The Effects of the Early and Late Phases of Septic Shock on the Population Pharmacokinetics of Vancomycin

Pathophysiologic changes in the early and late phases of septic shock affect the pharmacokinetic (PK) parameters, varying dose adjustments may be necessary. This study aimed to create the PK models of vancomycin in the early and late phases of septic shock and to describe the association between the area under the curve from 0 to 24 h (AUC0-24) and acute kidney injury (AKI). The data from patients with septic shock receiving vancomycin was collected either prospectively or retrospectively. A nonlinear mixed-effects modeling approach was used to develop the PK models. A total of 208 septic shock patients were enrolled and classified into the early (n = 96) and the late phase (n = 112). A two-compartment PK model is the best base model for both phases of septic shock. The model that best predicted the clearance (CL) of both phases was the 2021 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation, which was not indexed to body surface area (BSA). Albumin (ALB) was a covariate associated with vancomycin CL only in the late phase. The typical values of CL and volume of distribution (Vd) in the early phase were 1.71 L/h and 68.94 L. In the late phase, CL was 1.65 L/h, and Vd was 66.36 L. The AKI was observed in patients with a high simulated AUC0-24. The population PK model of vancomycin in the early and late phases of septic shock has been established. The CKD-EPI not indexed to BSA predicts vancomycin CL in both phases. ALB was associated with CL in the late phase.

Impact of Various Estimated Glomerular Filtration Rate Equations on the Pharmacokinetics of Meropenem in Critically Ill Adults

IMPORTANCE

Meropenem dosing is typically guided by creatinine-based estimated glomerular filtration rate (eGFR), but creatinine is a suboptimal GFR marker in the critically ill.

OBJECTIVES

This study aimed to develop and qualify a population pharmacokinetic model for meropenem in critically ill adults and to determine which eGFR equation based on creatinine, cystatin C, or both biomarkers best improves model performance.

DESIGN SETTING AND PARTICIPANTS

This single-center study evaluated adults hospitalized in an ICU who received IV meropenem from 2018 to 2022. Patients were excluded if they had acute kidney injury, were on kidney replacement therapy, or were treated with extracorporeal membrane oxygenation. Two cohorts were used for population pharmacokinetic modeling: a richly sampled development cohort (n = 19) and an opportunistically sampled qualification cohort (n = 32).

MAIN OUTCOMES AND MEASURES

A nonlinear mixed-effects model was developed using parametric methods to estimate meropenem serum concentrations.

RESULTS

The best-fit structural model in the richly sampled development cohort was a two-compartment model with first-order elimination. The final model included time-dependent weight normalized to a 70-kg adult as a covariate for volume of distribution (Vd) and time-dependent eGFR for clearance. Among the eGFR equations evaluated, eGFR based on creatinine and cystatin C expressed in mL/min best-predicted meropenem clearance. The mean (se) Vd in the final model was 18.2 (3.5) liters and clearance was 11.5 (1.3) L/hr. Using the development cohort as the Bayesian prior, the opportunistically sampled cohort demonstrated good accuracy and low bias.

CONCLUSIONS AND RELEVANCE

Contemporary eGFR equations that use both creatinine and cystatin C improved meropenem population pharmacokinetic model performance compared with creatinine-only or cystatin C-only eGFR equations in adult critically ill patients.

Population pharmacokinetic model of cefepime for critically ill adults: a comparative assessment of eGFR equations

Cefepime exhibits highly variable pharmacokinetics in critically ill patients. The purpose of this study was to develop and qualify a population pharmacokinetic model for use in the critically ill and investigate the impact of various estimated glomerular filtration rate (eGFR) equations using creatinine, cystatin C, or both on model parameters. This was a prospective study of critically ill adults hospitalized at an academic medical center treated with intravenous cefepime. Individuals with acute kidney injury or on kidney replacement therapy or extracorporeal membrane oxygenation were excluded. A nonlinear mixed-effects population pharmacokinetic model was developed using data collected from 2018 to 2022. The 120 included individuals contributed 379 serum samples for analysis. A two-compartment pharmacokinetic model with first-order elimination best described the data. The population mean parameters (standard error) in the final model were 7.84 (0.24) L/h for CL1 and 15.6 (1.45) L for V1. Q was fixed at 7.09 L/h and V2 was fixed at 10.6 L, due to low observed interindividual variation in these parameters. The final model included weight as a covariate for volume of distribution and the eGFRcr-cysC (mL/min) as a predictor of drug clearance. In summary, a population pharmacokinetic model for cefepime was created for critically ill adults. The study demonstrated the importance of cystatin C to prediction of cefepime clearance. Cefepime dosing models which use an eGFR equation inclusive of cystatin C are likely to exhibit improved accuracy and precision compared to dosing models which incorporate an eGFR equation with only creatinine.

