid determination of gemifloxacin in human plasma by high-performance liquid chromatography–tandem mass spectrometry

A method was developed for the determination of gemifloxacin (I) in human plasma using high-performance liquid chromatography–tandem mass spectrometry. Prior to analysis, the protein in plasma samples was precipitated with acetonitrile containing [13C2H3] gemifloxacin (II) to act as an internal standard. The supernatant was injected onto a PLRP-S column without any further clean-up. The mass spectrometer was operated in positive ion mode, employing a heat assisted nebulisation, electrospray interface. Ions were detected in multiple reaction monitoring (MRM) mode. The assay requires 50 μl of plasma and is precise and accurate within the range 10–5000 ng/ml. The average within-run and between-run coefficients of variation were <11% at 10 ng/ml and greater concentrations. The average accuracy of validation standards was generally within ±7% of the nominal concentration. There was no evidence of instability of I in human plasma following three complete freeze–thaw cycles and samples can safely be stored for at least 6 months at −20°C. The method proved very robust and was successfully applied to the analysis of clinical samples from patients dosed with gemifloxacin.