Background: Ideal therapy duration for Pseudomonas aeruginosa or Acinetobacter baumannii-calcoaceticus complex (ABC) bloodstream infections (BSI) is not defined, especially in the context of carbapenem resistance. In this study, we compared short- (≤7 days) and long-term (>7 days) antimicrobial therapy duration for these infections. Methods: We performed a retrospective cohort study in two tertiary-care hospitals in Porto Alegre, Brazil, from 2013 to 2019. Eligible patients aged ≥18 years were included and excluded for the following criteria: polymicrobial infections, treatment with non-susceptible antibiotics, complicated infections, or early mortality (<8 days of active antimicrobial therapy). The 30-day mortality risk was evaluated using a Cox regression model. Results: We included 237 BSI episodes, 51.5% caused by ABC and 48.5% by Pseudomonas aeruginosa. Short-term therapy was not associated with 30-day mortality, adjusted hazard ratio 1.01, 95% confidence interval 0.47–2.20, p = 0.98, when adjusted for Pitt score (p = 0.02), Charlson Comorbidity Index score (p < 0.01), and carbapenem resistance (p < 0.01). Among patients who survived, short-term therapy was associated with shorter hospital stay (p < 0.01). Results were maintained in the subgroups of BSI caused by carbapenem-resistant bacteria (p = 0.76), ABC (p = 0.61), and Pseudomonas aeruginosa (p = 0.39). Conclusions: Long-term therapies for non-complicated Pseudomonas aeruginosa and ABC BSI were not superior to short-term therapy for 30-day mortality.

Polymyxins are still widely used for the treatment of carbapenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa bloodstream infections (BSIs). This study seeks to evaluate the impact of polymyxin B versus colistin on mortality and nephrotoxicity in BSI caused by these bacteria. We conducted a retrospective cohort study from 2014 to 2021 in Porto Alegre, Brazil. We included patients aged ≥18 years and excluded patients with polymicrobial infection or treatment for ≤48 h. The 30-day mortality was the primary outcome evaluated through Cox regression. We included 259 patients with BSI episodes: 78.8% caused by A. baumannii and 21.2% caused by P. aeruginosa. Polymyxin B did not impact mortality compared to colistin (adjusted hazard ratio (aHR), 0.82; 95% confidence interval (CI), 0.52–1.30; p = 0.40 (when adjusted for COVID-19 comorbidity, p = 0.05), Pitt bacteremia score, p < 0.01; Charlson comorbidity index, p < 0.001; time to start active antimicrobial therapy, p = 0.02). Results were maintained in the subgroups of BSI caused by A. baumannii (aHR, 0.92; 95% CI, 0.55–1.54; p = 0.74), P. aeruginosa (aHR, 0.47; 95% CI, 0.17–1.32; p = 0.15) and critical care patients (aHR, 0.77; 95% CI, 0.47–1.26; p = 0.30). Treatment with polymyxin B or colistin did not impact 30-day mortality in patients with carbapenem-resistant A. baumannii or P. aeruginosa BSI.