Impact of an Antimicrobial Stewardship Program on Antibiotic Consumption, Bacterial Susceptibility, and Costs in a High-Complexity Public Hospital

<b>Background/Objectives</b>: Antimicrobial resistance (AMR) is a major global public health threat, particularly in hospitals. Antimicrobial Stewardship Programs (ASPs) aim to optimize prescribing, reduce unnecessary exposure to broad-spectrum agents, and mitigate resistance. This study evaluated the clinical, ecological, and economic impact of an ASP implemented in January 2021 in a high-complexity hospital in Brazil, focusing on antimicrobial consumption, temporal trends in bacterial susceptibility, and direct antimicrobial-related costs. <b>Methods</b>: A quasi-experimental pre-post study using an interrupted time-series design was conducted in the adult intensive care unit from January 2019 to December 2023. Antimicrobial consumption was measured as Defined Daily Doses per 1000 patient-days (DDD/1000-PD) for ceftriaxone, meropenem, piperacillin-tazobactam, vancomycin, and polymyxin B. Temporal trends were assessed using Joinpoint regression, and pre- and post-intervention periods were compared using Student's or Mann-Whitney tests. Susceptibility data were interpreted according to BrCAST standards. <b>Results</b>: Significant and sustained reductions were observed for all agents except polymyxin B. Susceptibility improved or stabilized among key Gram-negative pathogens, with a significant increase in aggregated Gram-negative susceptibility after 2021, while intrinsically resistant organisms showed limited change. Annual antimicrobial costs decreased by approximately USD 174,000. <b>Conclusions</b>: The ASP was associated with reduced broad-spectrum antimicrobial use, favorable ecological trends, and substantial cost savings.