In vitro pharmacodynamics of vancomycin and cefazolin alone and in combination against methicillin-resistant Staphylococcus aureus

Vancomycin, Daptomycin, Antistaphylococcal β-Lactam, and Trimethoprim-Sulfamethoxazole Monotherapy and Combination Therapy in the Management of Methicillin-Resistant Staphylococcus aureus: A Network Meta-Analysis

Objective: The aim was to evaluate the efficacy and safety of vancomycin or daptomycin (VAN/DAP), antistaphylococcal β-lactam (ASBL), trimethoprim-sulfamethoxazole (TMP-SMX), and combination therapy of VAN/DAP + ASBL in the management of methicillin-resistant Staphylococcus aureus (MRSA). Methods: Databases including PubMed, Cochrane Library, Embase database, and google scholar were searched on 1 September 2021. The randomized control trials (RCTs) and comparable clinical studies of VAN/DAP, VAN/DAP + ASBL, ASBL, and TMP-SMX in the management of MRSA were identified. A network meta-analysis was conducted with STATA 14.0. Results: Seven RCTs and two matched cohorts with 1,048 patients were included in the analysis. The pooled results showed that VAN/DAP + ASBL had a significantly lower rate of persistent bacteremia >3 days than VAN/DAP alone [OR:0.46, 95%CI (0.26, 0.81), p < 0.001]. No obvious differences were observed in the outcomes of all-cause mortality, relapsed bacteremia, microbiological treatment failure, embolic or metastatic infection, and total adverse events. However, the ranking results showed that VAN/DAP + ASBL had slightly better efficacy (all-cause mortality, persistent bacteremia >3 days, duration of bacteremia, microbiological treatment failure, and relapsed bacteremia) but slightly higher adverse events than VAN/DAP alone. No obvious differences in the comparisons of VAN/DAP vs. ASBL, and VAN/DAP vs TMP-SMX in the analyzed outcomes. The ranking results revealed that ASBL and TMP-SMX did not have better efficacy or lower adverse events compared with the treatment of VAN/DAP. Conclusion: The efficacy of VAN/DAP + ASBL was slightly but not significantly better than VAN/DAP alone in the management of MRSA.

Nemonoxacin enhances antibacterial activity and anti-resistant mutation ability of vancomycin against methicillin-resistant Staphylococcus aureus in an in vitro dynamic pharmacokinetic/pharmacodynamic model

Reduced susceptibility and emergence of resistance to vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) have led to the development of various vancomycin based combinations. Nemonoxacin is a novel nonfluorinated quinolone with antibacterial activity against MRSA. The present study aimed to investigate the effects of nemonoxacin on antibacterial activity and the anti-resistant mutation ability of vancomycin for MRSA and explore whether quinolone resistance genes are associated with a reduction in the vancomycin minimal inhibitory concentration (MIC) and mutant prevention concentration (MPC) when combined with nemonoxacin. Four isolates, all with a vancomycin MIC of 2 μg/mL, were used in a modified in vitro dynamic pharmacokinetic/pharmacodynamic model to investigate the effects of nemonoxacin on antibacterial activity (M04, M23 and M24) and anti-resistant mutation ability (M04, M23 and M25, all with MPC ≥19.2 μg/mL) of vancomycin. The mutation sites of gyrA, gyrB, parC, and parE of 55 clinical MRSA isolates were sequenced. We observed that in M04 and M23, the combination of vancomycin (1g q12h) and nemonoxacin (0.5g qd) showed a synergistic bactericidal activity and resistance enrichment suppression. All clinical isolates resistant to nemonoxacin harbored gyrA (S84→L) mutation; gyrA (S84→L) and parC (E84→K) mutations were the two independent risk factors for the unchanged vancomycin MPC in combination. Nemonoxacin enhances the bactericidal activity and suppresses resistance enrichment ability of vancomycin against MRSA with a MIC of 2 μg/mL. Our in vitro data support the combination of nemonoxacin and vancomycin for the treatment of MRSA infection with a high MIC.

Losing the Battle but Winning the War: Can Defeated Antibacterials Form Alliances to Combat Drug-Resistant Pathogens?

Despite the recent development of antibacterials that are active against multidrug-resistant pathogens, drug combinations are often necessary to optimize the killing of difficult-to-treat organisms. Antimicrobial combinations typically are composed of multiple agents that are active against the target organism; however, many studies have investigated the potential utility of combinations that consist of one or more antibacterials that individually are incapable of killing the relevant pathogen. The current review summarizes in vitro, in vivo, and clinical studies that evaluate combinations that include at least one drug that is not active individually against Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, or Staphylococcus aureus. Polymyxins were often included in combinations against all three of the Gram-negative pathogens, and carbapenems were commonly incorporated into combinations against K. pneumoniae and A. baumannii. Minocycline, sulbactam, and rifampin were also frequently investigated in combinations against A. baumannii, whereas the addition of ceftaroline or another β-lactam to vancomycin or daptomycin showed promise against S. aureus with reduced susceptibility to vancomycin or daptomycin. Although additional clinical studies are needed to define the optimal combination against specific drug-resistant pathogens, the large amount of in vitro and in vivo studies available in the literature may provide some guidance on the rational design of antibacterial combinations.

Standardized Treatment and Assessment Pathway Improves Mortality in Adults With Methicillin-resistant Staphylococcus aureus Bacteremia: STAPH Study

Background

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) management remains challenging for clinicians. Numerous in vitro studies report synergy when vancomycin (VAN) and daptomycin (DAP) are combined with beta-lactams (BLs), which has led to clinical implementation of these combinations. While shorter durations of bacteremia have often been reported, there has been no significant impact on mortality.

Methods

The Detroit Medical Center (DMC) developed and implemented a clinical pathway algorithm for MRSA BSI treatment in 2016 that included the early use of BL combination therapy with standard of care (VAN or DAP) and a mandatory Infectious Diseases consultation. This was a retrospective, quasi-experimental study at the DMC between 2013 and 2020. Multivariable logistic regression was used to assess the independent association between pathway implementation and 30-day mortality while adjusting for confounding variables.

Results

Overall, 813 adult patients treated for MRSA BSI were evaluated. Compared with prepathway (PRE) patients (n = 379), those treated postpathway (POST; n = 434) had a significant reduction in 30-day and 90-day mortality: 9.7% in POST vs 15.6% in PRE (P = .011) and 12.2% in POST vs 19.0% in PRE (P = .007), respectively.

The incidence of acute kidney injury (AKI) was higher in the PRE compared with the POST group: 9.6% vs 7.2% (P = .282), respectively. After adjusting for confounding variables including Infectious Diseases consult, POST was independently associated with a reduction in 30-day mortality (adjusted odds ratio [aOR], 0.608; 95% CI, 0.375–0.986).

Conclusions

Implementation of an MRSA BSI treatment pathway with early use of BL reduced mortality with no increased rate of AKI. Further prospective evaluation of this pathway approach is warranted.

Chemotherapeutic Strategies for Combating Staphylococcus aureus Infections

Staphylococcus aureus is a prominent human pathogen that causes nosocomial and community acquired infections. The accelerating emergence and prevalence of staphylococcal infections have grotesque health consequences which are mostly due to its anomalous capability to acquire drug resistance and scarcity of novel classes of antibacterials. Many combating therapies are centered on primary targets of S. aureus which are cell envelope, ribosomes and nucleic acids. This review describes various chemotherapeutic strategies for combating S. aureus infections which includes monotherapy, combination drug therapy, phage endolysin therapy, lysostaphins and antibacterial drones. Monotherapy has dwindled in due course of time but combination therapy, endolysin therapy, lysostaphin and antibacterial drones are emerging alternatives which efficiently conquer the shortcomings of monotherapy. Combinations of more than one antibiotic agents or combination of adjuvant with antibiotics provide a synergistic approach to combat infections causing pathogenic strains. Phage endolysin therapy and lysostaphin are also presents as possible alternatives to conventional antibiotic therapies. Antibacterial Drones goes a step further by specifically targeting the virulence genes in bacteria giving them a certain advantage over existing antibacterial strategies. But the challenge remains on the better understanding of these strategies for executing and implementing them in health sector. In this day and age, most of the S. aureus strains are resistant to ample number of antibiotics, so there is an urgent need to overcome such multidrug resistant strains for the welfare of our community.

