Comparing outcomes of meropenem administration strategies based on pharmacokinetic and pharmacodynamic principles: a qualitative systematic review

Prolonged vs short-term infusion of β-lactam antibiotics for the treatment of febrile neutropenia: A systematic review and meta-analysis

BACKGROUND

The optimisation of the use of β-lactam antibiotics (BLA) via prolonged infusions in life-threatening complications such as febrile neutropenia (FN) is still controversial. This systematic review and meta-analysis aim to evaluate the efficacy of this strategy in onco-haematological patients with FN.

METHODS

A systematic search was performed of PubMed, Web of Science, Cochrane, EMBASE, World Health Organization, and ClinicalTrials.gov, from database inception until December 2022. The search included randomised controlled trials (RCTs) and observational studies that compared prolonged vs short-term infusions of the same BLA. The primary outcome was all-cause mortality. Secondary outcomes were defervescence, requirement of vasoactive drugs, length of hospital stay and adverse events. Pooled risk ratios were calculated using random effects models.

RESULTS

Five studies were included, comprising 691 episodes of FN, mainly in haematological patients. Prolonged infusion was not associated with a reduction in all-cause mortality (pRR 0.83; 95% confidence interval 0.47-1.48). Nor differences were found in secondary outcomes.

CONCLUSIONS

The limited data available did not show significant differences in terms of all-cause mortality or significant secondary outcomes in patients with FN receiving BLA in prolonged vs. short-term infusion. High-quality RCTs are needed to determine whether there are subgroups of FN patients who would benefit from prolonged BLA infusion.

Continuous infusion of beta-lactam antibiotics: narrative review of systematic reviews, and implications for outpatient parenteral antibiotic therapy

INTRODUCTION

Continuous infusion (CI) of beta-lactam antibiotics may be of benefit in some patients, particularly those with severe infections. However, most studies have been small and conflicting results have been reported. The best available evidence on clinical outcomes of beta-lactam CI comes from systematic reviews/meta-analyses that integrate the available data.

AREAS COVERED

A search of PubMed from inception to the end of February 2022 for systematic reviews of clinical outcomes with beta-lactam CI for any indication identified 12 reviews, all of which focused on hospitalized patients, most of whom were critically ill. A narrative overview of these systematic reviews/meta-analyses is provided. No systematic reviews evaluating the use of beta-lactam CI for outpatient parenteral antibiotic therapy (OPAT) were identified, as few studies have focused on this area. Relevant data are summarized, and consideration is given to issues that need to be addressed when using beta-lactam CI in the setting of OPAT.

EXPERT OPINION

Evidence from systematic reviews supports a role for beta-lactam CI in the treatment of hospitalized patients with severe/life-threatening infections. Beta-lactam CI can play a role in patients receiving OPAT for severe chronic/difficult-to-treat infections, but additional data are needed to clarify its optimal use.

Clinical and pharmacokinetic/dynamic outcomes of prolonged infusions of beta-lactam antimicrobials: An overview of systematic reviews

OBJECTIVE

This overview of reviews aims to map and compare of objectives, methods, and findings of existing systematic reviews to develop a greater understanding of the information available about prolonged beta-lactam infusions in hospitalized patients with infection.

DESIGN

Overview of systematic reviews.

DATA SOURCES

Medline, Embase, PROSPERO and the Cochrane Library were systematically searched from January, 1990 to June, 2019 using a peer reviewed search strategy. Grey literature was also searched for relevant reviews.

ELIGIBILITY CRITERIA FOR SELECTING REVIEWS

Systematic reviews were sought that compared two or more infusion strategies for intravenous beta-lactam antimicrobials and report clinical cure or mortality. Populations of included reviews were restricted to hospitalized patients with infection, without restrictions on age, infection type, or disease.

DATA EXTRACTION AND ANALYSIS

Abstract screening, data extraction, quality and risk of bias assessment were conducted by two independent reviewers. Overlap between reviews was assessed using a modified corrected covered area. Overview findings are reported in accordance with Cochrane's recommendation for overview conduct. Clinical outcomes extracted included survival, clinical cure, treatment failure, microbiological cure, length of stay, adverse events, cost, and emergence of resistance.

