Simulated achievement rate of β-lactams/nacubactam treatment in humans using instantaneous MIC-based PK/PD analysis.

Background: Nacubactam (NAC), a new diazabicyclooctane β-lactamase inhibitor, is being developed for use together with aztreonam (AZT) and cefepime (CFPM). However, the effective clinical dosages of AZT/NAC and CFPM/NAC have not yet been established. We have previously shown that free time above instantaneous MIC (fT > MICi) is a valuable pharmacokinetic (PK)/pharmacodynamic parameter for β-lactam (BL)/NAC in a mouse thigh infection model.

Objectives: This study simulated the fT > MICi (%) for AZT/NAC and CFPM/NAC against carbapenemase-producing Enterobacterales (CPE) with different MIC in humans to estimate the clinical efficacy at practically achievable combination doses of AZT/NAC and CFPM/NAC.

Methods: Using previously reported PK parameters of each drug in humans and chequerboard MIC data, we calculated the fT > MICi (%) for AZT/NAC and CFPM/NAC in 10 000 simulated patients to predict the percentages of target attainment of bacteriostatic and bactericidal efficacies at various combined doses.

Results: The results predicted that both BL/NAC combinations could achieve 100% 2 log10-kill against CPE strains at the lowest combination dose (0.5 g/0.5 g q8h). Additionally, in MIC studies examining BLs/NAC at a 1:1 ratio, the dosage regimen for strains with MICcomb ≤ 1 mg/L was expected to offer 100% bactericidal efficacy (2 log10-kill) at 0.5 g/0.5 g q8h or higher doses. For strains with 1 mg/L < MICcomb ≤ 16 mg/L, BLs/NAC at a 2 g/2 g q8h was predicted to produce bactericidal efficacy (1 log10-kill). At MICcomb = 32 mg/L, some bacteriostatic effect was expected at high BL doses.

Conclusions: AZT/NAC and CFPM/NAC are bactericidal against CPE at practically achievable dosages.