In vitro susceptibility of recent clinical isolates of pneumococci to the investigational cephalosporin cefditoren

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From February to June 2000, 2,597 isolates of Streptococcus pneumoniae were prospectively collected from 146 clinical laboratories across the United States (US) and tested to evaluate the in vitro activity of cefditoren, an investigational oral cephalosporin. In all, 2,492 isolates (96.0%) had a cefditoren MIC of 0.5 μg/mL or less, 74 isolates (2.8%) had an MIC of 1 μg/mL, 30 isolates (1.2%) had an MIC of 2 μg/mL, and 1 isolate (<0.1%) had an MIC of 4 μg/mL. Among the β-lactams tested, the rank order of potency (MIC 90, μg/mL) was cefditoren (0.5) > ceftriaxone (1) > amoxicillin-clavulanate (2) > cefuroxime (4) > cefprozil (8). Penicillin-resistant isolates ( n = 443; 17.1%) were inhibited by lower concentrations (MIC 90, μg/mL; MIC range,) of cefditoren (1; 0.03–4) than ceftriaxone (2; 0.25- > 2), amoxicillin-clavulanate (8; 0.5- > 8), cefuroxime (16; 2- > 16), and cefprozil (32; 2- > 32). Cefditoren MIC 90s against cefuroxime-resistant ( n = 640) and ceftriaxone-resistant ( n = 89) isolates were 1 and 2 μg/mL, respectively. All isolates with reduced susceptibility to cefditoren (MIC, 2 or 4 μg/mL; n = 31) were resistant to penicillin, cefuroxime, and ceftriaxone. The potent in vitro activity of cefditoren against a recent US collection of pneumococci as demonstrated in this study supports its continued development for oral empiric therapy in outpatients with respiratory tract infections.