RESULTS

The search strategy identified 3327 unique citations from which 21 eligible reviews were included. Reviews varied by population, intervention and outcomes studied. Between reviews, overlap of primary studies was generally high, methodologic quality generally low and risk of bias variable. Nine of 14 reviews that quantitatively evaluated mortality and clinical cure identified a benefit with prolonged infusions of beta lactams when compared with intermittent infusions. Evidence of mortality and clinical cure benefit was greater among critically ill patients when compared to less sick patients and lower in randomized controlled trials when compared with observational studies.

CONCLUSIONS

Findings from our review demonstrate a consistent and reproducible lack of harm with prolonged infusions of beta-lactam antibiotics with variability in effect size and significance of benefits. Despite 21 systematic reviews addressing prolonged infusions of beta-lactams, this overview supports the continued need for a definitive systematic review given variability in populations, interventions and outcomes in the current systematic reviews. Subsequent systematic reviews should have more rigorous and transparent methods, only include RCTs and evaluate the proposed benefits found in various subgroup-analyses-i.e. high risk of mortality.

TRIAL REGISTRATION

Prospero registry, CRD42019117118.

Towards a Generic Tool for Prediction of Meropenem Systemic and Infection-Site Exposure: A Physiologically Based Pharmacokinetic Model for Adult Patients with Pneumonia

OBJECTIVE

The objective of this study was to develop a physiologically based pharmacokinetic model for meropenem using a retrograde approach, which could serve as a basis for prediction of the systemic and infection-site drug exposures in different populations and indications. We intended this model to be a useful tool to inform (local) pharmacokinetic-based optimal dosing of meropenem in different settings.

METHODS

We developed a reduced physiologically based pharmacokinetic model with NONMEM software using a top-down approach. We used historical (previously published) data for model development and qualification. We used steady-state systemic and infection-site concentrations from 60 adult patients diagnosed with severe lung infection for model development and internal evaluation. The data included rich plasma and sparse epithelial lining fluid samples. We based the internal validation of the model on successful numerical convergence, adequate precision in parameter estimation, acceptable goodness-of-fit plot with no indication of bias, and acceptable performance of visual predictive checks. We performed external validation by fitting the model to independent data from five previously published studies: four studies in patients with pneumonia, with different grades of renal impairment, and one study in morbidly obese patients.

RESULTS

We successfully fitted a reduced physiologically based pharmacokinetic model with six compartments (arterial and venous pools, infection site [lungs], liver, kidneys and rest of the body) to the data and adequately estimated model parameters. We successfully qualified the model (internally and externally) using established methods. Estimated values for tissue-to-plasma partition coefficients were 0.2629 and 0.1946 for lungs and non-fat tissues (kidneys and liver), respectively. Estimated total clearance was 8.174 L/h for a typical patient with a glomerular filtration rate of 65 mL/min. Consistent with the known mechanism of meropenem elimination and previously published models, renal clearance accounted for 70% of total clearance. The model had good predictive performances on data from five different sources including populations with different characteristics with regard to body size, renal function and morbidity.

CONCLUSIONS

We successfully developed a physiologically based pharmacokinetic model for meropenem in adult patients to be used as a basis for prediction of concentrations in different groups of patients, and eventually for effective dose individualisation in different subgroups of the population.

Usefulness of therapeutic drug monitoring of piperacillin and meropenem in routine clinical practice: a prospective cohort study in critically ill patients

Background

Beta-lactam anti-infective levels after standard dosing have been shown to be subtherapeutic when renal clearance is augmented.

Objective

To determine if piperacillin and meropenem are found to be in their therapeutic range in infected critically ill patients when administered by continuous intravenous infusion (CII) assisted by a therapeutic drug monitoring (TDM) report issued by the pharmacy service.

Methods

This prospective non-controlled intervention study evaluated septic patients in an intensive care unit. Patients received a loading dose of meropenem or piperacillin-tazobactam and the antibiotics were afterwards administered by CII. Blood concentrations were determined by high-performance liquid chromatography assays. The adequacy of β-lactam therapy in the cohort subjected to intervention was assessed by determining whether plasma levels during CII were >4 times the informed minimum inhibitory concentration during the first 96 hours of treatment.

