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AIM: Bacterial resistance to quinolones has traditionally mediated by alteration of the quinolone targets and/or overproduction of efflux pump. Recently, a new mechanism, the plasmid-mediated quinolone resistance named qnr, has been clarified. Qnr and its homologus are widely distributed among gram-negative bacteria. The presence of qnr only slightly elevates the resistance level, however it facilitates the selection of highly resistant strains. In our study, we examined the probable influence of such phenomenon to the clinical regimens of levofloxacin. METHODS: In-vitro hollow fiber infection model simulating oral two-compartment pharmacokinetic model was established. In the model, bacteria was incubated in the peripheral compartment without ‘washout effect’. We designed two therapeutic regimens of levofloxacin, including 500 mg qd (peak 5.12 mg/L; half-time 6.9 h) and 700 mg qd (peak 9.46 mg/L; half-time 6.9 h) for 3 days against E.coli J53 and E. coli 6503, which carrying qnr positive plasmid. RESULTS: Although 500 mg qd regimen could decrease the bacteria density of E. coli 6503 at the beginning, the bacteria population bounced back when the drug concentration was drecreased below 2 mg/L, and the regrowth bacteria had higher MICs than the parental strains. 700 mg qd for 3 days could inhibit the outgrowth of E. coli 6503 all the time. E. coli J53 was well inhibited by both the mentioned therapeutic regimens. DNA sequencing found the mutations in QRDR of E. coli 6503. CONCLUSION: We conclude that 500 mg qd which is the most popular regimen is at risk of selecting resistant mutations and treatment failure while treating the infections caused by qnr positive E. coli, and 750 mg qd might be preferred. In vivo pharmacodynamic studies to support our findings are warranted.
AIM: Bacterial resistance to quinolones has traditionally mediated by alteration of the quinolone targets and / or overproduction of efflux pump. Recently, a new mechanism, the plasmid-mediated quinolone resistance named qnr, has been clarified. Qnr and its homologus are widely distributed among The presence of qnr only slightly elevates the resistance level, however it facilitates the selection of highly resistant strains. In our study, we examined the probable influence of such such to the clinical regimens of levofloxacin. METHODS: In-vitro hollow the model infection mode simulating oral two-compartment pharmacokinetic model was established. In the model, bacteria was incubated in the peripheral compartment without ’washout effect’. We designed two therapeutic regimens of levofloxacin, including 500 mg qd (peak 5.12 mg / L; half-time 6.9 h) and 700 mg qd (peak 9.46 mg / L; half-time 6.9 h) for 3 days against E. coli J53 and E. coli 6503, which carry qnr posi tive plasmid. RESULTS: Although 500 mg qd regimen could decrease the bacteria density of E. coli 6503 at the beginning, the bacteria population bounced back when the drug concentration was drecreased below 2 mg / L, and the regrowth bacteria had higher MICs than the 700 mg qd for 3 days could inhibit the outgrowth of E. coli 6503 all the time. DNA sequencing found the mutations in QRDR of E. coli 6503. CONCLUSION : We conclude that 500 mg qd which is the most popular regimen is at risk of selecting resistant mutations and treatment failure while treating the infections caused by qnr positive E. coli, and 750 mg qd might be preferred. In vivo pharmacodynamic studies to support our findings are warranted.