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Introduction: The emergence of multidrug-resistant (MDR) and extensively drug-resistant strains of Pseudomonas aeruginosa in recent years has become a major issue due to treatment difficulties as well as high morbidity and mortality rates. Treatment options for infections caused by these microorganisms are very limited. Ceftolozane/tazobactam (C/T) and ceftazidime/avibactam (CZA) are recently developed cephalosporin/beta-lactamase inhibitor combinations for the treatment of infections caused by MDR P. aeruginosa strains. The aim of this study was to investigate the in vitro efficacy of C/T and CZA against MDR P. aeruginosa strains and to compare the in vitro efficacy of these two drugs. Materials and Methods: Thirty-two MDR P. aeruginosa isolates were included in the study. Identification and antimicrobial susceptibilities of the strains were performed using a VITEK 2® automated system. The efficacy of CZA and C/T was determined by the gradient strip test (Liofilchem MIC strip test, Italy). Modified carbapenemase inactivation method was used to detect carbapenemase production in all strains. Results: Rates of antibiotic resistance in the isolates were 78% for amikacin, 96.8% for levofloxacin, 90.6% for ciprofloxacin, 71.8% for gentamicin, and 78% for netilmicin. Ceftazidime/avibactam resistance was detected in 7 (21.8%) of the isolates and C/T resistance in 10 (31.2%). All strains with resistance to CZA also had resistance to C/T. Three strains were resistant to C/T but susceptible to CZA. Carbapenemase production was positive in all strains. Conclusion: The results of this study indicate that CZA and C/T may be an alternative treatment for some of the carbapenem-resistant P. aeruginosa infections. Further in vitro and in vivo studies are needed to evaluate the effectiveness of these new treatment options against the increasing threat of MDR P. aeruginosa.