In vitro antimicrobial activity and beta-lactamase stability of moxalactam, a new 1-oxa-cephalosporin.

The in vitro activity of a new semisynthetic 1-oxa-cephamycin, moxalactam, was compared with cefotaxime, cefoperazone, cefoxitin and gentamicin against 268 clinical bacterial isolates. Against Staphylococcus aureus, Staphylococcus pyogenes and Streptococcus faecalis the activity of moxalactam was similar to that of the other compounds. Moxalactam was the most active antibiotic against fermentative and non-fermentative Gram-negative bacilli, except for Pseudomonas aeruginosa. Moxalactam exhibited activity against gentamicin-resistant strains. Minimum inhibitory concentration and minimum bactericidal concentration differences were minor. Activity was not altered by changes in inoculum size, type of medium and presence of serum. The protein-binding was 35%. Moxalactam was not destroyed by common plasmid and chromosomal beta-lactamases. The penetrability studies demonstrated that, using E. coli UB 1005 and its mutants, the penetrability of moxalactam was higher than that of the other cephalosporins compared.