Medication Management in the Critically Ill Patient with Acute Kidney Injury

ABSTRACT

AKI occurs frequently in critically ill patients. Patients with AKI, including those who require KRT, experience multiple pharmacokinetic and pharmacodynamic perturbations that dynamically influence medication effectiveness and safety. Patients with AKI may experience both subtherapeutic drug concentrations, which lead to ineffective therapy, and supratherapeutic drug concentrations, which increase the risk for toxicity. In critically ill patients with AKI not requiring KRT, conventional GFR estimation equations, especially those based on serum creatinine, have several limitations that can limit the accuracy when used for medication dosing. Alternative methods to estimate kidney function may be informative, including use of measured urinary creatinine clearance, kinetic eGFR, and equations that integrate novel kidney biomarkers. For critically ill patients with AKI requiring KRT, physicochemical properties of the drug, the KRT prescription and circuit configuration, and patient-specific factors each contribute to medication clearance. Evidence-based guidance for medication dosing during AKI requiring KRT is often limited. A working knowledge of the basic tenets of drug elimination during KRT can provide a framework for how to approach decision making when the literature is lacking. Iterative re-evaluation of a patient's progress toward therapeutic goals with a medication must occur over the arc of critical illness, including and especially in the setting of dynamic kidney function.

Comparison of Race and Non-Race Based Equations for Kidney Function Estimation in Critically Ill Thai Patients for Vancomycin Dosing

Empiric antibiotic dosing frequently relies on an estimate of kidney function based on age, serum creatinine (SCr), sex, and race (on occasion). New non-Race based estimated glomerular filtration rate (eGFR) equations have been published but their role to support dosing is not known. Here, we report on a population pharmacokinetic model of vancomycin that serves as a useful probe substrate of eGFR in critically ill Thai patients. Data were obtained from medical records during a 10-year period. A nonlinear mixed-effects modeling approach was conducted to estimate vancomycin parameters. Data from 208 critically ill patients (58.2% male and 36.0% septic shock) with 398 vancomycin concentrations were collected. Twenty-three covariates including 12 kidney function estimates were tested and ranked based on the model performance. The median [min, max] age, weight, and SCr was 69 [18, 97] years, 60.0 [27, 120] kg, and 1.53 [0.18, 7.15] mg/dL. The best base model was a one-compartment linear with zero-order input and proportional error model. A Thai specific eGFR equation not indexed to body surface area (BSA) model best predicted vancomycin clearance (CL). The typical value for volume of distribution and CL was 67.5 L and 1.22 L/h, respectively. A loading dose of 2000 mg followed by maintenance dose regimens based on eGFR is suggested. The Thai-GFR not indexed to BSA model best predicts vancomycin CL and dosing in the critically ill Thai population. A 5-10% absolute gain in the vancomycin probability of target attainment is expected with the use of this population specific GFR equation. This article is protected by copyright. All rights reserved.

Creatinine Assessment in Non-Steady-State Conditions: A Critical Review

OBJECTIVES

To discuss methods for the assessment of creatinine clearance (Cl_cr) when serum creatinine (SCr) is not at steady state in order to estimate kidney function and apply the estimate to kidney function staging for clinical assessment or drug dosing.

DATA SOURCES

A PubMed search was conducted from 1976 to mid-January 2021 with other articles identified through review of bibliographies of retrieved articles and citations in Scopus.

STUDY SELECTION AND DATA EXTRACTION

Articles assessing Cl_cr under non-steady-state conditions and studies evaluating predictive equations were selected.

DATA SYNTHESIS

When SCr is systematically changing (ie, trending up or down), kinetic methods to estimate Cl_cr are appropriate. Estimates from kinetic methods should be individual based and not indexed to body surface area, and careful monitoring is required to confirm predictions as the situation evolves. Standard methods intended for steady-state conditions should not be used to estimate Cl_cr in patients with unstable SCr.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Creatinine continues to be a monitoring parameter of choice and is an important variable in all the commonly used equations for estimating Cl_cr and most important for estimating glomerular filtration rate. However, standard methods of estimating Cl_cr for medication dosing are not accurate under non-steady-state conditions.

CONCLUSION

The methods for kinetic clearance estimation and standards methods for clearance estimation, such as the Cockcroft-Gault equation, are mutually exclusive. There are no benefits of using the kinetic method in patients with stable SCr concentrations, and standard equations are not appropriate with unstable SCr concentrations.