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Worapong Nasomsong,1 Parnrada Nulsopapon,2,3 Dhitiwat Changpradub,1 Manat Pongchaidecha,2 Supanun Pungcharoenkijkul,4 Piraporn Juntanawiwat,5 Waristha Simsiriporn,5 Wichai Santimaleeworagun2,3 1Division of Infectious Diseases, Department of Internal Medicine, Phramongkutklao Hospital and College of Medicine, Bangkok, Thailand; 2Department of Pharmacy, Faculty of Pharmacy, Silpakorn University, Nakhon Pathom, Thailand; 3Pharmaceutical Initiative for Resistant Bacteria and Infectious Diseases Working Group [PIRBIG], Faculty of Pharmacy, Silpakorn University, Nakhon Pathom, Thailand; 4Pharmacy Unit, Nopparat Rajathanee Hospital, Bangkok, Thailand; 5Division of Microbiology, Department of Clinical Pathology, Phramongkutklao Hospital, Bangkok, ThailandCorrespondence: Wichai SantimaleeworagunDepartment of Pharmacy, Faculty of Pharmacy, Silpakorn University, Nakhon Pathom, 73000, ThailandTel +6634 255 800Fax +6634 255 801Email swichai1234@gmail.comPurpose: MBL and OXA-48 genes in carbapenem-resistant Enterobacterales (CRE) have emerged as a major public health problem worldwide, including Thailand. Due to the lack of susceptibility data and dosing regimens of ceftazidime-avibactam (CZA) against CRE in Thailand, especially in colistin-resistant era, we aimed to demonstrate in vitro susceptibility data of CZA and optimal dose based on Monte Carlo simulation of CZA to expand the treatment options.Patients and Methods: We collected 49 carbapenem-resistant Klebsiella pneumoniae (CRKP) clinical isolates from unique patients at Phramongkutklao Hospital (June–October 2020). CZA disk diffusion and E-test testing were performed to obtain minimum inhibitory concentration (MIC). Each drug regimen was simulated using the Monte Carlo technique to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR).Results: The most common genotypes of CRKP were blaOXA-48 (53.1%) and blaOXA-48 +blaNDM (42.8%). CZA showed 47.7% and 90.5% susceptible rate against all genotypes of carbapenemases and OXA-48 type CRKP isolates. The MIC50 and MIC90 of CZA against CRKP were 2 and > 256 μg/mL. The categorical agreement (CA) between disk diffusion and E-test testing of CZA against CRKP was 95.4%. The CZA dosing regimens of 2.5 g infused 2– 3 h every 8 h achieved ≥ 90% of the target of free ceftazidime plasma concentration over MIC (%fTime >MIC) ≥ 50% and 100% against isolates MICs of ≤ 8 and ≤ 8 μg/mL, respectively. The avibactam regimens also provided 100%fTime at 0.5 μg/mL. Based on CFR ≥ 90%, no CZA regimens were effective against all of the studied CRKP isolates except CRKP carrying OXA-48.Conclusion: CZA exhibited a fairly susceptible rate among the OXA-48-positive isolates in Thailand. The current suggested dose of CZA with prolonged infusion appears appropriate to achieve the pharmacokinetic/pharmacodynamic targets of ceftazidime and avibactam against CRKP carrying blaOXA-48.Keywords: CRE, metallo-beta-lactamase, Monte Carlo, oxacillinase

Background: The current treatment recommendation involves administering a high dose of sulbactam alongside at least one additional agent. However, there remains a lack of data regarding the optimal dosage of sulbactam. We investigated whether administering sulbactam at a dosage of 12 g/day decreases the mortality rate among patients with CRAB pneumonia compared to 9 g/day., Methods: The study was an open-label, superiority, randomized controlled trial conducted at Phramongkutklao Hospital between September 2019 and September 2023 in patients diagnosed with CRAB. Participants were randomly assigned to receive a combination of colistin with either 9 or 12 g/day of sulbactam. The primary endpoint was the all-cause mortality rate at 28 days postrandomization., Results: Among the 138 participants, there was a trend towards a lower mortality rate in the 12 g/day group (59.4% vs. 47.8%; P = 0.158). After adjusting for factors associated with mortality, a lower mortality was observed in the 12 g/day group (adjusted HR 0.54 [95% CI 0.33-0.87]; P = 0.0110). The microbiological cure rate at day 7 was higher in the 12 g/day group (73.2% vs. 89.4%; P = 0.02)., Conclusions: Colistin in combination with sulbactam at a dosage of 12 g/day may improve mortality compared to 9 g/day., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)