Inoculum-Based Dosing: A Novel Concept for Combining Time with Concentration-Dependent Antibiotics to Optimize Clinical and Microbiological Outcomes in Severe Gram Negative Sepsis

Certain classes of antibiotics show "concentration dependent" antimicrobial activity; higher concentrations result in increased bacterial killing rates, in contrast to "time dependent antibiotics", which show antimicrobial activity that depends on the time that antibiotic concentrations remain above the MIC. Aminoglycosides and fluoroquinolones are still widely used concentration-dependent antibiotics. These antibiotics are not hydrolyzed by beta-lactamases and are less sensitive to the inoculum effect, which can be defined as an increased MIC for the antibiotic in the presence of a relatively higher bacterial load (inoculum). In addition, they possess a relatively long Post-Antibiotic Effect (PAE), which can be defined as the absence of bacterial growth when antibiotic concentrations fall below the MIC. These characteristics make them interesting complementary antibiotics in the management of Multi-Drug Resistant (MDR) bacteria and/or (neutropenic) patients with severe sepsis. Global surveillance studies have shown that up to 90% of MDR Gram-negative bacteria still remain susceptible to aminoglycosides, depending on the susceptibility breakpoint (e.g., CLSI or EUCAST) being applied. This percentage is notably lower for fluoroquinolones but depends on the region, type of organism, and mechanism of resistance involved. Daily (high-dose) dosing of aminoglycosides for less than one week has been associated with significantly less nephro/oto toxicity and improved target attainment. Furthermore, higher-than-conventional dosing of fluoroquinolones has been linked to improved clinical outcomes. Beta-lactam antibiotics are the recommended backbone of therapy for severe sepsis. Since these antibiotics are time-dependent, the addition of a second concentration-dependent antibiotic could serve to quickly lower the bacterial inoculum, create PAE, and reduce Penicillin-Binding Protein (PBP) expression. Inadequate antibiotic levels at the site of infection, especially in the presence of high inoculum infections, have been shown to be important risk factors for inadequate resistance suppression and therapeutic failure. Therefore, in the early phase of severe sepsis, effort should be made to optimize the dose and quickly lower the inoculum. In this article, the authors propose a novel concept of "Inoculum Based Dosing" in which the decision for antibiotic dosing regimens and/or combination therapy is not only based on the PK parameters of the patient, but also on the presumed inoculum size. Once the inoculum has been lowered, indirectly reflected by clinical improvement, treatment simplification should be considered to further treat the infection.

Recommendations of Gentamicin Dose Based on Different Pharmacokinetic/Pharmacodynamic Targets for Intensive Care Adult Patients: A Redefining Approach

Background

In addition to the maximum plasma concentration (C_max) to the minimum inhibitory concentration (MIC) ratio, the 24-hour area under the concentration-time curve (AUC_24h) to MIC has recently been suggested as pharmacokinetic/pharmacodynamic (PK/PD) targets for efficacy and safety in once-daily dosing of gentamicin (ODDG) in critically ill patients.

Purpose

This study aimed to predict the optimal effective dose and risk of nephrotoxicity for gentamicin in critically ill patients for two different PK/PD targets within the first 3 days of infection.

Methods

The gathered pharmacokinetic and demographic data in critically ill patients from 21 previously published studies were used to build a one-compartment pharmacokinetic model. The Monte Carlo Simulation (MCS) method was conducted with the use of gentamicin once-daily dosing ranging from 5-10 mg/kg. The percentage target attainment (PTA) for efficacy, C_max/MIC ~8-10 and AUC_24h/MIC ≥110 targets, were studied. The AUC_24h >700 mg⋅h/L and C_min >2 mg/L were used to predict the risk of nephrotoxicity.

Results

Gentamicin 7 mg/kg/day could achieve both efficacy targets for more than 90% when the MIC was <0.5 mg/L. When the MIC increased to 1 mg/L, gentamicin 8 mg/kg/day could reach the PK/PD and safety targets. However, for pathogens with MIC ≥2 mg/L, no studied gentamicin doses were sufficient to reach the efficacy target. The risk of nephrotoxicity using AUC_24h >700 mg⋅h/L was small, but the risk was greater when applying a C_min target >2 mg/L.

Conclusion

Considering both targets of Cmax/MIC ~8-10 and AUC_24h/MIC ≥110, an initial gentamicin dose of 8 mg/kg/day should be recommended in critically ill patients for pathogens with MIC of ≤1 mg/L. Clinical validation of our results is essential.

Aminoglycosides for the Treatment of Severe Infection Due to Resistant Gram-Negative Pathogens

Aminoglycosides are a family of rapidly bactericidal antibiotics that often remain active against resistant Gram-negative bacterial infections. Over the past decade, their use in critically ill patients has been refined; however, due to their renal and cochleovestibular toxicity, their indications in the treatment of sepsis and septic shock have been gradually reduced. This article reviews the spectrum of activity, mode of action, and methods for optimizing the efficacy of aminoglycosides. We discuss the current indications for aminoglycosides, with an emphasis on multidrug-resistant Gram-negative bacteria, such as extended-spectrum β-lactamase-producing Enterobacterales, carbapenemase-producing Enterobacterales, multidrug-resistant Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii. Additionally, we review the evidence for the use of nebulized aminoglycosides.

Development of a Predictive Dosing Nomogram to Achieve PK/PD Targets of Amikacin Initial Dose in Critically Ill Patients: A Non-Parametric Approach

French guidelines recommend reaching an amikacin concentration of ≥8 × MIC 1 h after beginning infusion (C_1h), with MIC = 8 mg/L for probabilistic therapy. We aimed to elaborate a nomogram guiding clinicians in choosing the right first amikacin dose for ICU patients in septic shock. A total of 138 patients with 407 observations were prospectively recruited. A population pharmacokinetic model was built using a non-parametric, non-linear mixed-effects approach. The total body weight (TBW) influenced the central compartment volume, and the glomerular filtration rate (according to the CKD-EPI formula) influenced its clearance. A dosing nomogram was produced using Monte Carlo simulations of the amikacin amount needed to achieve a C_1h ≥ 8 × MIC. The dosing nomogram recommended amikacin doses from 1700 mg to 4200 mg and from 28 mg/kg to 49 mg/kg depending on the patient's TBW and renal clearance. However, a C_through ≤ 2.5 mg/L 24 h and 48 h after an optimal dose of amikacin was obtained with probabilities of 0.20 and 0.81, respectively. Doses ≥ 30 mg/kg are required to achieve a C_1h ≥ 8 × MIC with MIC = 8 mg/L. Targeting a MIC = 8 mg/L should depend on local ecology.

Systematic review of high-dose amikacin regimens for the treatment of Gram-negative infections based on EUCAST dosing recommendations

BACKGROUND

Updated European Committee on Antimicrobial Susceptibility Testing (EUCAST) amikacin breakpoints for Enterobacterales and Pseudomonas aeruginosa included revised dosing recommendations of 25-30 mg/kg to achieve key pharmacokinetic/pharmacodynamic parameters, higher than recommended in the British National Formulary. The objectives of this review were to identify clinical evidence for high-dose amikacin regimens and to determine drug exposures that are related to adverse events and toxicity.

METHODS

The literature search was conducted in October 2021 and updated in May 2022 using electronic databases for any study reporting adult participants treated with amikacin at doses ≥20 mg/kg/day. Reference lists of included papers were also screened for potential papers. Data were extracted for pharmacokinetic parameters and clinical outcomes, presented in a summary table and consolidated narratively. Meta-analysis was not possible. Each study was assessed for bias before, during and after the intervention using the ROBINS-I tool.

RESULTS

Nine studies (total 501 participants in 10 reports) were identified and included, eight of which were observational studies. Assessment of bias showed substantial flaws. Dosing regimens ranged from 25 to 30 mg/kg/day. Six studies adjusted the dose in obesity when participants had a body mass index of ≥30 kg/m². Target peak serum concentrations ranged from 60 mg/L to 80 mg/L and 59.6-81.8% of patients achieved these targets, but there was no information on clinical outcomes. Two studies reported the impact of high-dose amikacin on renal function. No studies reporting auditory or vestibular toxicity were identified.

