An update on the in vitro activity of ceftizoxime and other cephalosporin/cephamycin antimicrobial agents against clinically significant anaerobic bacteria.

The in vitro activity of certain beta-lactam agents against aerobic and anaerobic bacteria is influenced by the method and medium used for susceptibility testing. The in vitro activity of ceftizoxime and cefoxitin against Bacteroides fragilis group strains varies when either the broth microdilution or agar dilution method is used. In general, minimal inhibitory concentration values from broth microdilution are two- to fourfold lower than those from agar dilution. Broth microdilution test results with ceftizoxime have recently been shown to correlate more closely with clinical outcome in patients than those from agar dilution testing. Broth microdilution has become the recommended method of the National Committee for Clinical Laboratory Standards for testing ceftizoxime. Using broth microdilution testing, the in vitro activity of ceftizoxime has been shown to be as good as or better than that of cefoxitin, cefotetan, and cefotaxime against anaerobes, including the B fragilis group. Ceftizoxime also had good activity against B fragilis group strains resistant to cefoxitin or cefotetan. Time-kill kinetic studies have shown that the bactericidal activity of ceftizoxime is equal to or greater than that of cefoxitin or cefotetan against both cefoxitin-susceptible or cefoxitin-resistant strains of the B fragilis group.