Prediction of in vivo and in vitro infection model results using a semimechanistic model of avibactam and aztreonam combination against multidrug resistant organisms

The combination of aztreonam-avibactam is active against multidrug-resistant Enterobacteriaceae that express metallo-β-lactamases. A complex synergistic interaction exists between aztreonam and avibactam bactericidal activities that have not been quantitatively explored. A two-state semimechanistic pharmacokinetic/pharmacodynamic (PK/PD) logistic growth model was developed to account for antimicrobial activities in the combination of bacteria-mediated degradation of aztreonam and the inhibition of aztreonam degradation by avibactam. The model predicted that changing regimens of 2 g aztreonam plus 0.375 and 0.6 g avibactam as a 1-hour infusion were qualitatively similar to that observed from in vivo murine thigh infection and hollow-fiber infection models previously reported in the literature with 24-hour log kill ≥1. The current approach to characterize the effect of avibactam in enhancing aztreonam activity from time-kill study was accomplished by shifting the half-maximal effective concentration (EC50) of aztreonam in increasing avibactam concentration using a nonlinear equation as a function of avibactam concentration, providing a framework for translational predictions.