Results

A total of 124 patients were subject to TDM during antibiotic treatment but, for the analysis of the fulfilment of pharmacodynamic requirements, data from 31/124 (25%) were excluded. Of the whole cohort of treatment courses, 57/93 (61.3%) reached the target level. Plasma levels were adequate in 41/70 (58.6%) and 16/23 (69.6%) of the patients treated with piperacillin-tazobactam and meropenem, respectively. Globally, recommendations based on TDM results were followed in 35/93 (37.6%) of the treatment courses.

Conclusions

The results of the study show that, in critically ill patients with sepsis, there is a significant proportion of treatment courses where target levels are not reached even if the antibiotics are administered by CII and TDM support is provided by the pharmacy service. This TDM support should be offered on a real-time basis to be really useful.

Pharmacokinetics-pharmacodynamics issues relevant for the clinical use of beta-lactam antibiotics in critically ill patients

Antimicrobials are among the most important and commonly prescribed drugs in the management of critically ill patients and beta-lactams are the most common antibiotic class used. Critically ill patient's pathophysiological factors lead to altered pharmacokinetics and pharmacodynamics of beta-lactams.A comprehensive bibliographic search in PubMed database of all English language articles published from January 2000 to December 2017 was performed, allowing the selection of articles addressing the pharmacokinetics or pharmacodynamics of beta-lactam antibiotics in critically ill patients.In critically ill patients, several factors may increase volume of distribution and enhance renal clearance, inducing high intra- and inter-patient variability in beta-lactam concentration and promoting the risk of antibiotic underdosing. The duration of infusion of beta-lactams has been shown to influence the fT > minimal inhibitory concentration and an improved beta-lactam pharmacodynamics profile may be obtained by longer exposure with more frequent dosing, extended infusions, or continuous infusions.The use of extracorporeal support techniques in the critically ill may further contribute to this problem and we recommend not reducing standard antibiotic dosage since no drug accumulation was found in the available literature and to maintain continuous or prolonged infusion, especially for the treatment of infections caused by multidrug-resistant bacteria.Prediction of outcome based on concentrations in plasma results in overestimation of antimicrobial activity at the site of infection, namely in cerebrospinal fluid and the lung. Therefore, although no studies have assessed clinical outcome, we recommend using higher than standard dosing, preferably with continuous or prolonged infusions, especially when treating less susceptible bacterial strains at these sites, as the pharmacodynamics profile may improve with no apparent increase in toxicity.A therapeutic drug monitoring-guided approach could be particularly useful in critically ill patients in whom achieving target concentrations is more difficult, such as obese patients, immunocompromised patients, those infected by highly resistant bacterial strains, patients with augmented renal clearance, and those undergoing extracorporeal support techniques.

A Randomized Pharmacokinetic and Pharmacodynamic Evaluation of Every 8-Hour and 12-Hour Dosing Strategies of Vancomycin and Cefepime in Neurocritically ill Patients

PURPOSE

Neurocritically ill patients have clinically significant alterations in pharmacokinetic parameters of renally eliminated medications that may result in subtherapeutic plasma and cerebrospinal fluid antibiotic concentrations.

METHODS

We conducted a prospective randomized open-label study of adult neurocritically ill patients treated with vancomycin and cefepime. Vancomycin 15 mg/kg and cefepime 2 g were dosed at every-8- or 12-hour intervals. The primary outcomes were the achievement of pharmacodynamic (PD) targets related to time of unbound drug above minimum inhibitory concentrations (MIC) for 60% or more of the dosing interval (fT > MIC ≥ 60%) for β-lactams and ratio of 24-hour area under the curve (AUC):MIC of 400 or greater for vancomycin.

RESULTS

Twenty patients were included in the study. They were divided equally between the every-12-hour and every-8-hour dosing groups. Patients (mean age 51.8 ± 11 yrs) were primarily male (60%) and white (95%), and most had an admission diagnosis of intracranial hemorrhage (80%). Compared with the every-12-hour group, the every-8-hour vancomycin group achieved target trough concentrations (higher than 15 μg/ml) significantly more frequently at initial measurement (0% vs 80%, p<0.01) and at 7-10 days (0% vs 90%, p=0.045) and achieved PD targets more frequently at increasing MICs. Similarly, compared with every-12-hour dosing, the every-8-hour cefepime dosing strategy significantly increased PD target attainment (fT > MIC ≥ 60%) at an MIC of 8 μg/ml (20% vs 70%, p=0.02).

