Similar efficacy and safety of daptomycin versus linezolid for treatment of vancomycin-resistant enterococcal bloodstream infections: a meta-analysis

Pharmacotherapies for multidrug-resistant gram-positive infections: current options and beyond

INTRODUCTION

Infections due to multidrug-resistant organisms (MDRO) are a serious concern for public health with high morbidity and mortality. Though many antibiotics have been introduced to manage these infections, there are remaining concerns regarding the optimal management of Gram-positive MDROs.

AREAS COVERED

A literature search on the PubMed/Medline database was conducted. We applied no language and time limits for the search strategy. In this narrative review, we discuss the current options for managing Gram-positive MDROs as well as non-traditional antibacterial agents in development.

EXPERT OPINION

Despite their introduction more than 70 years ago, glycopeptides are still the cornerstone in treating Gram-positive infections: all registrative studies of new antibiotics have glycopeptides as control; these studies are designed as not inferior studies, therefore it is almost impossible to give recommendations other than the use of glycopeptides in the treatment of Gram-positive infections. The best evidence on treatments different from glycopeptides comes from post-hoc analysis and meta-analysis. Non-traditional antibacterial agents are being studied to aid in short and effective antibiotic therapies. The use of non-traditional antibacterial agents is not restricted to replacing traditional antibacterial agents with alternative therapies; instead, they should be used in combination with antibiotic therapies.

A cost minimisation analysis comparing oral linezolid and intravenous daptomycin administered via an outpatient parenteral antibiotic therapy programme in patients requiring prolonged antibiotic courses

This study is an economic analysis seeking to examine cost savings that may be accrued from usage of oral linezolid in place of OPAT IV daptomycin in patients requiring prolonged courses of IV or highly bioavailable oral antibiotic therapy. In order to do so we conducted a literature review to establish the scenarios in which the agents could be considered equivalent. We then, using a decision-tree model, conducted a cost analysis to establish differences in cost between the approaches. Under the model base-case, the total cost of treatment with OPAT daptomycin was €3,496.84 and the total cost of treatment with oral linezolid was €772.01. Therefore the oral linezolid strategy would be projected to save the Irish health service €2,724.83 per patient. These results were robust to one-way deterministic sensitivity analyses and probabilistic sensitivity analysis. Our study suggests that significant savings could be safely accrued in the management of these patients.

Therapeutics for Vancomycin-Resistant Enterococcal Bloodstream Infections

Vancomycin-resistant enterococci (VRE) are common causes of bloodstream infections (BSIs) with high morbidity and mortality rates. They are pathogens of global concern with a limited treatment pipeline. Significant challenges exist in the management of VRE BSI, including drug dosing, the emergence of resistance, and the optimal treatment for persistent bacteremia and infective endocarditis. Therapeutic drug monitoring (TDM) for antimicrobial therapy is evolving for VRE-active agents; however, there are significant gaps in the literature for predicting antimicrobial efficacy for VRE BSIs. To date, TDM has the greatest evidence for predicting drug toxicity for the three main VRE-active antimicrobial agents daptomycin, linezolid, and teicoplanin. This article presents an overview of the treatment options for VRE BSIs, the role of antimicrobial dose optimization through TDM in supporting clinical infection management, and challenges and perspectives for the future.

Risk factors for mortality after linezolid treatment of vancomycin-resistant Enterococcus bloodstream infection

OBJECTIVES

We analyzed the risk factors affecting linezolid treatment outcome in vancomycin-resistant Enterococcus (VRE) bloodstream infection (BSI).

METHODS

We conducted a multicenter observational study of patients who received linezolid 600 mg every 12 hours for VRE BSI. The primary outcome was 28-day mortality. The estimated area under the concentration-time curve and trough concentration were calculated. Multivariable logistic regression was used for the outcome analysis.

RESULTS

A total of 170 patients were included: 114 (67.1%) survived and 56 (32.9%) did not. A total of 26 (18.2%) isolates showed a linezolid minimum inhibitory concentration (MIC) of ≤1 mg/l, 113 (79.0%) of 2 mg/l, and 4 (2.8%) of 4 mg/l. The univariable analysis showed that the linezolid MIC and concentration-time curve/MIC were not associated with mortality (P = 0.95 and P = 0.42, respectively). After adjusting for underlying comorbidity and disease severity, the linezolid dose per body weight (LDBW), body height, and interaction between them were independent risks for mortality. Marginal analysis showed that increasing the LDBW was protective in patients with a body height <160 cm. A trough concentration of >12.2 mg/l was a risk factor for thrombocytopenia.

CONCLUSION

The LDBW and body height were interactively associated with clinical outcomes of linezolid treatment for VRE BSI.

