Augmented renal clearance in the ICU: results of a multicenter observational study of renal function in critically ill patients with normal plasma creatinine concentrations*. Crit Care Med. 2014;42:520-527. [PMID: 24201175 DOI: 10.1097/ccm.0000000000000029]

Decreasing the time to achieve therapeutic vancomycin concentrations in critically ill patients: developing and testing of a dosing nomogram

INTRODUCTION

Achievement of optimal vancomycin exposure is crucial to improve the management of patients with life-threatening infections caused by susceptible Gram-positive bacteria and is of particular concern in patients with augmented renal clearance (ARC). The aim of this study was to develop a dosing nomogram for the administration of vancomycin by continuous infusion for the first 24 hours of therapy based on the measured urinary creatinine clearance (8 h CLCR).

METHODS

This single-center study included all critically ill patients treated with vancomycin over a 13-month period (group 1), in which we retrospectively assessed the correlation between vancomycin clearance and 8 h CLCR. This data was used to develop a formula for optimised drug dosing. The efficiency of this formula was prospectively evaluated in a second cohort of 25 consecutive critically ill patients (group 2). Vancomycin serum concentrations between 20 to 30 mg/L were considered adequate. ARC was defined as 8 h CLCR more than 130 ml/min/1.73 m(2).

RESULTS

The incidence of ARC was 36% (n = 29/79) and 40% (10/25) in group 1 (n = 79) and 2 (n = 25), respectively. The mean serum vancomycin concentration on day 1 was 21.5 (6.4) and 24.5 (5.2) mg/L, for both groups respectively. On the treatment day, vancomycin plasma clearance was 5.12 (1.9) L/h in group 1 and correlated significantly with the 8 h CLCR (r(2) = 0.66; P < 0.001). The achievement of adequate vancomycin serum concentrations in group 2 was 84% (n = 21/25) versus 51% (n = 40/79) - P < 0.005.

CONCLUSIONS

This new vancomycin nomogram enabled the achievement of adequate serum concentrations in 84% of the patients on the first day of treatment.

Determining the mechanisms underlying augmented renal drug clearance in the critically ill: use of exogenous marker compounds

Introduction

The aim of this study was to explore changes in glomerular filtration (GFR) and renal tubular function in critically ill patients at risk of augmented renal clearance (ARC), using exogenous marker compounds.

Methods

This prospective, observational pharmacokinetic (PK) study was performed in a university-affiliated, tertiary-level, adult intensive care unit (ICU). Patients aged less than or equal to 60 years, manifesting a systemic inflammatory response, with an expected ICU length of stay more than 24 hours, no evidence of acute renal impairment (plasma creatinine concentration <120 μmol/L) and no history of chronic kidney disease or renal replacement therapy were eligible for inclusion. The following study markers were administered concurrently: sinistrin 2,500 mg (Inutest; Laevosan, Linz, Austria), p-aminohippuric acid (PAH) 440 mg (4% p-aminohippuric acid sodium salt; CFM Oskar Tropitzsch, Marktredwitz, Germany), rac-pindolol 5 or 15 mg (Barbloc; Alphapharm, Millers Point, NSW, Australia) and fluconazole 100 mg (Diflucan; Pfizer Australia Pty Ltd, West Ryde, NSW, Australia). Plasma concentrations were then measured at 5, 10, 15, 30, 60 and 120 minutes and 4, 6, 12 and 24 hours post-administration. Non-compartmental PK analysis was used to quantify GFR, tubular secretion and tubular reabsorption.

Results

Twenty patients were included in the study. Marker administration was well tolerated, with no adverse events reported. Sinistrin clearance as a marker of GFR was significantly elevated (mean, 180 (95% confidence interval (CI), 141 to 219) ml/min) and correlated well with creatinine clearance (r =0.70, P <0.01). Net tubular secretion of PAH, a marker of tubular anion secretion, was also elevated (mean, 428 (95% CI, 306 to 550) ml/min), as was net tubular reabsorption of fluconazole (mean, 135 (95% CI, 100 to 169) ml/min). Net tubular secretion of (S)- and (R)-pinodolol, a marker of tubular cation secretion, was impaired.

Conclusions

In critically ill patients at risk of ARC, significant alterations in glomerular filtration, renal tubular secretion and tubular reabsorption are apparent. This has implications for accurate dosing of renally eliminated drugs.