CONCLUSIONS

This study demonstrated that more frequent dosing of vancomycin and cefepime is required to achieve optimal PD targets in adult neurocritically ill patients. The need for increased total daily doses is potentially secondary to the development of augmented renal clearance.

Application of Antibiotic Pharmacodynamics and Dosing Principles in Patients With Sepsis

Sepsis is associated with marked mortality, which may be reduced by prompt initiation of adequate, appropriate doses of antibiotic. Critically ill patients often have physiological changes that reduce blood and tissue concentrations of antibiotic and high rates of multidrug-resistant pathogens, which may affect patients' outcomes. All critical care professionals, including critical care nurses, should understand antibiotic pharmacokinetics and pharmacodynamics to ensure sound antibiotic dosing and administration strategies for optimal microbial killing and patients' outcomes. Effective pathogen eradication occurs when the dose of antibiotic reaches or maintains optimal concentrations relative to the minimum inhibitory concentration for the pathogen. Time-dependent antibiotics, such as β-lactams, can be given as extended or continuous infusions. Concentration-dependent antibiotics such as aminoglycosides are optimized by using high, once-daily dosing strategies with serum concentration monitoring. Vancomycin and fluoroquinolones are dependent on both time and concentration above the minimum inhibitory concentration.

A Nonparametric Pharmacokinetic Approach to Determine the Optimal Dosing Regimen for 30-Minute and 3-Hour Meropenem Infusions in Critically Ill Patients

BACKGROUND

Pharmacokinetics of meropenem differ widely in the critically ill population. It is imperative to maintain meropenem concentrations above the inhibitory concentrations for most of the interdose interval. A population pharmacokinetic/pharmacodynamic model was developed to determine the probability of target attainment for 3-hour and 30-minute infusion regimens in this population.

METHODS

This study was performed in an intensive care setting among adult patients who were initiated on meropenem at a dose of 1000 mg. Multiple blood specimens were collected at predetermined time points during the interdose period, and meropenem concentrations were measured using high performance liquid chromatography. Using Pmetrics, a pharmacokinetic/pharmacodynamic model was developed and validated. Monte Carlo simulation was performed, and probability of target attainment (100% T > minimum inhibitory concentration (MIC), with a probability >0.9) for doubling MICs was determined for different regimens of meropenem.

RESULTS

A 2-compartment multiplicative gamma error model best described the population parameters from 34 patients. The pharmacokinetic parameters used in the final model were Ke (elimination rate constant from the central compartment), Vc (volume of distribution of central compartment), KCP and KPC (intercompartmental rate constants), and IC2 (the fitted amount of meropenem in the peripheral compartment). Inclusion of creatinine clearance (CLcreat) and body weight as covariates improved the model prediction (Ke = Ke0 × (Equation is included in full-text article.), Vc = Vc0 × Weight). The Ke and Vc [geometric mean (range)] of the individuals were 0.54 (0.01-2.61)/h and 9.36 (4.35-21.62) L, respectively. The probability of attaining the target, T > MIC of 100%, was higher for 3-hour infusion regimens compared with 30-minute infusion regimens for all ranges of CLcreat.

CONCLUSIONS

This study emphasizes that extended regimens of meropenem are preferable for treating infections caused by bacteria with higher MICs. The nonparametric analysis using body weight and CLcreat as covariate adequately predicted the pharmacokinetics of meropenem in critically ill patients with a wide range of renal function.

