Benchmarking the in vitro activity of moxifloxacin against recent isolates of Streptococcus pneumoniae, Moraxella catarrhalis, and Haemophilus influenzae. A European multi-centre study.

To benchmark the activity of moxifloxacin, a European study comprising 900 Streptococcus pneumoniae, 1051 Haemophilus influenzae, and 226 Moraxella catarrhalis referred from 30 institutions during 1998 is described. For S. pneumoniae, moxifloxacin and trovafloxacin MIC(90) and modal MICs values were 0.12 microg/ml and independent of susceptibility to other drug classes, geography, or site of infection. MIC(90)/modal MICs were, respectively, 0.25/0.12 microg/ml for grepafloxacin, 0.25/0.25 microg/ml for sparfloxacin, and 1.0/0.5 microg/ml for levofloxacin. The moxifloxacin C(max):MIC ratio of 20.8-26.3 is higher than comparator fluoroquinolones. Five isolates were intermediate or resistant to grepafloxacin, sparfloxacin, or levofloxacin of which four and three remained susceptible to trovafloxacin and moxifloxacin, respectively. For moxifloxacin, > 90% of S. pneumoniae isolates demonstrated MICs > or =3 dilutions below the susceptibility breakpoint used. Modal MICs and MIC(90) for M. catarrhalis (both 0.03 microg/ml) and H. influenzae (0.03 microg/ml and 0.06 microg/ml) were independent of beta-lactamase production. These data demonstrate the in vitro activity of moxifloxacin and establish a baseline for future surveillance studies that will be important for detecting and tracking any trends in changing activity of this fluoroquinolone.