Therapeutic drug monitoring (TDM) of β-lactam/β-lactamase inhibitor (BL/BLI) drug combinations: insights from a pharmacometric simulation study

BACKGROUND

The emergence of β-lactamase-producing bacteria has led to the use of β-lactam (BL) antibiotic and β-lactamase inhibitor (BLI) drug combinations. Despite therapeutic drug monitoring (TDM) being endorsed for BLs, the impact of TDM on BLIs remains unclear.

OBJECTIVES

Evaluate whether BLIs are available in effective exposures at the site of infection and assess if TDM of BLIs could be of interest.

METHODS

Population pharmacokinetic models for 9 BL and BLI compounds were used to simulate drug concentrations at infection sites following EMA-approved dose regimens, considering plasma protein binding and tissue penetration. Predicted target site concentrations were used for probability of target attainment (PTA) analysis.

RESULTS

Using EUCAST targets, satisfactory (≥90%) PTA was observed for BLs in patients with typical renal clearance (CrCL of 80 mL/min) across various sites of infection. However, results varied for BLIs. Avibactam achieved satisfactory PTA only in plasma, with reduced PTAs in abdomen (78%), lung (73%) and prostate (23%). Similarly, tazobactam resulted in unsatisfactory PTAs in intra-abdominal infections (79%), urinary tract infections (64%) and prostatitis (34%). Imipenem-relebactam and meropenem-vaborbactam achieved overall satisfactory PTAs, except in prostatitis and high-MIC infections for the latter combination.

CONCLUSIONS

This study highlights the risk of solely relying on TDM of BLs, as this can indicate acceptable exposures of the BL while the BLI concentration, and consequently the combination, can result in suboptimal performance in terms of bacterial killing. Thus, dose adjustments also based on plasma concentration measurements of BLIs, in particular for avibactam and tazobactam, can be valuable in clinical practice to obtain effective exposures at the target site.

Dosing strategies of imipenem in neonates based on pharmacometric modelling and simulation

OBJECTIVES

Imipenem is a broad-spectrum antibacterial agent used in critically ill neonates after failure of first-line treatments. Few studies have described imipenem disposition in this population. The objectives of our study were: (i) to characterize imipenem population pharmacokinetics (PK) in a cohort of neonates; and (ii) to conduct model-based simulations to evaluate the performance of six different dosing regimens aiming at optimizing PK target attainment.

METHODS

A total of 173 plasma samples from 82 neonates were collected over 15 years at the Lausanne University Hospital, Switzerland. The majority of study subjects were preterm neonates with a median gestational age (GA) of 27 weeks (range: 24-41), a postnatal age (PNA) of 21 days (2-153) and a body weight (BW) of 1.16 kg (0.5-4.1). PK data were analysed using non-linear mixed-effect modelling (NONMEM).

RESULTS

A one-compartment model best characterized imipenem disposition. Population PK parameters estimates of CL and volume of distribution were 0.21 L/h and 0.73 L, with an interpatient variability (CV%) of 20.1% on CL in a representative neonate (GA 27 weeks, PNA 21 days, BW 1.16 kg, serum creatinine, SCr 46.6 μmol/L). GA and PNA exhibited the greatest impact on PK parameters, followed by SCr. These covariates explained 36% and 15% of interindividual variability in CL, respectively.Simulated regimens using a dose of 20-25 mg/kg every 6-12 h according to postnatal age led to the highest PTA (T>MIC over 100% of time).

CONCLUSIONS

Dosing adjustment according to BW, GA and PNA optimizes imipenem exposure in neonates.

Pharmacokinetic and Pharmacodynamic Analysis of Critically Ill Patients Undergoing Continuous Renal Replacement Therapy With Imipenem

PURPOSE

This study explores factors that affect behavior in critically ill patients receiving continuous renal replacement therapy (CRRT) with imipenem and provides dosing regimens for these patients.

