Population pharmacokinetics of colistin sulfate in critically ill patients based on NONMEM

As the last defense against multidrug-resistant gram-negative bacteria, colistin sulfate's clinical use, which is often empirical, risks resistance and adverse reactions. This study aimed to develop a population pharmacokinetic (PPK) model of colistin sulfate for critically ill patients and determine the optimal dosing regimen. This retrospective study included 204 critically ill patients. We used a validated LC-MS/MS method to measure its plasma concentrations and RIFLE criteria for nephrotoxicity evaluation. NONMEM developed PPK models. Monte Carlo simulations set dosing regimens based on the probability of target attainment (PTA). A two-compartment model adequately described the data, creatinine clearance and weight were covariates for elimination rate and central volume, respectively. Only 11.8% had nephrotoxicity. With Monte Carlo simulations, all regimens except the maintenance dose of 0.5 MU administered every 12 h achieved > 90% PTA at the minimum inhibitory concentration (MIC) ≤ 0.5 mg/L. However, at MIC > 0.5 mg/L, the routine regimen resulted in insufficient exposure. Based on our PPK model, the dose of intravenous colistin sulfate should be adjusted according to creatinine clearance (CrCL) and weight. For critically ill patients with infections, under the conventional treatment regimens, when the MIC is ≥ 1 mg/L, it is difficult for patients to achieve the ideal therapeutic effect in terms of exposure dose. When CrCL is below 10 ml/min, the regimen of 1 MU every 8 h used could cause the potential for increasing nephrotoxicity risk, which is significantly concerned.