Inhibitory activity of cefotetan and other -lactams aginst anaerobes

The activity of cefotetan was determined against a variety of clinically important anaerobes by means of agar dilution tests and compared with that of cefoxitin and moxalactam. The IC 90 of cefotetan for strains of Bacteroides fragilis (β-lactamase-producers) was 8 mg/l (moxalactam 4, cefoxitin 16 mg/l). Lesser activity was found against Bact. thetaiotaomicron , known to be more resistant than Bact. fragilis to β-lactams: IC 90 values were 64, 32 and 64 mg/l for cefotetan, cefoxitin and moxalactam, respectively. Other saccharolytic species ( Bact. vulgatus, Bact. distasonis, Bact. variabilis, Bact. incommunis, Bact. uniformis ) were inhibited by cefotetan at 4 to 64 mg/l, whereas the bivius-disiens-oralis group was more susceptible (IC 90 16 mg/l for cefotetan, 4 mg/l for cefoxitin and 16 mg/l for moxalactam). Pigmented Bacteroides species were yet more sensitive to cefotetan. Fusobacteria were inhibited by 16 mg/l for each of the three drugs. Amongst the clostridia tested, the MIC of cefotetan was mostly ≤32 mg/l (moxalactam ≤4 mg/l, cefoxitin ≤8 mg/l). Clostridium difficile was inhibited by cefotetan at 32 mg/l compared with 64 and 128 mg/l for moxalactam and cefoxitin, respectively. Peptococcaceae were similar to clostridia in susceptibility to the drugs tested. Cefotetan ranks among the few β-lactam agents with good activity against anaerobes, including β-lactamase-producers.