Pharmacokinetics of imipenem-cilastatin in critically ill patients undergoing continuous venovenous hemofiltration

Antibiotic dosing recommendations in critically ill patients receiving new innovative kidney replacement therapy

BACKGROUND

The Tablo Hemodialysis System is a new innovative kidney replacement therapy (KRT) providing a range of options for critically ill patients with acute kidney injury. The use of various effluent rate and treatment durations/frequencies may clear antibiotics differently than traditional KRT. This Monte Carlo Simulation (MCS) study was to develop antibiotic doses likely to attain therapeutic targets for various KRT combinations.

METHODS

Published body weights and pharmacokinetic parameter estimates were used to predict drug exposure for cefepime, ceftazidime, imipenem, meropenem and piperacillin/tazobactam in virtual critically ill patients receiving five KRT regimens. Standard free β-lactam plasma concentration time above minimum inhibitory concentration targets (40-60%fT> MIC and 40-60%fT> MICx4) were used as efficacy targets. MCS assessed the probability of target attainment (PTA) and likelihood of toxicity for various antibiotic dosing strategies. The smallest doses attaining PTA ≥ 90% during 1-week of therapy were considered optimal.

RESULTS

MCS determined β-lactam doses achieving ∼90% PTA in all KRT options. KRT characteristics influenced antibiotic dosing. Cefepime and piperacillin/tazobactam regimens designed for rigorous efficacy targets were likely to exceed toxicity thresholds.

CONCLUSION

The flexibility offered by new KRT systems can influence β-lactam antibiotic dosing, but doses can be devised to meet therapeutic targets. Further clinical validations are warranted.

Crosstalk between kidney and liver in non-alcoholic fatty liver disease: mechanisms and therapeutic approaches

Liver and kidney are vital organs that maintain homeostasis and injury to either of them triggers pathogenic pathways affecting the other. For example, non-alcoholic fatty liver disease (NAFLD) promotes the progression of chronic kidney disease (CKD), vice versa acute kidney injury (AKI) endorses the induction and progression of liver dysfunction. Progress in clinical and basic research suggest a role of excessive fructose intake, insulin resistance, inflammatory cytokines production, activation of the renin-angiotensin system, redox imbalance, and their impact on epigenetic regulation of gene expression in this context. Recent developments in experimental and clinical research have identified several biochemical and molecular pathways for AKI-liver interaction, including altered liver enzymes profile, metabolic acidosis, oxidative stress, activation of inflammatory and regulated cell death pathways. This review focuses on the current preclinical and clinical findings on kidney-liver crosstalk in NAFLD-CKD and AKI-liver dysfunction settings and highlights potential molecular mechanisms and therapeutic targets.

Pharmacokinetics, Pharmacodynamics, and Dose Optimization of Cefiderocol during Continuous Renal Replacement Therapy

BACKGROUND

The need for continuous renal replacement therapy (CRRT) in critically ill patients with serious infections is associated with clinical failure, emergence of resistance, and excess mortality. These poor outcomes are attributable in large part to subtherapeutic antimicrobial exposure and failure to achieve target pharmacokinetic/pharmacodynamic (PK/PD) thresholds during CRRT. Cefiderocol is a novel siderophore cephalosporin with broad in vitro activity against resistant pathogens and is often used to treat critically ill patients, including those receiving CRRT, despite the lack of data to guide dosing in this population.

OBJECTIVE

The aim of this study was to evaluate the PK and PD of cefiderocol during in vitro and in vivo CRRT and provide optimal dosing recommendations.

METHODS

The PK and dialytic clearance of cefiderocol was evaluated via an established in vitro CRRT model across various modes, filter types, and effluent flow rates. These data were combined with in vivo PK data from nine patients receiving cefiderocol while receiving CRRT from phase III clinical trials. Optimal dosing regimens and their respective probability of target attainment (PTA) were assessed via an established population PK model with Bayesian estimation and 1000-subject Monte Carlo simulations at each effluent flow rate.

RESULTS

The overall mean sieving/saturation coefficient during in vitro CRRT was 0.90 across all modes, filter types, effluent flow rates, and points of replacement fluid dilution tested. Adsorption was negligible at 10.9%. Three-way analysis of variance (ANOVA) and multiple linear regression analyses demonstrated that effluent flow rate is the primary driver of clearance during CRRT and can be used to calculate optimal cefiderocol doses required to match the systemic exposure observed in patients with normal renal function. Bayesian estimation of these effluent flow rate-based optimal doses in nine patients receiving CRRT from the phase III clinical trials of cefiderocol revealed comparable mean (± standard deviation) area under the concentration-time curve values as patients with normal renal function (1709 ± 539 mg·h/L vs. 1494 ± 58.4 mg·h/L; p = 0.26). Monte Carlo simulations confirmed these doses achieved >90% PTA against minimum inhibitory concentrations ≤4 mg/L at effluent flow rates from 0.5 to 5 L/h.

CONCLUSION

The optimal dosing regimens developed from this work have been incorporated into the prescribing information for cefiderocol, making it the first and only antimicrobial with labeled dosing for CRRT. Future clinical studies are warranted to confirm the efficacy and safety of these regimens.

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.

Imipenem dosing recommendations for patients undergoing continuous renal replacement therapy: systematic review and Monte Carlo simulations

Background

The appropriate dosing of imipenem for critically ill AKI patients undergoing CRRT remains scarce.

Purpose

This study aimed to (1) gather the available published pharmacokinetic studies conducted in septic patients receiving continuous renal replacement therapy (CRRT) and (2) to define the optimal imipenem dosing regimens in these populations via Monte Carlo simulations.

Methods

The databases of PubMed, Embase, and ScienceDirect were searched from inception to May 2020. We used the Medical Subject Headings of “Imipenem,” “CRRT,” and “pharmacokinetics” or related terms or synonym to identify the studies for systematic reviews. A one-compartment pharmacokinetic model was conducted to predict imipenem levels for the initial 48 h of therapy. The pharmacodynamic target was 40% of free drug level above 4 times of the MIC (40% fT > 4 MIC). The dose that achieved at least 90% of the probability of target attainment was defined as an optimal dose.