CONCLUSION

All included papers were limited by a significant risk of bias, while methodological and reporting heterogeneity made drawing conclusions challenging. Lack of information on the impact on renal function or ototoxicity means high-dose regimens should be used cautiously in older people. There is a need for a consensus guideline for high-dose amikacin to be written.

TRIAL REGISTRATION NUMBER

PROSPERO (CRD42021250022).

Clinical Pharmacokinetics of Gentamicin in Various Patient Populations and Consequences for Optimal Dosing for Gram-Negative Infections: An Updated Review

Gentamicin is an aminoglycoside antibiotic with a small therapeutic window that is currently used primarily as part of short-term empirical combination therapy. Gentamicin dosing schemes still need refinement, especially for subpopulations where pharmacokinetics can differ from pharmacokinetics in the general adult population: obese patients, critically ill patients, paediatric patients, neonates, elderly patients and patients on dialysis. This review summarizes the clinical pharmacokinetics of gentamicin in these patient populations and the consequences for optimal dosing of gentamicin for infections caused by Gram-negative bacteria, highlighting new insights from the last 10 years. In this period, several new population pharmacokinetic studies have focused on these subpopulations, providing insights into the typical values of the most relevant pharmacokinetic parameters, the variability of these parameters and possible explanations for this variability, although unexplained variability often remains high. Both dosing schemes and pharmacokinetic/pharmacodynamic (PK/PD) targets varied widely between these studies. A gentamicin starting dose of 7 mg/kg based on total body weight (or on adjusted body weight in obese patients) appears to be the optimal strategy for increasing the probability of target attainment (PTA) after the first administration for the most commonly used PK/PD targets in adults and children older than 1 month, including critically ill patients. However, evidence that increasing the PTA results in higher efficacy is lacking; no studies were identified that show a correlation between estimated or predicted PK/PD target attainment and clinical success. Although it is unclear if performing therapeutic drug monitoring (TDM) for optimization of the PTA is of clinical value, it is recommended in patients with highly variable pharmacokinetics, including patients from all subpopulations that are critically ill (such as elderly, children and neonates) and patients on intermittent haemodialysis. In addition, TDM for optimization of the dosing interval, targeting a trough concentration of at least < 2 mg/L but preferably < 0.5–1 mg/L, has proven to reduce nephrotoxicity and is therefore recommended in all patients receiving more than one dose of gentamicin. The usefulness of the daily area under the plasma concentration–time curve for predicting nephrotoxicity should be further investigated. Additionally, more research is needed on the optimal PK/PD targets for efficacy in the clinical situations in which gentamicin is currently used, that is, as monotherapy for urinary tract infections or as part of short-term combination therapy.

Mortality risks associated with empirical antibiotic activity in Escherichia coli bacteraemia: an analysis of electronic health records

Background

Reported bacteraemia outcomes following inactive empirical antibiotics (based on in vitro testing) are conflicting, potentially reflecting heterogeneity in causative species, MIC breakpoints defining resistance/susceptibility, and times to rescue therapy.

Methods

We investigated adult inpatients with Escherichia coli bacteraemia at Oxford University Hospitals, UK, from 4 February 2014 to 30 June 2021 who were receiving empirical amoxicillin/clavulanate with/without other antibiotics. We used Cox regression to analyse 30 day all-cause mortality by in vitro amoxicillin/clavulanate susceptibility (activity) using the EUCAST resistance breakpoint (>8/2 mg/L), categorical MIC, and a higher resistance breakpoint (>32/2 mg/L), adjusting for other antibiotic activity and confounders including comorbidities, vital signs and blood tests.

Results

A total of 1720 E. coli bacteraemias (1626 patients) were treated with empirical amoxicillin/clavulanate. Thirty-day mortality was 193/1400 (14%) for any active baseline therapy and 52/320 (16%) for inactive baseline therapy (P = 0.17). With EUCAST breakpoints, there was no evidence that mortality differed for inactive versus active amoxicillin/clavulanate [adjusted HR (aHR) = 1.27 (95% CI 0.83–1.93); P = 0.28], nor of an association with active aminoglycoside (P = 0.93) or other active antibiotics (P = 0.18). Considering categorical amoxicillin/clavulanate MIC, MICs > 32/2 mg/L were associated with mortality [aHR = 1.85 versus MIC = 2/2 mg/L (95% CI 0.99–3.73); P = 0.054]. A higher resistance breakpoint (>32/2 mg/L) was independently associated with higher mortality [aHR = 1.82 (95% CI 1.07–3.10); P = 0.027], as were MICs > 32/2 mg/L with active empirical aminoglycosides [aHR = 2.34 (95% CI 1.40–3.89); P = 0.001], but not MICs > 32/2 mg/L with active non-aminoglycoside antibiotic(s) [aHR = 0.87 (95% CI 0.40–1.89); P = 0.72].

Conclusions

We found no evidence that EUCAST-defined amoxicillin/clavulanate resistance was associated with increased mortality, but a higher resistance breakpoint (MIC > 32/2 mg/L) was. Additional active baseline non-aminoglycoside antibiotics attenuated amoxicillin/clavulanate resistance-associated mortality, but aminoglycosides did not. Granular phenotyping and comparison with clinical outcomes may improve AMR breakpoints.

The impact of VITEK 2 implementation for identification and susceptibility testing of microbial isolates in a Brazilian public hospital

Introduction. The use of automated systems in identification and susceptibility tests can improve antimicrobial therapy, and positively impact clinical outcomes with a decrease in antimicrobial resistance, hospitalization time, costs, and mortality.Aim. The aim of this study was to evaluate the clinical impact of an automated method for identification and susceptibility testing of microbial isolates.Methodology. This was a retrospective cross-sectional study aimed to analyse the results before and after the implementation period of a VITEK 2 system in a Brazilian university hospital. Based on data from medical records, patients with a positive culture of clinical samples from January to July 2017 (conventional method) and from August to December 2017 (automated method) were included in this study. Demographic data, hospitalization time, time interval between culture collection and results, culture results and site, susceptibility profile, minimum inhibitory concentration, and outcome data were evaluated. Chi-square and Fischer's tests were used in the analysis.Results. Of the total samples, 836 were considered valid by the inclusion criteria, with 219 patients before VITEK 2 system implementation group and 545 in the post-implementation group. The comparison between the two periods showed a reduction of 25 % of the time to culture reports, a decrease of 33.5 to 17.0 days of hospitalization, and a reduction in mortality from 44.3-31.0 %, respectively.Conclusion. The VITEK 2 system provided early access to appropriate antimicrobial therapy for patients and effected a positive clinical impact with a reduction in mortality and hospitalization time.

Therapeutic Drug Monitoring of Antibiotics in Critically Ill Patients: Current Practice and Future Perspectives With a Focus on Clinical Outcome

PURPOSE

Early initiation of antibiotics is essential for ameliorating infections in critically ill patients. The correct dosage of antibiotics is imperative to ensure their adequate exposure. Critically ill patients have altered pharmacokinetic parameters and are often infected by less susceptible microorganisms. Differences in drug disposition are not considered with standard doses of antibiotics. This can lead to suboptimal antibiotic exposure in critically ill patients. To overcome this problem of suboptimal dosing, therapeutic drug monitoring (TDM) is a strategy commonly used to support individualized dosing of antibiotics. It is routinely used for vancomycin and aminoglycosides in clinical practice. In recent years, it has become apparent that TDM may also be used in other antibiotics.

METHODS

This review summarizes the evidence for TDM of antibiotics in critically ill patients, focuses on clinical outcomes, and summarizes possibilities for optimized TDM in the future.

RESULTS AND CONCLUSION

After reviewing the literature, we can conclude that general TDM implementation is advised for glycopeptides and aminoglycosides, as evidence of the relationship between TDM and clinical outcome is present. For antibiotics, such as beta-lactams, fluoroquinolones, and linezolid, it seems rational to perform TDM in specific patient cases. TDM involving other antibiotics is supported by individual cases, specifically to decrease toxicity. When focusing on future possibilities to improve TDM of antibiotics in critically ill patients, implementation of model-informed precision dosing should be investigated because it can potentially streamline the TDM process. The logistics of TDM, such as turnaround time and available equipment, are challenging but may be overcome by rapid bioanalytical techniques or real-time monitoring of drug concentrations through biosensors in the future. Education, clinical information on targets, and clinical outcome studies are other important factors that facilitate TDM implementation.