METHODS

A prospective, open-label study was conducted in a clinical setting. Both blood and effluent samples were collected pairwise at the scheduled time points. Plasma and effluent imipenem concentrations were determined by HPLC-UV. A population pharmacokinetic model was developed using a nonlinear mixed-effects modeling method. The final model was evaluated by a bootstrap and visual predictive check. A population pharmacokinetic and pharmacodynamic analysis using Monte Carlo simulations was performed to explore the effects of empirically used dosing regimens (0.5 g q6h, 0.5 g q8h, 0.5 g q12h, 1 g q6h, 1 g q8h, and 1 g q12h) on the probability of target attainment.

FINDINGS

Thirty patients were included in the population model analysis. Imipenem concentration data were best described by a 3-compartment model (central, peripheral, and dialysis compartments). The clearance of the dialysis compartment (CL_d) was used to characterize drug elimination from the dialyzer. Creatinine clearance (CrCl) was the covariate that influenced the central clearance (CLc), and the effects of dialysate flow (Qd) was significant for CLd. Model validation revealed that the final model had qualified stability and acceptable predictive properties. A pharmacokinetic and pharmacodynamic analysis was conducted by Monte Carlo simulation, and patients were categorized into 12 subgroups based on different CrCl values (<30, 31-60, 61-90, and >90 mL/min) and Qd values (300, 500, and 1000 mL/h). Under the same MIC value and administration regimen, probability of target attainment values decreased with an increase of CrCl and Qd.

IMPLICATIONS

CrCl and Qd had significant effects on CL_c and CL_d, respectively. The proposed final model may be used to guide practitioners in imipenem dosing in this specific patient population.

Novel Population Pharmacokinetic Approach to Explain the Differences between Cystic Fibrosis Patients and Healthy Volunteers via Protein Binding

The pharmacokinetics in patients with cystic fibrosis (CF) has long been thought to differ considerably from that in healthy volunteers. For highly protein bound β-lactams, profound pharmacokinetic differences were observed between comparatively morbid patients with CF and healthy volunteers. These differences could be explained by body weight and body composition for β-lactams with low protein binding. This study aimed to develop a novel population modeling approach to describe the pharmacokinetic differences between both subject groups by estimating protein binding. Eight patients with CF (lean body mass [LBM]: 39.8 ± 5.4kg) and six healthy volunteers (LBM: 53.1 ± 9.5kg) received 1027.5 mg cefotiam intravenously. Plasma concentrations and amounts in urine were simultaneously modelled. Unscaled total clearance and volume of distribution were 3% smaller in patients with CF compared to those in healthy volunteers. After allometric scaling by LBM to account for body size and composition, the remaining pharmacokinetic differences were explained by estimating the unbound fraction of cefotiam in plasma. The latter was fixed to 50% in male and estimated as 54.5% in female healthy volunteers as well as 56.3% in male and 74.4% in female patients with CF. This novel approach holds promise for characterizing the pharmacokinetics in special patient populations with altered protein binding.

Population pharmacokinetic-pharmacodynamic target attainment analysis of imipenem plasma and urine data in neonates and children

BACKGROUND

Population pharmacokinetic (PK)-pharmacodynamic target attainment analysis of imipenem was performed to elucidate the PK properties in neonates and children and to rationalize and optimize dosing regimens.

METHODS

Population PK models were separately developed in neonates and children by simultaneously fitting plasma and urine data from 60 neonates and 39 children. The newly developed models were then used to estimate the probability of attaining the pharmacodynamic target (40% of the time above the minimum inhibitory concentration) against clinical isolates of common bacteria in pediatric patients.

RESULTS

The data were best described by a 1-compartment model in neonates and a 2-compartment model in children, respectively. Renal clearance in children (0.187 L/h/kg) was double that of neonates (0.0783 L/h/kg), whereas the volume of distribution at steady-state was approximately 1.8-fold larger in neonates (0.466 L/kg) than in children (0.260 L/kg). Age was not a statistically significant covariate in the PK of both groups. Infusions (0.5 h) of 15 mg/kg every 8 h (45 mg/kg/day) and 25 mg/kg every 12 h (50 mg/kg/day) were shown to be sufficient against common bacterial isolates in both patient populations. However, 1.5-h infusions of 25 mg/kg every 8 h (75 mg/kg/day) in neonates and 25 mg/kg every 6 h (100 mg/kg/day) in children were required to be effective against Pseudomonas aeruginosa (minimum inhibitory concentration for 90% of the isolates=16 μg/mL).