Clinical manifestations, characteristics, and outcome of infections caused by vancomycin-resistant enterococci at a tertiary care center in Lebanon: A case-case-control study

BACKGROUND

Vancomycin-resistant enterococci (VRE) are prevalent infectious agents that particularly affect critically-ill patients, and they are on the rise in Lebanon. We aim at determining the potential risk factors and complications for VRE and vancomycin-susceptible enterococci (VSE) infections in a hospital setting and identify risk factors for in-hospital mortality.

METHODS

A case-case-control study design was used where patients with VRE and VSE were included as two separate groups and each group was compared to uninfected controls. We also constructed binary regression models to detect risk factors that were associated with the acquisition of a VRE or a VSE infection. We also identified independent mortality predictors for all patients with enterococcal infection as well as patients with only a VRE infection.

RESULTS

A total of 142 patients with enterococcal infections (VRE and VSE) were compared to 142 in-patients not infected with Enterococcus spp. independent risk factors for a VRE infection were steroid therapy within 30 days and the presence of another infection preceding the VRE infection (aOR 15.4, 95 % CI 2.4-99.3 and 23.9, 95 % CI 3.9-1482, respectively). An independent risk factor for VSE was diabetes mellitus (aOR 5.4, 95 % CI 1.1-26.6). Based on these risk factors, we developed a risk score to be used in quantifying the risk of VRE in a patient with an enterococcal infection. Male sex and low albumin were significant risk factors for mortality in our patient cohort.

CONCLUSIONS

VRE and VSE infections have distinct risk factors that can be used to guide empiric antimicrobial therapy.

Oral stepdown in Gram-positive bloodstream infections: A step in the right direction

Bloodstream infections (BSIs) due to Gram-positive organisms have traditionally been treated with prolonged courses of intravenous antimicrobials. However, this dogma is associated with substantial burden to the patient and health care system. Consequently, there is growing interest in the utilization of oral stepdown therapy, defined as the transition of intravenous therapy to an active oral agent, for this indication. This review highlights available literature examining oral stepdown in adult patients with BSI due to commonly encountered Gram-positive pathogens, including Staphylococcus aureus, Streptococcus spp., and Enterococcus spp. Support for oral stepdown in this setting is primarily derived from observational studies subject to selection bias. Nevertheless, this treatment strategy exhibits promising potential in carefully selected patients as it is consistently associated with reductions in hospital length of stay without jeopardizing clinical cure or survivability. Prospective, randomized trials are needed for validation of oral stepdown in Gram-positive BSI and to identify the optimal patient population and regimen.

Recommendations and guidelines for the treatment of infections due to multidrug resistant organisms

Antimicrobial drug resistance is one of the major threats to global health. It has made common infections increasingly difficult or impossible to treat, and leads to higher medical costs, prolonged hospital stays and increased mortality. Infection rates due to multidrug-resistant organisms (MDRO) are increasing globally. Active agents against MDRO are limited despite an increased in the availability of novel antibiotics in recent years. This guideline aims to assist clinicians in the management of infections due to MDRO. The 2019 Guidelines Recommendations for Evidence-based Antimicrobial agents use in Taiwan (GREAT) working group, comprising of infectious disease specialists from 14 medical centers in Taiwan, reviewed current evidences and drafted recommendations for the treatment of infections due to MDRO. A nationwide expert panel reviewed the recommendations during a consensus meeting in Aug 2020, and the guideline was endorsed by the Infectious Diseases Society of Taiwan (IDST). This guideline includes recommendations for selecting antimicrobial therapy for infections caused by carbapenem-resistant Acinetobacter baumannii, carbapenem-resistant Pseudomonas aeruginosa, carbapenem-resistant Enterobacterales, and vancomycin-resistant Enterococcus. The guideline takes into consideration the local epidemiology, and includes antimicrobial agents that may not yet be available in Taiwan. It is intended to serve as a clinical guide and not to supersede the clinical judgment of physicians in the management of individual patients.

Daptomycin-Resistant Enterococcus Bacteremia Is Associated with Prior Daptomycin Use and Increased Mortality after Liver Transplantation

Background

Risk factors for acquisition of vancomycin-resistant Enterococcus (VRE) include immunosuppression, antibiotic exposure, indwelling catheters, and manipulation of the gastrointestinal tract, all of which occur in liver transplant recipients. VRE infections are documented in liver transplantation (LT); however, only one single center study has assessed the impact of daptomycin-resistant Enterococcus (DRE) in this patient population.

Methods

We conducted a retrospective multicenter cohort study comparing liver transplant recipients with either VRE or DRE bacteremia. The primary outcome was death within 1 year of transplantation. Multivariable logistic regression analyses were performed to calculate adjusted odds ratios for outcomes of interest.