A Review of Clinical Outcomes Associated with Two Meropenem Dosing Strategies

Meropenem is a carbapenem antibiotic that exhibits time-dependent bactericidal activity, traditionally dosed intravenously at 1 g every 8 h. In order to maximize its pharmacodynamic activity and reduce costs, an alternative regimen employed by many institutions is 500 mg every 6 h. The objective of this review was to summarize and evaluate published literature comparing clinical outcomes associated with these two meropenem dosing regimens. The literature was searched up to October 2016 using the MEDLINE, EMBASE, and Google Scholar databases. Three retrospective cohort studies were identified that compared clinical outcomes in general infectious disease patients (two studies) and patients with febrile neutropenia (one study). All studies reported no difference in clinical outcomes (clinical success, time to defervescence, sign or symptom resolution, length of stay, mortality, need for other antibiotics, and seizure rates). One study reported reduced economic costs with the alternative dosing. Interpretation of findings was primarily limited by small sample sizes and generalizability. Based on the data reviewed, the alternative dosing regimen of meropenem 500 mg intravenously every 6 h could be considered a therapeutic option. Future studies are needed to confirm the findings of this review, especially in high-risk populations such as immunocompromised patients or those with severe infections.

Continuous and Prolonged Intravenous β-Lactam Dosing: Implications for the Clinical Laboratory

Beta-lactam antibiotics serve as a cornerstone in the management of bacterial infections because of their wide spectrum of activity and low toxicity. Since resistance rates among bacteria are continuously on the rise and the pipeline for new antibiotics does not meet this trend, an optimization of current beta-lactam treatment is needed. This review provides an overview of optimization through use of prolonged- and continuous-infusion dosing strategies compared with more traditional intermittent infusions. Included is an overview of the scientific basis for using these nontraditional prolonged- and continuous-infusion-based regimens, with a focus on major areas in which the clinical laboratory can support the clinical use of these regimens.

Determination of synergy between sulbactam, meropenem and colistin in carbapenem-resistant Klebsiella pneumoniae and Acinetobacter baumannii isolates and correlation with the molecular mechanism of resistance

Treatment of infections with carbapenem-resistant Gram negative organism is a major challenge especially among intensive care patients. Combinations of sulbactam, meropenem and colistin was studied for its synergistic activity against 100 invasive isolates of carbapenem-resistant Klebsiella pneumoniae and Acinetobacter baumannii-calcoaceticus complex by checkerboard assay and time kill assay (TKA). In addition, presence of carbapenemase production was determined by multiplex PCR. Time kill assay detected more synergy than checkerboard assay. Good bactericidal activity of 70-100% was noted with the combinations tested. Among K. pneumoniae, isolates producing NDM carbapenemase alone showed significantly more synergy than isolates producing OXA-48-like carbapenemases. In treatment of infection with carbapenem-resistant organisms, the site of infection and the type of carbapenemase produced may help to determine the most effective combination of antimicrobials.

Effect of meropenem administration in extended infusion on the clinical outcome of febrile neutropenia: a retrospective observational study

OBJECTIVES

Information on the efficacy of extended meropenem administration in neutropenic patients is scarce. Our objective was to determine whether the administration of meropenem in a 4 h extended infusion (EI) leads to a better clinical outcome in patients with febrile neutropenia than the conventional short infusion (SI).

METHODS

This was a retrospective observational study. The subjects were neutropenic patients who presented with fever after receiving haematopoietic stem-cell transplantation or induction chemotherapy for acute myeloid leukaemia. The primary endpoint was the success of treatment after 5 days of meropenem therapy, defined as follows: the disappearance of fever leading to a maintained (≥ 24 h) feverless state; the resolution or improvement of the clinical signs and symptoms of infection; the absence of persistent or breakthrough bacteraemia; and no additional antibiotics prescribed because of an unsatisfactory clinical evolution.

RESULTS

Eighty-eight patients received meropenem (1 g/8 h) in SI and 76 received the same dose in EI. Treatment success on day 5 was superior in the EI group [52/76 (68.4%) versus 36/88 (40.9%); P<0.001]. Meropenem administered in EI was independently associated with success (OR 3.13, 95% CI 1.61-6.10). Fewer additional antibiotics were prescribed in the EI group during the first 5 days of treatment [20/76 (26.3%) versus 44/88 (50.0%); P=0.002]. Using Kaplan-Meier survival analysis a more prompt defervescence and a faster decrease in C-reactive protein concentration were observed in the EI group (P=0.021 and P=0.037, respectively). There were no significant differences in the length of hospital stay and in the mortality rate.

CONCLUSIONS

Meropenem administration in EI results in a better clinical outcome for febrile neutropenia episodes, with fewer additional antibiotics needed.

