Evaluation and Validation of the Limited Sampling Strategy of Polymyxin B in Patients with Multidrug-Resistant Gram-Negative Infection

A Systematic Review of Pharmacokinetic Studies of Colistin and Polymyxin B in Adult Populations

BACKGROUND AND OBJECTIVE

The pharmacokinetics of polymyxins are highly variable and conventional dosing regimens may likely lead to sub-optimal exposures and outcomes, particularly in critically ill patients with multi-drug-resistant infections. The aim of this systematic review is to describe the published pharmacokinetic data and to investigate variables that have been shown to affect the pharmacokinetics of colistimethate sodium, colistin, and polymyxin B in adult populations.

METHODS

Sixty studies were identified. A total of 27 and 33 studies described the pharmacokinetics of colistin and polymyxin B, respectively.

RESULTS

The most common dosing regimen for colistimethate sodium was a loading dose of 9 MIU, followed by 9 MIU/day in two to three divided doses, while for polymyxin B, a loading dose of 100-200 mg, followed by 50-100 mg every 12 h was given. Studies that used colistin sulfate instead of colistimethate sodium reported lower inter-individual variability, which may be attributed to the formulation of colistin sulfate being an active drug. The volume of distribution for colistin is typically lower in healthy individuals than in critically ill patients, owing to variations in physiological and pathological conditions. The clearance of colistimethate sodium in critically ill patients not undergoing dialysis was higher, around 13 L/h, compared with those receiving continuous renal replacement therapy, where clearance ranged from 2.31 to 8.23 L/h. In patients receiving continuous renal replacement therapy, clearance of colistin was higher compared with colistimethate sodium (2.06-6.63 L/h and 1.57-3.85 L/h, respectively). Colistin protein binding in critically ill patients ranged from 51% to 79%. The volume of distribution of polymyxin B was similar between critically ill and acutely ill patients, with range of 6.3-33.1 L and 6.22-38.6 L, respectively. Clearance of polymyxin B was also almost similar between critically ill and acutely ill patients (range of 1.27-2.32 L/h). There were two studies that reported free drug concentrations instead of the total drug concentrations of polymyxin B. In critically ill patients, protein binding ranged from 48.8% to 92.4% for polymyxin B. Creatinine clearance was the most common patient characteristic associated with altered clearance of colistimethate sodium and/or colistin, and polymyxin B.

CONCLUSIONS

Critically ill patients exhibit complex pharmacokinetics for colistin and polymyxin B, influenced by renal function, body weight, and clinical factors such as acute kidney injury, augmented renal clearance, serum albumin, and liver function. These factors necessitate individualized dosing adjustments to avoid toxicity and achieve therapeutic efficacy. Model-informed precision dosing provides a promising approach to optimize their use by integrating population pharmacokinetic parameters, patient-specific variables, and therapeutic drug monitoring, ensuring a balance between efficacy, safety, and resistance prevention.

A limited sampling strategy for estimating busulfan exposure in pediatric hematopoietic stem cell transplantation

Background

Busulfan (Bu) is the foundation of conditioning regimens for pediatric hematopoietic stem cell transplantation (HSCT). Evidence indicates that the efficacy and side effects of Bu are intimately tied to the area under its concentration-time curve (AUC). Given its cytotoxic nature and a small therapeutic index, coupled with marked inter-individual pharmacokinetic variability, Bu requires therapeutic drug monitoring to facilitate individualized therapy. However, research investigating the relationship between Bu exposure and clinical outcomes among the Chinese population remains scarce. This study aimed to develop a limited sampling strategy (LSS) for estimating Bu exposure in pediatric HSCT recipients using multiple linear regression (MLR) analysis to predict the AUC0-360.

Methods

We enrolled 26 pediatric patients who underwent Bu-based conditioning for HSCT. Blood samples were collected at 11 time points after Bu infusion. Pharmacokinetic parameters were calculated using non-compartmental methods. MLR models were developed using 1-4 sampling points to predict the AUC0-360. Model accuracy was assessed using the Jackknife and Bootstrap methods, with consistency evaluated via intraclass correlation coefficient (ICC) and Bland-Altman (BA) analyses.