What do beta-lactams add to vancomycin or daptomycin in the treatment of patients with methicillin-resistant Staphylococcus aureus bacteraemia? A review

Several studies have documented the synergy between vancomycin/daptomycin and various beta-lactams, and clinical studies have studied this combination therapy in humans. We review the published literature on this topic to know the utility of the combined treatment with beta-lactams in treating bacteraemia methicillin-resistant Staphylococcus aureus (MRSA) infections. Fifteen observational studies, three randomised clinical trials and three systematics reviews are analysed in this article. Observational studies used ceftaroline, cefazolin, piperacillin/tazobactam or cefepime among the beta-lactams. Clinical trials used cloxacillin or flucloxacillin as the most used beta-lactam in two trials and ceftaroline in one. Three systematic reviews are published. One of them only includes studies with vancomycin and included six studies. The other two systematic reviews include patients with daptomycin or vancomycin and included 15 and 9 studies, respectively. Adding a beta-lactam to vancomycin or daptomycin may help shorten bacteraemia and avoid recurrences in patients with MRSA bacteraemia. There is no evidence that combined therapy improves mortality. Nephrotoxicity in clinical trials precludes the use of combination therapy mainly with cloxacillin or flucloxacillin, but systematic reviews have not found a significant difference in this point in observational studies with other beta-lactams. The role of other beta-lactams such as ceftaroline should be thoroughly studied in these patients.

Bacteriophage AB-SA01 Cocktail in Combination with Antibiotics against MRSA-VISA Strain in an In Vitro Pharmacokinetic/Pharmacodynamic Model

This study aimed to test the efficacy of bacteriophage-antibiotic combinations (BACs) in vitro in 24-h time-kill settings and in ex vivo simulated endocardial vegetation (SEV) pharmacokinetic/pharmacodynamic models for 96 h. BACs prevented the development of bacteriophage resistance, while some bacteriophage resistance emerged in bacteriophage-alone treatments. In addition, BACs resulted in an enhancement of bacterial eradication in SEV models. Our findings support the potential activity of BAC therapy for combating serious methicillin-resistant Staphylococcus aureus (MRSA) infections.

Dinoponera quadriceps venom as a source of active agents against Staphylococcus aureus

Staphylococcus aureus is a highly virulent pathogen, capable of biofilm formation and responsible for thousands of deaths each year. The prevalence of Methicillin-Resistant S. aureus (MRSA) strains has increased in recent years and thus, the development of new antibiotics has become necessary. Antimicrobial Peptides (AMPs) are effective against a variety of multidrug-resistant bacteria and low levels of resistance have been reported regarding these molecules. Dinoponera quadriceps ant venom (DqV) has been described regarding its effect against S. aureus. In this study, we have evaluated the antibacterial effect of DqV-AMPs, the dinoponeratoxins (DNTxs), against Methicillin-Sensitive and a Methicillin-Resistant S. aureus strains. Our results show DNTx M-PONTX-Dq3a as a potent inhibitor of both strains, being able to prevent biofilm formation at low micromolar range (0.78-3.12 μM). It also showed a short-time effect through membrane disruption. M-PONTX-Dq3a opens up new perspectives for the prevention of biofilm formation through the development of anti-adhesive surface coatings on medical devices, as well as the treatment of resistant strains in skin or soft tissue infections.

The Evolving Reduction of Vancomycin and Daptomycin Susceptibility in MRSA-Salvaging the Gold Standards with Combination Therapy

Methicillin-resistant Staphylococcus aureus (MRSA) is associated with substantial morbidity and mortality. Vancomycin (VAN) has been used as the gold standard treatment for invasive MRSA infections for decades but, unfortunately, the reliance of VAN as the primary treatment option against these infections has led to a reduction in VAN susceptibility in MRSA isolates. Although daptomycin (DAP) is another common treatment option against invasive MRSA infections, it has been shown that the development of VAN resistance can lead to DAP nonsusceptibility. VAN or DAP backbone regimens in combination with other antibiotics has been advocated as an alternative approach to improve patient outcomes in VAN/DAP-susceptible infections, enhance outcomes in infections caused by isolates with reduced VAN/DAP susceptibility, and/or prevent the emergence of VAN/DAP resistance or further resistance. A peer-reviewed literature search was conducted using Medline, Google Scholar and PubMed databases. The primary purpose of this review is to describe the mechanisms and epidemiology of MRSA isolates with a reduction in VAN and/or DAP susceptibility, evaluate in vitro and in vivo literature describing combination therapy (CT) against MRSA isolates with reduced VAN and/or DAP susceptibility and describe studies involving the clinical outcomes of patients treated with CT against invasive MRSA infections.

Adjuvant β-Lactam Therapy Combined with Vancomycin or Daptomycin for Methicillin-Resistant Staphylococcus aureus Bacteremia: a Systematic Review and Meta-analysis

Infections due to methicillin-resistant Staphylococcus aureus bacteremia (MRSAB) seriously threaten public health due to poor outcomes and high mortality. The objective of this study is to perform a systematic review and meta-analysis of the current evidence on adjuvant β-lactam (BL) therapy combined with vancomycin (VAN) or daptomycin (DAP) for MRSAB. PubMed, Embase, and Cochrane Library were systematically searched for publications reporting clinical outcomes of BLs+VAN or BLs+DAP for adult patients with MRSAB through 5 April 2020. Meta-analysis techniques were applied using random effects modeling. Three randomized controlled trials and 12 retrospective cohort studies were identified, totaling 2,594 patients. Combination treatment significantly reduced the risk of clinical failure (risk ratio [RR] = 0.80; 95% confidence interval [CI], 0.66 to 0.96; P = 0.02; I² = 39%), bacteremia recurrence (RR = 0.66; 95% CI, 0.50 to 0.86; P = 0.002; I² = 0%), and persistent bacteremia (RR = 0.65; 95% CI, 0.55 to 0.76; P < 0.00001; I² = 0%) and shortened the duration of bacteremia (standardized mean difference [SMD] = -0.37; 95% CI, -0.48 to -0.25; P < 0.00001; I² = 0%). There was no significant difference in the risk of crude mortality, nephrotoxicity, or thrombocytopenia between groups. Notably, combination treatment might nonsignificantly increase the risk of Clostridium difficile infection (CDI) (RR = 2.13; 95% CI, 0.98 to 4.63; P = 0.06; I² = 0%). Subgroup analysis suggested that DAP+BLs could reduce crude mortality (RR = 0.53; 95% CI, 0.28 to 0.98; P = 0.04; I² = 0%). The meta-analysis suggested that although combination therapy with BLs could improve some microbial outcomes, it could not reduce crude mortality but might increase the risk of CDI and should be applied very cautiously. Regarding mortality reduction, the combination of DAP+cephalosporins appears more promising.

Dalbavancin, Vancomycin and Daptomycin Alone and in Combination with Cefazolin against Resistant Phenotypes of Staphylococcus aureus in a Pharmacokinetic/Pharmacodynamic Model

The most efficacious antimicrobial therapy to aid in the successful elimination of resistant S. aureus infections is unknown. In this study, we evaluated varying phenotypes of S. aureus against dalbavancin (DAL), vancomycin (VAN), and daptomycin (DAP) alone and in combination with cefazolin (CFZ). The objective of this study was to observe whether there was a therapeutic improvement in adding a beta-lactam to a glycopeptide, lipopeptide, or a lipoglycopeptide. We completed a series of in vitro tests including minimum inhibitory concentration testing (MIC) of the antimicrobials in combination, time-kill analysis (TKA), and a 168 h (7-day) one-compartment pharmacokinetic/pharmacodynamic (PK/PD) model on two daptomycin non-susceptible (DNS), vancomycin intermediate S. aureus strains (VISA), D712 and 6913. Results from our MIC testing demonstrated a minimum 2-fold and a maximum 32-fold reduction in MIC values for DAL, VAN, and DAP in combination with CFZ, in contrast to either agent used alone. The TKAs completed on four strains paralleled the enhanced activity demonstrated via the combination MICs. In the one-compartment PK/PD models, the combination of DAP plus CFZ or VAN plus CFZ resulted in a significant (p < 0.001) improvement in bactericidal activity and overall reduction in CFU/ml over the 7-day period. While the addition of CFZ to DAL improved time to bactericidal activity, DAL alone demonstrated equal and more sustained overall activity compared to all other treatments. The use of DAL alone, with or without CFZ and the combinations of VAN or DAP with CFZ appear to result in increased bactericidal activity against various recalcitrant S. aureus phenotypes.

Systematic review and meta-analysis of the efficacy and safety of vancomycin combined with β-lactam antibiotics in the treatment of methicillin-resistant Staphylococcus aureus bloodstream infections

OBJECTIVE

Vancomycin combined with β-lactams (Combo therapy) has been encouraged in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSIs) in recent years, but its efficacy and safety have not been systematically evaluated. This is a systematic review and meta-analysis to clarify the efficacy and safety of Combo therapy in patients with MRSA BSIs.

METHODS

Relevant articles reporting on the clinical or microbiology outcomes of Combo treatment in adult patients with MRSA bacteraemia throughout November 2019 were searched in PubMed, EMBASE and Cochrane Library databases. Summary odds ratios (ORs) or mean differences (MDs) and 95% confidence intervals (CIs) were evaluated using a fixed- or random-effects model.

