Antimicrobial Activity of Cefmenoxime (SCE-1365)

The in vitro activity of cefmenoxime (SCE-1365 or A-50912), a new semisynthetic cephalosporin antibiotic, was compared with those of cefazolin, cefoxitin, and cefamandole against a broad spectrum of 486 organisms and with that of cefotaxime against 114 organisms. Cefmenoxime and cefotaxime exhibited nearly equivalent activities against those organisms tested and were the most active of these cephalosporins against all aerobic and facultative organisms exceptStaphylococcus aureus . The minimum inhibitory concentration (MIC) of cefmenoxime required to inhibit at least 90% of strains tested (MIC90 ) ranged from 0.06 to 8 μg/ml for theEnterobacteriaceae . The MIC90 s for gram-positive cocci were 0.015 and ≤0.008 μg/ml forStreptococcus pneumoniae andStreptococcus pyogenes , respectively, and 2 μg/ml forS. aureus . Group D streptococci were less susceptible. Cefmenoxime was very active againstHaemophilus influenzae, Neisseria gonorrhoeae , andNeisseria meningitidis with MIC90 s ranging from ≤0.008 to 0.25 μg/ml. Cefmenoxime, at a concentration of 16 μg/ml, inhibited 78% and 73% ofPseudomonas aeruginosa andAcinetobacter spp., respectively. MICs for anaerobes ranged from 0.5 to >128 μg/ml with good activity against the gram-positive organisms. In addition, cefmenoxime activity was bactericidal and only slightly affected by differences in inoculum size. The combination of cefmenoxime and gentamicin was synergistic against 80% of theEnterobacteriaceae and 100% ofP. aeruginosa strains tested. Development of resistance to cefmenoxime was slow or absent for organisms with low initial MICs but more rapid for those with higher initial MICs. Cefmenoxime exhibited good protective activity in mice infected withEscherichia coli, Enterobacter cloacae, Proteus mirabilis, Proteus vulgaris , orS. aureus but was less effective againstP. aeruginosa .