Results

Eleven articles were identified and included for our systematic review. The necessary pharmacokinetic parameters such as the volume of distribution and the CRRT clearance were mentioned in 100 and 90.9%, respectively. None of the current studies reported the complete necessary parameters. A regimen of 750 mg q 6 h was the optimal dose for the predilution-CVVH and CVVHD modality with two effluent rates (25 and 35 mL/kg/h) for the pharmacodynamic target of 40% fT > 4MIC.

Conclusions

None of the current studies showed the complete necessary pharmacokinetic parameters for drug dosing. Pharmacodynamic target significantly contributed to imipenem dosing regimens in these patients. Different effluent rates and types of CRRT had minimal impact on dosing regimens. Clinical validation of the recommendation is necessary.

Imipenem/Relebactam Ex Vivo Clearance during Continuous Renal Replacement Therapy

(1) Purpose of this study: determination of adsorption and transmembrane clearances (CL_TM) of imipenem and relebactam in ex vivo continuous hemofiltration (CH) and continuous hemodialysis (CHD) models. These clearances were incorporated into a Monte Carlo Simulation (MCS), to develop drug dosing recommendations for critically ill patients requiring continuous renal replacement therapy (CRRT); (2) Methods: A validated ex vivo bovine blood CH and CHD model using two hemodiafilters. Imipenem/relebactam and urea CL_TM at different ultrafiltrate/dialysate flow rates were evaluated in both CH and CHD. MCS was performed to determine dose recommendations for patients receiving CRRT; (3) Results: Neither imipenem nor relebactam adsorbed to the CRRT apparatus. The CL_TM of imipenem, relebactam, and urea approximated the effluent rates (ultrafiltrate/dialysate flow rates). The types of hemodiafilter and effluent rates did not influence CL_TM except in a dialysis flow rate of 1 L/h and 6 L/h in the CHD with relebactam (p < 0.05). Imipenem and relebactam 200 mg/100 mg every 6 h were sufficient to meet the standard time above the MIC pharmacodynamic targets in the modeled CRRT regimen of 25 kg/mL/h. (4) Conclusions: Imipenem and relebactam are not removed by adsorption to the CRRT apparatus, but readily cross the hemodiafilter membrane in CH and CHD. Dosage adjustment of imipenem/relebactam is likely required for critically ill patients receiving CRRT.

Drug dosing considerations in continuous renal replacement therapy

Acute kidney injury (AKI) is a common complication in critically ill patients, which is associated with increased in-hospital mortality. Delivering effective antibiotics to treat patients with sepsis receiving continuous renal replacement therapy (RRT) is complicated by variability in pharmacokinetics, dialysis delivery, lack of primary literature, and therapeutic drug monitoring. Pharmacokinetic alterations include changes in absorption, distribution, protein binding (PB), metabolism, and renal elimination. Drug absorption may be significantly changed due to alterations in gastric pH, perfusion, gastrointestinal motility, and intestinal atrophy. Volume of distribution for hydrophilic drugs may be increased due to volume overload. Estimation of renal clearance is challenged by the effective delivery of RRT. Drug characteristics such as PB, volume of distribution, and molecular weight impact removal of the drug by RRT. The totality of these alterations leads to reduced exposure. Despite our best knowledge, therapeutic drug monitoring of patients receiving continuous RRT demonstrates wide variability in antimicrobial concentrations, highlighting the need for expanded monitoring of all drugs. This review article will focus on changes in drug pharmacokinetics in AKI and dosing considerations to attain antibiotic pharmacodynamic targets in critically ill patients receiving continuous RRT.

Pharmacokinetics and dialytic clearance of apixaban during in vitro continuous renal replacement therapy

Background

To evaluate the transmembrane clearance (CL_TM) of apixaban during modeled in vitro continuous renal replacement therapy (CRRT), assess protein binding and circuit adsorption, and provide initial dosing recommendations.

Methods

Apixaban was added to the CRRT circuit and serial pre-filter bovine blood samples were collected along with post-filter blood and effluent samples. All experiments were performed in duplicate using continuous veno-venous hemofiltration (CVVH) and hemodialysis (CVVHD) modes, with varying filter types, flow rates, and point of CVVH replacement fluid dilution. Concentrations of apixaban and urea were quantified via liquid chromatography-tandem mass spectrometry. Plasma pharmacokinetic parameters for apixaban were estimated via noncompartmental analysis. CL_TM was calculated via the estimated area under the curve (AUC) and by the product of the sieving/saturation coefficient (SC/SA) and flow rate. Two and three-way analysis of variance (ANOVA) models were built to assess the effects of mode, filter type, flow rate, and point of dilution on CL_TM by each method. Optimal doses were suggested by matching the AUC observed in vitro to the systemic exposure demonstrated in Phase 2/3 studies of apixaban. Linear regression was utilized to provide dosing estimations for flow rates from 0.5–5 L/h.

Results

Mean adsorption to the HF1400 and M150 filters differed significantly at 38 and 13%, respectively, while mean (± standard deviation, SD) percent protein binding was 70.81 ± 0.01%. Effect of CVVH point of dilution did not differ across filter types, although CL_TM was consistently significantly higher during CRRT with the HF1400 filter compared to the M150. The three-way ANOVA demonstrated improved fit when CL_TM values calculated by AUC were used (adjusted R² 0.87 vs. 0.52), and therefore, these values were used to generate optimal dosing recommendations. Linear regression revealed significant effects of filter type and flow rate on CL_TM by AUC, suggesting doses of 2.5–7.5 mg twice daily (BID) may be needed for flow rates ranging from 0.5–5 L/h, respectively.

