PK analysis
Aztreonam/nacubactam was subcutaneously administered to neutropenic mice. At 5, 15, 30, 60, 120, 240, and 300 min after administration, blood samples were collected through cardiac puncture under anesthesia (n = 3 per time point). Immediately after blood sampling, the mice were euthanised by cervical dislocation. The blood samples were centrifuged to separate the plasma and stored at -80 °C until analysis. PK parameters were calculated by compartmental model analysis of free plasma nacubactam and aztreonam concentrations using Phoenix WinNonlinTM (ver. 8.0, Certara, NJ, USA).