Efficacy of usual and high doses of daptomycin in combination with rifampin versus alternative therapies in experimental foreign-body infection by methicillin-resistant Staphylococcus aureus

Comparison of daptomycin and glycopeptide efficacy and safety for the treatment of Gram-positive infections: a systematic review and meta-analysis

BACKGROUND

The indications of daptomycin have been extended to off-label indications including prosthesis-related infection, and bone and joint infection (BJI). However, efficacy and safety have not been thoroughly demonstrated compared with the standard of care. This systematic review and meta-analysis aimed to compare the treatment effect of daptomycin and glycopeptides for complicated infections.

MATERIALS AND METHODS

MEDLINE, Embase and Web of Science were searched for randomized controlled trials (RCTs) comparing daptomycin and standard of care for Gram-positive infections, published until 30 June 2021. The primary outcome was defined as all-cause mortality. Secondary outcomes were clinical and microbiological success. The main safety outcome was any severe adverse event (SAE) (grade  ≥3).

RESULTS

Overall, eight RCTs were included in the meta-analysis, totalling 1095 patients. Six (75%) were in complicated skin and soft-structure infections, one (12.5%) in bacteraemia and one (12.5%) in a BJI setting. Six RCTs used vancomycin as a comparator and two used either vancomycin or teicoplanin. All-cause mortality and clinical cure were not different between groups. The microbiological cure rate was superior in patients who received daptomycin [risk ratio (RR) = 1.17 (95% CI: 1.01-1.35)]. The risk of SAEs [RR = 0.57 (95% CI: 0.36-0.90)] was lower in the daptomycin arm.

CONCLUSIONS

While daptomycin is associated with a significantly lower risk of SAEs and a better microbiological eradication, substantial uncertainty remains about the best treatment strategy in the absence of good-quality evidence, especially in bacteraemia and endocarditis where further RCTs should be conducted.

Randomized clinical trial: Long-term Staphylococcus aureus decolonization in patients on home parenteral nutrition

BACKGROUND & AIMS

Staphylococcus aureus decolonization has proven successful in prevention of S. aureus infections and is a key strategy to maintain venous access and avoid hospitalization in patients receiving home parenteral nutrition (HPN). We aimed to determine the most effective and safe long-term S. aureus decolonization regimen.

METHODS

A randomized, open-label, multicenter clinical trial was conducted. Adult intestinal failure patients with HPN support and carrying S. aureus were randomly assigned to a 'continuous suppression' (CS) strategy, a repeated chronic topical antibiotic treatment or a 'search and destroy' (SD) strategy, a short and systemic antibiotic treatment. Primary outcome was the proportion of patients in whom S. aureus was totally eradicated during a 1-year period. Secondary outcomes included risk factors for decolonization failure and S. aureus infections, antimicrobial resistance, adverse events, patient compliance and cost-effectivity.

RESULTS

63 participants were included (CS 31; SD 32). The mean 1-year S. aureus decolonization rate was 61% (95% CI 44, 75) for the CS group and 39% (95% CI 25, 56) for the SD group with an OR of 2.38 (95% CI 0.92, 6.11, P = 0.07). More adverse effects occurred in the SD group (P = 0.01). Predictors for eradication failure were a S. aureus positive caregiver and presence of a (gastro)enterostomy.

CONCLUSION

We did not demonstrate an increased efficacy of a short and systemic S. aureus decolonization strategy over a continuous topical suppression treatment. The latter may be the best option for HPN patients as it achieved a higher long-term decolonization rate and was well-tolerated (NCT03173053).

Resistance-resistant antibacterial treatment strategies

Antibiotic resistance is a major danger to public health that threatens to claim the lives of millions of people per year within the next few decades. Years of necessary administration and excessive application of antibiotics have selected for strains that are resistant to many of our currently available treatments. Due to the high costs and difficulty of developing new antibiotics, the emergence of resistant bacteria is outpacing the introduction of new drugs to fight them. To overcome this problem, many researchers are focusing on developing antibacterial therapeutic strategies that are "resistance-resistant"-regimens that slow or stall resistance development in the targeted pathogens. In this mini review, we outline major examples of novel resistance-resistant therapeutic strategies. We discuss the use of compounds that reduce mutagenesis and thereby decrease the likelihood of resistance emergence. Then, we examine the effectiveness of antibiotic cycling and evolutionary steering, in which a bacterial population is forced by one antibiotic toward susceptibility to another antibiotic. We also consider combination therapies that aim to sabotage defensive mechanisms and eliminate potentially resistant pathogens by combining two antibiotics or combining an antibiotic with other therapeutics, such as antibodies or phages. Finally, we highlight promising future directions in this field, including the potential of applying machine learning and personalized medicine to fight antibiotic resistance emergence and out-maneuver adaptive pathogens.

