In-vitro Activity of Ceftazidime-avibactam Against Multidrug-resistant Pseudomonas Aeruginosa: Cross-sectional Study from a Tertiary Care Hospital

Introduction: Multidrug-resistant (MDR) Pseudomonas aeruginosa poses a major therapeutic challenge in tertiary-care settings, necessitating local, Clinical and Laboratory Standards Institute (CLSI) -anchored susceptibility data for empiric therapy and stewardship. This study characterises Ceftazidime– Avibactam (CZA) activity and Minimum Inhibitory Concentration (MIC) distribution to support stewardship and local guideline updates Aim: To evaluate the in-vitro activity of CZA against MDR Pseudomonas aeruginosa clinical isolates from a tertiary care hospital in North India. Materials and Methods: This was a hospital-based, crosssectional study conducted in the Bacteriology Division, Postgraduate Department of Microbiology, Government Medical College, Srinagar, Jammu and Kashmir, India, from January 2022 to December 2022 and included 108 non duplicate MDR Pseudomonas aeruginosa clinical isolates. Standardised workflows encompassed specimen culture and identification, Kirby-Bauer disc diffusion, and ceftazidime-avibactam MIC determination by E-test interpreted per CLSI M100 (2022), while demographic parameters recorded for context included age group and gender. Susceptibility was reported as proportions, and predictors of CZA non susceptibility were estimated using multivariable logistic regression. A p-value of <0.05 was considered statistically significant. Results: Ceftazidime-Avibactam susceptibility was 63/108 (58.38%) and exceeded most β-lactam comparators, while aztreonam showed the highest susceptibility at 98/108 (90.74%). The MIC distribution clustered at 2-8 µg/mL with a peak at 8 µg/ mL. In multivariable modelling, burn diagnosis {adjusted Odds Ratio (aOR)=2.15; 95% Confidence Interval (CI) 1.05-4.41}, carbapenem non susceptibility (aOR=2.72; 95% CI 1.34-5.51), and ceftazidime non susceptibility (aOR=2.08; 95% CI 1.01- 4.29) independently predicted CZA non susceptibility. Conclusion: Ceftazidime-avibactam was the most active among core antipseudomonal β-lactams, while aztreonam showed the highest overall susceptibility. The MIC histogram peaked at 8 µg/mL, with most isolates clustering between 2-8 µg/mL. Burn diagnosis, carbapenem non susceptibility, and ceftazidime non susceptibility independently predicted CZA non susceptibility