Purpose: Fourth generation fluoroquinolones (FQs) will soon be introduced to ophthalmology. In this in vitro study, differences in the susceptibility patterns and the potencies of fourth generation FQs (gatifloxacin-GAT and moxifloxacin-MOX) were compared with third generation (levofloxacin-LEV) and second generation FQs (ciprofloxacin-CIP and ofloxacin-OFX).
Design: Experimental laboratory investigation.
Methods: In retrospect, the minimum inhibitory concentrations (MICs) of 93 bacterial endophthalmitis isolates were determined to CIP, OFX, LEV, GAT, and MOX using E-tests. The National Committee of Clinical Laboratory Standards (NCCLS) susceptibility patterns and the potencies of the MICs were statistically compared.
Results: With in vitro tests, Staphylococcus aureus isolates that were resistant to CIP and OFX were statistically most susceptible (P =.01) to MOX. Coagulase negative Staphylococci that were resistant to CIP and OFX were statistically most susceptible (P =.02) to MOX and GAT. Streptococcus viridans were more susceptible (P =.02) to MOX, GAT, and LEV than CIP and OFX. Streptococcus pneumoniae was least susceptible (P =.01) to OFX compared with the other FQs. Susceptibilities were equivalent (P =.11) for all other bacterial groups. In general, MOX was the most potent FQ for gram-positive bacteria (P =.05) while CIP, MOX, GAT, and LEV demonstrated equivalent potencies to gram-negative bacteria.
Conclusions: This in vitro study indicated that fourth generation FQs appear to cover bacterial resistance to the second and third generation FQs, were more potent than the second and third generation FQs for gram-positive bacteria, and are equally potent for gram-negative bacteria. Clinical studies will need to confirm these results.