Nosocomial Infection

OBJECTIVE

The first 70 years of critical care can be considered a period of "industrial revolution-like" advancement in terms of progressing the understanding and care of critical illness. Unfortunately, like the industrial revolution's impact on the environment, advancing ICU care of increasingly elderly, immunosuppressed, and debilitated individuals has resulted in a greater overall burden and complexity of nosocomial infections within modern ICUs. Given the rapid evolution of nosocomial infections, the authors provide an updated review.

DATA SOURCES AND STUDY SELECTION

We searched PubMed and OVID for peer-reviewed literature dealing with nosocomial infections in the critically ill, as well as the websites of government agencies involved with the reporting and prevention of nosocomial infections. Search terms included nosocomial infection, antibiotic resistance, microbiome, antibiotics, and intensive care.

DATA EXTRACTION AND DATA SYNTHESIS

Nosocomial infections in the ICU setting are evolving in multiple domains including etiologic pathogens plus novel or emerging pathogens, prevalence, host risk factors, antimicrobial resistance, interactions of the host microbiome with nosocomial infection occurrence, and understanding of pathogenesis and prevention strategies. Increasing virulence and antimicrobial resistance of nosocomial infections mandate increasing efforts toward their prevention.

CONCLUSIONS

Nosocomial infections are an important determinant of outcome for patients in the ICU setting. Systematic research aimed at improving the prevention and treatment of nosocomial infections is still needed.

Assessment of the Effects of a High Amikacin Dose on Plasma Peak Concentration in Critically Ill Children

OBJECTIVES

This study aimed to assess the incidence of amikacin plasma peak concentration (C_max) below 60 mg·L^-1 in critically ill children receiving an amikacin dosing regimen of 30 mg kg^-1·day^-1. Secondary objectives were to identify factors associated with low C_max and to assess the incidence of acute kidney injury (AKI).

METHODS

A retrospective observational study was performed in two French pediatric intensive care units. All admitted children who received 30 mg·kg^-1 amikacin and had a C_max measurement were eligible. Clinical and biological data, amikacin dose, and concentrations were collected.

RESULTS

In total, 30 patients were included, aged from 3 weeks to 7 years. They received a median amikacin dosage of 30 mg kg^-1·day^-1 (range 29-33) based on admission body weight (BW), corresponding to 27 mg kg^-1·day^-1 (range 24-30) based on actual BW. C_max was < 60 mg·L^-1 in 21 (70%) children and none had a C_max ≥ 80 mg·L^-1. Among the 15 patients with a measured minimum inhibitory concentration (MIC), 13 (87%) had a C_max/MIC ratio > 8. Univariate analysis showed that factors associated with C_max < 60 mg·L^-1 were high estimated glomerular filtration rate (p = 0.015) and low blood urea concentration (p = 0.001). AKI progression or occurrence was observed after amikacin administration in two (7%) and six (21%) patients, respectively.

CONCLUSIONS

Despite the administration of the maximal recommended amikacin dose, C_max was below the pharmacokinetic target in 70% of our pediatric population. Further studies are needed to develop a pharmacokinetic model in a population of critically ill children to optimize target attainment.

Optimizing Antimicrobial Drug Dosing in Critically Ill Patients

A fundamental step in the successful management of sepsis and septic shock is early empiric antimicrobial therapy. However, for this to be effective, several decisions must be addressed simultaneously: (1) antimicrobial choices should be adequate, covering the most probable pathogens; (2) they should be administered in the appropriate dose, (3) by the correct route, and (4) using the correct mode of administration to achieve successful concentration at the infection site. In critically ill patients, antimicrobial dosing is a common challenge and a frequent source of errors, since these patients present deranged pharmacokinetics, namely increased volume of distribution and altered drug clearance, which either increased or decreased. Moreover, the clinical condition of these patients changes markedly over time, either improving or deteriorating. The consequent impact on drug pharmacokinetics further complicates the selection of correct drug schedules and dosing during the course of therapy. In recent years, the knowledge of pharmacokinetics and pharmacodynamics, drug dosing, therapeutic drug monitoring, and antimicrobial resistance in the critically ill patients has greatly improved, fostering strategies to optimize therapeutic efficacy and to reduce toxicity and adverse events. Nonetheless, delivering adequate and appropriate antimicrobial therapy is still a challenge, since pathogen resistance continues to rise, and new therapeutic agents remain scarce. We aim to review the available literature to assess the challenges, impact, and tools to optimize individualization of antimicrobial dosing to maximize exposure and effectiveness in critically ill patients.

Impact of the Epithelial Lining Fluid Milieu on Amikacin Pharmacodynamics Against Pseudomonas aeruginosa

Background

Even though nebulised administration of amikacin can achieve high epithelial lining fluid concentrations, this has not translated into improved patient outcomes in clinical trials. One possible reason is that the cellular and chemical composition of the epithelial lining fluid may inhibit amikacin-mediated bacterial killing.

Objective

The objective of this study was to identify whether the epithelial lining fluid components inhibit amikacin-mediated bacterial killing.

Methods

Two amikacin-susceptible (minimum inhibitory concentrations of 2 and 8 mg/L) Pseudomonas aeruginosa isolates were exposed in vitro to amikacin concentrations up to 976 mg/L in the presence of an acidic pH, mucin and/or surfactant as a means of simulating the epithelial lining fluid, the site of bacterial infection in pneumonia. Pharmacodynamic modelling was used to describe associations between amikacin concentrations, bacterial killing and emergence of resistance.

Results

In the presence of broth alone, there was rapid and extensive (> 6 − log₁₀) bacterial killing, with emergence of resistance identified in amikacin concentrations < 976 mg/L. In contrast, the rate and extent of bacterial killing was reduced (≤ 5 − log₁₀) when exposed to an acidic pH and mucin. Surfactant did not appreciably impact the bacterial killing or resistance emergence when compared with broth alone for either isolate. The combination of mucin and an acidic pH further reduced the rate of bacterial killing, with the maximal bacterial killing occurring 24 h following initial exposure compared with approximately 4–8 h for either mucin or an acidic pH alone.

Conclusions

Our findings indicate that simulating the epithelial lining fluid antagonises amikacin-mediated killing of P. aeruginosa, even at the high concentrations achieved following nebulised administration.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40268-021-00344-5.

Present and Future Perspectives on Therapeutic Options for Carbapenemase-Producing Enterobacterales Infections

Carbapenem-resistant Enterobacterales (CRE) are included in the list of the most threatening antibiotic resistance microorganisms, being responsible for often insurmountable therapeutic issues, especially in hospitalized patients and immunocompromised individuals and patients in intensive care units. The enzymatic resistance to carbapenems is encoded by different β-lactamases belonging to A, B or D Ambler class. Besides compromising the activity of last-resort antibiotics, CRE have spread from the clinical to the environmental sectors, in all geographic regions. The purpose of this review is to present present and future perspectives on CRE-associated infections treatment.

An international survey on aminoglycoside practices in critically ill patients: the AMINO III study

BACKGROUND

While aminoglycosides (AG) have been used for decades, debate remains on their optimal dosing strategy. We investigated the international practices of AG usage specifically regarding dosing and therapeutic drug monitoring (TDM) in critically ill patients. We conducted a prospective, multicentre, observational, cohort study in 59 intensive-care units (ICUs) in 5 countries enrolling all ICU patients receiving AG therapy for septic shock.

RESULTS

We enrolled 931 septic ICU patients [mean ± standard deviation, age 63 ± 15 years, female 364 (39%), median (IQR) SAPS II 51 (38-65)] receiving AG as part of empirical (761, 84%) or directed (147, 16%) therapy. The AG used was amikacin in 614 (66%), gentamicin in 303 (33%), and tobramycin in 14 (1%) patients. The median (IQR) duration of therapy was 2 (1-3) days, the number of doses was 2 (1-2), the median dose was 25 ± 6, 6 ± 2, and 6 ± 2 mg/kg for amikacin, gentamicin, and tobramycin respectively, and the median dosing interval was 26 (23.5-43.5) h. TDM of C_max and C_min was performed in 437 (47%) and 501 (57%) patients, respectively, after the first dose with 295 (68%) patients achieving a C_max/MIC > 8 and 353 (71%) having concentrations above C_min recommended thresholds. The ICU mortality rate was 27% with multivariable analysis showing no correlation between AG dosing or pharmacokinetic/pharmacodynamic target attainment and clinical outcomes.

