Correlation between in vitro and in vivo activity of levofloxacin and moxifloxacin against pneumococcal strains with different susceptibilities to fluoroquinolones

In vitro and in vivo models were developed to evaluate the efficacy of levofloxacin and moxifloxacin against three serotype 3 pneumococcal strains with different susceptibilities to fluoroquinolones (wild-type, parC mutant, and parC, parE and gyrA mutant). Levofloxacin and moxifloxacin reduced the bacterial burden in the in vitro pharmacodynamic and animal models for the wild-type strain but had very little activity against the fully resistant strain (parC, parE and gyrA mutant). Levofloxacin showed very little activity both in the in vitro pharmacodynamic model and in the animal model for the strain having a mutation in parC (levofloxacin and moxifloxacin minimum inhibitory concentrations, 2 mg/L and 0.25 mg/L, respectively). However, moxifloxacin still had a significant in vitro and in vivo activity against this strain.