The Optimal Use of the Polymyxins Before Their Time Is Up

An area under the concentration-time curve threshold as a predictor of efficacy and nephrotoxicity for individualizing polymyxin B dosing in patients with carbapenem-resistant gram-negative bacteria

BACKGROUND

Evidence supports therapeutic drug monitoring of polymyxin B, but clinical data for establishing an area under the concentration-time curve across 24 h at steady state (AUC_ss,24 h) threshold are still limited. This study aimed to examine exposure-response/toxicity relationship for polymyxin B to establish an AUC_ss,24 h threshold in a real-world cohort of patients.

METHODS

Using a validated Bayesian approach to estimate AUC_ss,24 h from two samples, AUC_ss,24 h threshold that impacted the risk of polymyxin B-related nephrotoxicity and clinical response were derived by classification and regression tree (CART) analysis and validated by Cox regression analysis and logical regression analysis.

RESULTS

A total of 393 patients were included; acute kidney injury (AKI) was 29.0%, clinical response was 63.4%, and 30-day all-cause mortality was 35.4%. AUC_ss,24 h thresholds for AKI of > 99.4 mg h/L and clinical response of > 45.7 mg h/L were derived by CART analysis. Cox and logical regression analyses showed that AUC_ss,24 h of > 100 mg h/L was a significant predictor of AKI (HR 16.29, 95% CI 8.16-30.25, P < 0.001) and AUC_ss,24 h of ≥ 50 mg h/L (OR 4.39, 95% CI 2.56-7.47, P < 0.001) was independently associated with clinical response. However, these exposures were not associated with mortality. In addition, the correlation between trough concentration (1.2-2.8 mg/L) with outcomes was similar to AUC_ss,24 h.

CONCLUSIONS

For critically ill patients, AUC_ss,24 h threshold of 50-100 mg h/L was associated with decreased nephrotoxicity while assuring clinical efficacy. Therapeutic drug monitoring is recommended for individualizing polymyxin B dosing.

Comparing the Population Pharmacokinetics of and Acute Kidney Injury Due to Polymyxin B in Chinese Patients with or without Renal Insufficiency

Despite excellent bactericidal effect, dosing adjustment of polymyxin B for patients with renal insufficiency and polymyxin B-related nephrotoxicity is still a major concern to clinicians. The aim of this study was to compare the population pharmacokinetics (PK) properties of polymyxin B in Chinese patients with different renal functions and to investigate the relationship between PK parameters and polymyxin B-related acute kidney injury (AKI). A total of 37 patients with normal renal function (creatinine clearance ≥ 80 ml/min) and 33 with renal insufficiency (creatinine clearance < 80 ml/min) were included. In the two-compartment population PK models, the central compartment clearance (CL) (2.19 liters/h versus 1.58 liters/h; P < 0.001) and intercompartmental clearance (Q) (13.83 liters/h versus 10.28 liters/h; P < 0.001) values were significantly different between the two groups. The simulated values for AUC across 24 h at steady state (AUC_ss,24h) for patients with normal renal function were higher than those for patients with renal insufficiency. However, renal dosing adjustment of polymyxin B seemed not to be necessary. In addition, during the treatment, AKI occurred in 23 (32.86%) patients. The polymyxin B AUC_ss,24h in patients with AKI was significantly higher than that in patients without AKI (108.66 ± 70.10 mg · h/liter versus 66.18 ± 34.79 mg · h/liter; P = 0.001). Both the receiver operating characteristic (ROC) curve and logistic regression analysis showed that an AUC_ss,24h of >100 mg · h/liter was a good predictor for the probability of nephrotoxicity.

Population Pharmacokinetics and Limited Sampling Strategy for Therapeutic Drug Monitoring of Polymyxin B in Chinese Patients With Multidrug-Resistant Gram-Negative Bacterial Infections

Polymyxin B is used as a last therapeutic option for the treatment of multidrug-resistant Gram-negative bacterial infections. This study aimed to develop a population pharmacokinetic model and limited sampling strategy, a method to estimate the area under the concentration curve (AUC) by using a limited number of samples, to assist therapeutic drug monitoring of polymyxin B in Chinese patients. Population pharmacokinetic analysis was performed using Phoenix^® NLME with data obtained from 46 adult patients at steady state. Various demographic variables were investigated as potential covariates for population pharmacokinetic modeling. The limited sampling strategies based on the Bayesian approach and multiple linear regression were validated using the intraclass correlation coefficient and Bland-Altman analysis. As a result, the data was described by a two-compartment population pharmacokinetic model. Through the modeling, creatinine clearance was found to be a statistically significant covariate influencing polymyxin B clearance. The limited sampling strategies showed the two-point model (C_0h and C_2h) could predict polymyxin B exposure with good linear relativity (r² > 0.98), and the four-point model (C_1h, C1_.5h, C_4h, and C_8h) performed best in predicting polymyxin B AUC (r² > 0.99). In conclusion, this study successfully developed a population pharmacokinetic model and limited sampling strategies that could be applied in clinical practice to assist in therapeutic drug monitoring of polymyxin B in Chinese patients.