Journal of Antimicrobial Chemotherapy (1999) 43, 345-349
© 1999 The British Society for Antimicrobial Chemotherapy
The antibacterial efficacy of levofloxacin and ciprofloxacin against Pseudomonas aeruginosaassessed by combining antibiotic exposure and bacterial susceptibility
Bristol Centre for Antimicrobial Research and Evaluation, Southmead Health Services NHS Trust and University of Bristol, Department of Medical Microbiology, Southmead Hospital, Westbury-on-Trym, Bristol BS10 5NB, UK
Ciprofloxacin has a four-fold greater in-vitro activity than levofloxacin against Pseudomonas aeruginosa, but levofloxacin has a four-fold higher area under the serum
concentration-time curve (AUC) for an equivalent dose. It has been proposed that the AUC/MIC
ratio is a general predictor of antibacterial efficacy for quinolones. Using an in-vitro kill curve
technique, performed in quadruplicate, with nine antibiotic concentrations and three strains of P. aeruginosa with varying quinolone susceptibility, we constructed sigmoidal dose-
response curves for AUC06.5/MIC and area under the bacterial kill curve
(AUBKC) or AUC024/MIC and log change in viable count at 24 h
(
24). For levofloxacin the log AUC06.5/MIC ratio to produce
50% of the maximal effect was 0.74 ± 0.13 (r2 =
0.9435) for levofloxacin and 0.82 ± 0.06 (r2 = 0.7935) for
ciprofloxacin. The log AUC024/MIC ratio to produce 50% maximal
effect was 1.58 ± 0.13 (r2 = 0.7788) for levofloxacin and
1.37 ± 0.12 (r2 = 0.7207) for ciprofloxacin. An AUC024/MIC ratio of 125 produced 85.4% of the maximal response with
levofloxacin and 81.5% with ciprofloxacin. These data suggest that levofloxacin and
ciprofloxacin have equivalent activity against P. aeruginosa at equivalent AUC/MIC
ratios.
* Corresponding author. Tel: +44-117-9595652; Fax: +44-117-9593154.
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