Conclusion

For CRRT flow rates most commonly employed in clinical practice, the standard labeled 5 mg BID dose of apixaban is predicted to achieve target systemic exposure thresholds. The safety and efficacy of these proposed dosing regimens warrants further investigation in clinical studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02248-7.

[Pharmacokinetic modifications and pharmacokinetic/pharmacodynamic optimization of beta-lactams in ICU]

Pharmacokinetic modifications in critically ill patients and those induced by ICU therapeutics raise a lot of issues about antibiotic dose adaptation. Beta-lactams are anti-infectious widely used in ICU. Frequent beta-lactam underdoses induce a risk of therapeutic failure potentially lethal and of emergence of bacterial resistance. Overdoses expose to a neurotoxic and nephrotoxic risk. Therefore, an understanding of pharmacokinetics modifications appears to be essential. A global pharmacokinetic/pharmacodynamic approach is required, including use of prolonged or continued beta-lactam infusions to optimise probability of pharmacokinetic/pharmacodynamic target attainment. Beta-lactam therapeutic drug monitoring should also be considered. Experts agree to target a free plasma betalactam concentration above four times the MIC of the causative bacteria for 100 % of the dosing interval. Bayesian methods could permit individualized doses adaptations.

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.

Drug Dosing Considerations in Critically Ill Patients Receiving Continuous Renal Replacement Therapy

Acute kidney injury is very common in critically ill patients requiring renal replacement therapy. Despite the advancement in medicine, the mortality rate from septic shock can be as high as 60%. This manuscript describes drug-dosing considerations and challenges for clinicians. For instance, drugs’ pharmacokinetic changes (e.g., decreased protein binding and increased volume of distribution) and drug property changes in critical illness affecting solute or drug clearance during renal replacement therapy. Moreover, different types of renal replacement therapy (intermittent hemodialysis, prolonged intermittent renal replacement therapy or sustained low-efficiency dialysis, and continuous renal replacement therapy) are discussed to describe how to optimize the drug administration strategies. With updated literature, pharmacodynamic targets and empirical dosing recommendations for commonly used antibiotics in critically ill patients receiving continuous renal replacement therapy are outlined. It is vital to utilize local epidemiology and resistance patterns to select appropriate antibiotics to optimize clinical outcomes. Therapeutic drug monitoring should be used, when possible. This review should be used as a guide to develop a patient-specific antibiotic therapy plan.

Population Pharmacokinetics and Dosing Optimization of Imipenem in Children with Hematological Malignancies

Imipenem is widely used for the treatment of children with serious infections. Currently, studies on the pharmacokinetics of imipenem in children with hematological malignancies are lacking. Given the significant impact of disease on pharmacokinetics and increased resistance, we aimed to conduct a population pharmacokinetic study of imipenem and optimize the dosage regimens for this vulnerable population. After children were treated with imipenem-cilastatin (IMP-CS), blood samples were collected from the children and the concentrations of imipenem were quantified using high-performance liquid chromatography with UV detection. Then, a population-level pharmacokinetic analysis was conducted using NONMEM software. Data were collected from 56 children (age range, 2.03 to 11.82 years) with hematological malignancies to conduct a population pharmacokinetic analysis. In this study, a two-compartment model that followed first-order elimination was found to be the most suitable. The parameters of current weight, age, and creatinine elimination rate were significant covariates that influenced imipenem pharmacokinetics. As a result, 41.4%, 56.1%, and 67.1% of the children reached the pharmacodynamic target (the percentage of the time during the total dosing interval that the free drug concentration remains above the MIC of 70%) against sensitive pathogens with an MIC of 0.5 mg/liter with imipenem at 15, 20, and 25 mg/kg of body weight every 6 h (q6h), respectively. However, only 11.1% of the children achieved the pharmacodynamic target against Pseudomonas aeruginosa isolates with an MIC of 2 mg/liter at a dose of 25 mg/kg q6h. The population pharmacokinetics of imipenem were assessed in children. The current dosage regimens of imipenem result in underdosing against resistant pathogens, including Pseudomonas aeruginosa and Acinetobacter baumannii However, for sensitive pathogens, imipenem has an acceptable pharmacodynamic target rate at a dosage of 25 mg/kg q6h. (The study discussed in this paper has been registered at ClinicalTrials.gov under identifier NCT03113344.).

Population pharmacokinetics and simulations of imipenem in critically ill patients undergoing continuous renal replacement therapy

Various dose regimens of imipenem have been prescribed in critically ill patients undergoing continuous renal replacement therapy (CRRT) but there are limited information on its pharmacokinetics (PK) and treatment efficacy. The aim of this study was to describe the population PK of imipenem in patients receiving CRRT, and utilize this model to inform optimal dosing regimens using pharmacokinetics/pharmacodynamics (PK/PD) target as a surrogate marker for treatment efficacy. Population PK modelling was undertaken in 20 patients receiving CRRT to characterize variabilities and identify influential covariates. Monte Carlo simulations were performed to evaluate differences in probability of target attainment (PTA) between empirically used dosing regimens (0.5 g q6h, 1 g q8h, and 1 g q6h), and to explore the impact of CRRT intensity and identified covariates on target attainment. Imipenem concentration data were adequately described using a one-compartment model. Residual diuresis and burn injury were identified modifiers for imipenem endogenous clearance. The simulations showed that the impact of CRRT intensity on target attainment is clinically irrelevant, whereas urine output and burn injury influence PTA for pathogens with an MIC ≥ 4 mg/L. At an MIC ≤ 2 mg/L, satisfactory PTAs (>80%) were achieved for all three investigated dose regimens regardless of urine output, burn injury, and CRRT intensity. Our results indicate that from a safety perspective, 0.5 g q6h imipenem is optimal in these patients for pathogens with an MIC ≤ 2 mg/L, and 1 g q6h is recommended for non-burn patients with anuria against MIC 4-16 mg/L.