Results

The mean ± standard deviation (SD) for AUC0-t, mean residence time 0-t, clearance, and volume of distribution were 845.54 ± 111.03 μmol min/L, 181.37 ± 10.55 min, 0.23 ± 0.04 L/h/kg, and 0.73 ± 0.15 L/kg, respectively. Models with 2-4 sampling points showed improved prediction accuracy compared to single-point models. The four-point model (60, 135, 240 and 360 min) demonstrated the highest accuracy with an adjusted r 2 of 0.965. Internal validation confirmed the models' stability and accuracy, with the four-point model exhibiting the best performance. External validation using three additional cases supported the predictive accuracy of the model.

Conclusion

The LSS model developed in this study accurately predicts the Bu AUC0-360 with 2-4 sampling points, offering a practical and clinically valuable tool for therapeutic drug monitoring in pediatric HSCT recipients. The four-point model was found to be the most accurate and is recommended for clinical applications.

Pharmacokinetics of polymyxin B in different populations: a systematic review

BACKGROUND AND OBJECTIVES

Despite being clinically utilized for the treatment of infections, the limited therapeutic range of polymyxin B (PMB), along with considerable interpatient variability in its pharmacokinetics and frequent occurrence of acute kidney injury, has significantly hindered its widespread utilization. Recent research on the population pharmacokinetics of PMB has provided valuable insights. This study aims to review relevant literature to establish a theoretical foundation for individualized clinical management.

METHODS

Follow PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, Pop-PK studies of PMB were searched in PubMed and EMBASE database systems from the inception of the database until March 2023.

RESULT

To date, a total of 22 population-based studies have been conducted, encompassing 756 subjects across six different countries. The recruited population in these studies consisted of critically infected individuals with multidrug-resistant bacteria, patients with varying renal functions, those with cystic fibrosis, kidney or lung transplant recipients, patients undergoing extracorporeal membrane oxygenation (ECMO) or continuous renal replacement therapy (CRRT), as well as individuals with obesity or pediatric populations. Among these studies, seven employed a one-compartmental model, with the range of typical clearance (CL) and volume (Vc) being 1.18-2.5L /h and 12.09-47.2 L, respectively. Fifteen studies employed a two-compartmental model, with the ranges of the clearance (CL) and volume of the central compartment (Vc), the volume of the peripheral compartment (Vp), and the intercompartment clearance (Q) were 1.27-8.65 L/h, 5.47-38.6 L, 4.52-174.69 L, and 1.34-24.3 L/h, respectively. Primary covariates identified in these studies included creatinine clearance and body weight, while other covariates considered were CRRT, albumin, age, and SOFA scores. Internal evaluation was conducted in 19 studies, with only one study being externally validated using an independent external dataset.

CONCLUSION

We conclude that small sample sizes, lack of multicentre collaboration, and patient homogeneity are the primary reasons for the discrepancies in the results of the current studies. In addition, most of the studies limited in the internal evaluation, which confined the implementation of model-informed precision dosing strategies.

Limited Sampling Strategies for Estimating Busulfan Area Under the Concentration-Time Curve: Based on Peak and Trough Concentrations in Saliva

Therapeutic drug monitoring for busulfan is currently performed by multiple plasma sampling. Saliva is considered a noninvasive therapeutic drug monitoring matrix. This study aimed to investigate intravenous busulfan pharmacokinetics (PK) in plasma and saliva, and establish a limited sampling strategy (LSS) for predicting the area under the concentration-time curve from time zero to infinity in plasma (AUC0-∞,p) by using saliva samples. Therefore, the PK of busulfan was studied in 37 Chinese patients. Pearson correlation analysis was used to evaluate the correlation between the AUC of busulfan in plasma and saliva. LSS models were established by the multiple linear regression analysis. The prediction error, the mean prediction error, and the root mean square error were used to evaluate the predictive accuracy. The agreement between the predicted and observed AUC0-∞ in saliva was investigated by the intraclass correlation coefficient and Bland-Altman analysis. The accuracy and robustness of the models were evaluated by using the bootstrap procedure. The result of PK analysis 62.2% of patients (23/37) was within the target range of AUC0-∞,p . A good correlation between saliva and plasma busulfan AUC0-∞ was observed (r = 0.63, p < .01). The bias and precision of the models 7 and 13 were less than 15%. The intraclass correlation coefficient exceeded 0.9, and the limits of agreement were within ±15%. The 2-point LSS model in saliva is a convenient and desirable approach to predict the AUC0-∞ of 4 times daily intravenous busulfan in plasma, which can be used to design personalized dosing for busulfan.