Daptomycin synergistic properties from in vitro and in vivo studies: a systematic review

INTRODUCTION

Daptomycin is a bactericidal lipopeptide antibiotic approved for the treatment of systemic infections (i.e. skin and soft tissue infections, bloodstream infections, infective endocarditis) caused by Gram-positive cocci. It is often prescribed in association with a partner drug to increase its bactericidal effect and to prevent the emergence of resistant strains during treatment; however, its synergistic properties are still under evaluation.

METHODS

We performed a systematic review to offer clinicians an updated overview of daptomycin synergistic properties from in vitro and in vivo studies. Moreover, we reported all in vitro and in vivo data evaluating daptomycin in combination with other antibiotic agents, subdivided by antibiotic classes, and a summary graph presenting the most favourable combinations at a glance.

RESULTS

A total of 92 studies and 1087 isolates (723 Staphylococcus aureus, 68 Staphylococcus epidermidis, 179 Enterococcus faecium, 105 Enterococcus faecalis, 12 Enterococcus durans) were included. Synergism accounted for 30.9% of total interactions, while indifferent effect was the most frequently observed interaction (41.9%). Antagonistic effect accounted for 0.7% of total interactions. The highest synergistic rates against S. aureus were observed with daptomycin in combination with fosfomycin (55.6%). For S. epidermidis and Enterococcus spp., the most effective combinations were daptomycin plus ceftobiprole (50%) and daptomycin plus fosfomycin (63.6%) or rifampicin (62.8%), respectively.

FUTURE PERSPECTIVES

We believe this systematic review could be useful for the future updates of guidelines on systemic infections where daptomycin plays a key role.

A High Daptomycin Dose Is Associated with Better Bacterial Clearance in Infections Caused by Vancomycin-Resistant Enterococcus faecium Regardless of Daptomycin Minimum Inhibitory Concentration in a Rat Infective Endocarditis Model

A high daptomycin dose has been suggested for treating vancomycin-resistant Enterococcus faecium (VREf) infections. However, even a 12 mg/kg daptomycin dose might be insufficient for treating VREf with high daptomycin minimum inhibitory concentrations (MICs). Additionally, animal pharmacodynamic and infection models to confirm the efficacy of 12 mg/kg daptomycin are lacking. Male Wistar rats were used for pharmacokinetic profiling and for the development of an infective endocarditis (IE) model. Daptomycin-susceptible dose-dependent VREf (DSE) (MIC of 0.5 mg/L) and daptomycin nonsusceptible VREf (DNSE) (MIC of 8 mg/L) were used for the IE models. The bacterial load of vegetation was the primary outcome and was evaluated after 3 days of daptomycin treatment. Daptomycin administered subcutaneously (s.c.) at 45 and 90 mg/kg, which corresponded to maximum serum concentrations (Cmax) of 122.6 mg/L and 178.5 mg/L, respectively, was equivalent to doses of 8 mg/kg and 12 mg/kg, respectively, in humans. The Cmax/MIC value was correlated with the bacterial load of vegetation after treatment (r = -0.88, P < 0.001). The 90 mg/kg s.c. group showed a significantly lower bacterial load of vegetation (log10 CFU/g) than the 45 mg/kg s.c. group against DSE (0 versus 4.75, P < 0.001) and DNSE (5.12 versus 6.98, P = 0.002). The 90 mg/kg s.c. group did not sterilize the vegetation against DNSE. Although the human equivalent dose of 12 mg/kg daptomycin was more effective than the smaller dose in reducing the bacterial load in DSE and DNSE IE, the dose could not sterilize the vegetation during a DNSE treatment. Further treatment strategies by which to manage severe VREf infections, especially at high daptomycin MICs, are urgently needed. IMPORTANCE Using a rat IE model with pharmacokinetic analysis, the treatment response of VREf IE was found to be daptomycin dose-dependent, presented as Cmax/MIC or as the 24 h area under the concentration-time curve (AUC0-24)/MIC. Daptomycin 90 mg/kg s.c. significantly reduced the bacterial load against DSE and DNSE. It also showed significant activity against DSE and DNSE, compared to 45 mg/kg s.c. Although daptomycin 90 mg/kg can eradicate the bacterial load after 3 days of treatment against DSE, eradication cannot be achieved with 90 mg/kg daptomycin against DNSE.