RESULTS

Six articles (806 patients) consisting of one RCT and five retrospective cohort studies were included in this study. The pooled data showed that Combo therapy could significantly reduce the risk of microbiological failure (OR = 0.54, 95% CI 0.35-0.83, I² 40%, P = 0.005) and persistent bacteraemia (OR=0.48, 95% CI 0.30-0.77, I² 13%, P = 0.002), as well as shorten the duration of bacteraemia (MD = -1.06, 95% CI -1.53 to -0.60, I² 0%, P < 0.00001). In addition, it did not significantly increase the incidence of nephrotoxicity (OR = 1.17, 95% CI 0.64-2.13, I² 0%, P = 0.61). However, no significant difference was detected between the groups regarding 28/30-day mortality, MRSA-related mortality, bacteraemia relapse or length of hospitalization.

CONCLUSIONS

These results demonstrate that Combo therapy clears the pathogenic bacteria of MRSA bacteraemia but does not improve the clinical prognosis. As the sample size was small and most of the studies were retrospective cohort studies with substantial heterogeneity, there is a need for further studies encompassing large-scale multicentre RCTs to validate our results.

Pathogen influence on epidemiology, diagnostic evaluation and management of infective endocarditis

Infective endocarditis (IE) is uncommon and has, in the past, been most often caused by viridans group streptococci (VGS). Due to the indolent nature of these organisms, the phrase 'subacute bacterial endocarditis', so-called 'SBE', was routinely used as it characterised the clinical course of most patients that extended for weeks to months. However, in more recent years, there has been a significant shift in the microbiology of IE with the emergence of staphylococci as the most frequent pathogens, and for IE due to Staphylococcus aureus, the clinical course is acute and can be associated with sepsis. Moreover, increases in IE due to enterococci have occurred and have been characterised by treatment-related complications and worse outcomes. These changes in pathogen distribution have been attributed to a diversification in the target population at risk of IE. While prosthetic valve endocarditis and history of IE remain at highest risk of IE, the rise in prevalence of injection drug use, intracardiac device implantations and other healthcare exposures have heavily contributed to the existing pool of at-risk patients. This review focuses on common IE pathogens and their impact on the clinical profile of IE.

Focusing the Lens on the CAMERA Concepts: Early Combination β-Lactam and Vancomycin Therapy in Methicillin-Resistant Staphylococcus aureus Bacteremia

Methicillin-resistant Staphylococcus aureus (MRSA) has grown to become a major burden on health care systems. The cumulation of limited therapeutic options and worsened patient outcomes with persistent MRSA bacteremia has driven research in optimizing its initial management. The guidelines published by the Infectious Diseases Society of America currently recommend combination therapy for refractory MRSA bacteremia, but the utility of combining antibiotics from the start of therapy is under investigation. The alternative strategy of early use of β-lactam antibiotics in combination with vancomycin upon initial MRSA bacteremia detection has shown promise. While this concept has gained international attention, providers should give this strategy serious consideration prior to implementation. The objective of this review is to examine retrospective and prospective evidence for early combination with vancomycin and β-lactam antibiotics, as well as explore potential consequences of combination therapy.

Monotherapy with Vancomycin or Daptomycin versus Combination Therapy with β-Lactams in the Treatment of Methicillin-Resistant Staphylococcus Aureus Bloodstream Infections: A Retrospective Cohort Analysis

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) are associated with high morbidity and mortality. More in vitro, in vivo, and clinical data suggest that vancomycin (VAN) or daptomycin (DAP) combination therapy with β-lactams (BL) improves outcomes of MRSA infections. We hypothesize that BL combination with VAN or DAP would reduce the odds of clinical failure compared to VAN or DAP monotherapy.

METHODS

A retrospective cohort study of adult patients ≥ 18 years treated with VAN or DAP for MRSA BSI from 2006 to 2019 at Detroit Medical Center. Combination therapy (CT) was defined as VAN or DAP plus any BL for ≥ 24 h within 72 h of index culture. Monotherapy (MT) was defined as ≥ 72 h VAN or DAP within 72 h of index culture and no BL for ≥ 24 h up to 7 days following VAN/DAP initiation. Primary outcome was composite endpoint of clinical failure defined as: (1) 30-day mortality, (2) 60-day recurrence, or (3) persistent bacteremia (PB). PB was defined as bacteremia > 5 days. Multivariable logistic regression was used to evaluate the association between CT and the primary outcome.

RESULTS

Overall, 597 patients were included in this analysis, 153 in the MT group and 444 in the CT group. CT was independently associated with reduced odds of clinical failure (adjusted odds ratio, 0.523; 95% confidence interval, 0.348-0.787). The composite endpoint was driven by 60-day recurrence and PB but not 30-day mortality. There were no difference in adverse events including nephrotoxicity between the two study arms.

CONCLUSIONS

In hospitalized adults with MRSA BSI, CT with any BL was independently associated with improved clinical outcomes and may ultimately be selected as preferred therapy.

Ability of Bicarbonate Supplementation To Sensitize Selected Methicillin-Resistant Staphylococcus aureus Strains to β-Lactam Antibiotics in an Ex Vivo Simulated Endocardial Vegetation Model

Supplementation of standard growth media (cation-adjusted Mueller-Hinton Broth [CAMHB]) with bicarbonate (NaHCO3) increases β-lactam susceptibility of selected methicillin-resistant Staphylococcus aureus (MRSA) strains ("NaHCO3 responsive"). This "sensitization" phenomenon translated to enhanced β-lactam efficacy in a rabbit model of endocarditis. The present study evaluated NaHCO3-mediated β-lactam MRSA sensitization using an ex vivo pharmacodynamic model, featuring simulated endocardial vegetations (SEVs), to more closely mimic the host microenvironment. Four previously described MRSA strains were used: two each exhibiting in vitro NaHCO3-responsive or NaHCO3-nonresponsive phenotypes. Cefazolin (CFZ) and oxacillin (OXA) were evaluated in CAMHB with or without NaHCO3 Intra-SEV MRSA killing was determined over 72-h exposures. In both "responsive" strains, supplementation with 25 mM or 44 mM NaHCO3 significantly reduced β-lactam MICs to below the OXA susceptibility breakpoint (≤4 mg/liter) and resulted in bactericidal activity (≥3-log killing) in the model for both OXA and CFZ. In contrast, neither in vitro-defined nonresponsive MRSA strain showed significant sensitization in the SEV model to either β-lactam. At both NaHCO3 concentrations, the fractional time above MIC was >50% for both CFZ and OXA in the responsive MRSA strains. Also, in media containing RPMI plus 10% Luria-Bertani broth (proposed as a more host-mimicking microenvironment and containing 25 mM NaHCO3), both CFZ and OXA exhibited enhanced bactericidal activity against NaHCO3-responsive strains in the SEV model. Neither CFZ nor OXA exposures selected for emergence of high-level β-lactam-resistant mutants within SEVs. Thus, in this ex vivo model of endocarditis, in the presence of NaHCO3 supplementation, both CFZ and OXA are highly active against MRSA strains that demonstrate similar enhanced susceptibility in NaHCO3-supplemented media in vitro.

The Impact of Concomitant Empiric Cefepime on Patient Outcomes of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections Treated With Vancomycin

Background

Data suggest that vancomycin + β-lactam combinations improve clearance of methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSIs). However, it is unclear which specific β-lactams confer benefit. This analysis evaluates the impact of concomitant empiric cefepime on outcomes of MRSA BSIs treated with vancomycin.

Methods

Retrospective cohort study of adults with MRSA BSI from 2006 to 2017. Vancomycin + cefepime therapy was defined as ≥24 hours of cefepime during the first 72 hours of vancomycin. The primary outcome was microbiologic failure, defined as BSI duration ≥7 days and/or 60-day recurrence. Multivariable logistic regression was used to evaluate the association between vancomycin + cefepime therapy and binary outcomes. Cause-specific and subdistribution hazard models were used to evaluate the association between vancomycin + cefepime and BSI clearance.

Results

Three hundred fifty-eight patients were included, 129 vancomycin and 229 vancomycin + cefepime. Vancomycin + cefepime therapy was independently associated with reduced microbiologic failure (adjusted odds ratio [aOR], 0.488; 95% confidence interval [CI], 0.271–0.741). This was driven by a reduction in the incidence of BSI durations ≥7 days (vancomycin + cefepime aOR, 0.354; 95% CI, 0.202–0.621). Vancomycin + cefepime had no association with 30-day mortality (aOR, 0.952; 95% CI, 0.435–2.425). Vancomycin + cefepime was associated with faster BSI clearance in both cause-specific (HR, 1.408; 95% CI, 1.125–1.762) and subdistribution hazard models (HR, 1.264; 95% CI, 1.040–1.536).

Conclusions

Concomitant empiric cefepime improved MRSA BSI clearance and may be useful as the β-lactam component of synergistic vancomycin + β-lactam regimens when empiric or directed gram-negative coverage is desired.

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.

Evidence from an In Vitro Study: Is Oxacillin Plus Vancomycin a Better Choice for Heteroresistant Vancomycin-Intermediate Staphylococcus aureus?

