In vitro activity of CGP 31608, a new penem.

The in vitro activity of CGP 31608, a semisynthetic penem derivative, was compared with that of Sch 34343, imipenem, cefoxitin, cefuroxime, and ceftazidime and other beta-lactams, when appropriate, against 628 recent isolates and other beta-lactam-resistant strains. The MICs of CGP 31608 against 90% of the members of the family Enterobacteriaceae, Pseudomonas aeruginosa, Haemophilus influenzae, Neisseria spp., Bacteroides spp., Clostridium spp., staphylococci, and Streptococcus pneumoniae were between 0.25 and 8 micrograms/ml. The susceptibility of beta-lactamase-producing strains and known porin mutants of the Enterobacteriaceae suggests that CGP 31608 is resistant to many important beta-lactamases (including the mutationally derepressed chromosomal enzymes) and is not excluded from the bacterial cell in strains expressing these known porin mutations. Generally, CGP 31608 was less active than imipenem, Sch 34343, and the cephalosporins, except against Pseudomonas aeruginosa. The activity of CGP 31608 against Staphylococcus aureus (including methicillin-resistant strains) was greater than that of the cephalosporins. The major target site in Escherichia coli K-12 for CGP 31608 was penicillin-binding protein 2. The serum protein binding of 5 micrograms of CGP 31608 per ml was 14%, and serum had little effect on activity.