Ceftazidime: comparative in-vitro study.

Ceftazidime showed moderate activity against Staphylococcus aureus and a high activity against Haemophilus influenzae and the streptococci except against the enterococci. Ceftazidime inhibited 90% of the 830 Enterobacteriaceae tested at a concentration of 0.5 mg/l and 99% at 8 mg/l, an activity very similar to that of cefotaxime. Against Pseudomonas spp. ceftazidime proved to be the most active beta-lactam antibiotic studied. It inhibited 67% of the 141 Ps. aeruginosa strains at 2 mg/l, 84% at 4 mg/l, 98% at 8 mg/l and 100% at 16 mg/l. The inhibitory and the bactericidal concentrations were very close and there was only a minor effect of the inoculum. Ceftazidime retained its high activity against microorganisms with acquired as well as with natural resistance to other beta-lactam antibiotics.