INTRODUCTION

Heteroresistant vancomycin-intermediate Staphylococcus aureus (hVISA) bacteremia may result in clinical failure of vancomycin therapy, together with prolonged infection and hospitalization. This clinical problem has resulted in a search for more effective treatment options. The current study was designed to further investigate the synergistic effect of oxacillin plus vancomycin against methicillin-resistant S. aureus (MRSA) and hVISA using checkerboard and time-kill assays.

METHODS

Non-duplicate S. aureus isolates including hVISA (n = 29), MRSA (n = 10) and methicillin susceptible S. aureus (MSSA, n = 11) were used for combinational testing using checkerboard and time-kill assays.

RESULTS

Twenty-one isolates, 15 hVISA and 6 MRSA, showed synergy between oxacillin and vancomycin by checkerboard assay with fractional inhibitory concentration indices of ≤ 0.5. The addition of oxacillin to vancomycin resulted in a reduction in baseline vancomycin MIC from 1-2 to 0.06-0.5 µg/ml against MRSA and hVISA isolates. In the time-kill assay, the combination of oxacillin and vancomycin resulted in synergistic activity against hVISA (n = 23) and MRSA (n = 7) isolates. Regrowth was observed in six hVISA isolates exposed to combination in the time-kill assay, but none of them reached the original inoculum density at 24 h. All re-growth isolates showed a onefold increase in vancomycin MIC (from 1 to 2 µg/ml) and were re-confirmed as hVISA using the population-analysis profile experiment. Overall, for hVISA and MRSA, the combination of oxacillin plus vancomycin had greater antibacterial effect than each individual drug alone.

CONCLUSION

The present study showed the potential activity of vancomycin plus oxacillin combination against hVISA and MRSA isolates. Further, continued evaluation of this combination is warranted and may have therapeutic benefits in treating complicated MRSA infections.

Ceftobripole: Experience in staphylococcal bacteremia

Ceftobiprole is a new cephalosporin with an extended spectrum activity against the majority of microorganisms isolated in bacteremia including methicillin-susceptible (MSSA) and -resistant S. aureus (MRSA). This antibiotic has demonstrated a potent activity against MRSA in animal models of endocarditis in monotherapy but particularly in combination with daptomycin, suggesting that this combination could be a future option to improve the outcome of staphylococcal endovascular infections. In addition, the extended-spectrum ceftobiprole activity, including coagulase-negative staphylococci, Enterococcus faecalis, Enterobacteriaceae and Pseudomonas aeruginosa represents an advantage for use as empirical therapy in bacteremia potentially caused by a broad spectrum of microorganisms, such as in catheter-related bacteremia.

Combination of Vancomycin and Cefazolin Lipid Nanoparticles for Overcoming Antibiotic Resistance of MRSA

Vancomycin is the treatment of choice for infections caused by methicillin-resistant Staphylococcus aureus (MRSA). Clinically, combinations of vancomycin (VAN) and beta-lactams have been shown to improve patient outcomes compared to VAN alone for the treatment of MRSA bloodstream infections. However, VAN is known to cause nephrotoxicity, which could be ameliorated using biocompatible lipid drug delivery systems or liposomes. Previous attempts have been made for encapsulation of VAN in liposomes; however, drug loading has been poor, mainly because of the high aqueous solubility of VAN. In this study, we report a robust method to achieve high loading of VAN and cefazolin (CFZ) in unilamellar liposomes. Liposomes of sizes between 170–198 nm were prepared by modified reverse phase evaporation method and achieved high loading of 40% and 26% (weight/weight) for VAN and CFZ, respectively. Liposomal VAN reduced minimum inhibitory concentration (MIC) values 2-fold in comparison to commercial VAN. The combination of liposomal VAN (LVAN) and liposomal CFZ (LCFZ) demonstrated a 7.9-fold reduction compared to LVAN alone. Rhodamine dye-loaded liposomes demonstrated superior cellular uptake in macrophage-like RAW 264.7 cells. Fluorescent images of LVAN-encapsulating near-infrared (NIR) dye, S0456 (LVAN-S0456) clearly indicated that LVAN-S0456 had reduced renal excretion with very low fluorescent intensity in the kidneys. It is anticipated that the long circulation and reduced kidney clearance of LVAN-S0456 compared to VAN-S0456 injected in mice can lead to enhanced efficacy against MRSA infections with reduced nephrotoxicity. Overall, our developed formulations of VAN when administered alone or in combination with CFZ, provide a rational approach for combating MRSA infections.

β-Lactam Combinations with Vancomycin Show Synergistic Activity against Vancomycin-Susceptible Staphylococcus aureus, Vancomycin-Intermediate S. aureus (VISA), and Heterogeneous VISA

Increasing utilization of vancomycin due to the high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections has led to the emergence of vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA) strains. In vitro data suggest the potential for potent synergy between several beta-lactams and vancomycin. The objective of this study is to evaluate the synergy between beta-lactams and vancomycin against MRSA that is vancomycin susceptible, vancomycin-susceptible Staphylococcus aureus (VSSA), hVISA, and VISA. Fifty randomly selected clinical MRSA strains with various susceptibility levels to vancomycin were evaluated for vancomycin alone and vancomycin in combination with various concentrations of cefazolin (CFZ), cefepime (FEP), ceftaroline (CPT), and nafcillin (NAF). The potential for synergy was assessed by 24-h time-kill studies. Beta-lactams reduced vancomycin MIC values against all strains (4- to 16-fold reduction). In time-kill studies against MRSA, CFZ, FEP, CPT, and NAF all demonstrated similar degrees of killing at 24 h, and all showed synergistic activity with vancomycin against VSSA, hVISA, and VISA. Each of these combinations was also superior to any single agent against isolates of all three phenotypes, and each was bactericidal (P < 0.001 for all comparisons). All single-agent exposures demonstrated no activity at 24 h. The combination of vancomycin and beta-lactams significantly improved antibacterial activity against VSSA, hVISA, and VISA strains compared to the activity of any agent alone, supporting the potential use of vancomycin-beta-lactam combination therapy in infections caused by MRSA. Further clinical research is warranted to investigate the synergy of vancomycin against these Staphylococcus strains.

Impact of cefazolin co-administration with vancomycin to reduce development of vancomycin-intermediate Staphylococcus aureus

OBJECTIVE

Development of antimicrobial resistance during monotherapy of complicated methicillin-resistant Staphylococcus aureus bacteremia is problematic due to cross-resistance between vancomycin (VAN) and daptomycin, the only approved agents for this condition. Our objective was to demonstrate that development of resistance under conditions of suboptimal VAN (200 mg q 12 h) exposure in S. aureus can be attenuated by addition of cefazolin (CFZ).

METHODS

Two strains of S. aureus, 1 methicillin-susceptible Staphylococcus aureus (MSSA) (RN9120) and 1 methicillin-resistant S. aureus (MRSA) (JH1), were evaluated. The organisms were exposed to subtherapeutic VAN concentrations in a 1-compartment pharmacokinetic/pharmacodynamic model combined with recycling in the presence and absence of CFZ. Changes in MIC to glyco/lipopeptides and β-lactams along with susceptibility to human cathelicidin LL-37 killing were studied. Population analysis profiles (PAPs) were performed to detect changes in VAN heteroresistance.

RESULTS

VAN MIC of both organisms increased from 1 to 4 mg/L within 144 h under subtherapeutic VAN exposure. Increase in VAN MIC was associated with increased glyco/lipopeptides MICs. Additionally, increased survival in LL-37 killing assays from 40% to >90% accompanied the increase in VAN MIC. Addition of CFZ prevented the emergence of VAN-intermediate S. aureus. PAPs demonstrated an attenuation of VAN area under the curve shift (reduced organism selection with higher MICs values) when suboptimal VAN exposure was accompanied with CFZ compared to VAN alone (MSSA 17.81 versus 36.027, MRSA -0.35 versus 17.92, respectively). Given the emerging data on the clinical benefits of β-lactam adjunctive therapy in refractory MRSA bacteremia, additional studies on a larger collection of clinical isolates are needed to establish the utility of VAN plus CFZ for treatment of MRSA bacteremia.

Morbidity, mortality, and management of methicillin-resistant S. aureus bacteremia in the USA: update on antibacterial choices and understanding

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is associated with significant healthcare costs, morbidity, and mortality in the United States. Complications of MRSA bacteremia include infective endocarditis, osteomyelitis, and sepsis, all of which are difficult to treat. Time to effective therapy and antibacterial choice greatly affect patient outcomes. Vancomycin and daptomycin remain first-line therapies; however, reports of vancomycin-associated treatment failure and reduced daptomycin susceptibility highlight the need to define alternative strategies for MRSA bacteremia treatment. In addition, several patient- and pathogen-specific factors influence the outcomes of MRSA bacteremia. It is, therefore, critical to explore the interaction between host- and pathogen-specific factors and its effect on MRSA bacteremia pathogenesis and mortality. This review discusses the factors that drive the development of MRSA bacteremia and examines alternative treatment strategies.