Results

We identified 139 cases of Enterococcus bacteremia following LT, of which 78% were VRE and 22% were DRE. When adjusted for total intensive care unit days in the first transplant year, liver-kidney transplantation, and calcineurin inhibitor use, patients with DRE bacteremia were 2.65 times more likely to die within 1 year of transplantation (adjusted odds ratio [aOR], 2.648; 95% CI, 1.025–6.840; P = .044). Prior daptomycin exposure was found to be an independent predictor of DRE bacteremia (aOR, 30.62; 95% CI, 10.087–92.955; P < .001).

Conclusions

In this multicenter study of LT recipients with Enterococcus bacteremia, DRE bacteremia was associated with higher 1-year mortality rates when compared with VRE bacteremia. Our data provide strong support for dedicated infection prevention and antimicrobial stewardship efforts for transplant patients. Further research is needed to support the development of better antibiotics for DRE and practical guidance focusing on identification and prevention of colonization and subsequent infection in liver transplant recipients at high risk for DRE bacteremia.

Optimization of Linezolid Dosing Regimens for Treatment of Vancomycin-Resistant Enterococci Infection

BACKGROUND

Linezolid, an oxazolidinone antibiotic, is recommended for vancomycin-resistant enterococci (VRE). However, 100% free-drug concentration above the minimum inhibitory concentration (fT>MIC) and an area under the curve of free drug to MIC ratio (fAUC24/MIC) >100 were associated with favorable clinical outcome with less emerging resistance. A plasma trough concentration (C_trough) of linezolid ≥9 μg/mL was also related to hematologic toxicity. Thus, linezolid dose optimization is needed for VRE treatment. The study aimed to determine the in vitro linezolid activity against clinical VRE isolates and linezolid dosing regimens in critically ill patients who met the target pharmacokinetics/pharmacodynamics (PK/PD) for VRE treatment.

MATERIALS AND METHODS

Enterococcal isolates from enterococcal-infected patients were obtained between 2014 and 2018 at Phramongkutklao Hospital. We used Monte Carlo simulation to calculate the probability of target attainment, and the cumulative fraction of response (CFR) of the free area under the curve to MIC ratio (fAUIC₂₄) was used to calculate the fAUC24/MIC 80 - 100 and fT/MIC >85 - 100% of the interval time of administration for clinical response and microbiological eradication as well as the C_trough ≥9 μg/mL for the probability of hematologic toxicity.

RESULTS

For linezolid MIC determination, the MIC median (MIC₅₀), MIC for 90% growth (MIC₉₀), and range for linezolid were 1.5 μg/mL, 2 μg/mL, and 0.72 - 2 μg/mL, respectively. A dosing regimen of 1,200 mg either once daily or as a divided dose every 12 h gave target attainments of fAUC24/MICs >80 and >100, which exceeded 90% for MICs ≤1 and ≤1 μg/mL, respectively, with a rate of hematologic toxicity <15%. If the expected fT>MICs were >85% and 100%, a 1,200-mg divided dose every 12 h could cover VRE isolates having linezolid MICs ≤1 μg/mL and ≤0.75 μg/mL. Even 600 mg every 8 h and 1,200 mg as a continuous infusion gave a higher target attainment of fAUC24/MIC and a fT>MIC and the target CFR, but those regimens gave C_trough ≥9 μg/mL rates of 40.7% and 99.6%.

CONCLUSION

The current dosing of 1,200 mg/day might be optimal treatment for infection by VRE isolates with documented MICs ≤1 μg/mL. For treatment of VRE with a MIC of 2 μg/mL or to achieve the target CFR, the use of linezolid with other antibiotic combinations might help achieve the PK/PD target, provide better clinical outcome, and prevent resistance.

A Pharmacokinetic-Pharmacodynamic Analysis to Dose Optimize Daptomycin in Vancomycin-Resistant Enterococcus faecium: Is the Answer Fixed Dosing or Lowering Breakpoints?

BACKGROUND

The optimal daptomycin dose for vancomycin-resistant Enterococcus faecium remains unclear. Dosing of 8 to 12 mg/kg/d has been recommended to improve outcomes, but literature suggests fixed dosing may improve methicillin-resistant Staphylococcus aureus bacteremia pharmacodynamic (PD) targets.

OBJECTIVE

This study sought to evaluate weight-based versus fixed dosing of daptomycin based on pharmacokinetic and PD (PK-PD) targets in vancomycin-resistant E faecium bacteremia.

METHODS

PK-PD analyses were conducted using previously published PK models for daptomycin. Probability of target attainment (PTA) was assessed for 8 to 12 mg/kg/d and various fixed doses. The percentage of simulated participants who achieved a free area under the concentration-time curve from 0 to 24 hours to minimum inhibitory concentration ratio (fAUC_0-24/MIC) >27.43 for susceptible dose-dependent (SDD) MICs and the probability of a minimum concentration (C_min) > 24.3 mg/L were calculated.

