In-vitro activity of ceftazidime compared with other beta-lactam antibiotics

Ceftazidime and ceftriaxone (Ro 13-9904), two new parenteral cephalosporins, were compared with other beta-lactam antibiotics against a total of 237 recent clinical isolates. Both ceftazidime and ceftriaxone had good activity against the Enterobacteriaceae, with 90% of isolates being inhibited by 0.5 mg/l of ceftazidime and by 0.25 mg/l of ceftriaxone. Against Pseudomonas aeruginosa, ceftazidime was about four times more active than ceftriaxone which, in turn, was at least eight times more active than carbenicillin. Both ceftazidime and ceftriaxone were highly active against beta-lactamase producing and non-beta-lactamase producing Haemophilus influenzae. Against the Bacteroides fragilis group, neither ceftazidime nor ceftriaxone showed good activity, the MIC90 for ceftazidime being > 128 mg/l and the MIC90 for ceftriaxone being 32 mg/l. Both ceftazidime and ceftriaxone were less active than cephalothin against Staphylococcus aureus.