Antibiotic stewardship in the intensive care unit

The rapid emergence and dissemination of antimicrobial-resistant microorganisms in ICUs worldwide constitute a problem of crisis dimensions. The root causes of this problem are multifactorial, but the core issues are clear. The emergence of antibiotic resistance is highly correlated with selective pressure resulting from inappropriate use of these drugs. Appropriate antibiotic stewardship in ICUs includes not only rapid identification and optimal treatment of bacterial infections in these critically ill patients, based on pharmacokinetic-pharmacodynamic characteristics, but also improving our ability to avoid administering unnecessary broad-spectrum antibiotics, shortening the duration of their administration, and reducing the numbers of patients receiving undue antibiotic therapy. Either we will be able to implement such a policy or we and our patients will face an uncontrollable surge of very difficult-to-treat pathogens.

Risk factors for target non-attainment during empirical treatment with β-lactam antibiotics in critically ill patients

PURPOSE

Risk factors for β-lactam antibiotic underdosing in critically ill patients have not been described in large-scale studies. The objective of this study was to describe pharmacokinetic/pharmacodynamic (PK/PD) target non-attainment envisioning empirical dosing in critically ill patients and considering a worst-case scenario as well as to identify patient characteristics that are associated with target non-attainment.

METHODS

This analysis uses data from the DALI study, a prospective, multi-centre pharmacokinetic point-prevalence study. For this analysis, we assumed that these were the concentrations that would be reached during empirical dosing, and calculated target attainment using a hypothetical target minimum inhibitory concentration (MIC), namely the susceptibility breakpoint of the least susceptible organism for which that antibiotic is commonly used. PK/PD targets were free drug concentration maintained above the MIC of the suspected pathogen for at least 50 % and 100 % of the dosing interval respectively (50 % and 100 % f T (>MIC)). Multivariable analysis was performed to identify factors associated with inadequate antibiotic exposure.

RESULTS

A total of 343 critically ill patients receiving eight different β-lactam antibiotics were included. The median (interquartile range) age was 60 (47-73) years, APACHE II score was 18 (13-24). In the hypothetical situation of empirical dosing, antibiotic concentrations remained below the MIC during 50 % and 100 % of the dosing interval in 66 (19.2 %) and 142 (41.4 %) patients respectively. The use of intermittent infusion was significantly associated with increased risk of non-attainment for both targets; creatinine clearance was independently associated with not reaching the 100 % f T( >MIC) target.

CONCLUSIONS

This study found that-in empirical dosing and considering a worst--case scenario--19 % and 41 % of the patients would not achieve antibiotic concentrations above the MIC during 50 % and 100 % of the dosing interval. The use of intermittent infusion (compared to extended and continuous infusion) was the main determinant of non-attainment for both targets; increasing creatinine clearance was also associated with not attaining concentrations above the MIC for the whole dosing interval. In the light of this study from 68 ICUs across ten countries, we believe current empiric dosing recommendations for ICU patients are inadequate to effectively cover a broad range of susceptible organisms and need to be reconsidered.

Assessment of pharmacokinetic changes of meropenem during therapy in septic critically ill patients

Background

Meropenem is a carbapenem antibiotic commonly used in critically ill patients to treat severe infections. The available pharmacokinetic (PK) data has been mostly obtained from healthy volunteers as well as from clinical studies addressing selected populations, often excluding the elderly and also patients with renal failure. Our aim was to study PK of meropenem in a broader population of septic critically ill patients.

Methods

We characterized the PK of meropenem in 15 critically ill patients during the first 36 hrs of therapy. Aditionally, whenever possible, we collected a second set of late plasma samples after 5 days of therapy to evaluate PK intra-patient variability and its correlation with clinical course.

Patients received meropenem (1 g every 8 hrs IV). Drug plasma profiles were determined by high-performance liquid chromatography. The PK of meropenem was characterized and compared with clinical parameters.

Results

Fifteen septic critically ill patients (8 male, median age 73 yrs) were included. The geometric mean of the volume of distribution at the steady state (V_ss)/weight was 0.20 (0.15-0.27) L/kg. No correlation of V_ss/weight with severity or comorbidity scores was found. However the Sequential Organ Failure Assessment score correlated with the V_ss/weight of the peripheral compartment (r² = 0.55, p = 0.021). The median meropenem clearance (Cl) was 73.3 (45–120) mL/min correlated with the creatinine (Cr) Cl (r² = 0.35, p = 0.033).

After 5 days (N = 7) although V_ss remained stable, a decrease in the proportion of the peripheral compartment (V_ss2) was found, from 61.3 (42.5-88.5)% to 51.7 (36.6-73.1)%. No drug accumulation was noted.

Conclusions

In this cohort of septic, unselected, critically ill patients, large meropenem PK heterogeneity was noted, although neither underdosing nor accumulation was found. However, Cr Cl correlated to meropenem Cl and the V_ss2 decreased with patient’s improvement.