RESULTS

At MICs ≤2 mg/L, fixed doses had the best overall PTA. At the SDD breakpoint of 4 mg/L, all weight-based doses had <60% PTA. A fixed dose of 1500 mg/d was necessary for >/= 90% PTA at higher MICs considered SDD; however, this dose had elevated risks of C_min ≥24.3 mg/L.

CONCLUSION AND RELEVANCE

Fixed doses were more likely to achieve a fAUC/MIC of 27.43 than weight-based doses up to 12 mg/kg/d. However, fixed doses necessary for 90% PTA against SDD isolates with higher MICs were associated with elevated risks of toxicity. A reevaluation of Clinical Laboratory Standards Institute breakpoints may need to be considered, with an emphasis on lowering the SDD breakpoint to 1 mg/L.

[Infections due to multidrug-resistant pathogens : Pathogens, resistance mechanisms and established treatment options]

The increase in resistant pathogens has long been a global problem. Complicated life-threatening infections due to multidrug-resistant pathogens (MRD) meanwhile occur regularly in intensive care medicine. An important and also potentially modifiable factor of the rapid spread of resistance is the irrational use of broad spectrum antibiotics in human medicine. In addition to many other resistance mechanisms, beta-lactamases play an important role in Gram-negative pathogens. They are not uncommonly the leading reason of difficult to treat infections and the failure of known routinely used broad spectrum antibiotics, such as cephalosporins, (acylamino)penicillins and carbapenems. Strategies for containment of MRDs primaríly target the rational use of antibiotics. In this respect interdisciplinary treatment teams, e.g. antibiotic stewardship (ABS) and infectious diseases stewardship (IDS) play a major role.

Pharmacodynamic Analysis of Daptomycin-treated Enterococcal Bacteremia: It Is Time to Change the Breakpoint

BACKGROUND

Currently, there is debate over whether the daptomycin susceptibility breakpoint for enterococci (ie, minimum inhibitory concentration [MIC] ≤4 mg/L) is appropriate. In bacteremia, observational data support prescription of high doses (>8 mg/kg). However, pharmacodynamic targets associated with positive patient outcomes are undefined.

METHODS

Data were pooled from observational studies that assessed outcomes in daptomycin-treated enterococcal bacteremia. Patients who received an additional antienterococcal antibiotic and/or a β-lactam antibiotic at any time during treatment were excluded. Daptomycin exposures were calculated using a published population pharmacokinetic model. The free drug area under the concentration-time curve to MIC ratio (fAUC/MIC) threshold predictive of survival at 30 days was identified by classification and regression tree analysis and confirmed with multivariable logistic regression. Monte Carlo simulations determined the probability of target attainment (PTA) at clinically relevant MICs.

RESULTS

Of 114 patients who received daptomycin monotherapy, 67 (58.8%) were alive at 30 days. A fAUC/MIC >27.43 was associated with survival in low-acuity (n = 77) patients (68.9 vs 37.5%, P = .006), which remained significant after adjusting for infection source and immunosuppression (P = .026). The PTA for a 6-mg/kg/day (every 24 hours) dose was 1.5%-5.5% when the MIC was 4 mg/L (ie, daptomycin-susceptible) and 91.0%-97.9% when the MIC was 1 mg/L.

CONCLUSIONS

For enterococcal bacteremia, a daptomycin fAUC/MIC >27.43 was associated with 30-day survival among low-acuity patients. As pharmacodynamics for the approved dose are optimized only when MIC ≤1 mg/L, these data continue to stress the importance of reevaluation of the susceptibility breakpoint.

Sequential intravenous-to-oral outpatient antibiotic therapy for MRSA bacteraemia: one step closer

Background

Published guidelines call for prolonged courses of intravenous (iv) antibiotics for the treatment of MRSA bloodstream infection (BSI) to ensure eradication of deep foci and decrease relapse risk. Sequential iv-to-oral antibiotic therapy has been successfully applied to other serious infections but has not been evaluated for MRSA BSI.

Objectives

To compare outcomes in adults completing MRSA BSI therapy with oral versus parenteral antibiotics in the outpatient setting [oral outpatient antibiotic therapy (OOAT) versus outpatient parenteral antibiotic therapy (OPAT)].

Methods

This was a single-centre, retrospective, cohort study between 2008 and 2018. The primary outcome was 90 day clinical failure (MRSA BSI recurrence, deep-seated MRSA infection or all-cause mortality). Analyses were adjusted for confounding using inverse probability of treatment weighting (IPTW).

