Risk factors for acute kidney injury in patients treated with polymyxin B or colistin methanesulfonate sodium

Polymyxin B (PMB) and colistin, administered as the prodrug colistin methanesulfonate sodium (CMS), are increasingly used to treat carbapenem-resistant Gram-negative bacteria. Nephrotoxicity is the major dose-limiting adverse effect of both polymyxins. A retrospective cohort study of 132 patients was conducted to evaluate risk factors for acute kidney injury (AKI), classified according to Acute Kidney Injury Network criteria, in patients treated with ≥48 h of intravenous PMB or CMS, with particular focus on potential differences between each polymyxin. The overall incidence of AKI was 25.8% (34/132) [20.8% (20/96) and 38.9% (14/36) in patients treated with PMB and CMS, respectively; P = 0.06]. In the Cox regression model, doses ≥2 million International Units (MIU) of PMB or >9 MIU of CMS were the only variable independently associated with AKI [adjusted hazard ratio (aHR) = 2.11, 95% confidence interval (CI) 1.01-4.41; P = 0.04]. Vancomycin co-administration was strongly associated with AKI, although this was not statistically significant (aHR = 2.22, 95% CI 0.98-5.04; P = 0.058). There was no statistically significant difference in the incidence of AKI between patients treated with PMB or CMS in the multivariate model (aHR = 1.74, 95% CI 0.82-3.69; P = 0.15). High dose was the main risk factor for AKI regardless of the polymyxin administered. Vancomycin co-administration likely increases the risk of AKI. Although there was a higher overall incidence of AKI in patients treated with CMS compared with PMB, CMS was not significantly associated with this outcome after adjusting for the above variables.