Outcomes of Vancomycin plus a β-Lactam versus Vancomycin Only for Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia

The objective of this retrospective study was to compare the rates of treatment failure, which was a composite of clinical and microbiologic failure, of patients receiving vancomycin and a β-lactam to those receiving vancomycin only for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. Patients 16 to 89 years of age with MRSA bacteremia admitted to a university-affiliated hospital from 1 January 2014 to 31 December 2016 were screened for study inclusion. Patients were eligible if they received >48 h of vancomycin and a β-lactam (combination group) or vancomycin only (standard group) within 48 h after bacteremia onset. A total of 182 patients were screened: 47 were included in the standard group, and 63 were in the combination group. The combination group had a higher baseline body mass index (29.2 ± 8.0 kg/m² versus 25.8 ± 7.1 kg/m², P = 0.022), acute physiologic assessment and chronic health evaluation-II (APACHE-II) score (median [interquartile range], 21 [15 to 26] versus 16 [10 to 22], P = 0.003), and incidence of septic shock (31.8% versus 14.9%, P = 0.047). Using multivariate analysis, combination therapy was the only variable that decreased treatment failures (odds ratio [95% confidence interval], 0.337 [0.142 to 0.997]), while vancomycin MIC > 1 mg/liter and male gender increased treatment failures (4.018 [1.297 to 12.444] and 2.971 [1.040 to 8.488], respectively). The 30-day mortality rates (15.0% versus 14.9%, P = 1.000) and the incidence of adverse drug events (19.1% versus 23.4%, P = 0.816) were not statistically different between the combination and standard groups. Combination therapy of vancomycin with a β-lactam led to significantly fewer treatment failures than vancomycin monotherapy for MRSA bacteremia.

Combination Antibiotic Exposure Selectively Alters the Development of Vancomycin Intermediate Resistance in Staphylococcus aureus

Invasive methicillin-resistant Staphylococcus aureus (MRSA) treated with vancomycin (VAN) is associated with reduced VAN susceptibility and treatment failure. VAN combination therapy is one strategy to improve response, but comprehensive assessments of combinations to prevent resistance are limited. This study identifies optimal combinations to prevent the emergence of VAN-intermediate Staphylococcus aureus (VISA). Two standard MRSA and two heterogeneous VISA (hVISA) strains were exposed for 28 days in vitro to VAN alone, VAN with cefazolin (CFZ), fosfomycin, gentamicin, meropenem, rifampin, piperacillin-tazobactam (TZP), or trimethoprim-sulfamethoxazole. In addition to VAN susceptibility testing, cell wall thickness (CWT), carotenoid content, and membrane fluidity were determined for Mu3. VAN plus any β-lactam limited the VAN MIC increase to 1 to 4 mg/liter throughout the 28-day exposure, with CFZ and TZP being the most effective agents (VAN MIC = 1 to 2 mg/liter). Similar MIC trends occurred with the lipo-/glycopeptide agents daptomycin and telavancin, where β-lactam combinations with VAN prevented MIC increases to these agents as well. Combinations with non-β-lactams were ineffective in preventing VAN MIC increases with VAN MICs of 4 to 16 mg/liter emerging during weeks 2 to 4 of treatment. VAN plus β-lactam decreased CWT significantly, whereas VAN plus other antibiotics significantly increased the CWT. No correlation was observed between carotenoid content or membrane fluidity and antibiotic exposure. Only the combination exposures of VAN plus β-lactam suppress the development of VISA. Rational selection of VAN plus β-lactam should be further explored as a long-term combination treatment of MRSA infections due to their ability to suppress VAN resistance.

Cephalosporin-Glycopeptide Combinations for Use against Clinical Methicillin-Resistant Staphylococcus aureus Isolates: Enhanced In vitro Antibacterial Activity

The empirical combination of both a beta-lactam and glycopeptide to counter potential staphylococcal pathogens may improve the clinical outcomes for cases of Staphylococcus aureus bacteremia. We reported comparative in vitro studies of combination effects of different cephalosporins (i.e., cefazolin, cefmetazole, cefotaxime, and cefepime) combined with glycopeptides for 34 randomly selected methicillin-resistant S. aureus (MRSA) isolates by three methods, including the checkerboard, time-killing, and combination MIC measurement methods. Thirteen SCCmec type III isolates with a cefazolin MIC of ≥ 128 μg/mL were classified as the high-cefazolin MIC (HCM) group, whereas 13 SCCmec type IV and 8 SCCmec type V isolates were classified as the low-cefazolin MIC (LCM) group. With the checkerboard method, synergism was present for vancomycin-based combinations at 30.8–69.2 and 13.6–66.7%, as well as teicoplanin-based combinations of 38.5–84.6 and 0–47.6%, of the HCM and LCM isolates, respectively. No antagonism was noted. The in vitro inhibitory activity was evident even at a low concentration of 1/512x MIC of cephalosporin combined with sub-inhibitory concentrations (1/2x MIC) of a glycopeptide. With time-killing assays, synergism was noted at 1/2x or 1x susceptible breakpoint concentrations (SBCs) of a cephalosporin combined with 1/4 or 1/2 MIC of a glycopeptide. In the presence of 1/2 SBC of a cephalosporin, vancomycin or teicoplanin MICs decreased an average of 2.0- to 6.6- or 1.6- to 5.5-fold, respectively. With 8 μg/mL cephalosporin, the decline of glycopeptide MICs was most obvious in the presence of cefmetazole. In conclusion, cephalosporin-glycopeptide combinations at clinically achievable concentrations can exhibit in vitro synergistic antibacterial activity against clinical MRSA isolates. Such combinations require more clinical data to support their application for use in human MRSA infections.

Combination Therapy With Vancomycin and Ceftaroline for Refractory Methicillin-resistant Staphylococcus aureus Bacteremia: A Case Series

PURPOSE

Although vancomycin has been the mainstay of therapy for methicillin-resistant Staphylococcus aureus (MRSA) infections, its effectiveness has been challenged. Combination therapy may be used for patients with persistent MRSA bacteremia refractory to initial therapy. Studies have reported in vitro synergy between vancomycin and ceftaroline; however, clinical experience with this therapy is limited. Here, we report our experience with 5 cases of vancomycin-refractory MRSA bacteremia treated with the combination of vancomycin and ceftaroline.

METHODS

Between January 2014 and August 2016, 5 patients were identified who received vancomycin and ceftaroline combination therapy due to persistent bacteremia or deterioration of their clinical status on vancomycin alone (despite a vancomycin MIC within the susceptible range).

FINDINGS

Five patients presented with MRSA bacteremia secondary to endocarditis (n = 2), epidural abscess (n = 2), or left iliopsoas abscess (n = 1). Four of the 5 patients experienced microbiologic cure, and 1 patient transitioned to palliative care.

IMPLICATIONS

This case series serves to describe additional clinical experience with vancomycin and ceftaroline combination therapy. This combination may be considered when vancomycin monotherapy does not lead to microbiological and/or clinical improvement in patients with metastatic MRSA bacteremia. Additional studies are warranted to further define its role in salvage therapy for persistent MRSA bacteremia.

CAMERA2 - combination antibiotic therapy for methicillin-resistant Staphylococcus aureus infection: study protocol for a randomised controlled trial

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia is a serious infection resulting in 20-50 % 90-day mortality. The limitations of vancomycin, the current standard therapy for MRSA, make treatment difficult. The only other approved drug for treatment of MRSA bacteraemia, daptomycin, has not been shown to be superior to vancomycin. Surprisingly, there has been consistent in-vitro and in-vivo laboratory data demonstrating synergy between vancomycin or daptomycin and an anti-staphylococcal β-lactam antibiotic. There is also growing clinical data to support such combinations, including a recent pilot randomised controlled trial (RCT) that demonstrated a trend towards a reduction in the duration of bacteraemia in patients treated with vancomycin plus flucloxacillin compared to vancomycin alone. Our aim is to determine whether the addition of an anti-staphylococcal penicillin to standard therapy results in improved clinical outcomes in MRSA bacteraemia.

METHODS/DESIGN

We will perform an open-label, parallel-group, randomised (1:1) controlled trial at 29 sites in Australia, New Zealand, Singapore, and Israel. Adults (aged 18 years or older) with MRSA grown from at least one blood culture and able to be randomised within 72 hours of the index blood culture collection will be eligible for inclusion. Participants will be randomised to vancomycin or daptomycin (standard therapy) given intravenously or to standard therapy plus 7 days of an anti-staphylococcal β-lactam (flucloxacillin, cloxacillin, or cefazolin). The primary endpoint will be a composite outcome at 90 days of (1) all-cause mortality, (2) persistent bacteraemia at day 5 or beyond, (3) microbiological relapse, or (4) microbiological treatment failure. The recruitment target of 440 patients is based on an expected failure rate for the primary outcome of 30 % in the control arm and the ability to detect a clinically meaningful absolute decrease of 12.5 %, with a two-sided alpha of 0.05, a power of 80 %, and assuming 10 % of patients will not be evaluable for the primary endpoint.

