Mid‐dosing interval concentration is important for polymyxin B exposure and acute kidney injury in critically ill patients

Abstract This study aimed to evaluate the association between polymyxin B (PMB) exposure and acute kidney injury (AKI) and analyze the risk factors for PMB‐induced AKI in critically ill patients. Plasma concentrations of PMB were determined using an ultraperformance liquid chromatography–tandem mass spectrometer in intensive care unit patients who were administered PMB. Univariate and multivariate analyses were conducted to identify risk factors. A receiver operating characteristic curve was constructed to assess the discriminant power of the factors and to identify the cutoff value for AKI. The white blood cell count and estimated area under the concentration–time curve (AUC) of patients administered PMB were independent risk factors for PMB‐induced AKI, where AUC were calculated using a first‐order pharmacokinetic equation based on the mid‐dosing interval concentration (C1/2t) and peak concentration. The area under the receiver operating characteristic curve of the final model was 0.805 (95% confidence interval, 0.690–0.921). The cutoff value for the combined predictor was 0.57. Alternatively, when using C1/2t, which was strongly correlated with AUC, as the only independent risk factor, the analysis showed that the 3.47 μg/ml threshold provides favorable differentiation between the AKI and non‐AKI groups. These results provide insightful information for therapeutic drug monitoring–guiding PMB dosing in clinical practice.