In vitro properties of ceftazidime, a highly active broad-spectrum cephalosporin with antipseudomonal activity.

Ceftazidime is an aminothiazolyl cephalosporin that exhibits a high level of broad-spectrum activity, with particularly good activity against Pseudomonas sp. Although activity in vitro against staphylococci is moderate, the majority of enterobacteria are susceptible, with MIC50 values in the range from 0.06 to 4 micrograms/ml. This cephalosporin is also highly active against indole-positive Proteus sp, Providencia sp, Citrobacter sp, and Serratia sp, with MIC50 values ranging from less than or equal to 0.06 to 0.13 microgram/ml. Good activity against Pseudomonas sp is a notable feature, with MIC90 values in the range of 4 to 8 micrograms/ml. Ceftazidime is bactericidal at concentrations identical or close to the MIC. Antibiotic performance in vitro appears to be unaffected by the presence of body fluids. Good stability to hydrolysis by a range of the prevalent beta-lactamases, good penetration into the intact bacterium, and a high affinity for the essential penicillin-binding proteins combine to account for the broad spectrum and high activity of ceftazidime. Comparative in vitro studies have shown ceftazidime to be as active and sometimes more active than available aminoglycoside antibiotics. Since the mode of action of ceftazidime differs fundamentally from that of the aminoglycosides, high activity is maintained against the majority of aminoglycoside-resistant isolates. Ceftazidime should therefore represent a viable and potentially safer alternative to aminoglycoside antibiotics.