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.