High-performance liquid chromatography-tandem mass spectrometry
(LC-MS/MS) analysis
The concentration of antibiotics in each plasma sample was measured
using a validated LC-MS/MS method. Detailed measurement conditions are
summarised in Table S1. The protein binding rates of nacubactam and
aztreonam in mouse plasma were determined by the ultrafiltration method.
In short, plasma containing nacubactam and aztreonam at concentrations
of 1, 10, and 400 mg L-1 (n = 3 per concentration) was
incubated at 37 °C for 30 min and then set into
Centrifree® 4104 Ultrafiltration Centrifugal Filters
(Millipore, Bedford, MA, USA). The filtrate was obtained by
centrifugation at 1,500 g for 5 min. The concentrations of the
antibiotics in the initial sample and the filtrate were measured using
LC-MS/MS, and the protein binding rate was calculated.