CONCLUSION

Short courses of high AG doses are mainly used in ICU patients with septic shock, although wide variability in AG usage is reported. We could show no correlation between PK/PD target attainment and clinical outcome. Efforts to optimize the first AG dose remain necessary. Trial registration Clinical Trials, NCT02850029, registered on 29th July 2016, retrospectively registered, https://www.clinicaltrials.gov.

Use of Gentamicin for Sepsis and Septic Shock in Anaesthesia-Intensive Care Unit: A Clinical Practice Evaluation

Objective

Numerous cases of gentamicin underdosing have been described in the literature in the context of sepsis and septic shock in anaesthesia-intensive care units (ICU). A survey of clinical practice was conducted with the aim to rationalise the use of gentamicin in the unit. The secondary objective was to propose a corrective formula for adjusting individual dosage.

Methods

A single-centre survey was used to determine the initial dose of gentamicin administered, in an anaesthesia-ICU, during the first hours of sepsis/septic shock. An initial retrospective phase allowed focusing on the points of improvement in terms of prescription. A second prospective phase enabled the evaluation of benefits following the implemented changes.

Results

Fifty-one patients were included during the retrospective phase (2014–2015) and 28 patients during the prospective phase (2016–2017). Out-of-guideline prescriptions significantly decreased between these two study periods (i.e., pulmonary infections decreased from 70.5% to 18%, p<0.001) and the mean±standard deviation administered dosage increased from 7.3±1.2 mg kg⁻¹ to 9.5±1.5 mg kg⁻¹ (p<0.001). Nevertheless, the proportion of Cmax (peak plasma concentration) ≥30 mg L⁻¹ and the mean Cmax did not change significantly. A significant association (p<0.05) was found between Cmax, body mass index, haematocrit and creatinine, enabling a corrective formula to be proposed.

Conclusion

The present study allowed improvement in gentamicin prescription in an anaesthesia-ICU. A Cmax ≥30 mg L⁻¹ remains difficult to achieve, but a Cmax ≥16 mg L⁻¹ could be considered relevant for community infections and would be more attainable. A corrective formula could be used to adjust the dosage.

Observed concentrations of amikacin and gentamycin in the setting of burn patients with gram-negative bacterial infections: Preliminary data from a prospective study

AIM OF THE STUDY

Critically ill populations often have shown subtherapeutic aminoglycosides' concentrations mostly because of unavoidable changes in drug volume distribution and clearance. We present a real life prospective study evaluating plasma concentrations for once-daily dosing for amikacin and gentamycin among a population of severe burn adults.

METHODS

We conducted a real life prospective study on the plasma observed concentrations of amikacin and gentamycin among severe burn patients, using aminoglycoside as combination therapy. Antibiotics were prescribed at the standard doses of 15-20mg/kg/day for amikacin and 3-5mg/kg/day for gentamycin.

RESULTS

Eight patients (4 in amikacin and 4 in gentamycin groups, respectively) were enrolled in the study. All subjects were admitted for severe burns. The most common site of infection was bloodstream (5; 62.5%) and pneumonia (4; 50%). Pseudomonas aeruginosa, followed by Klebsiella pneumoniae and multi-drug resistant Acinetobacter baumannii were the most prevalent agents isolated. Amikacin and gentamycin never achieved the target peak concentration of 60mg/L and 30mg/L: in our study C_max, for amikacin, was 33.1±15.6mg/L (SD), while for gentamycin was 14.3mg/L±9. C_max and total body surface area have shown a strong negative correlation with borderline statistical significance (amikacin: ρ=0.922, P=0.078; gentamycin: ρ=0.937, P=0.063). At the standard dosage, the pharmacokinetic/pharmacodynamic (PK/PD) target of C_max>8×highest MIC was reached for 8 (53.3%) out of 15 isolated pathogens.

CONCLUSIONS

The present study found that, in a population of septic burn patients, standard doses of gentamycin and amikacin most often lead to plasma concentrations under the PK/PD target.

Evaluation of amikacin use and comparison of the models implemented in two Bayesian forecasting software packages to guide dosing

AIMS

Bayesian forecasting software can assist in guiding therapeutic drug monitoring (TDM)-based dose adjustments for amikacin to achieve therapeutic targets. This study aimed to evaluate amikacin prescribing and TDM practices, and to determine the suitability of the amikacin model incorporated into the DoseMeRx® software as a replacement for the previously available software (Abbottbase®).

METHODS

Patient demographics, pathology, amikacin dosing history, amikacin concentrations and Abbottbase® predicted TDM targets (area under the curve up to 24 hours, maximum concentration and trough concentration) were collected for adults receiving intravenous amikacin (2012-2017). Concordance with the Australian Therapeutic Guidelines was assessed. Observed and predicted amikacin concentrations were compared to determine the predictive performance (bias and precision) of DoseMeRx®. Amikacin TDM targets were predicted by DoseMeRx® and compared to those predicted by Abbottbase®.

RESULTS

Overall, guideline compliance for 63 courses of amikacin in 47 patients was suboptimal. Doses were often lower than recommended. For therapy >48 h, TDM sample collection timing was commonly discordant with recommendations, therapeutic target attainment low and 34% of dose adjustments inappropriate. DoseMeRx® under-predicted amikacin concentrations by 0.9 mg/L (95% confidence interval [CI] -1.4 to -0.5) compared with observed concentrations. However, maximum concentration values (n = 19) were unbiased (-1.7 mg/L 95%CI -5.8 to 0.8) and precise (8.6% 95%CI 5.4-18.1). Predicted trough concentration values (n = 7) were, at most, 1 mg/L higher than observed. Amikacin area under the curve values estimated using Abbottbase® (181 mg h/L 95%CI 161-202) and DoseMeRx® (176 mg h/L 95%CI 152-199) were similar (P = .59).

CONCLUSION

Amikacin dosing and TDM practice was suboptimal compared with guidelines. The model implemented by DoseMeRx® is satisfactory to guide amikacin dosing.

Pharmacodynamic Evaluation of Plasma and Epithelial Lining Fluid Exposures of Amikacin against Pseudomonas aeruginosa in a Dynamic In Vitro Hollow-Fiber Infection Model

Given that aminoglycosides, such as amikacin, may be used for multidrug-resistant Pseudomonas aeruginosa infections, optimization of therapy is paramount for improved treatment outcomes. This study aims to investigate the pharmacodynamics of different simulated intravenous amikacin doses on susceptible P. aeruginosa to inform ventilator-associated pneumonia (VAP) and sepsis treatment choices. A hollow-fiber infection model with two P. aeruginosa isolates (MICs of 2 and 8 mg/liter) with an initial inoculum of ∼10⁸ CFU/ml was used to test different amikacin dosing regimens. Three regimens (15, 25, and 50 mg/kg) were tested to simulate a blood exposure, while a 30 mg/kg regimen simulated the epithelial lining fluid (ELF) for potential respiratory tract infection. Data were described using a semimechanistic pharmacokinetic/pharmacodynamic (PK/PD) model. Whole-genome sequencing was used to identify mutations associated with resistance emergence. While bacterial density was reduced by >6 logs within the first 12 h in simulated blood exposures following this initial bacterial kill, there was amplification of a resistant subpopulation with ribosomal mutations that were likely mediating amikacin resistance. No appreciable bacterial killing occurred with subsequent doses. There was less (<5 log) bacterial killing in the simulated ELF exposure for either isolate tested. Simulation studies suggested that a dose of 30 and 50 mg/kg may provide maximal bacterial killing for bloodstream and VAP infections, respectively. Our results suggest that amikacin efficacy may be improved with the use of high-dose therapy to rapidly eliminate susceptible bacteria. Subsequent doses may have reduced efficacy given the rapid amplification of less-susceptible bacterial subpopulations with amikacin monotherapy.

