A reappraisal of polymyxin B dosing based on population pharmacokinetic model in patient with renal insufficiency

Background: Current FDA-approved label recommends polymyxin B dosing should be adjusted according to renal function, despite several studies proved poor correlation between polymyxin B PK and creatinine clearance. The study aims to assess the impact of renal function on polymyxin B metabolism and identify an alternate dosing strategy by population analysis. Methods: Blood samples from adult patients were collected at steady state during routine therapeutic drug monitoring. Nonlinear mixed effects modeling was employed to build a population PK model of polymyxin B. Monte Carlo simulations were performed to design polymyxin B dosing regimens across various renal function. Results: Pharmacokinetic analyses included 112 polymyxin B concentrations at steady state from 32 adult patients aged 37-93 received intravenous polymyxin B (100-200 mg/d). The creatinine clearance in patients was 5.91-244 mL/min. In the final population PK model, CrCL was the significant covariate on CL (typical value, 1.59 L/hr; between-subject variability, 13%). Mean (SD) individual empirical Bayesian estimates of CL was 1.75 (0.43) L/hr. A new dosing strategy combining the PK/PD targets and Monte Carlo simulation indicated that polymyxin B dose reductions improved the probability of achieving optimal exposures in simulated patients with renal insufficiency. For severe infections caused by organisms with MIC of ≥ 2 mg/L, though a high daily dose (e.g. 200mg/day) would possible for bacterial eradication, the risk of nephrotoxicity is significantly increased. Conclusion: A population PK model was established to develop individualized polymyxin B dosage regimens that the dose of polymyxin B should be adjusted according to CrCL.