In Vitro Susceptibility to Gemifloxacin and Trovafloxacin of Streptococcus pneumoniae Strains Exhibiting Decreased Susceptibility to Ciprofloxacin

 The in vitro susceptibility to trovafloxacin and gemifloxacin of Streptococcus pneumoniae strains exhibiting decreased susceptibility to ciprofloxacin (MIC ≥2 μg/ml; 30 strains with intermediate resistance MIC 2 μg/ml] and 43 strains with complete resistance MIC ≥4 μg/ml]) was determined. Seventy-three strains collected in a surveillance study carried out from May 1996 to April 1997 in Spain (prior to commercialisation of trovafloxacin and gemifloxacin) from patients with respiratory tract infections were tested. The antibacterial activity of gemifloxacin was affected to a lesser extent than that of trovafloxacin by the increase in the MIC of ciprofloxacin, with gemifloxacin showing significantly (P≤0.001) better antibacterial activity than trovafloxacin in all ciprofloxacin MIC categories (MIC50/MIC90 values of 0.015/0.03, 0.015/0.06, 0.03/0.06 and 0.12/0.25 μg/ml for gemifloxacin vs 0.12/0.12, 0.12/1, 0.25/0.5 and 2/4 μg/ml for trovafloxacin in the 2, 4, 8 and ≥16 μg/ml ciprofloxacin MIC categories, respectively). Nine (12.3%) of these 73 strains exhibited decreased susceptibility to trovafloxacin (≥2 μg/ml), whereas all strains were inhibited by 0.25 μg/ml of gemifloxacin.