Efficacy of Cefiderocol against Carbapenem-Resistant Gram-Negative Bacilli in Immunocompetent-Rat Respiratory Tract Infection Models Recreating Human Plasma Pharmacokinetics

Cefiderocol (S-649266), a novel siderophore cephalosporin, shows potent activity against carbapenem-resistant Gram-negative bacilli. In this study, we evaluated the efficacy of cefiderocol against carbapenem-resistant Gram-negative bacilli (Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae) in immunocompetent-rat respiratory tract infection models recreating plasma pharmacokinetics (PK) profiles in healthy human subjects. A total of 6 clinical isolates (1 cephalosporin-susceptible P. aeruginosa isolate, 1 multidrug-resistant P. aeruginosa isolate, 2 multidrug-resistant A. baumannii isolates, and 2 carbapenem-resistant K. pneumoniae isolates) were evaluated. Four-day treatment with a human exposure of 1 g ceftazidime every 8 h as a 0.5-h infusion showed potent efficacy only against a ceftazidime-susceptible isolate, not against five ceftazidime-resistant isolates harboring carbapenemase. With cefiderocol, a human exposure of 2 g every 8 h as a 3-h infusion for 4 days produced a > 3 log(10) reduction in the number of viable cells of these carbapenem-resistant isolates in the lungs. When the infusion time was 1 h, bactericidal activity was also observed against all isolates tested, although for 2 of 5 carbapenem-resistant isolates, a 3 log10 reduction was not achieved. The difference in efficacy achieved by changing the infusion period from 1 h to 3 h was considered to be due to the higher percentage of the dosing interval during which free-drug concentrations were above the MIC (%fT(MIC)), as observed for beta-lactam antibiotics. These results suggest the potential utility of cefiderocol for the treatment of lung infections caused by carbapenem-resistant P. aeruginosa, A. baumannii, and K. pneumoniae strains.