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Background and Importance Multidrug-resistant Gram-negative bacteria (GNB), including MBL-producing Enterobacteriaceae, are a growing global concern due to their increasing prevalence and limited treatment options. One available therapy is the ceftazidime-avibactam-aztreonam combination (ceftazidime is used due to aztreonam-avibactam being unavailable until 2025).Aim and Objectives To describe the utilisation profile of ceftazidime-avibactam-aztreonam in the treatment of multidrug-resistant GNB infections.Material and Methods Retrospective study of patients with active infection treated with ceftazidime-avibactam-aztreonam (Jan 2022–Apr 2025). Sociodemographic, clinical/infection-related, and treatment data were collected. Quantitative data were expressed in mean and SD; qualitative in percentage with 95% CI. Analysis: M365 Copilot.Results 104 patients received ceftazidime-avibactam-aztreonam: 19.2% (11.5-26.9) colonisations and 80.7% (73.1-88.5) infections.Abstract 4CPS-109 Table 1Sociodemographic profileMale gender 62.5% (52.9-72.1) Age (years) 68.7 (13.1) Hospital stay (days) 50.2 (41.3) Intensive care unit (ICU) admission 32.7% (24.0-42.3) ICU stay (days) 18.1 (31.1) Abstract 4CPS-109 Table 2Infection associated parametersInfection Source:UrinaryAbdominalRespiratorySkin and Soft TissueEndovascularThoracicUnknown 30.7% (22.1-39.4)24.0% (16.3-32.7)21.1% (13.5-28.8)6.7% (1.9-11.5)4.8% (1.0-9.6)1.2% (0.0-2.9)11.5% (5.8-18.3) Another infection source 13.5% (7.7–20.2) Sepsis 28.9% (20.2–37.5) Polymicrobial infection 45.1% (35.6–54.8) Abstract 4CPS-109 Table 3Microbiological profileResistance mechanisms ESBL+carbapenemase 56.6 (48.2-64.7) Carbapenemase 29.4 (22.4-37.6) Multidrug-resistant 6.6 (3.5-12.1) ESBL 2.3 (0.8-6.3) ESBL+carbapenemase+AMPc 0.7 (0.1-4.0) Carbapenem-resistant 0.7 (0.1-4.0) Ausence 3.7 (1.6-8.3) Carbapenemase OXA-48+NDM 48.3 (39.4-57.3) VIM 18.1 (12.2-26.1) IMP 10.3 (6.0-17.2) OXA-48 9.5 (5.4-16.2) NDM 6.9 (3.5-13.0) VIM+IMP 2.6 (0.9-7.3) VIM+KPC 2.6 (0.9-7.3) GES 1.7 (0.5-6.1) Abstract 4CPS-109 Table 4Treatment-related dataTargeted treatment 83.7% (76.0–90.4) Treatment duration (days) 7.3 (3.2) days Inappropriate renal dose adjustment 18.3% (11.5–26.0) Treatment interruption reasons:Clinical/microbiological cureDe-escalation/optimisationNegative colonisation sampleDeathCeftazidime-avibactam-aztreonam resistance 51.0% (41.3–60.6)24.0% (16.3–32.7)12.5% (6.7–19.2)11.5% (5.8–18.3)1.0% (0.1–2.9) Conclusion and Relevance Ceftazidime-avibactam-aztreonam has been predominantly used as targeted therapy in severe infections caused by multidrug-resistant GNB. A high prevalence of complex resistance mechanisms, including OXA-48 and NDM carbapenemases was detected. Despite the clinical complexity, over half of the patients achieved clinical or microbiological cure, highlighting the potential effectiveness of this combination. However, the notable rate of incorrect renal dose adjustments and its use in MBL-negative Enterobacteriaceae underscores the need for improved antimicrobial stewardship and dosing optimisation to maximise therapeutic outcomes and minimise resistance development.Conflict of Interest No conflict of interest