Ceftiolene (42980RP) is a new cephalosporin with a broad antibacterial spectrum similar to cefotaxime or ceftriaxone. The affinities of ceftiolene for penicillin-binding proteins are very comparable with those of ceftriaxone and cefotaxime for Escherichia coli, and generally greater than those of latamoxef (moxalactam) for the higher molecular weight PBPs of E. coli. Enterobacter cloacae. The affinity of ceftiolene for PBP1 of Staphylococcus aureus is greater than those of cefotaxime or latamoxef but comparable with these antibiotics for PBP3. The bacteriolytic activity of ceftiolene at defined concentrations against Gram-negative organisms is similar to that of ceftriaxone and significantly better than that of the other third-generation cephalosporins tested.