Population pharmacokinetic evaluation and optimization of amikacin dosage regimens for the management of mycobacterial infections

Background

There is limited information on amikacin pharmacokinetics (PK) and dose requirements in patients with mycobacterial infections.

Objectives

To conduct a population PK analysis of amikacin data from patients with mycobacterial infections and compare predicted concentrations from standard and modified dosage guidelines with recommended target ranges.

Methods

A population PK model was developed using NONMEM. Cmax, Cmin, concentration 1 h post-infusion (C1h) and AUC0–24 using 15 mg/kg daily (once daily), the WHO table, 25 mg/kg three times weekly (TTW) and modified guidelines were compared using Monte Carlo simulations of 1000 patients.

Results

Data were available from 124 patients (684 concentrations) aged 16–92 years. CL was 4.64 L/h per 100 mL/min CLCR; V was 0.344 L/kg. With once-daily regimens, Cmax was 35–45 mg/L in 30%–35% of patients and 35–50 mg/L in 46%–48%; C1h was 25–40 mg/L in 53%–59%. The WHO table produced high Cmax values in patients &lt;60 kg and low in patients &gt;75 kg. With TTW dosing, around 30% of Cmax values were 65–80 mg/L, 40% were 60–80 mg/L, and 48% of C1h were 45–65 mg/L. Increasing the dosage interval for patients with CLCR &lt;50 mL/min reduced Cmin values &gt;2 mg/L from 34% to 25% for once-daily dosing and from 18% to 13% for TTW. In patients whose Cmin was &lt;2 mg/L, 82% of AUC0–24 values were 100–300 mg.h/L.

Conclusions

Standard amikacin dosing guidelines achieve low percentages of target concentrations for mycobacterial infections. Extending the dosing interval in renal impairment and widening target ranges would reduce the need for dose adjustment.

Aminoglycosides in critically ill patients: which dosing regimens for which pathogens?

Modifications of antibiotic pharmacokinetic parameters have been reported in critically ill patients, resulting in a risk of treatment failure. We aimed to determine optimised amikacin (AMK), gentamicin (GEN) and tobramycin (TOB) intravenous dosing regimens in this patient population. Patients admitted to the medical ICU and treated with AMK, GEN or TOB were included. Analyses were performed using a parametric population approach. Monte Carlo simulations were performed and the probability of target attainment (PTA) was calculated using C_max/MIC ≥ 8 and trough concentrations as targets. A total of 117 critically ill hospitalised patients were studied. Median values (interindividual variability, ɷ²) of clearance were 3.51 (0.539), 3.53 (0.297), 2.70 (0.339) and 5.07 (0.339) L/h for AMK, GEN, TOB, and TOB in cystic fibrosis (CF), respectively. Median values (ɷ²) of central volume of distribution were 30.2 (0.215), 20.0 (0.109) and 25.6 (0.177) L for AMK, GEN and TOB, respectively. Simulations showed that doses should be adjusted to actual body weight and creatinine clearance (CLCR) for AMK and GEN, and according to CLCR and presence of CF for TOB. In conclusion, our recommendations for treating Pseudomonas aeruginosa infections in this population include using initial doses of 35 mg/kg for AMK or 10 mg/kg for TOB (CF and non-CF patients). GEN demonstrated the best rates of target attainment against Staphylococcus aureus infections with a dose of 5 mg/kg. As high aminoglycoside doses are required in this population, efficacy and safety targets are conflicting and therapeutic drug monitoring remains an important tool to manage this issue.

Quality of evidence supporting Surviving Sepsis Campaign Recommendations

Introduction

The Surviving Sepsis Campaign (SSC) guidelines, released in 2017, are a combination of expert opinion and evidence-based medicine, adopted by many institutions as a standard of practice. The aim was to analyse the quality of evidence supporting recommendations on the management of sepsis.

Methods

The strength and quality of evidence (high, moderate, low-very low and best practice statements) of each recommendation were extracted. Randomised controlled trials were required to qualify as high-quality evidence.

Results

A total of 96 recommendations were formulated, and 87 were included. Among thirty-one (43%) strong recommendations, only 15.2% were supported by high-quality evidence. Overall, thirty-seven (42.5%) recommendations were based on low-quality evidence, followed by 28 (32.2%) based on moderate-quality, 15 (17.2%) were best practice statements and only seven (8.0%) were supported by high-quality evidence. Randomised controlled trials supported 21.4%, 9.5% and 8.6% recommendations on mechanical ventilation, resuscitation, and management/adjuvant therapy, respectively. In contrast, none high-quality evidence recommendation supported antimicrobial/source control (82.4% were low-very low evidence or best practice statements), and nutrition.

Conclusions

In the SSC guidelines most recommendations were informed by indirect evidence and non-systematic observations. While awaiting trials results, Delphi-like approaches or multi-criteria decision analyses should guide recommendations.

Amikacin pharmacokinetic/pharmacodynamic in intensive care unit: a prospective database

Background

Aminoglycosides have a concentration-dependent therapeutic effect when peak serum concentration (C_max) reaches eight to tenfold the minimal inhibitory concentration (MIC). With an amikacin MIC of 8 mg/L, the C_max should be 64–80 mg/L. This objective is based on clinical breakpoints and not on measured MIC. This study aimed to assess the proportion of patients achieving the pharmacokinetic/pharmacodynamic (PK/PD) target C_max/MIC ≥ 8 using the measured MIC in critically ill patients treated for documented Gram-negative bacilli (GNB) infections.

Methods

Retrospective analysis from February 2016 to December 2017 of a prospective database conducted in 2 intensive care units (ICU). All patients with documented severe GNB infections treated with amikacin (single daily dose of 25 mg/kg of total body weight (TBW)) with both MIC and C_max measurements at first day of treatment (D1) were included. Results are expressed in n (%) or median [min–max].

Results

93 patients with 98 GNB-documented infections were included. The median C_max was 55.2 mg/L [12.2–165.7] and the median MIC was 2 mg/L [0.19–16]. C_max/MIC ratio ≥ 8 was achieved in 87 patients (88.8%) while a C_max ≥ 64 mg/L was achieved in only 38 patients (38.7%). Overall probability of PK/PD target attainment was 93%. No correlation was found between C_max/MIC ratio and clinical outcome at D8 and D28.

Conclusion

According to PK/PD parameters observed in our study, single daily dose of amikacin 25 mg/kg of TBW appears to be sufficient in most critically ill patients treated for severe GNB infections.

Population Pharmacokinetic Study of the Suitability of Standard Dosing Regimens of Amikacin in Critically Ill Patients with Open-Abdomen and Negative-Pressure Wound Therapy

The aim was to assess the appropriateness of recommended regimens for empirical MIC coverage in critically ill patients with open-abdomen and negative-pressure therapy (OA/NPT). Over a 5-year period, every critically ill patient who received amikacin and who underwent therapeutic drug monitoring (TDM) while being treated by OA/NPT was retrospectively included. A population pharmacokinetic (PK) modeling was performed considering the effect of 10 covariates (age, sex, total body weight [TBW], adapted body weight [ABW], body surface area [BSA], modified sepsis-related organ failure assessment [SOFA] score, vasopressor use, creatinine clearance [CL_CR], fluid balance, and amount of fluids collected by the NPT over the sampling day) in patients who underwent continuous renal replacement therapy (CRRT) or did not receive CRRT. Monte Carlo simulations were employed to determine the fractional target attainment (FTA) for the PK/pharmacodynamic [PD] targets (maximum concentration of drug [C _max]/MIC ratio of ≥8 and a ratio of the area under the concentration-time curve from 0 to 24 h [AUC_0-24]/MIC of ≥75). Seventy critically ill patients treated by OA/NPT (contributing 179 concentration values) were included. Amikacin PK concentrations were best described by a two-compartment model with linear elimination and proportional residual error, with CL_CR and ABW as significant covariates for volume of distribution (V) and CL_CR for CL. The reported V) in non-CRRT and CRRT patients was 35.8 and 40.2 liters, respectively. In Monte Carlo simulations, ABW-adjusted doses between 25 and 35 mg/kg were needed to reach an FTA of >85% for various renal functions. Despite an increased V and a wide interindividual variability, desirable PK/PD targets may be achieved using an ABW-based loading dose of 25 to 30 mg/kg. When less susceptible pathogens are targeted, higher dosing regimens are probably needed in patients with augmented renal clearance (ARC). Further studies are needed to assess the effect of OA/NPT on the PK parameters of antimicrobial agents.

