Differences between Two New Quinolones (Gemifloxacin and Trovafloxacin) and Ciprofloxacin in Their Concentration-Dependent Killing of Streptococcus pneumoniaeJoyanes P. · Pascual A. · Giménez M.J. · García I. · Aguilar L. · Perea E.
aMicrobiology Department, School of Medicine, University of Seville, bMedical Department, SmithKline Beecham Pharmaceuticals (GlaxoSmithKline), Madrid, Spain
Background: Ciprofloxacin resistance influences the in vitro effect of new quinolones on Streptococcus pneumoniae.Methods: The early (over 3 h) in vitro bactericidal activity of gemifloxacin, trovafloxacin and ciprofloxacin was explored by time-kill tests against two ciprofloxacin-susceptible (MIC = 0.5 and 1 µg/ml) and two ciprofloxacin-resistant (MIC = 16 µg/ml) S. pneumoniae strains. Results: At subinhibitory concentrations (0.5 × MIC) and inhibitory concentrations (1 × MIC), only gemifloxacin exhibited significant bactericidal activity with, respectively, approximately 85 and approximately 95% decrease in the initial inoculum of the two ciprofloxacin-resistant strains. At concentrations similar to peak serum concentrations (1.5, 3 and 2.5 µg/ml for gemifloxacin, trovafloxacin and ciprofloxacin, respectively) after standard doses, only gemifloxacin exhibited an approximately 99.9% (3 log10) reduction in the initial inoculum for the four strains tested, regardless of their susceptibility to ciprofloxacin. No bactericidal activity was exhibited for the other two quinolones against the ciprofloxacin-resistant strains. Conclusions: Gemifloxacin offers high early bactericidal activity at concentrations similar to peak and trough levels, theoretically preventing regrowth over the dosing interval, and thus dealing with the problem of ciprofloxacin resistance in S. pneumoniae.
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