Pharmacokinetics of Imipenem/Cilastatin Burn Intensive Care Unit Patients Undergoing High-Dose Continuous Venovenous Hemofiltration

STUDY OBJECTIVE

High-dose continuous venovenous hemofiltration (CVVH) is a continuous renal replacement therapy (CRRT) used frequently in patients with burns. However, antibiotic dosing is based on inference from studies assessing substantially different methods of CRRT. To address this knowledge gap for imipenem/cilastatin (I/C), we evaluated the systemic and extracorporeal clearances (CLs) of I/C in patients with burns undergoing high-dose CVVH.

DESIGN

Prospective clinical pharmacokinetic study.

PATIENTS

Ten adult patients with burns receiving I/C for a documented infection and requiring high-dose CVVH were studied.

METHODS

Blood and effluent samples for analysis of I/C concentrations were collected for up to 6 hours after the I/C infusion for calculation of I/C total CL (CL_Total ), CL by CVVH (CL_HF ), half-life during CVVH, volume of distribution at steady state (Vd_ss ), and the percentage of drug eliminated by CVVH.

RESULTS

In this patient sample, the mean age was 50 ± 17 years, total body surface area burns was 23 ± 27%, and 80% were male. Nine patients were treated with high-dose CVVH for acute kidney injury and one patient for sepsis. The mean delivered CVVH dose was 52 ± 14 ml/kg/hour (range 32-74 ml/kg/hr). The imipenem CL_HF was 3.27 ± 0.48 L/hour, which accounted for 23 ± 4% of the CL_Total (14.74 ± 4.75 L/hr). Cilastatin CL_HF was 1.98 ± 0.56 L/hour, which accounted for 45 ± 19% of the CL_Total (5.16 + 2.44 L/hr). The imipenem and cilastatin half-lives were 1.77 ± 0.38 hours and 4.21 ± 2.31 hours, respectively. Imipenem and cilastatin Vd_ss were 35.1 ± 10.3 and 32.8 ± 13.8 L, respectively.

CONCLUSION

Efficient removal of I/C by high-dose CVVH, a high overall clearance, and a high volume of distribution in burn intensive care unit patients undergoing this CRRT method warrant aggressive dosing to treat serious infections effectively depending on the infection site and/or pathogen.

The Effects of Continuous Renal Replacement on Anti-infective Therapy in the Critically Ill

Acute renal failure represents a frequent, severe complication in critically ill patients leading to a direct increase in mortality and resource utilization. Today, continuous renal replacement therapy (CRRT) has replaced traditional hemodialysis, providing more precise fluid and metabolic control and decreased hemodynamic instability. There are a limited number of studies conducted for the ideal dosing of individual anti-infective agents for patients receiving CRRT. However, knowledge of the basic principles of CRRT, in conjunction with pharmacokinetics and pharmacodynamics of anti-infectives, allows sound dosing recommendations to be formulated to ensure maximal killing effects with minimal risk of toxicity in patients receiving CRRT.

Clinical Validation of Therapeutic Drug Monitoring of Imipenem in Spent Effluent in Critically Ill Patients Receiving Continuous Renal Replacement Therapy: A Pilot Study

Objectives

The primary objective of this pilot study was to investigate whether the therapeutic drug monitoring of imipenem could be performed with spent effluent instead of blood sampling collected from critically ill patients under continuous renal replacement therapy.

Methods

A prospective open-label study was conducted in a real clinical setting. Both blood and effluent samples were collected pairwise before imipenem administration and 0.5, 1, 1.5, 2, 3, 4, 6, and 8 h after imipenem administration. Plasma and effluent imipenem concentrations were determined by reversed-phase high-performance liquid chromatography with ultraviolet detection. Pharmacokinetic and pharmacodynamic parameters of blood and effluent samples were calculated.

Results

Eighty-three paired plasma and effluent samples were obtained from 10 patients. The Pearson correlation coefficient of the imipenem concentrations in plasma and effluent was 0.950 (P<0.0001). The average plasma-to-effluent imipenem concentration ratio was 1.044 (95% confidence interval, 0.975 to 1.114) with Bland-Altman analysis. No statistically significant difference was found in the pharmacokinetic and pharmacodynamic parameters tested in paired plasma and effluent samples with Wilcoxon test.

Conclusion

Spent effluent of continuous renal replacement therapy could be used for therapeutic drug monitoring of imipenem instead of blood sampling in critically ill patients.

How can we ensure effective antibiotic dosing in critically ill patients receiving different types of renal replacement therapy?

Determining appropriate antibiotic dosing for critically ill patients receiving renal replacement therapy (RRT) is complex. Worldwide unstandardized and heterogeneous prescribing of RRT as well as altered patient physiology and pathogen susceptibility all cause drug disposition to be much different to that seen in non-critically ill patients. Significant changes to pharmacokinetic parameters, including volume of distribution and clearance, could be expected, in particular, for antibiotics that are hydrophilic with low plasma protein binding and that are usually primarily eliminated by the renal system. Antibiotic clearance is likely to be significantly increased when higher RRT intensities are used. The combined effect of these factors that alter antibiotic disposition is that non-standard dosing strategies should be considered to achieve therapeutic exposure. In particular, an aggressive early approach to dosing should be considered and this may include administration of a 'loading dose', to rapidly achieve therapeutic concentrations and maximally reduce the inoculum of the pathogen. This approach is particularly important given the pharmacokinetic changes in the critically ill as well as the increased likelihood of less susceptible pathogens. Dose individualization that applies knowledge of the RRT and patient factors causing altered pharmacokinetics remains the key approach for ensuring effective antibiotic therapy for these patients. Where possible, therapeutic drug monitoring should also be used to ensure more accurate therapy. A lack of pharmacokinetic data for antibiotics during the prolonged intermittent RRT and intermittent hemodialysis currently limits evidence-based antibiotic dose recommendations for these patients.