PK/PD targets of amikacin and gentamicin in ICU patients

OBJECTIVES

We aimed to evaluate the probability to achieve PK-PD targets in patients with sepsis hospitalized in the intensive care unit (ICU) after a single dose of 30mg/kg of amikacin or 8mg/kg of gentamicin.

PATIENTS AND METHODS

This single-center prospective study included 138 ICU patients with severe sepsis or septic shock with an indication for intravenous amikacin (N=89) or gentamicin (N=49). Maximum concentration (C_max) was measured 30 minutes after infusion completion. PK/PD objectives were respectively C_max≥60mg/L and ≥30mg/L for amikacin and gentamicin for empirical therapy, and a C_max/MIC ratio≥8, as per French guidelines.

RESULTS

The median Simplified Acute Physiology Score II was 43 and ICU case fatality rate was 34.8%. A causative bacterial agent was identified in 94 patients (68.1%). Three pathogens had acquired aminoglycoside resistance and 15 were naturally resistant. The targeted C_max for the first dose was achieved in 53 patients (59.6%) receiving amikacin, and one (2.2%) patient receiving gentamicin. C_max/MIC ratio≥8 was obtained in all patients infected with susceptible pathogens (N=72). Factors associated with C_max≥60mg/L of amikacin in multivariate analysis were dose per kg of adapted body weight (OR=1.39, P<0.001) and renal clearance estimated with CKD-EPI formula (OR=0.98, P=0.003).

CONCLUSIONS

Despite high doses, amikacin and gentamicin first C_max remain dramatically low in ICU patients. However, an adequate C_max/MIC ratio was reached in all patients.

The "Old" and the "New" Antibiotics for MDR Gram-Negative Pathogens: For Whom, When, and How

The recent expansion of multidrug resistant and pan-drug-resistant pathogens poses significant challenges in the treatment of healthcare associated infections. An important advancement, is a handful of recently launched new antibiotics targeting some of the current most problematic Gram-negative pathogens, namely carbapenem-producing Enterobacteriaceae (CRE) and carbapenem-resistant P. aeruginosa (CRPA). Less options are available against carbapenem-resistant Acinetobacter baumannii (CRAB) and strains producing metallo-beta lactamases (MBL). Ceftazidime-avibactam signaled a turning point in the treatment of KPC and partly OXA- type carbapenemases, whereas meropenem-vaborbactam was added as a potent combination against KPC-producers. Ceftolozane-tazobactam could be seen as an ideal beta-lactam backbone for the treatment of CRPA. Plazomicin, an aminoglycoside with better pharmacokinetics and less toxicity compared to other class members, will cover important proportions of multi-drug resistant pathogens. Eravacycline holds promise in the treatment of infections by CRAB, with a broad spectrum of activity similar to tigecycline, and improved pharmacokinetics. Novel drugs and combinations are not to be considered "panacea" for the ongoing crisis in the therapy of XDR Gram-negative bacteria and colistin will continue to be considered as a fundamental companion drug for the treatment of carbapenem-resistant Enterobacteriaceae (particularly in areas where MBL predominate), for the treatment of CRPA (in many cases being the only in vitro active drug) as well as CRAB. Aminoglycosides are still important companion antibiotics. Finally, fosfomycin as part of combination treatment for CRE infections and P. aeruginosa, deserves a greater attention. Optimal conditions for monotherapy and the "when and how" of combination treatments integrating the novel agents will be discussed.

Individualising Therapy to Minimize Bacterial Multidrug Resistance

The scourge of antibiotic resistance threatens modern healthcare delivery. A contributing factor to this significant issue may be antibiotic dosing, whereby standard antibiotic regimens are unable to suppress the emergence of antibiotic resistance. This article aims to review the role of pharmacokinetic and pharmacodynamic (PK/PD) measures for optimising antibiotic therapy to minimise resistance emergence. It also seeks to describe the utility of combination antibiotic therapy for suppression of resistance and summarise the role of biomarkers in individualising antibiotic therapy. Scientific journals indexed in PubMed and Web of Science were searched to identify relevant articles and summarise existing evidence. Studies suggest that optimising antibiotic dosing to attain defined PK/PD ratios may limit the emergence of resistance. A maximum aminoglycoside concentration to minimum inhibitory concentration (MIC) ratio of > 20, a fluoroquinolone area under the concentration-time curve to MIC ratio of > 285 and a β-lactam trough concentration of > 6 × MIC are likely required for resistance suppression. In vitro studies demonstrate a clear advantage for some antibiotic combinations. However, clinical evidence is limited, suggesting that the use of combination regimens should be assessed on an individual patient basis. Biomarkers, such as procalcitonin, may help to individualise and reduce the duration of antibiotic treatment, which may minimise antibiotic resistance emergence during therapy. Future studies should translate laboratory-based studies into clinical trials and validate the appropriate clinical PK/PD predictors required for resistance suppression in vivo. Other adjunct strategies, such as biomarker-guided therapy or the use of antibiotic combinations require further investigation.

Predictors of insufficient peak amikacin concentration in critically ill patients on extracorporeal membrane oxygenation

Background

Amikacin infusion requires targeting a peak serum concentration (C_max) 8–10 times the minimal inhibitory concentration, corresponding to a C_max of 60–80 mg/L for the least susceptible bacteria to theoretically prevent therapeutic failure. Because drug pharmacokinetics on extracorporeal membrane oxygenation (ECMO) are challenging, we undertook this study to assess the frequency of insufficient amikacin C_max in critically ill patients on ECMO and to identify relative risk factors.

Methods

This was a prospective, observational, monocentric study in a university hospital. Patients on ECMO who received an amikacin loading dose for suspected Gram-negative infections were included. The amikacin loading dose of 25 mg/kg total body weight was administered intravenously and C_max was measured 30 min after the end of the infusion. Independent predicators of C_max < 60 mg/L after the first amikacin infusion were identified with mixed-model multivariable analyses. Various dosing simulations were performed to assess the probability of reaching 60 mg/L < C_max < 80 mg/L.

Results

A total of 106 patients on venoarterial ECMO (VA-ECMO) (68%) or venovenous-ECMO (32%) were included. At inclusion, their median (1st; 3rd quartile) Sequential Organ-Failure Assessment score was 15 (12; 18) and 54 patients (51%) were on renal replacement therapy. Overall ICU mortality was 54%. C_max was < 60 mg/L in 41 patients (39%). Independent risk factors for amikacin under-dosing were body mass index (BMI) < 22 kg/m² and a positive 24-h fluid balance. Using dosing simulation, increasing the amikacin dosing regimen to 30 mg/kg and 35 mg/kg of body weight when the 24-h fluid balance is positive and the BMI is ≥ 22 kg/m² or < 22 kg/m² (Table 3), respectively, would have potentially led to the therapeutic target being reached in 42% of patients while reducing under-dosing to 23% of patients.

Conclusions

ECMO-treated patients were under-dosed for amikacin in one third of cases. Increasing the dose to 35 mg/kg of body weight in low-BMI patients and those with positive 24-h fluid balance on ECMO to reach adequate targeted concentrations should be investigated.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2122-x) contains supplementary material, which is available to authorized users.

New paradigm for rapid achievement of appropriate therapy in special populations: coupling antibiotic dose optimization rapid microbiological methods

INTRODUCTION

Some special patient populations (e.g. critically ill, burns, hematological malignancy, post-major surgery, post-major trauma) have characteristics that lead to higher rates of failure and mortality associated with infection. Choice of effective antibiotics and optimized doses are challenging in these patients that are commonly infected by multidrug-resistant pathogens. Areas covered: A review of the importance of diagnosis and the place of newer microbiological methods (e.g. whole-genome sequencing) to ensure rapid transition from empiric to directed antibiotic therapy is provided. The effects of pathophysiological changes on antibiotic pharmacokinetics are also provided. Expert opinion: Product information dosing regimens do not address the pharmacokinetic alterations that can occur in special patient populations and increase the likelihood of therapeutic failure and the emergence of bacterial resistance. Altered dosing approaches, supplemented with the use of dosing software and therapeutic drug monitoring, may be needed to ensure optimal antibiotic exposure and better therapeutic outcomes in these patients with severe infection. Dose optimization needs to be coupled with advanced microbiological techniques that enable rapid microbiological identification and characterization of resistance mechanism to ensure that maximally effective directed therapy can be chosen.