Results

A total of 492 patients were included (70 OOAT, 422 OPAT). In general, OOAT patients had characteristics consistent with a lower risk of poor outcomes; however, after IPTW key prognostic factors were balanced. In IPTW-adjusted analysis, there was non-significant reduction in the rate of 90 day clinical failure in the OOAT group compared with the OPAT group [adjusted HR (aHR) 0.379, 95% CI 0.131-1.101]. In analyses restricted to pre-specified subgroups defined by index infection complexity and comorbidity burden, findings were consistent with the main analysis. Furthermore, OOAT patients had a significantly reduced rate of 90 day hospital readmission (aHR 0.603, 95% CI 0.388-0.937).

Conclusions

We provide preliminary evidence that selected patients with MRSA BSI may have at least equivalent clinical outcomes with OOAT versus OPAT and provide support to ongoing and future studies evaluating oral antibiotics for MRSA BSI.

Treatment and outcomes of Enterococcus faecium bloodstream infections in solid organ transplant recipients

Optimal antimicrobial therapy for Enterococcus faecium bloodstream infection (EFBSI) in the solid organ transplant (SOT) population is not well defined. The purpose of this study was to describe the pharmacotherapy and outcomes of EFBSI in SOT patients. This was a single-center retrospective cohort of SOT patients with EFBSI from 2013 to 2019. Susceptibility testing was performed with Vitek^® 2 or Etest. Estimates of optimal DAP pharmacokinetic/pharmacodynamic exposures (dose <10 mg/kg, fAUC/MIC >27.4) were made from previously established literature and equations. Fifty-one unique cases were included in the analysis. The median age was 61 years and liver (64%), intestinal (19%), and kidney (12%) were the most common organs transplanted. Most patients had indwelling central lines (75%) at the time of bacteremia; intra-abdominal abscesses/fluid collections were present in 44% of patients and 8% had endocarditis. Nineteen (37%) patients had polymicrobial infections. The most common definitive antimicrobial regimens were as follows: DAP plus beta-lactam (46%), DAP monotherapy (18%), and LZD (25%). Of the 33 patients that received DAP, 21% of E faecium isolates developed DAP resistance. 30-day mortality was 25% overall but higher in patients who received an initial DAP dose <10 mg/kg (43% vs 13%). Vancomycin-resistance, severity of illness, neutropenia, and source control were also associated with mortality. Inadequate DAP dosing for EFBSI may be associated with mortality in the SOT population. Larger, controlled analyses are necessary to determine the impact of optimized pharmacodynamics in this population.

Association of daptomycin dosing regimen and mortality in patients with VRE bacteraemia: a review

VRE are associated with ∼1300 deaths per year in the USA. Recent literature suggests that daptomycin, a cyclic lipopeptide antibiotic with concentration-dependent bactericidal activity, is the preferred treatment option for VRE bacteraemia, yet the optimal dosing strategy for this indication has not been established. In vitro evidence suggests that higher-than-labelled doses of daptomycin are required to optimally treat VRE bacteraemia and to inhibit the development of resistance. However, concern of dose-dependent toxicities, notably increases in creatine phosphokinase and the development of rhabdomyolysis, are a barrier to initiating high-dose schemes in clinical practice. Thus, the effectiveness and safety of high-dose daptomycin regimens in clinical practice have remained unclear. While early studies failed to identify differences in mortality, newer, larger investigations suggest high-dose (≥9 mg/kg) daptomycin is associated with reduced mortality in patients with VRE bacteraemia compared with standard (6 mg/kg) dosing regimens. Additionally, the high-dose regimens appear to be safe and may be associated with improved microbiological outcomes. The purpose of this review is to examine the published evidence on the effectiveness and safety of high-dose daptomycin compared with standard dosing regimens for VRE bacteraemia.

Practice Patterns of Infectious Diseases Physicians in Transitioning From Intravenous to Oral Therapy in Patients With Bacteremia

Background

Bacteremia in adult patients has traditionally been treated with extended courses of intravenous antibiotics. Data on the use of (or rapid transition to) oral therapy are limited.

Methods

Adult infectious disease physicians participating in the Infectious Diseases Society of America Emerging Infections Network (EIN) were surveyed regarding their use of oral antibiotics in patients with bacteremia. Respondents were asked to assume that patients were hemodynamically stable, recovered bacteria were susceptible to potential antibiotics, adequate source control had been achieved, and patients had adequate gastrointestinal absorption. Variables of specific bacteria, oral agent, and associated infection were included.