Antibiotic Dosing in Patients With Acute Kidney Injury: "Enough But Not Too Much"

Increasing evidence suggests that antibiotic dosing in critically ill patients with acute kidney injury (AKI) often does not achieve pharmacodynamic goals, and the continued high mortality rate due to infectious causes appears to confirm these findings. Although there are compelling reasons why clinicians should use more aggressive antibiotic dosing, particularly in patients receiving aggressive renal replacement therapies, concerns for toxicity associated with higher doses are real. The presence of multisystem organ failure and polypharmacy predispose these patients to drug toxicity. This article examines the pharmacokinetic and pharmacodynamic consequences of critical illness, AKI, and renal replacement therapy and describes potential solutions to help clinicians give "enough but not too much" in these very complicated patients.

[Pharmacokinetic and pharmacodynamic aspects in antibiotic treatment]

Severe sepsis and septic shock have a high mortality and, therefore require fast and effective antibiotic treatment with low toxicity. Because of sepsis-induced pathophysiological changes, pharmacokinetics of antimicrobial agents can be altered. Particularly water-soluble drugs display an enhanced volume of distribution during early sepsis. Therefore high loading doses are necessary. Renal clearance can also be increased at this time. Later on, organ damage frequently occurs resulting in delayed drug elimination which requires further dose adjustment. The different classes of antibiotics differ in their relevant pharmacokinetic-pharmacodynamic target parameters. Thus, the efficacy of an antimicrobial agent can depend on its concentration, on the exposure time, and on the total exposure as expressed by the area under the time-concentration curve. During treatment with time-dependent antibiotics (e.g. β-lactams), their concentration should be maintained above the minimal inhibitory concentration (MIC) warranting more frequent administration or continuous infusion. For concentration dependent agents (e.g. aminoglycosides), the single dose is pivotal, whereas the dosage interval can be extended. Drug-drug interactions involving antibiotics are mainly caused by inhibition of their metabolism, particularly of cytochrome P 450 iso-enzymes, or by additive toxic effects. They can result in severe complications such as renal failure or ventricular arrhythmias. Conversely, enzyme induction may lead to subtherapeutic drug levels. When continuous renal replacement therapy is required, the dosage of antibiotics has to be adapted according to the results of respective pharmacokinetic studies.

[Dosage of antipseudomonal antibiotics in patients with acute kidney injury subjected to continuous renal replacement therapies]

Critically ill patients are often affected by infections produced by Pseudomonas, which can be a cause of sepsis and renal failure. Early and adequate antibiotic treatment at correct dosage levels is crucial. Acute kidney injury is also frequent in critically ill patients. In those patients who require renal replacement therapy, continuous techniques are gaining relevance as filtering alternatives to intermittent hemodialysis. It must be taken into account that many antibiotics are largely cleared by continuous renal replacement therapies (CRRT). The aim of this review is to assess the clinical evidence on the pharmacokinetics and dosage recommendations of the main antibiotic groups used to treat Pseudomonas spp. infections in critically ill patients subjected to CRRT.

Clinical review: Drug metabolism and nonrenal clearance in acute kidney injury

Decreased renal drug clearance is an obvious consequence of acute kidney injury (AKI). However, there is growing evidence to suggest that nonrenal drug clearance is also affected. Data derived from human and animal studies suggest that hepatic drug metabolism and transporter function are components of nonrenal clearance affected by AKI. Acute kidney injury may also impair the clearance of formed metabolites. The fact that AKI does not solely influence kidney function may have important implications for drug dosing, not only of renally eliminated drugs but also of those that are hepatically cleared. A review of the literature addressing the topic of drug metabolism and clearance alterations in AKI reveals that changes in nonrenal clearance are highly complicated and poorly studied, but they may be quite common. At present, our understanding of how AKI affects drug metabolism and nonrenal clearance is limited. However, based on the available evidence, clinicians should be cognizant that even hepatically eliminated drugs and formed drug metabolites may accumulate during AKI, and renal replacement therapy may affect nonrenal clearance as well as drug metabolite clearance.

Population pharmacokinetics and pharmacodynamics of continuous versus short-term infusion of imipenem-cilastatin in critically ill patients in a randomized, controlled trial

Beta-lactams are regularly administered in intermittent short-term infusions. The percentage of the dosing interval during which free drug concentrations exceed the MIC (fT(>MIC)) is the measure of drug exposure that best correlates with clinical outcome for beta-lactams. Therefore, administration by continuous infusion has gained increasing interest recently. We studied 20 critically ill patients with nosocomial pneumonia and investigated whether continuous infusion with a reduced total dose, compared to the standard regimen of intermittent short-term infusion, results in a superior probability of target attainment as assessed by the fT(>MIC) value of imipenem. In this prospective, randomized, controlled clinical study, patients received either a loading dose of 1 g/1 g imipenem and cilastatin (as a short-term infusion) at time zero, followed by 2 g/2 g imipenem-cilastatin per 24 h as a continuous infusion for 3 days (n = 10), or 1 g/1 g imipenem-cilastatin three times per day as a short-term infusion for 3 days (total daily dose, 3 g/3 g; n = 10). Imipenem concentrations in plasma were determined by using a validated liquid chromatography-tandem mass spectrometry assay. A two-compartment open model was employed for population pharmacokinetic modeling. We simulated 10,000 intensive-care-unit patients via Monte Carlo simulations for pharmacodynamic evaluation using the target 40% fT(>MIC). The probability of target attainment by MIC for intermittent infusion was robust (>90%) up to MICs of 1 to 2 mg/liter. The corresponding value for continuous infusion was 2 to 4 mg/liter. Although all 20 patients had an fT(>MIC) of 100%, 3 patients died. Patient survival was best described by employing a sepsis-related organ failure assessment score as a covariate in a logistic regression analysis. Larger clinical trials are warranted for evaluation of continuous infusions at a reduced dose of imipenem for critically ill patients.

Using imipenem and cilastatin during continuous renal replacement therapy

AIM

To identify and review studies which have sought to define the pharmacokinetics of imipenem and cilastatin in patients receiving continuous renal replacement therapy (CRRT).

