Serum bactericidal activities of moxifloxacin and levofloxacin against aerobic and anaerobic intra-abdominal pathogens

We studied the serum bactericidal activity (SBA) of moxifloxacin and levofloxacin against common pathogens associated with complicated intra-abdominal infections. Ten healthy volunteers received a single dose of moxifloxacin (400 mg) and levofloxacin (750 mg) and serum samples were collected at 2, 4, 8, 12, and 24 h after the dose of each drug. Bactericidal titers in serum over time were determined for aerobic gram-negative bacilli (Escherichia coli, Klebseilla pneumoniae, and Enterobacter cloacae) and anaerobic bacteria (Bacteroides fragilis, Bacteroides thetaiotaomicron, Prevotella bivia, and Finegoldia magna). Both fluoroquinolones provided rapid (2 h) attainment and prolonged (24 h) SBA (titers ⩾1:8) against each of the aerobic bacilli studied. SBA was observed for at least 12 h against B. fragilis strains with MICs⩽2 μg/ml to moxifloxacin and ⩽4 μg/ml to levofloxacin. Prolonged (12 h) SBA (titers ⩾1:2) was also observed against isolates of B. thetaiotaomicron, P. bivia, and F. magna with moxifloxacin MICs⩽2 μg/ml.