DISCUSSION

Key potential advantages of adding anti-staphylococcal β-lactams to standard therapy for MRSA bacteraemia include their safety profile, low cost, and wide availability.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02365493 . Registered 24 February 2015.

In Vitro Pharmacodynamics of Vancomycin against Methicillin-Susceptible and -Resistant Staphylococcus aureus: Considering the Variability in Observed Tissue Exposure

Vancomycin is considered a first-line antibiotic for complicated skin and skin structure infections (cSSSI) because of the risk of methicillin-resistant Staphylococcus aureus (MRSA). The vancomycin exposure of tissue can vary widely in patients with cSSSI, yet most models test only the average exposure. The in vitro pharmacodynamic model was used to simulate three tissue exposure levels attained by administering vancomycin at 1 g every 12 h (q12h), based on the median (50th), 25th, and 10th percentile tissue area under the concentration-time curve (AUC) values observed during an in vivo microdialysis study of diabetic patients. Four clinical isolates (two of MRSA [vancomycin MIC, 1 and 2 μg/ml] and two of methicillin-susceptible S. aureus [MSSA] [MIC, 1 and 2 μg/ml]) were evaluated. Experiments were performed over 72 h in duplicate. Time-kill curves were constructed, and the area under the bacterial killing and regrowth curve (AUBC) during the final 24-h dosing interval (48 to 72 h) (AUBC48-72) was calculated. Reductions in the 72-h number of CFU/ml and AUBC48-72 at the different exposure levels were compared. Target tissue vancomycin exposure levels for the 50th (AUC0-12, 102.0 ± 9.1 μg · h/ml), 25th (AUC0-12, 44.3 ± 1.8 μg · h/ml), and 10th (AUC0-12, 25.3 ± 3.1 μg · h/ml) percentiles were obtained in all studies. No differences in the 72-h number of CFU or AUBC were observed between exposure levels when all of the isolates were analyzed together. However, for the two MRSA isolates, the 10th percentile exposure level achieved a lower 72-h number of CFU/ml (-1.4 ± 0.4 log10 CFU/ml, P = 0.007) and a greater AUBC48-72 (97.1 ± 20.0 log10 CFU · h/ml, P = 0.011) than the higher exposure levels. The majority of the tissue exposure levels achieved with a vancomycin dosing regimen of 1 g q12h resulted in substantial killing of MSSA and MRSA; however, the lowest exposure levels observed in a minority of the population may explain the poor vancomycin response.

In Vitro Pharmacodynamics of Human Simulated Exposures of Telavancin against Methicillin-Susceptible and -Resistant Staphylococcus aureus with and without Prior Vancomycin Exposure

Telavancin is a lipoglycopeptide with potent activity against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA). The activity of telavancin against MRSA and MSSA after prior vancomycin exposure was studied in an in vitro pharmacodynamic model. Two clinical MRSA and two MSSA isolates, all with vancomycin MICs of 2 μg/ml, were subjected to humanized free drug exposures of vancomycin at 1 g every 12 h (q12h) for 96 h, telavancin at 750 mg q24h for 96 h, and vancomycin at 1 g q12h for 72 h followed by telavancin at 750 mg q24h for 48 h (120 h total). The microbiological responses were measured by changes from 0 h in log10 CFU/ml at the end of experiments and area under the bacterial killing and regrowth curves over 96 h (AUBC0-96). The control isolates grew to 8.8 ± 0.3 log10 CFU/ml. Initially, all regimens caused -4.5 ± 0.9 reductions in log10 CFU/ml by 48 h followed by slight regrowth over the following 48 to 72 h. After 96 h, vancomycin and telavancin achieved -3.7 ± 0.9 and -3.8 ± 0.8 log10 CFU/ml changes from baseline, respectively (P = 0.74). Sequential exposure to telavancin after vancomycin did not result in additional CFU reductions or increases, with ultimate log10 CFU/ml reductions of -4.3 ± 1.1 at 96 h and -4.2 ± 1.3 at 120 h (P > 0.05 for all comparisons at 96 h). The AUBC0-96 was significantly smaller for the regimen of telavancin for 96 h than for the regimens of vancomycin for 96 h and vancomycin followed by telavancin (P ≤ 0.04). No resistance was observed throughout the experiment. Against these MRSA and MSSA isolates with vancomycin MICs of 2 μg/ml, telavancin was comparable with vancomycin and its activity was unaffected by prior vancomycin exposure.

Clinical pharmacological approach for balancing the use of daptomycin and linezolid in comparison with that of vancomycin in the treatment of MRSA-related infections

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most challenging bacterial pathogens responsible for severe infections among hospitalized patients. In recent years there is increasing evidence that the clinical efficacy of vancomycin is progressively decreasing. Although daptomycin and linezolid are valuable alternatives to vancomycin for the treatment of MRSA-related bloodstream infections and pneumonia, respectively, a great deal of debate exists about their role in daily clinical practice due to cost-effectiveness issues. In this article we put into perspective the importance of pharmacokinetic/pharmacodynamic (PK/PD) considerations based on recent experimental and clinical data to argue whether they could be helpful in identifying clinical conditions in which these agents could be advantageous as compared to vancomycin.

Clinical implications of vancomycin heteroresistant and intermediately susceptible Staphylococcus aureus

Staphylococcus aureus (S. aureus) has proven to be a major pathogen with the emergence of methicillin-resistant S. aureus (MRSA) infections and recently with heteroresistant vancomycin-intermediate S. aureus (hVISA) and vancomycin-intermediate S. aureus (VISA) infections. Although vancomycin is traditionally a first-line and relatively effective antibiotic, its continued use is under question because reports of heteroresistance in S. aureus isolates are increasing. Both hVISA and VISA infections are associated with complicated clinical courses and treatment failures. The prevalence, mechanism of resistance, clinical significance, and laboratory detection of hVISA and VISA infections are not conclusive, making it difficult to apply research findings to clinical situations. We provide an evidence-based review of S. aureus isolates expressing heterogenic and reduced susceptibility to vancomycin.

In vitro activity of human-simulated epithelial lining fluid exposures of ceftaroline, ceftriaxone, and vancomycin against methicillin-susceptible and -resistant Staphylococcus aureus

Staphylococcus aureus, including methicillin-susceptible (MSSA) and -resistant (MRSA) strains, is an important pathogen of bacterial pneumonia. As antibiotic concentrations at the site of infection are responsible for killing, we investigated the activity of human-simulated epithelial lining fluid (ELF) exposures of three antibiotics (ceftaroline, ceftriaxone, and vancomycin) commonly used for treatment of S. aureus pneumonia. An in vitro pharmacodynamic model was used to simulate ELF exposures of vancomycin (1 g every 12 h [q12h]), ceftaroline (600 mg q12h and q8h), and ceftriaxone (2 g q24h and q12h). Four S. aureus isolates (2 MSSA and 2 MRSA) were evaluated over 72 h with a starting inoculum of ∼ 10(6) CFU/ml. Time-kill curves were constructed, and microbiological response (change in log10 CFU/ml from 0 h and the area under the bacterial killing and regrowth curve [AUBC]) was assessed in duplicate. The change in 72-h log10 CFU/ml was largest for ceftaroline q8h (reductions of >3 log10 CFU/ml against all strains). This regimen also achieved the lowest AUBC against all organisms (P < 0.05). Vancomycin produced reliable bacterial reductions of 0.9 to 3.3 log10 CFU/ml, while the activity of ceftaroline q12h was more variable (reductions of 0.2 to 2.3 log10 CFU/ml against 3 of 4 strains). Both regimens of ceftriaxone were poorly active against MSSA tested (0.1 reduction to a 1.8-log10 CFU/ml increase). Against these S. aureus isolates, ELF exposures of ceftaroline 600 mg q8h exhibited improved antibacterial activity compared with ceftaroline 600 mg q12h and vancomycin, and therefore, this q8h regimen deserves further evaluation for the treatment of bacterial pneumonia. These data also suggest that ceftriaxone should be avoided for S. aureus pneumonia.