The effect of the molecular adsorbent recirculating system on moxifloxacin and meropenem plasma levels

BACKGROUND

Adequate plasma antibiotic concentrations are necessary for effective elimination of invading microorganism; however, extracorporeal organ support systems are well known to alter plasma concentrations of antibiotics, requiring dose adjustments to achieve effective minimal inhibitory concentrations in the patient's blood.

METHODS

A mock molecular adsorbent recirculating system (MARS) circuit was set using 5000 ml of bovine heparinized whole blood to simulate an 8-h MARS treatment session. After the loading dose of 400 mg of moxifloxacin or 2 g of meropenem had been added, blood was drawn from the different parts of the MARS circuit at various time points and analyzed by high-performance liquid chromatography. The experiments were performed in triplicate. Additionally, meropenem concentrations were determined in the plasma of one patient treated with MARS suffering from acute liver failure due to an idiosyncratic reaction to immunosuppressive medication.

RESULTS

In our single-compartment model, a significant decrease in the quasi-systemic concentration of moxifloxacin and meropenem could be detected as early as 15 min after the commencing of the MARS circuit. Moreover, within 60 min the moxifloxacin and meropenem concentrations were less than 50% of the initial value. The activated charcoal removed the majority of moxifloxacin and meropenem in the albumin circuit. In our patient, the meropenem concentrations in the return line after MARS were constantly lower than in the access line, indicating a likely removal of meropenem through MARS.

CONCLUSION

Our data provide evidence that moxifloxacin and meropenem are effectively removed from the patient's blood by MARS, leading to low plasma levels. Dose adjustments of both antibiotic compounds may be required.

Treatment of Klebsiella pneumoniae carbapenemase (KPC) infections: a review of published case series and case reports

The emergence of Klebsiella pneumoniae carbapenemases (KPCs) producing bacteria has become a significant global public health challenge while the optimal treatment remains undefined. We performed a systematic review of published studies and reports of treatment outcomes of KPC infections using MEDLINE (2001–2011). Articles or cases were excluded if one of the following was fulfilled: no individual patient data provided, no treatment regimen specified, no treatment outcome specified, report of colonization, or greater than three antibiotics were used to treat the KPC infection. Data extracted included patient demographics, site of infection, organism, KPC subtype, antimicrobial therapy directed at KPC-infection, and treatment outcome. Statistical analysis was performed in an exploratory manner. A total of 38 articles comprising 105 cases were included in the analysis. The majority of infections were due to K. pneumoniae (89%). The most common site of infection was blood (52%), followed by respiratory (30%), and urine (10%). Forty-nine (47%) cases received monotherapy and 56 (53%) cases received combination therapy directed at the KPC-infection. Significantly more treatment failures were seen in cases that received monotherapy compared to cases who received combination therapy (49% vs 25%; p= 0.01). Respiratory infections were associated with higher rates of treatment failure with monotherapy compared to combination therapy (67% vs 29% p= 0.03). Polymyxin monotherapy was associated with higher treatment failure rates compared to polymyxin-based combination therapy (73% vs 29%; p= 0.02); similarly, higher treatment failure rates were seen with carbapenem monotherapy compared to carbapenem-based combination therapy (60% vs 26%; p= 0.03). Overall treatment failure rates were not significantly different in the three most common antibiotic-class combinations: polymyxin plus carbapenem, polymyxin plus tigecycline, polymyxin plus aminoglycoside (30%, 29%, and 25% respectively; p=0.6). In conclusion, combination therapy is recommended for the treatment of KPC infections; however, which combination of antimicrobial agents needs to be established in future prospective clinical trials.

Dosing nomograms for attaining optimum concentrations of meropenem by continuous infusion in critically ill patients with severe gram-negative infections: a pharmacokinetics/pharmacodynamics-based approach