CONCLUSIONS

These results explain the changes in imipenem PK properties during the human growth process and provide guidance for tailoring dosing regimens in each pediatric age group.

Homozygous carrier of the NOD2 1007fs frame-shift mutation presenting with refractory community-acquired spontaneous bacterial peritonitis and developing fatal pulmonary mucormycosis: A case report

Genetic variants of the innate immune system contribute to episodes of spontaneous bacterial peritonitis (SBP) in patients with cirrhosis. We herein report the case of a patient with the homozygous nucleotide-binding oligomerization domain containing 2 (NOD2) frame-shift mutation 1007fs presenting with sepsis and community-acquired SBP by Escherichia coli. Secondary peritonitis, pancreatic ascites and malignant causes were excluded by extensive diagnostic work-up. First-line treatment with ceftriaxone was not successful despite in vitro sensitivity of the isolated strain. Despite prolonged second-line treatment with imipenem/cilastatin and intermittent ascites drainage, the ascitic fluid neutrophil count remained markedly elevated in this patient. In the course of the disease the patient developed pneumonia with identification of the typical hyphae of mucormycosis in the bronchoalveolar lavage and died of sepsis with multi-organ failure. On the basis of this observation, variants of the innate immunity have to be considered in therapy-refractory SBP, even when they are community-acquired and caused by cephalosporin-sensitive Enterobacteriaceae.

[Personalized optimization of beta-lactam regimens based on studies of the pharmacokinetics-pharmacodynamics at the target sites]

Beta-lactam antibiotics are used for the treatment of various infections such as intra-abdominal infections and bacterial meningitis. Beta-lactams act at the infection site and their antibacterial effects relate to the exposure time during which the drug concentrations remain above the minimum inhibitory concentration for bacteria (T>MIC). The penetration into and exposure of beta-lactams at the target sites, such as the abdominal cavity and the cerebrospinal space, are therefore considered to be good indicators of their efficacies. However, earlier clinical research has focused primary on the drug concentrations in plasma. We therefore examined the pharmacokinetics-pharmacodynamics of beta-lactams at the target sites, and analyzed them using a population pharmacokinetic modeling and statistical technique called Monte Carlo simulation. This review summarizes our recent findings on carbapenem and cephem antibiotics in peritoneal and cerebrospinal fluids, and our new approaches to personalize and optimize beta-lactam dosing regimens based on their site-specific pharmacokinetic-pharmacodynamic profiles.

Development of breakpoints of carbapenems for intraabdominal infections based on pharmacokinetics and pharmacodynamics in peritoneal fluid

This study aimed to develop breakpoints of carbapenems for intraabdominal infections, based on pharmacokinetics (PK) and pharmacodynamics (PD) at the target site. Imipenem, meropenem, and doripenem were each administered to 8-11 patients before abdominal surgery, and venous blood and peritoneal fluid samples were obtained. The drug concentrations in plasma and peritoneal fluid were determined and analyzed using population pharmacokinetic modeling. Using the pharmacokinetic model parameters, a Monte Carlo simulation was performed to estimate the probabilities of attaining the bacteriostatic and bactericidal targets (20% and 40% of the time above the minimum inhibitory concentration [MIC], respectively) in peritoneal fluid. The bacteriostatic and bactericidal breakpoints were defined as the highest MIC values at which the bacteriostatic and bactericidal probabilities in peritoneal fluid were 80% or more. The breakpoints for the minimum and maximum approved dosages of each drug were identical for imipenem, meropenem, and doripenem, and some of these values varied with dosing interval and infusion time. Site-specific PK-PD-based breakpoints are proposed here for the first time, and should help us to select appropriate carbapenem regimens for intraabdominal infections.