Results

A total of 655 (50%) of 1321 EIN participants responded. Under certain conditions, 88% would transition patients with Gram-negative bacteremia to complete a course of therapy with oral antibiotics; 71% would transition patients with Gram-positive bacteremia to oral agents. Only 78 (12%) respondents would not treat any bacteremic patient with oral agents. Most respondents (≥75%) were comfortable treating infections secondary to Enterobacteriaceae, Salmonella, Pseudomonas, Stenotrophomonas, Streptococcus pneumoniae, and β-hemolytic streptococci with oral agents. Fewer than 20% endorsed use of oral antibiotics for Staphylococcus aureus or in cases of endocarditis. Fluoroquinolones and trimethoprim-sulfamethoxazole were the preferred agents in Gram-negative bacteremia; linezolid and β-lactams were the preferred agents in Gram-positive bacteremia.

Conclusions

In select circumstances, the majority of respondents would transition patients to oral antibiotics, in both Gram-negative and Gram-positive bacteremia. Most agreed with the use of oral agents in Gram-negative bacteremia caused by Enterobacteriaceae, but they would not use oral agents for Gram-positive bacteremia caused by S aureus or in endocarditis.

Agricultural Origins of a Highly Persistent Lineage of Vancomycin-Resistant Enterococcus faecalis in New Zealand

Historical antimicrobial use in NZ agriculture has driven the evolution of ST108, a VRE lineage carrying a range of clinically relevant antimicrobial resistances. The persistence of this lineage in NZ for over a decade indicates that coselection may be an important stabilizing mechanism for its persistence.

Enterococcus faecalis and Enterococcus faecium are human and animal gut commensals. Vancomycin-resistant enterococci (VRE) are important opportunistic pathogens with limited treatment options. Historically, the glycopeptide antibiotics vancomycin and avoparcin selected for the emergence of vancomycin resistance in human and animal isolates, respectively, resulting in global cessation of avoparcin use between 1997 and 2000. To better understand human- and animal-associated VRE strains in the postavoparcin era, we sequenced the genomes of 231 VRE isolates from New Zealand (NZ; 75 human clinical, 156 poultry) cultured between 1998 and 2009. E. faecium lineages and their antibiotic resistance carriage patterns strictly delineated between agricultural and human reservoirs, with bacitracin resistance ubiquitous in poultry but absent in clinical E. faecium strains. In contrast, one E. faecalis lineage (ST108) predominated in both poultry and human isolates in the 3 years following avoparcin discontinuation. Both phylogenetic and antimicrobial susceptibility (i.e., ubiquitous bacitracin resistance in both poultry and clinical ST108 isolates) analyses suggest an agricultural origin for the ST108 lineage. VRE isolate resistomes were carried on multiple, heterogeneous plasmids. In some isolate genomes, bacitracin, erythromycin, and vancomycin resistance elements were colocalized, indicating multiple potentially linked selection mechanisms.

IMPORTANCE Historical antimicrobial use in NZ agriculture has driven the evolution of ST108, a VRE lineage carrying a range of clinically relevant antimicrobial resistances. The persistence of this lineage in NZ for over a decade indicates that coselection may be an important stabilizing mechanism for its persistence.

Pharmacodynamic Analysis of Daptomycin-treated Enterococcal Bacteremia: It Is Time to Change the Breakpoint

BACKGROUND

Currently, there is debate over whether the daptomycin susceptibility breakpoint for enterococci (ie, minimum inhibitory concentration [MIC] ≤4 mg/L) is appropriate. In bacteremia, observational data support prescription of high doses (>8 mg/kg). However, pharmacodynamic targets associated with positive patient outcomes are undefined.

METHODS

Data were pooled from observational studies that assessed outcomes in daptomycin-treated enterococcal bacteremia. Patients who received an additional antienterococcal antibiotic and/or a β-lactam antibiotic at any time during treatment were excluded. Daptomycin exposures were calculated using a published population pharmacokinetic model. The free drug area under the concentration-time curve to MIC ratio (fAUC/MIC) threshold predictive of survival at 30 days was identified by classification and regression tree analysis and confirmed with multivariable logistic regression. Monte Carlo simulations determined the probability of target attainment (PTA) at clinically relevant MICs.

RESULTS

Of 114 patients who received daptomycin monotherapy, 67 (58.8%) were alive at 30 days. A fAUC/MIC >27.43 was associated with survival in low-acuity (n = 77) patients (68.9 vs 37.5%, P = .006), which remained significant after adjusting for infection source and immunosuppression (P = .026). The PTA for a 6-mg/kg/day (every 24 hours) dose was 1.5%-5.5% when the MIC was 4 mg/L (ie, daptomycin-susceptible) and 91.0%-97.9% when the MIC was 1 mg/L.

CONCLUSIONS

For enterococcal bacteremia, a daptomycin fAUC/MIC >27.43 was associated with 30-day survival among low-acuity patients. As pharmacodynamics for the approved dose are optimized only when MIC ≤1 mg/L, these data continue to stress the importance of reevaluation of the susceptibility breakpoint.

