T-2588, the pivaloyloxymethyl ester of T-2525, [6R, 7R]-7-[(z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetoamido] -3- [(5-methyl-2H-tetrazol-2-yl)methyl]-3-cephem-4-carboxylic acid, is a new oral cephalosporin. T-2525 had a widely expanded antibacterial spectrum against gram-negative and gram-positive bacteria. T-2525 was more active in vitro than cefaclor, cephalexin, and amoxicillin against members of the family Enterobacteriaceae and Branhamella catarrhalis. Moreover, it exhibited superior in vitro activity against Streptococcus pyogenes, Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria gonorrhoeae. T-2525 was highly stable to various beta-lactamases, which were classified as Richmond and Sykes types Ia, Ib, Ic, III, IV, and Vc. It had high affinities for the lethal (essential) penicillin-binding proteins of Escherichia coli, Clostridium perfringens, and Bacteroides fragilis. T-2588 had excellent therapeutic effect on systemic infections in mice with various species of gram-negative bacteria, including beta-lactamase-producing bacteria.

The in-vitro antibacterial activity of AMA-1080 against both Gram-positive and Gram-negative clinical isolates was studied in comparison with that of aztreonam, cefotaxime, ceftazidime and cefoperazone. AMA-1080 showed a potent antibacterial activity against Gram-negative bacteria, particularly, the strains of Enterobacteriaceae. In addition, AMA-1080 inhibited the strains of genus Pseudomonas at the low concentrations. However, AMA-1080 showed less active against Gram-positive bacteria. It was found that AMA-1080 was highly resistant to hydrolysis by both chromosomal and plasmid-mediated beta-lactamases.

The in vitro activity of BO-2727, a new carbapenem, was compared with those of meropenem, biapenem, imipenem, and ceftazidime. BO-2727 was four-or eightfold more active than the other carbapenems against methicillin-resistant staphylococci and Pseudomonas aeruginosa strains, including imipenem-and ceftazidimeresistant bacteria. BO-2727 was quite stable to penicillinases, cephalosporinases, and oxyiminocephalosporinases, but not to metallo-␤-lactamase. Time-kill studies against Staphylococcus aureus Smith, Escherichia coli ML4707, and P. aeruginosa GN11189 showed that BO-2727 has potent bactericidal activity at concentrations greater than the MIC.