Mechanism of action of the new orally active cephalosporin FK027.

The mechanism of action of a new orally active cephalosporin, FK027, was compared to that of cephalexin and cefaclor to elucidate its excellent antibacterial activity against Gram-negative bacteria. FK027 showed very high affinity for the penicillin-binding proteins (PBPs) 3, 1a and 1bs of Escherichia coli whereas cephalexin showed fairly high affinity for PBPs 1a, 4 and 3. The ability of FK027 to penetrate the outer membranes of E. coli and Enterobacter cloacae was less than that of cephalexin and cefaclor. However, FK027 was extremely stable to both plasmid-mediated penicillinases and chromosomal beta-lactamases except the Bacteroides fragilis enzyme and its stability was superior to that of cephalexin and cefaclor. These results indicate that the potent antibacterial activity of FK027 is based on its enhanced affinity for the target enzymes and its high stability to beta-lactamases.