Activities and postantibiotic effects of gemifloxacin compared to those of 11 other agents against Haemophilus influenzae and Moraxella catarrhalis

The activity of gemifloxacin against Haemophilus influenzae and Moraxella catarrhalis was compared to those of 11 other agents. All quinolones were very active (MICs, less than or equal to 0.125 mu g/ml) against 248 quinolone-susceptible H. influenzae isolates (40.7% of which were beta-lactamase positive); cefixime (MICs, less than or equal to 0.125 mu g/ml) and amoxicillin-clavulanate (MICs less than or equal to 4.0 mu g/ml) were active, followed by cefuroxime (MICs, less than or equal to 16.0 mu g/ml); azithromycin MICs were less than or equal to 4.0 mu g/ml. For nine H. influenzae isolates with reduced quinolone susceptibilities, the MICs at which 50% of isolates are inhibited (MIC(50)s) were 0.25 mu g/ml for gemifloxacin and 1.0 mu g/ml for the other quinolones tested. All strains had mutations in GyrA (Ser84, Asp88); most also had mutations in ParC (Asp83, Ser84, Glu88) and ParE (Asp420, Ser458), and only one had a mutation in GyrB (Gln468), All quinolones tested were equally active (MICs, less than or equal to 0.06 mu g/ml) against 50 M. catarrhalis strains; amoxicillin-clavulanate, cefixime, cefuroxime, and azithromycin were very active. Against 10 H. influenzae strains gemifloxacin, levofloxacin, sparfloxacin, and trovafloxacin at 2x the MIC and ciprofloxacin at 4x the MIC were uniformly bactericidal after 24 h, and against 9 of 10 strains grepafloxacin at 2x the MIC was bactericidal after 24 h, After 24 h bactericidal activity was seen with amoxicillin-clavulanate at 2x the MIC for all strains, cefixime at 2x the MIC for 9 of 10 strains, cefuroxime at 4x the MIC for all strains, and azithromycin at 2x the MIC for all strains. All quinolones except grepafloxacin (which was bactericidal against four of five strains) and all beta-lactams at 2x to 4x the MIC were bactericidal against five M, catarrhalis strains after 24 h; azithromycin at the MIC was bactericidal against all strains after 24 h, The postantibiotic effects (PAEs) against four quinolone-susceptible H. influenzae strains were as follows: gemifloxacin, 0.3 to 2.3 h; ciprofloxacin, 1.3 to 4.2 h; levofloxacin, 2.8 to 6.2 h; sparfloxacin, 0.6 to 3.0 h; grepafloxacin, 0 to 2.1 h; trovafloxacin, 0.8 to 2.8 h, At 10x the MIG, no quinolone PAEs were found against the strain for which quinolone MICs were increased. Azithromycin PAEs were 3.7 to 7.3 h.