Prophylaxis with teicoplanin and cefuroxime reduces the rate of prosthetic joint infection after primary arthroplasty

The aim of this study was to compare the prosthetic joint infection (PJI) rate after total joint arthroplasty in two consecutive periods of treatment with different antibiotic prophylaxes: cefuroxime versus cefuroxime plus teicoplanin. We retrospectively reviewed 1,896 patients who underwent total hip arthroplasty or total knee arthroplasty between March 2010 and February 2013. From March 2010 to August 2011, patients received 1.5 g of cefuroxime during induction of anesthesia and another 1.5 g 2 h later (the C group). From September 2011, 800 mg of teicoplanin was added to cefuroxime (the CT group). Throughout the period studied, there were no variations in pre- or postoperative protocols. Univariate and multivariate analyses were performed to evaluate independent predictors of PJI. There were 995 (55.7%) patients in the C group and 791 (44.3%) in the CT group. Patients in the CT group had a significantly lower PJI rate than patients in the C group (1.26% versus 3.51%, P=0.002). There were no infections due to Staphylococcus aureus in the CT group (0% versus 1.6% in the C group, P<0.001). A stepwise forward Cox regression model identified male sex (hazard ratio [HR], 3.85; 95% confidence interval [CI], 2.09 to 7.18), a body mass index of ≥35 kg/m2 (HR, 2.93; 95% CI, 1.37 to 6.27), the presence of lung disease (HR, 2.46; 95% CI, 1.17 to 5.15), and red blood cell transfusion (HR, 3.70; 95% CI, 1.89 to 7.23) to be independent variables associated with a higher risk of PJI. The addition of teicoplanin was associated with a lower risk of infection (HR, 0.35; 95% CI, 0.17 to 0.74). In conclusion, the addition of teicoplanin to cefuroxime during primary arthroplasty was associated with a significant reduction in the global PJI rate due to a reduction of infections caused by Gram-positive bacteria.

Vancomycin and piperacillin-tazobactam against methicillin-resistant Staphylococcus aureus and vancomycin-intermediate Staphylococcus aureus in an in vitro pharmacokinetic/pharmacodynamic model

PURPOSE

Synergy between β-lactams and vancomycin against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate Staphylococcus aureus (VISA) has been observed in vitro and in vivo. However, studies investigating piperacillin-tazobactam with vancomycin against MRSA and VISA are limited despite broad clinical use of these antibiotics in combination. This study evaluated vancomycin and piperacillin-tazobactam against MRSA and VISA by using an in vitro pharmacokinetic/pharmacodynamic model.

METHODS

Two clinical MRSA strains (M3425 and M494) and one VISA strain (Mu50) were tested in duplicate by using a 72-hour, 1-compartment pharmacokinetic/pharmacodynamic model with the following exposures: growth control, vancomycin only, piperacillin-tazobactam only, and vancomycin with piperacillin-tazobactam. Vancomycin 1 g every 12 hours (free trough concentration, 8.75 mg/L; Cmin, 17.5 mg/L) and piperacillin-tazobactam 13.5 g per 24 hours' continuous infusion (free steady-state concentration, 27 mg/L) were simulated. Time-kill curves were constructed, and reductions in log10 CFU/mL at all time points were compared between regimens tested.

FINDINGS

Vancomycin and piperacillin-tazobactam MICs for M494, M3425, and Mu50 were 1, 1, and 4 and 1.5, 32, and >256 mg/L, respectively. All isolates had an oxacillin MIC ≥ 4 mg/L. Against all 3 isolates, vancomycin with piperacillin-tazobactam achieved a significant reduction in inoculum at 72 hours compared with vancomycin alone (all, P ≤ 0.015). The superiority of vancomycin with piperacillin-tazobactam compared with vancomycin alone became detectable at 8 hours for M3425 (P < 0.001) and at 24 hours for M494 and Mu50 (both, P ≤ 0.008). Although vancomycin with piperacillin-tazobactam achieved enhanced antibacterial activity at 72 hours against M3425 compared with vancomycin alone, bacterial regrowth occurred. Reduced susceptibility to vancomycin at 72 hours for M3425 was confirmed by using population analysis profile/AUC analysis. At 72 hours, M3425 had a PAP/AUC ratio of 0.77 compared to 0.51 at baseline.

IMPLICATIONS

Vancomycin with piperacillin-tazobactam demonstrated enhanced antimicrobial activity against MRSA and VISA compared with vancomycin alone. These results further enhance existing data that support using vancomycin in combination with a β-lactam for invasive MRSA infections. Combination therapy with vancomycin and a β-lactam against MRSA warrants clinical consideration.

Evaluation of vancomycin in combination with piperacillin-tazobactam or oxacillin against clinical methicillin-resistant Staphylococcus aureus Isolates and vancomycin-intermediate S. aureus isolates in vitro

Vancomycin with piperacillin-tazobactam is used as empirical therapy for critically ill patients. Studies of this combination against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate S. aureus (VISA) are limited, but β-lactams in combination with vancomycin have shown synergistic activity against MRSA and VISA. The goal of this study was to evaluate whether piperacillin-tazobactam and vancomycin were synergistic against MRSA and VISA in vitro. Bloodstream MRSA (n = 20) and VISA (n = 4) strains were selected. In vitro antimicrobial activities of piperacillin-tazobactam and oxacillin were evaluated by disk diffusion, and MICs were determined by Etest using Muller-Hinton agar with and without vancomycin at one-half the MIC. Time-kill studies evaluated 14 MRSA and all 4 VISA isolates using piperacillin-tazobactam at 300/35 mg/liter or oxacillin at 40 mg/liter alone and with vancomycin at one-half the MIC. Mean zones of inhibition for piperacillin-tazobactam and oxacillin increased with vancomycin against MRSA and VISA (P < 0.001 for all), and the MIC90 decreased with vancomycin against MRSA and VISA to values meeting susceptibility criteria for S. aureus (P < 0.001 for both antibiotics against MRSA). In MRSA time-kill studies, the mean 24-h reductions in inoculum for piperacillin-tazobactam, piperacillin-tazobactam with vancomycin, and oxacillin with vancomycin were 3.53, 3.69, and 2.62 log10 CFU/ml, respectively. The mean 24-h reductions in VISA inoculum for piperacillin-tazobactam, piperacillin-tazobactam with vancomycin, and oxacillin with vancomycin were 2.85, 2.93, and 3.45 log10 CFU/ml, respectively. Vancomycin with piperacillin-tazobactam or oxacillin demonstrated synergistic activity against MRSA and VISA. The clinical implications of these combinations against MRSA and VISA should be investigated.

In vitro pharmacodynamics of human simulated exposures of ceftaroline and daptomycin against MRSA, hVISA, and VISA with and without prior vancomycin exposure

The effects of prior vancomycin exposure on ceftaroline and daptomycin therapy against methicillin-resistant Staphylococcus aureus (MRSA) have not been widely studied. Humanized free-drug exposures of vancomycin at 1 g every 12 h (q12h), ceftaroline at 600 mg q12h, and daptomycin at 10 mg/kg of body weight q24h were simulated in a 96-h in vitro pharmacodynamic model against three MRSA isolates, including one heteroresistant vancomycin-intermediate S. aureus (hVISA) isolate and one VISA isolate. A total of five regimens were tested: vancomycin, ceftaroline, and daptomycin alone for the entire 96 h, and then sequential therapy with vancomycin for 48 h followed by ceftaroline or daptomycin for 48 h. Microbiological responses were measured by the changes in log10 CFU during 96 h from baseline. Control isolates grew to 9.16 ± 0.32, 9.13 ± 0.14, and 8.69 ± 0.28 log10 CFU for MRSA, hVISA, and VISA, respectively. Vancomycin initially achieved ≥3 log10 CFU reductions against the MRSA and hVISA isolates, followed by regrowth beginning at 48 h; minimal activity was observed against VISA. The change in 96-h log10 CFU was largest for sequential therapy with vancomycin followed by ceftaroline (-5.22 ± 1.2, P = 0.010 versus ceftaroline) and for sequential therapy with vancomycin followed by ceftaroline (-3.60 ± 0.6, P = 0.037 versus daptomycin), compared with daptomycin (-2.24 ± 1.0), vancomycin (-1.40 ± 1.8), and sequential therapy with vancomycin followed by daptomycin (-1.32 ± 1.0, P > 0.5 for the last three regimens). Prior exposure of vancomycin at 1 g q12h reduced the initial microbiological response of daptomycin, particularly for hVISA and VISA isolates, but did not affect the response of ceftaroline. In the scenario of poor vancomycin response for high-inoculum MRSA infection, a ceftaroline-containing regimen may be preferred.

β-Lactams enhance vancomycin activity against methicillin-resistant Staphylococcus aureus bacteremia compared to vancomycin alone

Vancomycin (VAN) is often used to treat methicillin-resistant Staphylococcus aureus (MRSA) bacteremia despite a high incidence of microbiological failure. Recent in vitro analyses of β-lactams in combination with VAN demonstrated synergistic activity against MRSA. The goal of this study was to examine the impact of combination therapy with VAN and a β-lactam (Combo) on the microbiological eradication of MRSA bacteremia compared to VAN alone. This was a retrospective cohort study of patients with MRSA bacteremia who received Combo therapy or VAN alone. Microbiological eradication of MRSA, defined as a negative blood culture obtained after initiation of therapy, was used to evaluate the efficacy of each regimen. A total of 80 patients were included: 50 patients in the Combo group and 30 patients in the VAN-alone group. Microbiological eradication was achieved in 48 patients (96%) in the Combo group compared to 24 patients (80%) in the VAN-alone group (P = 0.021). In a multivariable model, the Combo treatment had a higher likelihood of achieving microbiological eradication (adjusted odds ratio, 11.24; 95% confidence interval, 1.7 to 144.3; P = 0.01). In patients with infective endocarditis (n = 22), 11/11 (100%) who received Combo therapy achieved microbiological eradication compared to 9/11 (81.8%) treated with VAN alone, but the difference was not statistically significant (P = 0.20). Patients with MRSA bacteremia who received Combo therapy were more likely to experience microbiological eradication of MRSA than patients who received VAN alone.