Linezolid: a review of its properties, function, and use in critical care

Linezolid can be considered as the first member of the class of oxazolidinone antibiotics. The compound is a synthetic antibiotic that inhibits bacterial protein synthesis through binding to rRNA. It also inhibits the creation of the initiation complex during protein synthesis which can reduce the length of the developed peptide chains, and decrease the rate of reaction of translation elongation. Linezolid has been approved for the treatment of infections caused by vancomycin-resistant Enterococcus faecium, hospital-acquired pneumonia caused by Staphylococcus aureus, complicated skin and skin structure infections (SSSIs), uncomplicated SSSIs caused by methicillin-susceptible S. aureus or Streptococcus pyogenes, and community-acquired pneumonia caused by Streptococcus pneumoniae. Analysis of high-resolution structures of linezolid has demonstrated that it binds a deep cleft of the 50S ribosomal subunit that is surrounded by 23S rRNA nucleotides. Mutation of 23S rRNA was shown to be a linezolid resistance mechanism. Besides, mutations in specific regions of ribosomal proteins uL3 and uL4 are increasingly associated with linezolid resistance. However, these proteins are located further away from the bound drug. The methicillin-resistant S. aureus and vancomycin-resistant enterococci are considered the most common Gram-positive bacteria found in intensive care units (ICUs), and linezolid, as an antimicrobial drug, is commonly utilized to treat infected ICU patients. The drug has favorable in vitro and in vivo activity against the mentioned organisms and is considered as a useful antibiotic to treat infections in the ICU.

Combatting resistant enterococcal infections: a pharmacotherapy review

INTRODUCTION

The role of enterococci in infectious diseases has evolved from a gut and urinary commensal to a major pathogen of concern. Few options exist for resistant enterococci, and appropriate use of the available agents is crucial.

AREAS COVERED

Herein, the authors discuss antibiotics with clinically useful activity against Enterococcus faecalis and E. faecium. The article specifically discusses: antibiotics active against enterococci and their mechanism of resistance, pharmacokinetic and pharmacodynamic principles, in vitro combinations, and clinical studies which focus on urinary tract, intra-abdominal, central nervous system, and bloodstream infections due to enterococci.

EXPERT OPINION

Aminopenicillins are preferred over all other agents when enterococci are susceptible and patients can tolerate them. Daptomycin and linezolid have demonstrated clinical efficacy against vancomycin-resistant enterococci (VRE). Synergistic combinations are often warranted in complex infections of high inoculum and biofilms while monotherapies are generally appropriate for uncomplicated infections. Although active against resistant enterococci, the pharmacokinetics, efficacy and safety of tigecycline and quinupristin/dalfopristin can problematical for severe infections. For cystitis, amoxicillin, nitrofurantoin, or fosfomycin are ideal. Recently, approved agents such as tedizolid and oritavancin have good in vitro activity against VRE but clinical studies against other resistant enterococci are lacking.

Top Questions in Uncomplicated, Non-Staphylococcus aureus Bacteremia

The Infectious Diseases Society of America infection-specific guidelines provide limited guidance on the management of focal infections complicated by secondary bacteremias. We address the following 3 commonly encountered questions and management considerations regarding uncomplicated bacteremia not due to Staphylococcus aureus: the role and choice of oral antibiotics focusing on oral beta-lactams, the shortest effective duration of therapy, and the role of repeat blood cultures.

Effectiveness of Vancomycin or Beta-Lactam Therapy in Ampicillin-Susceptible Enterococcus spp. Bloodstream Infections

BACKGROUND

De-escalation to a beta-lactam improves outcomes for patients with a methicillin-susceptible Staphylococcus aureus bloodstream infection (BSI). Whether a similar strategy is appropriate for enterococcal species is less clear.

OBJECTIVE

To determine whether definitive antibiotic selection affects outcomes for patients with an ampicillin-susceptible enterococcal BSI.

METHODS

This retrospective cohort study included patients over 18 years of age receiving definitive therapy with vancomycin or a beta-lactam for one or more blood cultures positive for Enterococcus spp. isolates between 2007 and 2014. Survival differences were examined using a Kaplan-Meier curve with log-rank test.

RESULTS

One-hundred eighty-six patients received definitive therapy with either vancomycin (n = 45, 24.2%) or a beta-lactam (n = 141, 75.8%). The primary outcome, 30-day all-cause mortality, was not different between groups (6.7% vs 7.1%; P = .992). A post hoc analysis of all-cause mortality 1 year after the index BSI was significantly higher in the vancomycin group (51% vs 33%; P = .032). In a Cox proportional hazards regression model, definitive vancomycin was associated with an increased risk of all-cause mortality at 1 year (hazard ratio [HR]: 2.39; 95% confidence interval [CI]: 1.41-4.04).