METHOD

Literature was primarily identified using Pharmline, Embase and Medline databases using the search terms "imipenem," "haemofiltration," "haemodialysis" and "pharmacokinetics." Papers that discussed only intermittent haemodialysis were excluded.

RESULTS

Seven papers were identified which described the pharmacokinetics of imipenem in patients receiving CRRT. Four different modes of CRRT were used. The methods of sampling, dosages used and assumptions made during pharmacokinetic calculations varied widely between the studies. Total body clearance of imipenem during CRRT in patients suffering from acute renal failure was found to range between 89 and 149 ml/min. Total body clearance of cilastatin ranged between 9 and 32 ml/min. Total body clearance of both imipenem and cilastatin was reduced in patients with chronic renal failure. Total body clearance of cilastatin was also reduced by impaired liver function. Dose recommendations made ranged between 500 mg 6-hourly and 500 mg 12-hourly.

CONCLUSIONS

The heterogeneity of the studies identified prevents them being analysed as a single group. For meaningful dosage recommendations to be made, further studies are required using larger populations and with more detail regarding liver dysfunction and duration of renal failure.

Pharmacokinetic changes in critical illness

Physiologic alterations in critically ill patients can significantly affect the pharmacokinetics of drugs used in the critically ill patient population. Understanding these pharmacokinetic changes is essential relative to optimizing drug therapy. This article outlines the major differences seen in the absorption, distribution, metabolism, and excretion of drugs in critically ill patients. Important strategies for drug therapy dosing and monitoring in these patients are also addressed.

Elimination of piperacillin and tazobactam by renal replacement therapies with AN69 and polysulfone hemofilters: evaluation of the sieving coefficient

BACKGROUND/AIM

Piperacillin-tazobactam is commonly used to treat infections in ICU patients. Controversial data have been published about the sieving/saturation coefficient (Sc/Sa) of piperacillin during continuous renal replacement therapies (CRRT). The objective was to evaluate the Sc/Sa of piperacillin-tazobactam during continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodialysis (CVVHD) using AN69 and polysulfone.

METHODS

Ringer lactate, BSA-containing Ringer lactate and plasma were circulated at 150 ml/min. The ultrafiltrate/dialysis flow was kept at 1,500 ml/min. A bolus was injected and samples were taken. Drugs were measured using HPLC. Sc/Sa was calculated according to standard formula.

RESULTS

Free passage of drugs through the membranes was reported with protein free solutions. In the presence of proteins the Sc/Sa lowered and correlated to protein free fraction. Polysulfone had a significantly higher permeability than AN69 during CVVH.

CONCLUSION

Drug binding to albumin contributes to the decrease of the Sc/Sa of piperacillin but it does not completely justify the in vivo value obtained by some authors.

Antibiotic Dosing in Critically Ill Adult Patients Receiving Continuous Renal Replacement Therapy

Continuous renal replacement therapy (CRRT) is now commonly used as a means of support for critically ill patients with renal failure. No recent comprehensive guidelines exist that provide antibiotic dosing recommendations for adult patients receiving CRRT. Doses used in intermittent hemodialysis cannot be directly applied to these patients, and antibiotic pharmacokinetics are different than those in patients with normal renal function. We reviewed the literature for studies involving the following antibiotics frequently used to treat critically ill adult patients receiving CRRT: vancomycin, linezolid, daptomycin, meropenem, imipenem-cilastatin, nafcillin, ampicillin-sulbactam, piperacillin-tazobactam, ticarcillin-clavulanic acid, cefazolin, cefotaxime, ceftriaxone, ceftazidime, cefepime, aztreonam, ciprofloxacin, levofloxacin, moxifloxacin, clindamycin, colistin, amikacin, gentamicin, tobramycin, fluconazole, itraconazole, voriconazole, amphotericin B (deoxycholate and lipid formulations), and acyclovir. We used these data, as well as clinical experience, to make recommendations for antibiotic dosing in critically ill patients receiving CRRT.

Pharmacokinetics and pharmacodynamics of imipenem during continuous renal replacement therapy in critically ill patients

The pharmacokinetics of imipenem were studied in adult intensive care unit (ICU) patients during continuous venovenous hemofiltration (CVVH; n=6 patients) or hemodiafiltration (CVVHDF; n=6 patients). Patients (mean+/-standard deviation age, 50.9+/-15.9 years; weight, 98.5+/-15.9 kg) received imipenem at 0.5 g every 8 to 12 h (total daily doses of 1 to 1.5 g/day) by intravenous infusion over 30 min. Pre- and postmembrane blood (plasma) and corresponding ultrafiltrate or dialysate samples were collected 1, 2, 4, and 8 or 12 h (depending on dosing interval) after completion of the drug infusion. Drug concentrations were measured using validated high-performance liquid chromatography methods. Mean systemic clearance (CL(S)) and elimination half-life (t1/2) of imipenem were 145+/-18 ml/min and 2.7+/-1.3 h during CVVH versus 178+/-18 ml/min and 2.6+/-1.6 h during CVVHDF, respectively. Imipenem clearance was substantially increased during both CVVH and CVVHDF, with membrane clearance representing 25% and 32% of CL(S), respectively. The results of this study indicate that CVVH and CVVHDF contribute to imipenem clearance to a greater degree than previously reported. Imipenem doses of 1.0 g/day appear to achieve concentrations adequate to treat most common gram-negative pathogens (MIC up to 2 microg/ml) during CVVH or CVVHDF, but doses of 2.0 g/day or more may be required to adequately treat and prevent resistance in pathogens with higher MICs (MIC=4 to 8 microg/ml). Higher doses should only be used after consideration of potential central nervous system toxicities or other risks of therapy in these severely ill patients.