The worrisome increase in Gram-negative bacteria with borderline susceptibility to carbapenems and of carbapenemase-producing Enterobacteriaceae has significantly undermined their efficacy. Continuous infusion may be the best way to maximize the time-dependent activity of meropenem. The aim of this study was to create dosing nomograms in relation to different creatinine clearance (CL(Cr)) estimates for use in daily clinical practice to target the steady-state concentrations (C(ss)s) of meropenem during continuous infusion at 8 to 16 mg/liter (after the administration of an initial loading dose of 1 to 2 g over 30 min). The correlation between meropenem clearance (CL(m)) and CL(Cr) was retrospectively assessed in a cohort of critically ill patients (group 1, n = 67) to create a formula for dosage calculation to target C(ss). The performance of this formula was validated in a similar cohort (group 2, n = 56) by comparison of the observed and the predicted C(ss)s. A significant relationship between CL(m) and CL(Cr) was observed in group 1 (r = 0.72, P < 0.001). The application of the formula to meropenem dosing in group 2, infusion rate (g/24 h) = [0.078 × CL(Cr) (ml/min) + 2.85] × target C(ss) × (24/1,000), led to a significant correlation between the observed and the predicted C(ss)s (r = 0.92, P < 0.001). Dosing nomograms based on CL(Cr) were created to target the meropenem C(ss) at 8, 12, and 16 mg/liter in critically ill patients. These nomograms could be helpful in improving the treatment of severe Gram-negative infections with meropenem, especially in the presence of borderline susceptible pathogens or even of carbapenemase producers and/or of pathophysiological conditions which may enhance meropenem clearance.

Carbapenem therapy for bacteremia due to extended-spectrum-β-lactamase-producing Escherichia coli or Klebsiella pneumoniae: implications of ertapenem susceptibility

A retrospective study was conducted at two medical centers in Taiwan to evaluate the clinical characteristics, outcomes, and risk factors for mortality among patients treated with a carbapenem for bacteremia caused by extended-spectrum-beta-lactamase (ESBL)-producing organisms. A total of 251 patients with bacteremia caused by ESBL-producing Escherichia coli and Klebsiella pneumoniae isolates treated by a carbapenem were identified. Among these ESBL-producing isolates, rates of susceptibility to ertapenem (MICs ≤ 0.25 μg/ml) were 83.8% and 76.4%, respectively; those to meropenem were 100% and 99.3%, respectively; and those to imipenem were 100% and 97.9%, respectively. There were no significant differences in the critical illness rate (P = 0.1) or sepsis-related mortality rate (P = 0.2) for patients with bacteremia caused by ESBL-producing K. pneumoniae (140 isolates, 55.8%) and E. coli (111 isolates, 44.2%). Multivariate analysis of variables related to sepsis-related mortality revealed that the presence of severe sepsis (odds ratio [OR], 15.9; 95% confidence interval [CI], 5.84 to 43.34; P < 0.001), hospital-onset bacteremia (OR, 4.65; 95% CI, 1.42 to 15.24; P = 0.01), and ertapenem-nonsusceptible isolates (OR, 5.12; 95% CI, 2.04 to 12.88; P = 0.001) were independent risk factors. The patients receiving inappropriate therapy had a higher sepsis-related mortality than those with appropriate therapy (P = 0.002), irrespective of ertapenem, imipenem, or meropenem therapy. Infections due to the ertapenem-susceptible isolates (MICs ≤ 0.25 μg/ml) were associated with a more favorable outcome than those due to ertapenem-nonsusceptible isolates (MICs > 0.25 μg/ml), if treated by a carbapenem. However, the mortality for patients with bacteremic episodes due to isolates with MICs of ≤ 0.5 μg/ml was similar to the mortality for those whose isolates had MICs of >0.5 μg/ml (P = 0.8). Such a finding supports the rationale of the current CLSI 2011 criteria for carbapenems for Enterobacteriaceae.

Status report on carbapenemases: challenges and prospects

Antimicrobial resistance in hospital and community-onset bacterial infections is a significant source of patient morbidity and mortality. In the past decade, we have witnessed the increasing recovery of carbapenem-resistant Gram-negative bacteria. For many isolates, carbapenem resistance is due to the production of carbapenemases, β-lactamases that can inactivate carbapenems and frequently other β-lactam antibiotics. Currently, these enzymes are mainly found in three different β-lactamase classes (class A, B and D). Regardless of the molecular classification, there are few antimicrobials available to treat infections with these organisms and data regarding agents in development are limited to in vitro studies. This article focuses on the epidemiology of carbapenemase-producing Gram-negative bacteria. We also review available agents and those in development with potential activity against this evolving threat.

