358: Evaluation of Pseudomonas Aeruginosa Susceptibility Patterns and Associated Treatment Strategies

Introduction: Institution antibiograms provide broad overviews of organism-specific susceptibility data. However, the minimum inhibitory concentration (MIC) distribution is not reported. Understanding MIC distribution among susceptible Pseudomonas aeruginosa (PsA) isolates may impact dosing strategies for various beta-lactams and help minimize overall resistance rates. Cefepime and piperacillin-tazobactam serve as the primary anti-Pseudomonal agents at the study institution. Given their central role in treatment, this study aimed to evaluate MIC distribution and treatment regimens in cefepime-susceptible PsA isolates. Methods: This single, center retrospective study included patients admitted with culture-proven PsA, susceptible to cefepime. The primary outcome was the MIC distributions of cefepime, piperacillin-tazobactam, and meropenem. Exploratory outcomes included empiric and definitive treatment regimens, incidence of recurrent infections, and treatment failure. Results: 60 patient charts and culture data were reviewed. Ultimately, 29 patients were included in our analysis. Mean age was 67.2 years, 51.7% were admitted to an intensive care unit (ICU), and the most common sources of infection were pneumonia (37.9%) and genitourinary (21.1%). Cefepime’s MIC distribution of < 2, < 4, and 8 accounted for 55.2%, 37.9% and 6.9% of isolates, respectively. Piperacillin-tazobactam demonstrated 100% susceptibility, with 96.6% of isolates having an MIC < 8. Conversely, two isolates were resistant to meropenem. Of the remaining isolates, 96.3% had an MIC < 1. Definitive treatment with cefepime, piperacillin-tazobactam, and meropenem occurred in 34.5%, 27.6% and 17.2% of isolates, respectively. Treatment regimens varied considerably for the remaining 20.7% of isolates, as many patients had concomitant infections requiring nonstandard approaches. Only three patients experienced recurrent infections within the same admission. Four isolates developed resistance during therapy, indicating treatment failure. Conclusions: Among cefepime-susceptible PsA isolates, MIC distribution showed the greatest variability with cefepime. This highlights the importance of evaluating dosing strategies tailored to MIC values to ensure effective and targeted antimicrobial therapy.