L-658,310, a new injectable cephalosporin. I. In vitro antibacterial properties.

The in vitro antibacterial spectrum of L-658,310, a new semisynthetic cephalosporin, was compared with ceftazidime, aztreonam and piperacillin against a wide variety of randomly selected human clinical isolates. The compound was found to be a broad spectrum bactericidal agent that was more potent than any of the comparison drugs against glucose nonfermenting bacteria. It has especially potent activity against Pseudomonas aeruginosa including multiply-resistant strains. The superior activity of L-658,310 against this group of organisms is attributed to the presence of the dihydroxy substituents on the 2-methylisoindoline moiety of the compound. L-658,310 is not cross-resistant with either imipenem, ceftazidime or piperacillin (representatives of three different classes of beta-lactam compounds) against P. aeruginosa. The lack of cross-resistance with ceftazidime extends to other glucose nonfermenters and several strains of Enterobacteriaceae as well. The compound is active against bacteria known to possess either R-plasmid- or chromosomally-mediated beta-lactamases.