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The aim of this study was to develop a specific and sensitive liquid chromatography mass spectrometry (LC/MS) method for the determination of rifampicin and levofloxacin concentrations from infected tissues within teflon catheter segments which were subcutaneously implanted in mice. A solid-phase extraction procedure was used to extract analytes from tissue homogenates of the catheter segments and reverse-phase HPLC combined with positive electrospray ionization mass spectrometry was used for analyte separation and quantification. The assay was found to be linear over the concentration range of 0.02-2 microg/g for rifampicin and levofloxacin in tissues and provided good validation data for accuracy and precision. The intra-day accuracy as determined by the relative error was -1.3% for levofloxacin and 6.1% for rifampicin, and precision was evaluated by R.S.D.s with a maximum of 5.1% for levofloxacin and 8.1% for rifampicin. The inter-day accuracy was -3.3% for levofloxacin and -4.6% for rifampicin, and precision was 8.6% for levofloxacin and 7.1% for rifampicin. The assay uses less tissue than previously described methods and can be applied to determine the penetration of rifampicin and the fluoroquinolone in catheter segments from a mouse model of a device-related infection. Finally, the HPLC-MS assay should be applicable to studies of rifamycin+quinolone combination therapies in other animal models of bacterial infection.