Carbapenemase-producing Klebsiella pneumoniae: (when) might we still consider treating with carbapenems?

Infections caused by carbapenemase-producing Klebsiella pneumoniae (CPKP) are increasing in frequency worldwide. CPKP isolates exhibit extensive drug resistance phenotypes, complicate therapy, and limit treatment options. Although CPKP isolates are often highly resistant to carbapenems, a proportion of these have relatively low MICs for carbapenems, raising the question of whether this class of agents has any therapeutic potential against CPKP infections. Results from animal studies and patient outcome data indicate that carbapenems retain meaningful in vitro activity against CPKP isolates with carbapenem MICs of ≤ 4 mg/L. Accumulating clinical experience also suggests that the therapeutic efficacy of carbapenems against CPKP isolates with MICs of ≤ 4 mg/L is enhanced when these agents are administered in combination with another active antibiotic. The results of human pharmacokinetic/pharmacodynamic studies are in line with the above observations; it is highly probable that a high-dose/prolonged-infusion regimen of a carbapenem would attain a time above the MIC value of 50% for CPKP isolates with MICs up to 4 mg/L, ensuring acceptable drug exposure and favourable treatment outcome. The analyses summarized in this review support the notion that carbapenems have their place in the treatment of CPKP infections and that the currently proposed EUCAST clinical breakpoints could direct physicians in making treatment decisions.

Antibiotic dosing in critically ill patients with acute kidney injury

A common cause of acute kidney injury (AKI) is sepsis, which makes appropriate dosing of antibiotics in these patients essential. Drug dosing in critically ill patients with AKI, however, can be complicated. Critical illness and AKI can both substantially alter pharmacokinetic parameters as compared with healthy individuals or patients with end-stage renal disease. Furthermore, drug pharmacokinetic parameters are highly variable within the critically ill population. The volume of distribution of hydrophilic agents can increase as a result of fluid overload and decreased binding of the drug to serum proteins, and antibiotic loading doses must be adjusted upwards to account for these changes. Although renal elimination of drugs is decreased in patients with AKI, residual renal function in conjunction with renal replacement therapies (RRTs) result in enhanced drug clearance, and maintenance doses must reflect this situation. Antibiotic dosing decisions should be individualized to take into account patient-related, RRT-related, and drug-related factors. Efforts must also be made to optimize the attainment of antibiotic pharmacodynamic goals in this population.

Evaluation of updated interpretative criteria for categorizing Klebsiella pneumoniae with reduced carbapenem susceptibility

We studied the accuracy of various susceptibility testing methods, including the 2009, 2010, and updated 2010 CLSI recommendations, to identify Klebsiella pneumoniae isolates with reduced susceptibility to carbapenems associated with different mechanisms of resistance. Forty-three wild-type (WT) strains, 42 extended-spectrum β-lactamase (ESBL) producers, 18 ESBL producers with outer membrane porin protein loss (ESBL/Omp strains), and 42 blaKPC-possessing K. pneumoniae (KPC-Kp) isolates were evaluated. Imipenem (IPM), meropenem (MEM), ertapenem (ERT), and doripenem (DOR) were tested by broth microdilution (BMD), Etest, and disk diffusion (DD), and the modified Hodge test (MHT) was performed using IPM and MEM disks. Results were interpreted according to original as well as recently updated interpretative criteria. MHT was positive for all 42 KPC-Kp isolates and 10 of 18 ESBL/Omp strains and therefore had poor specificity in differentiating between KPC-Kp and ESBL/Omp isolates. Based on the updated CLSI standards, phenotypic susceptibility testing by BMD and DD differentiated most carbapenem-susceptible from carbapenem-nonsusceptible K. pneumoniae isolates without the need for MHT, while the Etest method characterized many KPC-Kp isolates as susceptible, and breakpoints may need to be lowered for this method. However, both the original and updated CLSI criteria do not adequately differentiate between isolates in the KPC-Kp group, which are unlikely to respond to carbapenem therapy, and those in the ESBL/Omp group, which are likely to respond to carbapenem therapy if MICs are within pharmacokinetic/pharmacodynamic targets. Further studies are required to determine if there is a clinical need to differentiate between KPC-Kp and ESBL/Omp groups.