Nacubactam is a novel, β-lactamase inhibitor with dual mechanism of action as an inhibitor of serine β-lactamases (classes A, C, and some class D) and an inhibitor of penicillin binding protein 2 in The safety, tolerability, and pharmacokinetics of intravenous nacubactam were evaluated in single and multiple ascending dose, placebo-controlled studies. Healthy participants received single ascending doses of nacubactam 50 to 8,000 mg, multiple ascending doses of nacubactam 1,000 to 4,000 mg every 8 hours (q8h) for up to 7 days, or nacubactam 2,000 mg plus meropenem 2,000 mg q8h for 6 days after a 3-day lead-in period. Nacubactam was generally well tolerated, with the most frequently reported adverse events (AEs) being mild-to-moderate complications associated with intravenous access and headache. There was no apparent relationship between drug dose and the pattern, incidence, or severity of AEs. No clinically relevant dose-related trends were observed in laboratory safety test results. No serious AEs, dose-limiting AEs, or deaths were reported. After single or multiple doses, nacubactam pharmacokinetics appeared linear, and exposure increased in an approximately dose-proportional manner across the dose range investigated. Nacubactam was excreted largely unchanged into urine. Co-administration of nacubactam with meropenem did not significantly alter the pharmacokinetics of either drug. These findings support the continued clinical development of nacubactam and demonstrate the suitability of meropenem as a potential β-lactam partner for nacubactam.ClinicalTrials.gov NCT02134834 (single ascending dose study); ClinicalTrials.gov NCT02972255 (multiple ascending dose study).