Improved Neurological Outcome in a Patient With Complicated Mitral Valve Endocarditis Treated With Daptomycin-Rifampin Regimen

Complicated infective endocarditis (IE) with symptomatic neurological involvement is associated with a poor prognosis. Vancomycin is the first-line antibiotic employed for the treatment of IE as general resistance of Methicillin-resistant Staphylococcus aureus (MRSA) to vancomycin is low and the antibiotic is well tolerated. In this case report, we describe a case of severely complicated MRSA endocarditis initially treated unsuccessfully with vancomycin. Our patient presented with severe encephalopathy with multiple septic infarctions noted on imaging. After treatment with a daptomycin-rifampin regimen, significant clinical improvement was noted. Based on the findings of this case report, what remains to be analyzed further with future studies is whether the daptomycin-rifampin regimen effect is independent of initial vancomycin-based treatment as most cases of IE are first treated with vancomycin and are only transitioned into daptomycin-rifampin regimen after treatment failure or persistent positive blood cultures, as is described in this case.

Orthopaedic Implant-Associated Staphylococcal Infections: A Critical Reappraisal of Unmet Clinical Needs Associated with the Implementation of the Best Antibiotic Choice

Infections associated with orthopaedic implants represent a major health concern characterized by a remarkable incidence of morbidity and mortality. The wide variety of clinical scenarios encountered in the heterogeneous world of infections associated with orthopaedic implants makes the implementation of an optimal and standardized antimicrobial treatment challenging. Antibiotic bone penetration, anti-biofilm activity, long-term safety, and drug choice/dosage regimens favouring outpatient management (i.e., long-acting or oral agents) play a major role in regards to the chronic evolution of these infections. The aim of this multidisciplinary opinion article is to summarize evidence supporting the use of the different anti-staphylococcal agents in terms of microbiological and pharmacological optimization according to bone penetration, anti-biofilm activity, long-term safety, and feasibility for outpatient regimens, and to provide a useful guide for clinicians in the management of patients affected by staphylococcal infections associated with orthopaedic implants Novel long-acting lipoglycopeptides, and particularly dalbavancin, alone or in combination with rifampicin, could represent the best antibiotic choice according to real-world evidence and pharmacokinetic/pharmacodynamic properties. The implementation of a multidisciplinary taskforce and close cooperation between microbiologists and clinicians is crucial for providing the best care in this scenario.

Animal experimental investigation on the efficacy of antibiotic therapy with linezolid, vancomycin, cotrimoxazole, and rifampin in treatment of periprosthetic knee joint infections by MRSA

Aims

Periprosthetic joint infections (PJIs) are rare, but represent a great burden for the patient. In addition, the incidence of methicillin-resistant Staphylococcus aureus (MRSA) is increasing. The aim of this rat experiment was therefore to compare the antibiotics commonly used in the treatment of PJIs caused by MRSA.

Methods

For this purpose, sterilized steel implants were implanted into the femur of 77 rats. The metal devices were inoculated with suspensions of two different MRSA strains. The animals were divided into groups and treated with vancomycin, linezolid, cotrimoxazole, or rifampin as monotherapy, or with combination of antibiotics over a period of 14 days. After a two-day antibiotic-free interval, the implant was explanted, and bone, muscle, and periarticular tissue were microbiologically analyzed.

Results

Vancomycin and linezolid were able to significantly (p < 0.05) reduce the MRSA bacterial count at implants. No significant effect was found at the bone. Rifampin was the only monotherapy that significantly reduced the bacterial count on implant and bone. The combination with vancomycin or linezolid showed significant efficacy. Treatment with cotrimoxazole alone did not achieve a significant bacterial count reduction. The combination of linezolid plus rifampin was significantly more effective on implant and bone than the control group in both trials.

