Status of Antibiotic Susceptibility of Polymyxin B And Colistin in the Treatment of Carbapenem Resistant Gram Negative Bacterial Infections: An Observational Study

Abstract

Introduction: The emergence and rapid spread of multidrug-resistant gram-negative bacteria is a global concern. Polymyxin B and Colistin have gained significance due to the scarcity of new antibiotics and the high morbidity and mortality associated with carbapenem-resistant gram-negative bacteria. This study aims to assess the antibiotic susceptibility of Colistin and Polymyxin B against carbapenem-resistant gram-negative bacteria.

Methods: This was a descriptive cross-sectional study conducted in a tertiary center of Nepal, from June to August 2025. Specimen resistant to any of the carbapenem drugs at the Clinical Laboratory was evaluated. The incidence of susceptibility or resistance of the Polymyxin and Colistin in the carbapenem- resistant gram-negative bacteria was recorded and assessed.

Results: A total of 1,412 Gram-negative bacterial samples were analyzed within the predetermined study period. Among these samples, the prevalence of 395 (27.97%) was from carbapenem-resistant Gram-negative bacteria. There were 185 (46.84%) carbapenem-resistant Klebsiella species, followed by 105 (26.60%) Acinetobacter species. Both Polymyxin B and Colistin showed 100% susceptibility across all carbapenem-resistant gram-negative bacteria species and sample sources evaluated.

Conclusions: Polymyxin B and Colistin continue to be vital last-line treatments for carbapenem-resistant gram-negative bacteria. This study found a susceptibility rate of 100% to colistin and polymyxin B among carbapenem-resistant gram- negative bacteria. To maintain the efficacy and reliability of these antibiotics, it is essential to use them judiciously, conduct routine susceptibility testing, and implement ongoing surveillance.