The ability to identify agents with the optimal combination of potency, pharmacokinetics and pharmacodynamics should help to maximize bacteriological cure and thus minimize the potential for selection and spread of resistance.
Gemifloxacin demonstrated excellent correlation between efficacy and the AUC0-24h/MIC ratio whereas there was little correlation with time above MIC. Thus,
gemifloxacin is similar to other
quinolones in that it is the amount of
drug present, not the frequency of administration, that determines antibacterial effect. In a neutropenic murine thigh model of
infection, caused by Gram-negative bacilli, a AUC0-24h/MIC ratio of approximately 100 was necessary to protect >90% of the animals, which is similar to data reported previously for other
quinolones. However, in order to achieve the same protection in an immunocompetent murine
infection caused by Streptococcus pneumoniae, the AUC-24h/MIC ratio was approximately 25. The magnitude of this AUC0-24h/MIC ratio did not alter for strains exhibiting
penicillin or
macrolide resistance. Importantly, when
gemifloxacin was examined against strains of S. pneumoniae with well-characterized
ciprofloxacin resistance (including mutations in gyrase, parC and parE as well as efflux strains) there was little impact on the in vivo efficacy. Overall, the data showed a trend towards a decrease in the AUC0-24h/MIC ratio for these more resistant strains. The lower AUC0-24h/MIC ratio was especially noticeable for the efflux mutants suggesting that the
quinolone efflux mechanism may be down-regulated in vivo and may be of minimal relevance to the clinical activity of
gemifloxacin against S. pneumoniae. The efficacy of
gemifloxacin, in comparison with other oral agents used to treat
respiratory infections, has also been evaluated in a rat model using doses, and therefore AUC0-24h/MIC ratios, that approximate those in man. These data confirm the excellent activity of
gemifloxacin against strains of Haemophilus influenzae and S. pneumoniae, including those demonstrating
penicillin,
macrolide and
quinolone resistance.