Objectives: To compare the efficacy of intravenous polymyxin B with other antimicrobials in the treatment of nosocomial Pseudomonas aeruginosa bacteraemia, assessing many potential confounding factors, including optimal dosage regimens of drugs. Methods: A retrospective cohort study was performed. Patients ≥18 years of age and who received appropriate therapy for ≥48 h for P. aeruginosa bacteraemia were analysed. Clinical covariates were assessed and compared between patients treated with

more »

... xin B and other drugs (comparators). Data were retrieved from medical records. Renal toxicity was also assessed. A Cox regression model was performed including variables with a P ≤0.20 in the comparison between both groups. Results: A total of 133 patients were included: 45 (33.8%) treated with polymyxin B and 88 (66.2%) with comparators. Most comparators (83.0%) were b-lactams. The overall in-hospital mortality was 41.4% (55/133): 66.7% (30/45) and 28.4% (25/88) in polymyxin B and comparator groups, respectively (P≤ 0.001). The final multivariate model showed that treatment with polymyxin B was independently associated with in-hospital mortality (adjusted hazard ratio 1.91, 95% confidence interval 1.05-3.45), after adjustment for Pitt bacteraemia score, and the presence of mechanical ventilation and primary bloodstream infection. Patients treated with polymyxin B presented a higher rate of ≥100% increase in creatinine level from baseline than comparators [11/45 (24.4%) versus 4/88 (4.5%); P ¼ 0.002], although this was not subjected to multivariate analysis. Conclusions: Intravenous polymyxin B therapy was inferior to other drugs in the treatment of P. aeruginosa bacteraemia, as indicated by the higher rate of in-hospital mortality.