β-Lactam antibiotics targeting PBP1 selectively enhance daptomycin activity against methicillin-resistant Staphylococcus aureus

The activity of daptomycin (DAP) against methicillin-resistant Staphylococcus aureus (MRSA) is enhanced in the presence of subinhibitory concentrations of antistaphylococcal β-lactam antibiotics by an undefined mechanism. Given the variability in the penicillin-binding protein (PBP)-binding profiles of different β-lactam antibiotics, the purpose of this study was to examine the relative enhancement of DAP activity against MRSA by different β-lactam antibiotics to determine if a specific PBP-binding profile is associated with the ability to enhance the anti-MRSA activity of DAP. We determined that both broad- and narrow-spectrum β-lactam antibiotics known to exhibit PBP1 binding demonstrated potent enhancement of DAP anti-MRSA activity, whereas β-lactam antibiotics with minimal PBP1 binding (cefoxitin, ceftriaxone, cefaclor, and cefotaxime) were less effective. We suspect that PBP1 disruption by β-lactam antibiotics affects pathways of cell division in S. aureus that may be a compensatory response to DAP membrane insertion, resulting in DAP hypersusceptibility.

Current and prospective treatments for multidrug-resistant gram-positive infections

INTRODUCTION

Staphylococcus aureus and Enterococcus spp. are two of the most common organisms causing nosocomial infections today; and are consistently associated with high mortality rates (approximately 20 and 44%, respectively). Resistance among these pathogens to first line agents such as methicillin and vancomycin continues to rise while isolates with reduced susceptibility to newer agents including linezolid and daptomycin continue to emerge, representing a serious concern for clinicians.

AREAS COVERED

Mechanisms of action and resistance as well as in vitro and clinical experience in the treatment of resistant staphylococci and enterococci with currently available agents are discussed. Additionally, novel combination regimens showing enhanced efficacy and available data pertaining to prospective therapies including solithromycin, tedizolid, dalbavancin and oritavancin will be covered.

EXPERT OPINION

With an increase in organisms displaying reduced susceptibility to vancomycin and the associated treatment failures, the significance of alternative therapies such as daptomycin, linezolid, ceftaroline, and prospective anti-gram-positive agents is on the rise. As our understanding of antimicrobial pharmacokinetic-pharmacodynamics principles continues to evolve, the selection of highly effective agents and optimization of dosages may lead to improved patient outcomes and delay the development of resistance.

Novel combinations of vancomycin plus ceftaroline or oxacillin against methicillin-resistant vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA

We demonstrated a significant inverse correlation between vancomycin and beta-lactam susceptibilities in vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA (hVISA) isolates. Using time-kill assays, vancomycin plus oxacillin or ceftaroline was synergistic against 3 of 5 VISA and 1 of 5 hVISA isolates or 5 of 5 VISA and 4 of 5 hVISA isolates, respectively. Beta-lactam exposure reduced overall vancomycin-Bodipy (dipyrromethene boron difluoride [4,4-difluoro-4-bora-3a,4a-diaza-s-indacene] fluorescent dye) binding but may have improved vancomycin-cell wall interactions to improve vancomycin activity. Further research is warranted to elucidate the mechanism behind vancomycin and beta-lactam synergy.

Ceftaroline increases membrane binding and enhances the activity of daptomycin against daptomycin-nonsusceptible vancomycin-intermediate Staphylococcus aureus in a pharmacokinetic/pharmacodynamic model

New antimicrobial agents and novel combination therapies are needed to treat serious infections caused by methicillin-resistant Staphylococcus aureus (MRSA) with reduced susceptibility to daptomycin and vancomycin. The purpose of this study was to evaluate the combination of ceftaroline plus daptomycin or vancomycin in an in vitro pharmacokinetic/pharmacodynamic model. Simulations of ceftaroline-fosamil at 600 mg per kg of body weight every 8 h (q8h) (maximum free-drug concentration in serum [fC(max)], 15.2 mg/liter; half-life [t(1/2)], 2.3 h), daptomycin at 10 mg/kg/day (fC(max), 11.3 mg/liter; t(1/2), 8 h), vancomycin at 2 g q12h (fC(max), 30 mg/liter; t(1/2), 6 h), ceftaroline plus daptomycin, and ceftaroline plus vancomycin were evaluated against a clinical, isogenic MRSA strain pair: D592 (daptomycin susceptible and heterogeneous vancomycin intermediate) and D712 (daptomycin nonsusceptible and vancomycin intermediate) in a one-compartment in vitro pharmacokinetic/pharmacodynamic model over 96 h. Therapeutic enhancement of combinations was defined as ≥2 log(10) CFU/ml reduction over the most active single agent. The effect of ceftaroline on the membrane charge, cell wall thickness, susceptibility to killing by the human cathelicidin LL37, and daptomycin binding were evaluated. Therapeutic enhancement was observed with daptomycin plus ceftaroline in both strains and vancomycin plus ceftaroline against D592. Ceftaroline exposure enhanced daptomycin-induced depolarization (81.7% versus 72.3%; P = 0.03) and killing by cathelicidin LL37 (P < 0.01) and reduced cell wall thickness (P < 0.001). Fluorescence-labeled daptomycin was bound over 7-fold more in ceftaroline-exposed cells. Whole-genome sequencing and mutation analysis of these strains indicated that change in daptomycin susceptibility is related to an fmtC (mprF) mutation. The combination of daptomycin plus ceftaroline appears to be potent, with rapid and sustained bactericidal activity against both daptomycin-susceptible and -nonsusceptible strains of MRSA.

Synergy between vancomycin and nafcillin against Staphylococcus aureus in an in vitro pharmacokinetic/pharmacodynamic model

INTRODUCTION

Continued pressure from glycopeptide use has led to non-susceptible strains of Staphylococcus aureus including heterogeneously vancomycin-intermediate S. aureus (hVISA). Infections with hVISA are associated with poor patient outcomes, thus incentivizing novel treatments. Evidence suggests that vancomycin and anti-staphylococcal penicillin susceptibility are inversely related which indicates that the use of this combination may be particularly useful against methicillin-resistant S. aureus with reduced susceptibility to vancomycin, such as hVISA. The aim of this study was to evaluate the potential for synergy between vancomycin and nafcillin against hVISA.

METHODS

Twenty-five hVISA strains were evaluated for vancomycin and nafcillin minimum inhibitory concentration (MIC) by broth microdilution in duplicate. Potential for synergy was assessed by time-kill at 1/2x MIC in triplicate. Five strains were chosen, representing the range nafcillin MIC's available in the cohort -4, 16, 64, 128, and 256 µg/mL, and were run in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model in duplicate over 72 hours to evaluate the potential of the combination with simulated human pharmacokinetics. In addition, 4 fully glycopeptide susceptible strains of S. aureus including 2 methicillin-susceptible (MSSA) and 2 methicillin-resistant (MRSA) were run in the PK/PD model for comparison.

RESULTS

In the time-kill, 92% of strains (23 of 25) displayed synergy with the combination of vancomycin and nafcillin. In the PK/PD model, all five strains of hVISA showed an improvement in overall activity (P≤0.004) and organism burden at 72 hours (P≤0.001) with the combination compared to either drug alone. The combination was also successful against both MRSA and MSSA in overall activity (P≤0.009) and organism burden at 72 hours (P≤0.016), though the magnitude of the effect was diminished against MSSA.

CONCLUSIONS

The combination of vancomycin and nafcillin significantly improved antibacterial activity against hVISA, MRSA, and MSSA compared to either drug alone.

Daptomycin approved in Japan for the treatment of methicillin-resistant Staphylococcus aureus

Daptomycin is a lipoglycopeptide antibacterial drug that is rapidly bactericidal for methicillin-resistant Staphylococcus aureus (MRSA) infection and has antibiotic activity against a wide range of Gram-positive organisms. It has been approved by the Ministry of Health, Labor and Welfare in Japan for the treatment for bacteremia, right-sided endocarditis, and skin and skin-structure infections, such as necrotizing fasciitis, due to MRSA on the basis of a Phase III trial conducted in Japan since July, 2011. In Japanese Phase I and III trials, daptomycin therapy given at 4 mg/kg and 6 mg/kg once per day was well tolerated and effective as standard therapy for the treatment of acute bacterial skin and skin-structure infections and bacteremia caused by MRSA, but side effects remain to be evaluated in large-scale trials.