Pharmacodynamic effects of ciprofloxacin, fleroxacin and lomefloxacin in vivo and in vitro

The present study investigates the postantibiotic effect (PAE) in vivo, and the postantibiotic subinhibitory concentration effects (PA-SE) in vitro and SE in vivo of three 4-fluoroquinolones (ciprofloxacin, fleroxacin and lomefloxacin) against standard strains of Staphylococcus aureus and Escherichia coli. In vivo killing kinetics have also been performed using two different short administrations to study if the PAE duration could cover the time that the antibiotic was below the minimal inhibitory concentration (MIC) in serum. The results show that the three antimicrobial agents induced long PAEs (1.9-3.1 h) against the two microorganisms. Moderate but significant in vitro PA-SEs were also produced (1->9 h). The in vivo SEs were not significant except when the effect of lomefloxacin on E. coli was assayed (0.54 h). Finally, the in vivo killing kinetics showed that the administrations that included the PAE duration were as effective as the schedule that maintained the antibiotic levels in serum above the MIC. Only when fleroxacin and S. aureus were assayed, this last administration was more effective (+0.9 log(10) colony-forming units/thigh).