Determinants of amikacin first peak concentration in critically ill patients

Amikacin antimicrobial effect has been correlated with the ratio of the peak concentration (C_max ) to the minimum inhibitory concentration. A target C_max ≥ 60-80 mg/L has been suggested. It has been shown that such target is not achieved in a large proportion of critically ill patients in intensive care units. A retrospective analysis was performed to examine the determinants of C_max ≥ 80 mg/L on the first peak in 339 critically ill patients treated by amikacin. The influence of available variables on C_max target attainment was analyzed using a classification and regression tree (CART) and logistic regression. Mean C_max in the 339 patients was 73.0 ± 23.9 mg/L, with a target attainment rate (TAR, C_max ≥ 80 mg/L) of 37.5%. In CART analysis, the strongest predictor of amikacin target peak attainment was dose per kilogram of lean body weight (dose/LBW). TAR was 60.1% in patients with dose/LBW ≥ 37.8 vs. 19.9% in patients with lower dose/LBW (OR = 6.0 (95% CI: 3.6-10.2)). Renal function was a secondary predictor of C_max . Logistic regression analysis identified dose per kilogram of ideal body weight (OR = 1.13 (95% CI: 1.09-1.17)) and creatinine clearance (OR = 0.993 (95% CI: 0.988-0.998)) as predictors of target peak achievement. Based on our results, an amikacin dose ≥ 37.8 mg/kg of LBW should be used to optimize the attainment of C_max ≥ 80 mg/L after the first dose in critically ill patients. An even higher dose may be necessary in patients with normal renal function.

Therapeutic Drug Monitoring of Gentamicin Peak Concentrations in Critically Ill Patients

BACKGROUND

Adequate gentamicin peak concentrations (Cmax) are important for optimal clinical efficacy. Within a critically ill patient, substantial variability in Cmax can occur over time, hampering the usefulness of therapeutic drug monitoring (TDM). The aim of this study was to evaluate the effect of gentamicin dosing based on Cmax after the first dose on gentamicin target attainment in critically ill patients.

METHODS

From gentamicin-treated critically ill patients, dosing information, clinical parameters, and serum concentrations were collected prospectively. A population pharmacokinetic model was developed using nonlinear mixed-effects modeling to estimate Cmax after each dose. To evaluate the usefulness of routine TDM, percentages of Cmax within (%Cther, 15-20 mg/L), above (>20 mg/L), and below (%Csubther, <15 mg/L) the therapeutic range after the first and second doses were compared. In addition, simulations were performed to evaluate the impact of TDM.

RESULTS

Four hundred sixteen measurements from 59 patients receiving 130 gentamicin doses were included. In the 30 patients who received >1 dose, TDM increased %Cther from 40% after a first median dose of 5.0 mg/kg to 50% after the second dose, and decreased %Csubther from 47% to 30%. Simulations using a 5 mg/kg starting dose revealed %Cther after the second dose of 28.4% without and 36.8% with TDM and %Csubther of 56.9% and 29.3%, respectively. Increasing the simulated starting dose to 6 mg/kg increased %Cther after the first dose from 27.7% to 33.5% and decreased %Csubther from 58.6% to 35.6%. TDM after a first dose of 6 mg/kg had no substantial effect on %Cther or %Csubther after the second dose.

CONCLUSIONS

Gentamicin dosing based on Cmax after the first dose increased %Cther and decreased %Csubther, but did not result in therapeutic Cmax in half of the patients. When simulating a higher starting dose, %Csubther after the first dose decreased, and TDM showed no additional influence. These data suggest that a starting dose of 6 mg/kg should be considered and that repeated Cmax measurements are not of added value.

Predictive performance of a gentamicin population pharmacokinetic model in two western populations of critically ill patients

External validation of population pharmacokinetic (PK) models is warranted before they can be clinically applied to aid in antibiotic dose selection. The primary objective of this study was to assess the predictive performance of a gentamicin population PK model in intensive care unit (ICU) patients in two independent western populations of critically ill patients.

METHODS

Data were collected from the ICU where the model was developed (Academic Medical Centre, Amsterdam [AMC]) and from the Centre Hospitalier Universitaire de Nîmes (CHU Nîmes). Primary endpoints were bias and accuracy. The model was regarded as valid if bias was not significantly different from 0 and accuracy was equal to or less than 2.5 mg/L. Non-linear mixed-effects modelling (NONMEM) was used for data analysis.

RESULTS

The AMC validation dataset consisted of 192 samples from 66 ICU patients and the CHU Nîmes dataset of 230 gentamicin samples from 50 ICU patients. The structural model predicted the gentamicin plasma concentrations in the AMC population with a non-significant bias (0.35, 95%CI: -0.11-0.81) and a sufficient accuracy of 2.5 mg/L (95%CI: 2.3-2.8). The gentamicin plasma concentrations were overpredicted in the CHU Nîmes population with a significant bias of 4.8 mg/L (95%CI: 4.00-5.62) and an accuracy of 5.5 mg/L (95%CI: 4.7-6.2).

CONCLUSION

The model is valid for use in the AMC ICU population but not in the CHU Nîmes ICU population. This illustrates that caution is needed when using a population PK model in an external population.

Pharmacokinetic and Pharmacodynamic Considerations of Antibiotics of Last Resort in Treating Gram-Negative Infections in Adult Critically Ill Patients

PURPOSE OF REVIEW

We provide an overview of antimicrobials that are considered last resort for the treatment of resistant gram-negative infections in adult critically ill patients. The role in therapy, pharmacodynamic (PD) goals, and pharmacokinetic (PK) changes in critical illness for aminoglycosides, polymyxins, tigecycline, fosfomycin, and fluoroquinolones are summarized.

RECENT FINDINGS

Altered PK in septic patients in the intensive care unit (ICU) is observed with many of our agents of last resort. Based on the available literature, dosage adjustments may be required to optimize PK parameters and meet PD targets for most effective bacterial killing. Data is limited, studies are conducted in heterogeneous patient populations, and conclusions are frequently conflicting. Strategic dosing regimens such as high-dose extended interval dosing of aminoglycosides or loading doses with colistin and polymyxin B are examples of ways to optimize antibiotic PK in critically ill patients. Benefits of these strategies must be balanced with risks of increased toxicity. Patients with resistant gram-negative infections may present with septic shock in the ICU. Sepsis can significantly alter the PK of antibiotics and require dosage adjustments to attain optimal drug levels. An understanding of PK and PD properties of these agents of last resort will help to maximize therapeutic efficacy while minimizing toxic effects.

Short-Course Adjunctive Gentamicin as Empirical Therapy in Patients With Severe Sepsis and Septic Shock: A Prospective Observational Cohort Study

Background.

Metaanalyses failed to demonstrate clinical benefits of beta lactam plus aminoglycoside combination therapy compared to beta lactam monotherapy in patients with sepsis. However, few data exist on the effects of short-course adjunctive aminoglycoside therapy in sepsis patients with organ failure or shock.

Methods.

We prospectively enrolled consecutive patients with severe sepsis or septic shock in 2 intensive care units in the Netherlands from 2011 to 2015. Local antibiotic protocols recommended empirical gentamicin add-on therapy in only 1 of the units. We used logistic regression analyses to determine the association between gentamicin use and the number of days alive and free of renal failure, shock, and death, all on day 14.

Results.