Conclusion

Although rifampicin is effective as a monotherapy, it should not be used because of the high rate of resistance development. Our animal experiments showed the great importance of combination antibiotic therapies. In the future, investigations with higher case numbers, varied bacterial concentrations, and changes in individual drug dosages will be necessary to be able to draw an exact comparison, possibly within a clinical trial.

Cite this article: Bone Joint Res 2022;11(3):143–151.

Daptomycin for the Treatment of Gram-Positive Periprosthetic Hip Infections: Can Daptomycin Prevent the Implant Removal?

Introduction

Management of periprosthetic hip infections (PHIs) generally consists of implant removal and thorough debridement, accompanied by appropriate antibiotic therapy. Daptomycin (DAP) is a novel antibiotic, which allowed for implant retention in several patients after treating their infected joints. However, there is no consensus about implant retention or removal during the treatment of PHIs. The aim of this study was to examine the effect of DAP and to determine a surgical treatment strategy.

Methods

This study retrospectively evaluated 20 patients between August 2014 and December 2018, divided into implant retention (n=9) and implant removal groups (n=11). Infection control and risk of recurrent infection were evaluated. Infection control was defined as not requiring implant removal after the final treatment.

Results

Infection control rates in implant retention and implant removal groups were 67% and 90%, respectively. All late chronic infections resulted in failure cases within the implant retention group. In the implant retention group, mean preoperative risk scores for successful cases were significantly higher than those for failure cases (p<0.05).

Conclusions

Patients with low risk did not require implant removal, suggesting that DAP may be a breakthrough alternative to traditional PHI management.

New-Generation Antibiotics for Treatment of Gram-Positive Infections: A Review with Focus on Endocarditis and Osteomyelitis

Infective endocarditis, osteomyelitis, and osteosynthesis-associated infections are mostly caused by Gram-positive bacteria. They are often difficult to treat and are associated with a poor prognosis. In the past 20 years, nine antibiotic drugs with predominant activity against Gram-positive bacteria have been introduced and approved by the Food and Drug Administration or the European Medicines Agency: ceftaroline, daptomycin, telavancin, dalbavancin, oritavancin, linezolid, tedizolid, delafloxacin, and omadacycline. This narrative review aims to provide an overview on these antibiotics with a special focus on their use in infective endocarditis, osteomyelitis, and osteosynthesis-associated infections. Although some of these approved antibiotics are promising, they should not be used as first- or second-line therapy, awaiting more clinical data.

Population pharmacokinetics of daptomycin in patients with bone and joint infection: minimal effect of rifampicin co-administration and confirmation of a sex difference

BACKGROUND

Daptomycin is increasingly used in the treatment of bone and joint infection (BJI), but its pharmacokinetics (PK) and dosage requirements have not been thoroughly investigated in this indication. Daptomycin may be co-administered with rifampicin, which raises questions about a potential drug interaction.

OBJECTIVES

To investigate the population PK and dosage requirements of daptomycin in patients with BJI, and examine the influence of rifampicin co-administration.

METHODS

A population approach was used to analyse PK data from patients who received daptomycin in our regional reference for BJI. We examined the influence of available covariates, including rifampicin co-administration on daptomycin PK. Simulations performed with the final model investigated the influence of dosages and covariates on PTA for both efficacy and safety.

RESULTS

A total of 1303 daptomycin concentrations from 183 patients were analysed. A two-compartment model best described the data. Significant intra-individual variability was observed. Daptomycin clearance was influenced by renal function and sex, with females having a 26% lower typical clearance than males. Central volume of distribution (V1) was influenced by body weight, age, sex and rifampicin co-administration. Typical V1 was 11% lower in patients who were co-administered rifampicin. In PK/PD simulations, sex influenced the probability of AUC24/MIC target attainment, while rifampicin had a marginal effect.

CONCLUSIONS

A daptomycin dosage of 8 mg/kg/24 h in women and 10 mg/kg/24 h in men should optimize efficacy but may lead to excessive trough concentrations in many patients, especially in women. Therapeutic drug monitoring appears necessary for precision dosing of daptomycin.

High-Dose Daptomycin and Clinical Applications

OBJECTIVE

To evaluate evidence for high-dose daptomycin (doses ≥ 8 mg/kg/d).

