Efficacy of sparfloxacin and autoradiographic diffusion pattern of [14C]sparfloxacin in experimental Staphylococcus aureus joint prosthesis infection

Abstract

Using a new rabbit model of methicillin-susceptible Staphylococcus aureus knee prosthesis infection, we compared the efficacies of sparfloxacin (50 mg/kg of body weight subcutaneously, twice a day) and pefloxacin (50 mg/kg subcutaneously, twice a day). A partial knee replacement was performed with a silicone implant fitted into the intramedullary canal of the tibia, and 5 x 107 CFU of methicillin-susceptible S. aureus was injected into the knee. The 7-day treatment regimen was started 15 days later. The MICs and MBCs of sparfloxacin and pefloxacin were, respectively, 0.06 and 0.25 μg/ml (MIC) and 0.25 and 1 μg/ml (MBC). The peak levels of sparfloxacin and pefloxacin in serum were 3.6 and 21 μg/ml, respectively. Three weeks after the end of treatment, animals were sacrificed and tibias were removed, pulverized, and quantitatively cultured. In contrast to pefloxacin (3.61 ± 1.64 log10 CFU/g of bone), sparfloxacin significantly reduced the bacterial density (2.12 ± 1.1 log10 CFU/g of bone) (P = 0.01) in comparison with the level in controls (4.59 ± 1.21 log10 CFU/g of bone), without selection of resistant variants. Sparfloxacin was significantly more effective than pefloxacin (P = 0.025). The autoradiographic pattern of [14C]sparfloxacin diffusion was studied in noninfected animals with prostheses and in infected animals 15 days after inoculation. Sixty minutes after completion of infusion of 250 μCi of [14C]sparfloxacin, in infected animals the highest levels of radioactivity were detected around the prosthesis, in femoral cartilage, and in articular ligaments. Radioactivity was slightly less intense in bone marrow and muscles and was very weak in compact bone. The distribution of sparfloxacin in uninfected rabbits was similar. Thus, sparfloxacin may represent a valid alternative therapy in these infections provided that it is carefully monitored for potential side effects.