Of 648 patients enrolled, 245 received gentamicin (222 of 309 [72%] in hospital A and 23 of 339 [7%] in hospital B) for a median duration of 2 days (interquartile range, 1-3). The adjusted odds ratios associated with gentamicin use were 1.39 (95% confidence interval [CI], 1.00-1.94) for renal failure, 1.34 (95% CI, 0.96-1.86) for shock duration, and 1.41 (95% CI, 0.94-2.12) for day-14 mortality. Based on in vitro susceptibilities, inappropriate (initial) gram-negative coverage was given in 9 of 245 (4%) and 18 of 403 (4%) patients treated and not treated with gentamicin, respectively (P = .62).

Conclusions.

Short-course empirical gentamicin use in patients with sepsis was associated with an increased incidence of renal failure but not with faster reversal of shock or improved survival in a setting with low prevalence of antimicrobial resistance.

In vitro activity of minocycline combined with aminoglycosides against Klebsiella pneumoniae carbapenemase-producing K. pneumoniae

This study assessed the in vitro antibacterial activity of minocycline-aminoglycoside combination against Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae. Seventy non-duplicate clinical isolates of KPC-producing K. pneumoniae were collected from patients with bloodstream infections. The synergistic activity of minocycline-aminoglycoside combination was studied by the checkerboard method and time-kill assays in strains with different susceptibilities, and the mutant prevention concentration (MPC) and mutant selection window (MSW) of drugs alone and in combination were determined. The checkerboard method found this combination displayed synergistic and partial synergistic activity against aminoglycoside-susceptible isolates, but indifferent activity against aminoglycoside-resistant isolates. Time-kill assays further demonstrated strong synergistic and bactericidal effect of this combination existed against isolates which were susceptible to both drugs. But for resistant isolates, the time-kill assays showed no synergy. The MPCs of minocycline or aminoglycosides were 8- to 32-fold higher than the MICs, suggesting the MSWs of these drugs were quite wide. For the antibiotic combinations, the addition of 1×MIC concentration of amikacin or gentamicin could reduce the MPCs of minocycline by 4- to 16-fold. Generally, no mutants recovered in the plates containing 1×MIC concentration of minocycline and 2×MIC concentration of amikacin or gentamicin. In summary, these results suggest that minocycline-aminoglycoside combination can be an alternative for infections caused by KPC-producing K. pneumoniae because this combination displays strong synergistic and bactericidal activity in susceptible isolates, and can effectively prevent the emergence of resistant mutants. Further in vitro pharmacokinetic/pharmacodynamic studies and clinical trials should be performed to fully evaluate the efficacy of this drug combination.

Antibiotic dosing for multidrug-resistant pathogen pneumonia

PURPOSE OF REVIEW

Nosocomial pneumonia caused by multidrug-resistant pathogens is increasing in the ICU, and these infections are negatively associated with patient outcomes. Optimization of antibiotic dosing has been suggested as a key intervention to improve clinical outcomes in patients with nosocomial pneumonia. This review describes the recent pharmacokinetic/pharmacodynamic data relevant to antibiotic dosing for nosocomial pneumonia caused by multidrug-resistant pathogens.

RECENT FINDINGS

Optimal antibiotic treatment is challenging in critically ill patients with nosocomial pneumonia; most dosing guidelines do not consider the altered physiology and illness severity associated with severe lung infections. Antibiotic dosing can be guided by plasma drug concentrations, which do not reflect the concentrations at the site of infection. The application of aggressive dosing regimens, in accordance to the antibiotic's pharmacokinetic/pharmacodynamic characteristics, may be required to ensure rapid and effective drug exposure in infected lung tissues.

SUMMARY

Conventional antibiotic dosing increases the likelihood of therapeutic failure in critically ill patients with nosocomial pneumonia. Alternative dosing strategies, which exploit the pharmacokinetic/pharmacodynamic properties of an antibiotic, should be strongly considered to ensure optimal antibiotic exposure and better therapeutic outcomes in these patients.

Evaluation of haemodialysis as a protective technique for preventing high daily dose amikacin nephrotoxicity: an experimental study in an ovine model

Changes in pharmacokinetic parameters of critically ill patients make the treatment of infections challenging, particularly when multidrug-resistant bacteria are involved. The aim of this study was to evaluate the ability of haemodialysis to reduce the exposure to high dose amikacin and prevent nephrotoxicity. Amikacin 50 mg/kg was administered intravenously to six adult sheep once-daily for four days. The sheep were divided into two groups according to the implementation (group 1) or not (group 2) of haemodialysis. In group 1, haemodialysis was performed for 4 h, initiated 2 h after starting amikacin infusion. Amikacin area under the curve (AUC) and trough concentrations (C_min) were used as markers of amikacin-induced nephrotoxicity. The median haemodialysis amikacin clearance was 2.14 L/h (35.6 mL/min), 14% of the mean total body clearance for 24 h. Haemodialysis reduced C_min (group 1: 0.3 µg/mL [0.3-1.1]; group 2: 1.4 µg/mL [1.1-3.9]; P = 0.0003). A trend towards reduced AUC with haemodialysis was observed (group 1: 1450 µg/mL⋅h [1311-1716]; group 2: 3126 µg/mL⋅h [2581-3171]; P = 0.10). In conclusion, haemodialysis seems interesting in reducing AUC and C_min after the injection of high-dose of amikacin, parameters known to be involved in its induced nephrotoxicity, in an experimental ovine model.

Aminoglycosides against carbapenem-resistant Enterobacteriaceae in the critically ill: the pitfalls of aminoglycoside susceptibility

INTRODUCTION

The emergence of carbapenem-resistant Enterobacteriaceae (CRE) has brought aminoglycosides to the frontline since an aminoglycoside may be the only antimicrobial to which CRE isolates show in vitro susceptibility. The appropriateness of aminoglycoside-based therapies for severe infections by CRE is discussed considering the current breakpoints and recent pharmacokinetic (PK) studies in critically ill patients. Areas covered: Many aminoglycoside-susceptible CRE isolates present minimal inhibitory concentrations (MICs) at or slightly below the breakpoint of amikacin or gentamicin. However, recent PK studies with these aminoglycosides in critically ill have invariably shown that the PK/pharmacodynamic (PD) target is very unlikely attained even when high doses are administered, if the MICs are near the breakpoint. Expert commentary: While new antimicrobials are not widely available, the authors forecast an increasing use of aminoglycosides as backbone antibiotics against CRE isolates. However, the altered PK of aminoglycosides in critically ill patients severely impairs their predicted efficacy in these patients. Aminoglycoside breakpoints may hide 'aminoglycoside-susceptible' CRE isolates for that aminoglycosides will unlikely be effective if used in monotherapy. Therefore, these breakpoints may need to be revised due to the increasing use of aminoglycosides as backbone antibiotics to treat severe infections by CRE isolates in critically ill patients.

Determinants of gentamicin concentrations in critically ill patients: a population pharmacokinetic analysis

When treating critically ill patients with gentamicin for severe infection, peak concentrations (C_max) determine clinical efficacy and trough concentrations (C_min) determine toxicity. Despite administration of body weight-standardised starting doses, a wide range of C_max is generally observed. Furthermore, in therapeutic drug monitoring, several measures of renal function are used to predict appropriate C_min and gentamicin dosing intervals, but the most accurate predictor is not known. This study aimed to quantify the impact of several patient parameters on gentamicin C_max values and to determine which measure of renal function best predicts gentamicin clearance (CL). Clinical data and serum gentamicin levels were retrospectively collected from all critically ill patients treated with gentamicin at our intensive care unit between 1 January and 30 June 2011. Data were analysed using non-linear mixed-effects modelling (NONMEM v.7.1.2). A two-compartmental model was developed based on 303 gentamicin concentration-time data from 44 critically ill patients. Serum albumin levels explained 25% of interindividual variability in the volume of distribution (V_d). Creatinine clearance calculated from the creatinine concentration in a 6-h urine portion (CalcCL_Cr) resulted in acceptable estimation of gentamicin CL, whilst serum creatinine (SCr) and creatinine clearance estimated by the Cockcroft-Gault formula (CGCL_Cr) overestimated gentamicin CL and therefore underestimated C_min. In conclusion, low albumin concentrations resulted in a larger V_d and lower C_max of gentamicin. These results suggest that use of a higher gentamicin starting dose in critically ill patients with hypoalbuminaemia may prevent underdosing. Urinary CalcCL_Cr is a better predictor of C_min than SCr or CGCL_Cr.