In vitro antibacterial activity of meropenem

The in vitro antibacterial activity of meropenem (MEPM), a new carbapenem antibiotic, was compared with those of imipenem (IPM), cefazolin, cefotiam, ceftazidime (CAZ), cefotaxime and latamoxef. MEPM was found to be a very broad spectrum antibacterial agent that was similar to IPM. Against clinical isolates of staphylococci, including methicillin-resistant Staphylococcus aureus, the MIC₉₀ of MEPM ranged from 0.78 to 12.5 µg/ml. Its activity was inferior to that of IPM but superior to that of the cephalosporins tested. MIC₉₀ values of MEPM against clinical isolates of Streptococcus pyogenes, Streptococcus pneumoniae, Escherichia coli, Citrobacter freundii, Klebsiella pneumoniae, Enterobacter cloacae, Enterobacter aerogenes, Serratia marcescens, Proteus mirabilis, Proteus vulgaris and Pseudomonas aeruginosa were ≦0.003, ≦0.003, 0.025, 0.025, 0.025, 0.20, 0.10, 1.56, 0.20, 0.20 and 1.56 µg/ml, respectively. MEPM was 2- to 4-fold more active than IPM and CAZ against P. aeruginosa. It also showed potent activity against Haemophilus influenzae and Bacteroides fragilis. The antibacterial activity of MEPM was slightly affected by inoculum size, culture medium, pH of the medium and the addition of human serum. It showed bactericidal activity against a variety of bacteria.