Comparative in vitro study in new cephalosporins.

Three new cephalosporins, ceftazidime, ceftizoxime, and cefotiam, were evaluated in vitro against clinical isolates, and their activities were compared with those of other cephalosporins, mezlocillin, and tobramycin. All three new cephalosporins were very active against gram-positive cocci (except enterococci), but mezlocillin was more active against Streptococcus ssp. Cefotiam and cefamandole were the most active antibiotics against Streptococcus aureus. Ceftazidime had broad-spectrum activity against all gram-negative bacilli tested, except Enterobacter spp. Ceftizoxime was active against all, except Enterobacter spp. and Pseudomonas aeruginosa. Although cefotiam was quite active against Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, it was inactive against indole-positive Proteus spp., Serratia spp, and P. aeruginosa. The in vitro activity suggests that ceftazidime should prove useful as a broad-spectrum antibiotic, in those settings in which the most likely pathogens are gram-negative bacilli.