Drug dosing during intermittent hemodialysis and continuous renal replacement therapy : special considerations in pediatric patients

Chronic renal failure is, fortunately, an unusual occurrence in children; however, many children with various underlying illnesses develop acute renal failure, and transiently require renal replacement therapy - peritoneal dialysis, intermittent hemodialysis (IHD), or continuous renal replacement therapy (CRRT). As children with acute and chronic renal failure often have multiple comorbid conditions requiring drug therapy, generalists, intensivists, nephrologists, and pharmacists need to be aware of the issues surrounding the management of drug therapy in pediatric patients undergoing renal replacement therapy. This article summarizes the pharmacokinetics and dosing of many drugs commonly prescribed for pediatric patients, and focuses on the management of drug therapy in pediatric patients undergoing IHD and CRRT in the intensive care unit setting. Peritoneal dialysis is not considered in this review. Finally, a summary table with recommended initial dosages for drugs commonly encountered in pediatric patients requiring IHD or CRRT is presented.

Pharmacokinetics and dosage adaptation of meropenem during continuous venovenous hemodiafiltration in critically ill patients

Meropenem, a carbapenem broad-spectrum antibiotic, is regularly used in patients undergoing continuous venovenous hemodiafiltration (CVVHDF). Its disposition was studied over one dosage interval in 15 patients under CVVHDF on a steady regimen of 500 or 1000 mg every 8 to 12 hours. Meropenem levels were measured in plasma and filtrate-dialysate by high-performance liquid chromatography (HPLC) with UV detection. The mean CVVHDF flow rates were 7.1 +/- 0.9 L/h for blood (mean +/- SD), 0.5 +/- 0.3 L/h for predilution solution, 1.2 +/- 0.3 L/h for countercurrent dialysate, and 1.8 +/- 0.5 L/h for the total filtrate-dialysate. The pharmacokinetic analysis was based both on a noncompartmental approach and on a four-compartment modeling. The mean (coefficient of variation [CV]) total body clearance, volume of distribution at steady state, and mean residence time were, respectively, 5.0 L/h (46%), 14.3 L (29%), and 4.8 h (36%). The hemodiafiltration clearances calculated from plasma data alone and plasma with filtrate-dialysate data were 1.2 L/h (26%) and 1.6 L/h (39%), respectively. The compartmental model was used to optimize the therapeutic schedule of meropenem, considering reference minimal inhibitory concentration (MIC) of sensitive strains (4 mg/L). The results indicate that two different therapeutic schedules of meropenem are equally applicable to patients receiving CVVHD: either 750 mg tid or 1500 bid.

Higher renal replacement therapy dose delivery influences on drug therapy

Higher doses of renal replacement therapy have profound effects on pharmacotherapy, yet little research has been conducted in this area. High-volume renal replacement therapies influence both the pharmacokinetic and the pharmacodynamic profiles of all drugs administered to these critically ill patients. Intermittent high-dose "hybrid" hemodialysis therapies remove drugs to a much different degree than standard thrice-weekly hemodialysis, yet pharmacokinetic studies have not been performed in patients receiving these therapies. High-volume continuous renal replacement therapies offer dosing challenges not seen with standard low-dose therapies. This article describes the pharmacokinetic and pharmacodynamic issues presented by high-volume renal replacement therapies. Given the importance that pharmacotherapy has on optimal patient outcomes, a better understanding of the influence that high-volume renal replacement therapy has on drugs is essential if these high volume therapies are to be used successfully in the intensive care unit.

Optimizing antimicrobial dosing in the critically ill patient

"We know everything about antibiotics except how much to give," Maxwell Finland once stated. Finally, with the proliferation of pharmacodynamics as a science, we are addressing the question of how much to give. We have moved from an era of more or less arbitrary antimicrobial dosage selection toward one characterized by evidence-based optimal dosing strategies. Optimizing antimicrobial therapy in critically ill patients is more than just the selection of a suitable dose for a particular patient. Optimizing therapy also involves the selection of an appropriate single or combination antibiotic regimen that is active against the suspected or documented pathogens at the site(s) of infection. The regimen should offer the fewest potential adverse events, and the duration of therapy should be the shortest possible so as not to encourage resistance. Dosing of the chosen regimen should reflect variables that are often ignored, such as the patient's weight and age. The new continuous renal replacement therapies are commonly used in the critical care unit and must be considered. Finally, the cost of the regimen should be considered, but not only the cost to purchase the chosen antimicrobial agent but the cost to administer it (, the cost of minibags or syringes, intravenous tubing, saline flushes [all multiplied by the number of times per day the drug is given]), and, most importantly, if the patient fails to respond to therapy, the cost necessary to re-treat the patient to bring about a cure. In this review, we discuss some of the principles required to optimize antimicrobial dosing and recently obtained data regarding its application to the critically ill patient.

Pharmacokinetics and dosing regimen of meropenem in critically ill patients receiving continuous venovenous hemofiltration

OBJECTIVE

To study the pharmacokinetics of meropenem in critically ill patients with acute renal failure receiving continuous venovenous hemofiltration (CWHF).

DESIGN

Prospective, open-labeled study.

SETTING

Medical intensive care unit of the University Medical Center Utrecht.

PATIENTS

Five critically ill patients receiving CWHF for acute renal failure treated with meropenem for documented or suspected bacterial infection.

INTERVENTION

All patients received meropenem (500 mg) administered intravenously every 12 hrs. Plasma samples and ultrafiltrate aliquots were collected during one dosing interval.

MEASUREMENTS AND RESULTS

Mean age and body weight of the patients studied were 46.6 yrs (range, 28-61 yrs) and 85.8 kg (range, 70-100 kg), respectively. The following pharmacokinetic variables for meropenem were obtained: mean peak plasma concentration was 24.5 +/- 7.2 mg/L, mean trough plasma concentration was 3.0 +/- 0.9 mg/L, mean terminal elimination half-life was 6.37 +/- 1.96 hrs, mean total plasma clearance was 4.57 +/- 0.89 L/hr, mean CWHF clearance was 1.03 +/- 0.42 L/hr, mean nonrenal clearance was 3.54 +/- 1.06 L/hr, and mean volume of distribution was 0.37 +/- 0.15 L/kg.

