Cefepime is a novel methoxyimino-aminothiazolyl cephalosporin with a quaternized N'-methyl-pyrrolidine moiety at the 3′ position conferring zwitterionic properties. Because of this the molecule penetrates the outer cell membrane of Gram-negative bacteria rapidly. In addition it is resistant to degradation by several plasmid and chromosomally-mediated βlactamases, for which it also shows very low affinity and no inducing capacity. It has good affinity for PBPs 2 and 3 of Escherichia coli and for PBP 3 of Pseudomonas aeruginosa. Its broad-spectrum of activity includes Gram-positive and Gram-negative pathogens. It is more active than cefotaxime or ceftazidime, against Enterobacteriaceae. The MIC90, for P. aeruginosa is higher than that of ceftazidime, but lower than those of cefpirome, cefoperazone and latamoxef. Other Gram-negative organisms, Haemophilus influenzae, Neiserria meningitidis, Neiserria gonorrhoeae, Moraxella catarrhalis are highly susceptible to cefepime. Among Gram-positive species methicillin-susceptible Staphylococcus aureus and coagulase-negative staphylococci, whether β-lactamase producers or not, Streptococcus pneumoniae and Streptococcus pyogenes are susceptible. Cefepime is active against cefotaxime- and/or ceftazidime-resistant Enterobacteriaceae. Only strains of P. aeruginosa producing large amounts of β-lactamase may be resistant to both ceftazidime and cefepime. In experimental infections such as meningitis, induced with various bacterial species in neonatal rats and chronic staphylococcal osteomyelitis in rabbits, cefepime has shown good efficacy.