Clinical efficacy and correlation of clinical outcomes with in vitro susceptibility for anaerobic bacteria in patients with complicated intra-abdominal infections treated with moxifloxacin.

Background: Appropriate antimicrobial therapy results in improved clinical outcomes in complicated intra-abdominal infections (cIAIs). Recent in vitro studies have reported increasing moxifloxacin resistance of Bacteroides species, thereby cautioning empiric use in infections with these organisms.
Methods: This pooled analysis of 4 randomized clinical trials (2000-2010) evaluated the comparative efficacy of moxifloxacin in cIAIs, including infection with anaerobic organisms. The intent-to-treat population included 1209 patients who received moxifloxacin (745 microbiologically valid cases) and 1193 patients who received comparator agents (741 microbiologically valid cases).
Results: Overall clinical success rates in the per-protocol population were 85.6% (817 of 955 patients) for moxifloxacin and 87.8% (860 of 979 patients) for comparators. Of 642 pretherapy anaerobes from moxifloxacin-treated patients, 561 (87.4%) were susceptible at ≤2 mg/L, 34 (5.3%) were intermediate at 4 mg/L, and 47 (7.3%) were resistant at ≥8 mg/L. Moxifloxacin achieved similar clinical success rates against all anaerobes including those isolated from patients infected with Bacteroides fragilis (158 [82.7%] of 191 patients), Bacteroides thetaiotaomicron (74 [82.2%] of 90 patients) and Clostridium species (37 [80.4%] of 46 patients). The overall clinical success rate for all anaerobes was 82.3%. For all anaerobes combined, the clinical success rate was 83.1% (466 of 561 patients) for a minimum inhibitory concentration (MIC) of ≤2 mg/L, 91.2% (31 of 34 patients) for an MIC of 4 mg/L, 82.4% (14 of 17 patients) for an MIC of 8 mg/L, 83.3% (5 of 6 patients) for an MIC of 16 mg/L, and 66.7% (16 of 24 patients) for an MIC of ≥32 mg/L.
Conclusions: Moxifloxacin demonstrated clinical success for intra-abdominal infections caused by both aerobic and anaerobic isolates. More than 87% of baseline anaerobic isolates from intra-abdominal infections were susceptible to moxifloxacin, and efficacy was maintained beyond the current susceptibility breakpoint MIC of ≤2 mg/L against major anaerobes.