In Vitro and In Vivo Activities of Syn2190, a Novel β-Lactamase Inhibitor

Syn2190, a monobactam derivative containing 1,5-dihydroxy-4-pyridone as the C-3 side chain, is a potent inhibitor of group 1 β-lactamase. The concentrations of inhibitor needed to reduce the initial rate of hydrolysis of substrate by 50% for Syn2190 against these enzymes were in the range of 0.002 to 0.01 μM. These values were 220- to 850-fold lower than those of tazobactam. Syn2190 showed in vitro synergy with ceftazidime and cefpirome. This synergy was dependent on the concentration of the inhibitor against group 1 β-lactamase-producing strains, such asPseudomonas aeruginosa ,Enterobacter cloacae ,Citrobacter freundii , andMorganella morganii . However, against β-lactamase-derepressed mutants ofP. aeruginosa , the MICs of ceftazidime plus Syn2190 were not affected by the amount of β-lactamase, and the values were the same for the parent strains. The MICs at which 50% of isolates are inhibited (MIC50 s) of ceftazidime plus Syn2190 were 2- to 16-fold lower than those of ceftazidime alone for ceftazidime-resistant, clinically isolated gram-negative bacteria. Similarly, the MIC50 s of cefpirome plus Syn2190 were two- to eightfold lower for cefpirome-resistant clinical isolates. The synergies of Syn2190 plus ceftazidime or cefpirome observed in vitro were also reflected in vivo. Syn2190 improved the efficacies of both cephalosporins in both a murine systemic infection model with cephalosporin-resistant rods and urinary tract infection models with cephalosporin-resistantP. aeruginosa .