CONCLUSION

In critically ill patients with acute renal failure, nonrenal clearance became the main elimination route. CWHF substantially contributed to the clearance of meropenem (23% of mean total plasma clearance). We recommend meropenem to be dosed at 500 mg intravenously every 12 hrs in patients receiving CWHF, according to our operational characteristics. This dosing regimen resulted in adequate trough plasma levels for susceptible microorganisms.

Comparative pharmacokinetics of the carbapenems: clinical implications

During the last few decades, several carbapenems have been developed. The major characteristic of the newer drugs, such as MK-826, is a prolonged half-life. Alternatively, some carbapenems have been developed that can be given orally, such as CS-834 and L-084. Although imipenem and panipenem have to be administered with a co-drug to prevent degradation by the enzyme dehydropeptidase-1 and reduce nephrotoxicity, the newer drugs such as meropenem, biapenem and lenapenem are relatively stable towards that enzyme. Structural modifications have, besides changes in pharmacology, also led to varying antimicrobial properties. For instance, meropenem is relatively more active against Gram-negative organisms than most other carbapenems, but is slightly less active against Gram-positive organisms. Except for half-life and bioavailability, the pharmacokinetic properties of the carbapenems are relatively similar. Distribution is mainly in extracellular body-water, as observed both from the volumes of distribution and from blister studies. Some carbapenems have a better penetration in cerebrospinal fluid than others. In patients with renal dysfunction, doses have to be adjusted, and special care must be taken with imipenem/cilastatin and panipenem/betamipron to prevent accumulation of the co-drugs, as the pharmacokinetic properties of the co-drugs differ from those of the drugs themselves. However, toxicity of the co-drugs has not been shown. The carbapenems differ in proconvulsive activity. Imipenem shows relatively the highest proconvulsive activity, especially at higher concentrations. Pharmacodynamic studies have shown that the major surrogate parameter for antimicrobial efficacy is the percentage of time of the dosage interval above the minimum inhibitory concentration (MIC). The minimum percentage percentage of time above the MIC (TaM) needed for optimal effect is known in animals (30 to 50%), but not in humans. It is probably less than 100%, but may be higher than 50%. Dosage regimens currently in use result in a TaM of about 50% at 4 mg/L, which is the current 'susceptible' breakpoint determined by the National Committee for Clinical Laboratory Standards (NCCLS) for most micro-organisms. Dosage regimens in patients with reduced renal clearance should be based on the TaM. The increased half-life of the newer carbapenems will probably lead to less frequent administration, although continuous infusion may still be the optimal mode of administration for these drugs. The availability of oral carbapenems will have a profound effect on the use of carbapenems in the community.

Pharmacokinetics of meropenem in critically ill patients with acute renal failure undergoing continuous venovenous hemofiltration

OBJECTIVE

Meropenem is a broad-spectrum antibiotic used for severe infections. In patients with chronic end-stage renal failure, meropenem clearance is reduced and doses must be adjusted according to the creatinine clearance. The aim of this study was to assess pharmacokinetic data of meropenem in patients with acute renal failure and to determine the amount of drug removed by continuous venovenous hemofiltration, an often-used renal replacement therapy in patients with acute renal failure.

METHODS

Nine critically ill anuric patients with acute renal failure undergoing continuous venovenous hemofiltration received 500 mg meropenem 2 or 3 times daily. Plasma and hemofiltrate concentrations were determined during 1 dosing interval at steady state. Pharmacokinetic parameters were calculated for a 2-compartment open model and dose requirements were calculated.

RESULTS

The total meropenem clearance was 52.0 +/- 8.4 mL/min, with a hemofiltration clearance of 22.0 +/- 4.7 mL/min and a nonrenal-nonhemofiltration clearance of 29.9 +/- 5.4 mL/min; 235.9 +/- 88.6 mg, or 47.2% +/- 17.7%, of the dose were removed through continuous venovenous hemofiltration. The terminal elimination half-life was 8.7 +/- 3.5 hours and the volume of distribution at steady state was 12.4 +/- 1.8 L. Peak and trough concentrations for a dosing interval of 12 hours were 38.9 +/- 9.7 mg/L and 7.3 +/- 1.3 mg/L, respectively. The corresponding concentrations for a dosing interval of 8 hours were 44.7 +/- 10.4 mg/L and 11.9 +/- 0.7 mg/L, respectively.

CONCLUSION

Pharmacokinetic data of anuric patients with acute renal failure were similar to those of patients with end-stage renal failure. Because hemofiltration contributes significantly to meropenem elimination, the recommended dose for critically ill anuric patients receiving continuous venovenous hemofiltration should be increased by 100% to avoid potential underdosing.

Single-dose pharmacokinetics of meropenem during continuous venovenous hemofiltration

The pharmacokinetic properties of meropenem were investigated in nine critically ill patients treated by continuous venovenous hemofiltration (CVVH). All patients received one dose of 1 g of meropenem intravenously. High-flux polysulfone membranes were used as dialyzers. Meropenem levels were measured in plasma and ultrafiltrate by high-performance liquid chromatography. The total body clearance and elimination half-life were 143.7 +/- 18.6 ml/min and 2.46 +/- 0.41 h, respectively. The post- to prehemofiltration ratio of meropenem was 0.24 +/- 0.06. Peak plasma drug concentrations measured 60 min postinfusion were 28.1 +/- 2.7 microgram/ml, and trough levels after 6 h of CVVH were 6.6 +/- 1.5 microgram/ml. The calculated total daily meropenem requirement in these patients with acute renal failure and undergoing CVVH was 2,482 +/- 321 mg. Based on these data, we conclude that patients with severe infections who are undergoing CVVH can be treated effectively with 1 g of meropenem every 8 h.