In vitro and in vivo antibacterial activity of moxalactam, an oxa-beta-lactam antibiotic.

Moxalactam, a new synthetic beta-lactam antibiotic, was evaluated for in vitro and in vivo antibacterial activity and was found to have a broad spectrum of activity against gram-positive and gram-negative bacteria. Moxalactam showed more potent activity than did the cephalosporins tested against clinical gram-negative isolates, including cefazolin-resistant Enterobacteriaceae, glucose-nonfermenting bacteria, and Bacteroides fragilis. Moxalactam was the only beta-lactam antibiotic of those tested (including nine penicillins and 15 cephalosporins) that was not affected by beta-lactamase produced by 15 strains of 10 gram-negative species. The potent in vitro activity and high stability to beta-lactamase of moxalactam corresponded to lower ED50 (50% effective doses) required against intraperitoneal infections in mice due to various bacteria resistant to cefazolin, cefoxitin, or cefotiam. Furthermore, moxalactam showed the greatest therapeutic activity among the nine beta-lactam antibiotics tested in models of intraperitoneal mixed infection in mice with Escherichia coli and Pseudomonas aeruginosa.