Bactericidal effects of levofloxacin in comparison with those of ciprofloxacin and sparfloxacin.

OBJECTIVE: To investigate and compare the in vitro activity of levofloxacin with the activities of ciprofloxacin and sparfloxacin. METHODS: The following experiments were performed: (1) comparative studies of the rate of killing by the three quinolones of different strains of Streptococcus pneumoniae at a concentration corresponding to the 1-h serum level following a 500-mg dose in humans; (2) comparative studies of the rate of killing by levofloxacin and ciprofloxacin of different strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa at the same concentrations as above; (3) comparative studies of the rate of killing by levofloxacin at four different concentrations of reference and clinical strains of Streptococcus pneumoniae, Staphylococcus aureus, E. coli and P. aeruginosa. RESULTS: Levofloxacin exhibited statistically significantly higher bactericidal activity than sparfloxacin after 2 and/or 3 h against all strains of Streptococcus pneumoniae. Compared to ciprofloxacin, levofloxacin showed a statistically significantly higher bactericidal activity after 2 and/or 3 h against all strains of Streptococcus pneumoniae except the one resistant to both penicillin and cefotaxime. No differences in killing rate between levofloxacin and ciprofloxacin were seen against Staphylococcus aureus, E. coli and P. aeruginosa, with almost complete killing after 3 h of the P. aeruginosa strains and after 6 h for the E. coli strains. No concentration-dependent killing was seen at concentrations above 4xMIC of levofloxacin against Staphyloccus aureus, E. coli and P. aeruginosa. CONCLUSION: Levofloxacin was shown to be active against both Gram-positive and Gram-negative bacteria. In terms of MIC values, ciprofloxacin was the most active drug against the Gram-negative organisms, and sparfloxacin against the strains of Streptococcus pneumoniae, but levofloxacin exhibited a similar or even better bactericidal activity against the investigated strains compared with the other two fluoroquinolones when killing curves were compared.