In vitro activity of cefditoren and other antimicrobial agents against 288 Streptococcus pneumoniae and 220 Haemophilus influenzae clinical strains isolated in Zaragoza, Spain

In vitro cefditoren antimicrobial activity was tested against 288 Streptococcus pneumoniae and 220 Haemophilus influenzae clinical strains isolated in our hospital from January 2005 to May 2006 by agar dilution and broth microdilution method, respectively. MICs were also determined for 13 and 10 comparison drugs, respectively. The pneumococci tested comprised 113 (39.2%) penicillin susceptible, 91 (31.6%) penicillin intermediate, and 84 (29.2%) penicillin resistant. Cefditoren was the most active drug on the basis of the MICs (MIC90 = 0.5 μg/mL), followed by ceftriaxone and levofloxacin (MIC90 = 1 μg/mL). Cefditoren MICs ranged from 0.25 to 1 μg/mL for ceftriaxone-resistant isolates, with a modal MIC of 0.5 μg/mL and an MIC90 of 1.0 μg/mL. No S. pneumoniae isolates evaluated in this study showed MICs to cefditoren higher than 1 μg/mL (MIC range, ≤0.015 to 1 μg/mL). Against penicillin-resistant pneumococci, the rank order of intrinsic activity (MIC90, μg/mL) was cefditoren (0.5) < ceftriaxone (2.0) = cefotaxime (2.0) < amoxicillin/clavulanate (8.0) = amoxicillin (8.0) = cefuroxime (8.0). Among the 220 strains of H. influenzae, 42 (19.09%) produced a β-lactamase (Hi β+) and 3 (1.1%) were β-lactamase (Hi β-) negative but have reduced susceptibility to ampicillin (BLNAR). The most active drugs on the basis of MICs were cefditoren and levofloxacin, showing MIC50 and MIC90 values of 0.015/0.06 μg/mL. Cefditoren at concentration of 0.06 μg/mL inhibited all 3 BLNAR (ampicillin MICs >4 μg/mL). Against H. influenzae (Hi β+), the rank order of intrinsic activity (MIC90, μg/mL) was cefditoren (0.03) < cefixime (0.06) < ceftriaxone (0.12) = cefotaxime (0.12) < cefuroxime (1.0) < amoxicillin/clavulanate (2.0) < ampicillin (>8.0).