The in-vitro activity and tentative breakpoint of gemifloxacin, a new fluoroquinolone

The in-vitro activity of gemifloxacin, a new fluoroquinolone, against a wide range (c. 700) of recent clinical isolates, was compared with that of three other fluoroquinolones and other relevant agents. Gemifloxacin inhibited 90% of the Enterobacteriaceae strains at 0.5 mg/L or less, exceptions being Serratia spp. (MIC90 1 mg/L) and strains possessing a putative mechanism of resistance to fluoroquinolones. Ninety per cent of Pseudomonas aeruginosa were inhibited by 4 mg/L. Gemifloxacin had good activity against respiratory pathogens, with 90% of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis being inhibited by 0.06 mg/L or less. Staphylococcus aureus (MSSA) were highly susceptible (MIC90 0.06 mg/L) but MRSA less susceptible (MIC90 8 mg/L) to gemifloxacin. Enterococcus spp, were markedly more susceptible to the study agent than to ciprofloxacin. Gemifloxacin showed good activity against Bacteroides fragilis (MIC90 0.5 mg/L) and anaerobic cocci. A tentative in-vitro breakpoint of 0.5 mg/L was studied using a 1 mu g disc content for all genera except Pseudomonas where a 5 mu g disc content was employed. The false sensitivity reporting rate was 0.5% and false resistance rate was 6.0%, which was considered acceptable. In conclusion, gemifloxacin is a highly active fluoroquinolone that should prove clinically useful in the treatment of a wide range of infections. Susceptibility testing criteria have been developed that should prove robust in a clinical laboratory.