CONCLUSION

For patients with an ampicillin-susceptible enterococcal BSI, definitive therapy with vancomycin or a beta-lactam was not independently associated with a difference in 30-day all-cause mortality. Whether definitive vancomycin is associated with poor long-term outcomes warrants further exploration.

Vancomycin-resistant enterococcus infection in the hematopoietic stem cell transplant recipient: an overview of epidemiology, management, and prevention

Vancomycin-resistant enterococcus (VRE) is now one of the leading causes of nosocomial infections in the United States. Hematopoietic stem cell transplantation (HSCT) recipients are at increased risk of VRE colonization and infection. VRE has emerged as a major cause of bacteremia in this population, raising important clinical questions regarding the role and impact of VRE colonization and infection in HSCT outcomes as well as the optimal means of prevention and treatment. We review here the published literature and scientific advances addressing these thorny issues and provide a rational framework for their approach.

Dual antibacterial behavior of a curcumin–upconversion photodynamic nanosystem for efficient eradication of drug-resistant bacteria in a deep joint infection

The curcumin–upconversion photodynamic nanosystem exhibits dual antibacterial behavior for MRSA-induced periprosthetic joint infection under NIR irradiation.

Effect of Continuous and Sequential Therapy among Veterans Receiving Daptomycin or Linezolid for Vancomycin-Resistant Enterococcus faecium Bacteremia

Vancomycin-resistant Enterococcus faecium bloodstream infections (VREF-BSI) cause significant mortality, highlighting the need to optimize their treatment. We compared the effectiveness and safety of daptomycin (DAP) and linezolid (LZD) as continuous or sequential therapy for VREF-BSI in a national, retrospective, propensity score (PS)-matched cohort study of hospitalized Veterans Affairs patients (2004 to 2014). We compared clinical outcomes and adverse events among patients treated with continuous LZD, continuous DAP, or sequential LZD followed by DAP (LZD-to-DAP). Secondarily, we analyzed the impact of infectious diseases (ID) consultation and source of VREF-BSI. A total of 2,630 patients were included in the effectiveness analysis (LZD [n = 1,348], DAP [n = 1,055], LZD-to-DAP [n = 227]). LZD was associated with increased 30-day mortality versus DAP (risk ratio [RR], 1.11; 95% confidence interval [CI], 1.01 to 1.22; P = 0.042). After PS matching, this relationship persisted (RR, 1.13; 95% CI, 1.02 to 1.26; P = 0.015). LZD-to-DAP switchers had lower mortality than those remaining on LZD (RR, 1.29; 95% CI, 1.03 to 1.63; P = 0.021), suggesting a benefit may still be derived with sequential therapy. LZD-treated patients experienced more adverse events, including a ≥50% reduction in platelets (RR, 1.07; 95% CI, 1.03 to 1.11; P = 0.001). DAP was associated with lower mortality than was LZD in patients with endocarditis (RR, 1.20; 95% CI, 1.02 to 1.41; P = 0.024); however, there was no statistically significant association between treatment group and mortality with regard to other sources of infection. Therefore, source of infection appears to be important in selection of patients most likely to benefit from DAP over LZD.

Predictive score of haematological toxicity in patients treated with linezolid

OBJECTIVE

The aims of our study were to determine the factors associated with developing haematological toxicity (HT) in patients taking linezolid (LZD), to develop a predictive model of HT in these patients, and to evaluate factors associated with 30-day mortality.

METHODS

This was an observational retrospective cohort study of patients treated for at least 5 days with LDZ in 2015. Demographic, clinical and analytical data were collected. Development of HT was defined as a 25% platelet count decrease between the basal count and the 1-week lab test.

RESULTS

Five hundred forty-nine patients were finally included, mean age was 73.3 (SD 15.4) years, and 303 (55.2%) were men. One hundred seventy-five (30.1%) patients achieved HT criteria during treatment with LZD and 41 (7.5%) died. The final model included the presence of cerebrovascular disease (2 points), moderate or severe liver disease (2 points), renal failure (2 points) and basal platelet count less than 90,000/mm3 (8 points). This new model showed an AUC of 0.711 (IC 95% 0.664-0.757; p < 0.001) to predict the development of HT. The probability of HT based on this classification was 6.2, 29.9 and 76.5% for low (0-4 points), intermediate (5-10 points) and high risk (>10 points), respectively. The independent variables associated with 30-day mortality were metastatic solid tumor, lymphoma, age >75 years and HT.

CONCLUSION

This score could help in the identification of patients with high risk for HT and assess the use of an antibiotic other than LZD, an important issue considering its relation with 30-day mortality observed in our study.