Efficacy of piperacillin in combination with novel β-lactamase inhibitor IID572 against β-lactamase-producing strains of Enterobacteriaceae and Staphylococcus aureus in murine neutropenic thigh infection models

Objectives The neutropenic murine thigh infection model was used to assess the effectiveness of IID572, a novel β-lactamase inhibitor, in rescuing piperacillin activity against bacterial strains expressing various β-lactamase enzymes. Methods Mice (n = 4/group) were inoculated with Enterobacteriaceae or Staphylococcus aureus bacterial strains expressing a range of β-lactamases via intramuscular injection. Two hours after bacterial inoculation, subcutaneous treatment with piperacillin/IID572 or piperacillin/tazobactam every 3 h was initiated. Animals were euthanized via CO2 24 h after the start of therapy and bacterial cfu (log10 cfu) per thigh was determined, and the static dose was calculated. Results In a dose-dependent manner, piperacillin/IID572 reduced the thigh bacterial burden in models established with Enterobacteriaceae producing class A, C and D β-lactamases (e.g. ESBLs, KPC, CMY-2 and OXA-48). Piperacillin/IID572 was also efficacious against MSSA strains, including one producing β-lactamase. Static doses of piperacillin/IID572 were calculable from animals infected with all strains tested and the calculated static doses ranged from 195 to 4612 mg/kg/day piperacillin, the active component in the combination. Of the 13 strains investigated, a 1 log10 bacterial reduction was achieved for 9 isolates and a 2 log10 reduction was achieved for 3 isolates; piperacillin/tazobactam was not efficacious against 6 of the 13 isolates tested. Conclusions In contrast to tazobactam, IID572 was able to rescue piperacillin efficacy in murine thigh infection models established with β-lactamase-producing strains of Enterobacteriaceae and S. aureus, including those expressing ESBLs or serine carbapenemases.