DATA SOURCES

A PubMed/MEDLINE literature search was performed (January 2000 to December 2020) using the search terms daptomycin, high dose, and dosing. Review article references and society guidelines were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials, observational studies, retrospective studies, meta-analyses, and systematic reviews reporting on high-dose daptomycin were included.

DATA SYNTHESIS

Experimentally, daptomycin outperforms other antimicrobials for high inoculum and biofilm-associated infections. Clinically, high-dose daptomycin is supported as salvage and first-line therapy for endocarditis and bacteremia, primarily when caused by methicillin-resistant Staphylococcus aureus (when vancomycin minimum inhibitory concentration is >1 mg/L) and Enterococcus. High-dose daptomycin appears effective for osteomyelitis and central nervous system infections, although comparative studies are lacking. High dosing in renal replacement therapy requires considering clearance modality to achieve exposures like normal renal function. Weight-based dosing in obesity draws concern for elevated exposures, although high doses have not been evaluated kinetically in obesity. Some data show benefits of high doses in overweight populations. Burn patients clear daptomycin more rapidly, and high doses may only achieve drug exposures similar to standard doses (6 mg/kg).

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This review analyzes the efficacy and safety of high-dose daptomycin in serious gram-positive infections. Discussion of specific infectious etiologies and patient populations should encourage clinicians to evaluate their daptomycin dosing standards.

CONCLUSIONS

The efficacy of high-dose daptomycin and limited safety concerns encourage clinicians to consider high-dose daptomycin more liberally in severe gram-positive infections.

When antibiotics fail: a clinical and microbiological perspective on antibiotic tolerance and persistence of Staphylococcus aureus

Staphylococcus aureus is a major human pathogen causing a vast array of infections with significant mortality. Its versatile physiology enables it to adapt to various environments. Specific physiological changes are thought to underlie the frequent failure of antimicrobial therapy despite susceptibility in standard microbiological assays. Bacteria capable of surviving high antibiotic concentrations despite having a genetically susceptible background are described as 'antibiotic tolerant'. In this review, we put current knowledge on environmental triggers and molecular mechanisms of increased antibiotic survival of S. aureus into its clinical context. We discuss animal and clinical evidence of its significance and outline strategies to overcome infections with antibiotic-tolerant S. aureus.

Tedizolid as Step-Down Therapy following Daptomycin versus Continuation of Daptomycin against Enterococci and Methicillin- and Vancomycin-Resistant Staphylococcus aureus in a Rat Endocarditis Model

Tedizolid (TZD) and daptomycin (DAP) were assessed in a rat endocarditis model against Enterococcus faecalis, Enterococcus faecium (resistant to vancomycin and ampicillin), and Staphylococcus aureus As a monotherapy, TZD for 5 days was not effective in a comparison with no-treatment controls, while DAP for 5 days was significantly effective against these bacteria. Step-down therapy (DAP for 3 days followed by TZD for 2 days) was as effective as DAP for 5 days and was comparable to 3 days of DAP plus ceftriaxone against all bacteria and to 3 days of DAP plus gentamicin against E. faecalis OG1RF.

Assessing the Role of Daptomycin as Antibiotic Therapy for Staphylococcal Prosthetic Joint Infection

Background: The role of daptomycin, a potent, safe, convenient anti-staphylococcal antibiotic, in treatment of prosthetic joint infection (PJI) is unclear. We evaluated our experience with the largest cohort of patients with staphylococcal PJI managed with daptomycin. Methods: A cohort of staphylococcal hip and knee PJI treated with daptomycin was identified by hospital records from 2009 to 2016. All cases met Musculoskeletal Infection Society International Consensus criteria for PJI. The primary endpoint was 2 year prosthesis retention. Univariate analyses and regression statistics were calculated. Results: 341 patients with staphylococcal PJI were analyzed. 154 two-stages (77%) and 74 DAIR procedures (52%) met criteria for treatment success at 2 years. 77 patients were treated with daptomycin, of which 34 two-stages (68%) and 15 DAIRs (56%) achieved treatment success. Pairwise and regression analysis found no association between treatment success and daptomycin use. Organism (DAIR only) and Charlson Comorbidity Index scores (DAIR and two-stage) were significantly associated with treatment outcome. Six daptomycin patients (7.8%) had adverse side effects. Discussion: Daptomycin fared no better or worse than comparable antibiotics in a retrospective cohort of staphylococcal hip and knee PJI patients, regardless of surgical strategy. Conclusion: The convenient dosing, safety, and potency of daptomycin make it an attractive antibiotic for staphylococcal PJI. However, these advantages must be weighed against higher costs and rare, but serious side effects.

