Evaluation of Dose Fractionated Polymyxin B on Acute Kidney Injury: A Translational In Vitro Model

The polymyxins are last-line defense for highly resistant infections. Nephrotoxicity, however, is a dose-limiting factor. Yet, approaches to mitigate nephrotoxicity are poorly defined. This study aimed to investigate the impact of dose fractionated (once, twice and thrice daily) polymyxin B (PB) on acute kidney injury (AKI) in a pre-clinical model. Secondarily, we aimed to describe the pharmacokinetic (PK) profile of PB. Sprague-Dawley rats were assigned to experimental groups with different dosing intervals but constant total daily exposure (12 mg/kg/day into single, twice daily, and thrice daily doses) and controls received normal saline subcutaneously over 3 days. Blood and urine samples were collected, and kidneys were harvested at necropsy. A three-compartment model best described the data and Bayesian observed vs. predicted concentration demonstrated bias, imprecision, and R2 of 0.129 mg/L, 0.729 mg2/L2 and 0.652, respectively. PB exposure (i.e. AUC24h) were similar across treatment groups over time (p=0.87). As a representative, urinary KIM-1 were elevated on days 1 and 2 for experimental groups compared to controls, and thrice daily group experienced the most KIM-1 increase [mean increase (95% CI) day 1 from day -1, 4.44 (0.89, 8.00) ng/mL; p=0.018] as compared to control [mean increase (95% CI) day 1 from day -1, 0.03 (-0.42, 0.49) ng/mL; p=0.99]. Correspondingly, significant histopathological damage was observed with the same group (p=0.013) (controls as a referent). Our findings suggested that fractionating the PB dose thrice daily resulted in the most injury in a rat model.