In vitro activity of fluoroquinolones against ocular bacterial isolates in São Paulo, Brazil.

PURPOSE: To compare the in vitro susceptibility profiles of bacterial ocular isolates and to determine minimum inhibitory concentrations (MICs) of gatifloxacin and moxifloxacin (fourth-generation fluoroquinolones) versus ciprofloxacin and ofloxacin (second-generation fluoroquinolones).

METHODS

Gram-positive and gram-negative isolates were recovered from cases of keratitis, conjunctivitis, and endophthalmitis between 2002 and 2004 and were identified and extracted from the Microbiology Data Bank of the Federal University of São Paulo, São Paulo, Brazil. The comparison of in vitro MIC and susceptibility profiles for ofloxacin, ciprofloxacin, gatifloxacin, and moxifloxacin in gram-positive and gram-negative (n = 219) isolates was performed using the E test method.

RESULTS

The fourth-generation fluoroquinolones were statistically more potent than the second generations for gram-positive bacteria. The MIC90 level was lower for moxifloxacin than that for gatifloxacin against Staphylococcus aureus, methicillin-susceptible coagulase-negative Staphylococcus (CoNS), and S. pneumoniae, whereas the levels were equal against S. viridans and the gatifloxacin MIC90 was lower in methicillin-resistant CoNS. There was no statistically significant difference between moxifloxacin and gatifloxacin when the permutation method from the MULTTEST procedure (SAS proc multtest) was used to obtain the adjusted P value. MIC90 for ciprofloxacin was lower in gram-negative bacteria. MIC90 for ofloxacin was higher against Haemophilus spp. and Moraxella spp. Ciprofloxacin was the most statistically potent fluoroquinolone for Pseudomonas spp. Ciprofloxacin was statistically just as potent as gatifloxacin for the other gram-negative isolates.

CONCLUSION

From susceptibility profiles achieved with in vitro testing, the fourth-generation fluoroquinolones may offer some advantages over the currently available fluoroquinolones; however, a combination of the pharmacodynamics and pharmacokinetics of the drug, infection site, and the MIC is needed to predict the in vivo efficacy and best clinical applicability.