Inhibits bacterial cell wall synthesis by binding to one or more of the penicillin-binding proteins. Less active against Gram-negative bacteria than some other second generation cephalosporins. Inactive against fungi and viruses. Active in vitro and in clinical infections against Gram-positive aerobic bacteria such as staphylococci (including coagulase-positive, coagulase-negative, and penicillinase producing strains), Streptococcus pneumoniae, and S. pyogenes (group A β-hemolytic streptococci). Enterococci (e.g. Enterococcus faecalis) and oxacillin-resistant (methicillin-resistant) staphylococci are resistant. Active in vitro and in clinical infections against Gram-negative aerobic bacteria such as H. influenzae (except β-lactamase-negative, ampicillin-resistant (BLNAR) strains), Moraxella catarrhalis (including β-lactamase-producing strains), Escherichia coli, Klebsiella, and Proteus mirabilis, H. parainfluenzae, Citrobacter diversus, and Neisseria gonorrhoeae. Inactive against Acinetobacter, Enterobacter, Morganella morganii, Proteus vulgaris, Providencia, Pseudomonas, and Serratia. Active in vitro against anaerobic bacteria such as Bacteroides (excluding B. fragilis), Peptococcus niger, Peptostreptococcus, and Propionibacterium acnes.