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.