Linezolid versus daptomycin treatment for periprosthetic joint infections: a retrospective cohort study

BACKGROUND

Linezolid (LZD) and daptomycin (DAP) are predominantly used to target gram-positive pathogens; however, treatment effectiveness and adverse reactions for periprosthetic joint infections (PJIs) remain unknown. The aim of this study was to compare the effectiveness and adverse reactions of LZD and DAP for PJIs.

METHODS

This study retrospectively evaluated 82 patients between June 2009 and December 2017, to compare the effectiveness of LZD (group L, n = 39) and DAP (group D, n = 43) for treatment of PJIs harboring gram-positive microorganisms. Surgical options used with LZD or DAP therapy included implant retention, implant removal, and a shift to another appropriate antibiotic. Infection control was defined as not requiring implant removal after the final treatment.

RESULTS

Gram-positive pathogens were isolated from 72% of group L and 70% of group D patients, respectively. Whole infection control rates against gram-positive pathogens in groups L and D were 79% and 77%, respectively. Furthermore, infection control rates were 94% and 58% in group L and 75% and 80% in group D, without and with implant removal, respectively. Significantly higher clinical success rates and lower adverse event rates were observed in group D, including higher red blood cell and platelet counts and lower C-reactive protein (CRP) levels.

CONCLUSIONS

Although the effectiveness of LZD and DAP was equivalent in terms of infection control rates for refractory PJIs with gram-positive pathogens, DAP therapy significantly decreased CRP levels and caused fewer adverse events than LZD treatment.

Treatments and limitations for methicillin-resistant Staphylococcus aureus: A review of current literature

Methicillin-resistant Staphylococcus aureus (MRSA) has remained a major threat to healthcare; in both hospital and community settings over the past five decades. With the current use of antibiotics for a variety of infections, including MRSA, emerging resistance is a major concern. Currently available treatments have restrictions limiting their use. These issues include, but are not limited to, side effects, cross-resistance, lack of understanding of pharmacokinetics and clinical pharmacodynamics, gradual increment in minimal inhibitory concentration over the period (MIC creep) and ineffectiveness in dealing with bacterial biofilms. Despite availability of various therapeutic options for MRSA, the clinical cure rates remain low with high morbidity and mortality. Given these challenges with existing treatments, there is a need for development of novel agents for MRSA. Along with prompt infection control strategies and strict implementation of antibiotic stewardship, cautious use of newer anti-MRSA agents will be of utmost importance. This article reviews the treatments and limitations of MRSA management and highlights the future path.

The role of fosfomycin in osteoarticular infection

Osteoarticular infections include septic arthritis and osteomyelitis, with Gram-positive microorganisms isolated most frequently. In recent years, there has been an increase in the number of resistant strains in this type of infection, which complicates the treatment. Fosfomycin is active against a large percentage of Gram-positive and Gram-negative pathogens, including multidrug-resistant strains, and its properties include low protein binding, low molecular weight and good bone dissemination. In this article, we discuss fosfomycin's activity in vitro, its pharmacokinetic and pharmacodynamic parameters of interest in osteoarticular infections, the experimental models of osteomyelitis and foreign body infection and the clinical experience with these types of infections.

Comprehensive antibiotic-linked mutation assessment by resistance mutation sequencing (RM-seq)

Mutation acquisition is a major mechanism of bacterial antibiotic resistance that remains insufficiently characterised. Here we present RM-seq, a new amplicon-based deep sequencing workflow based on a molecular barcoding technique adapted from Low Error Amplicon sequencing (LEA-seq). RM-seq allows detection and functional assessment of mutational resistance at high throughput from mixed bacterial populations. The sensitive detection of very low-frequency resistant sub-populations permits characterisation of antibiotic-linked mutational repertoires in vitro and detection of rare resistant populations during infections. Accurate quantification of resistance mutations enables phenotypic screening of mutations conferring pleiotropic phenotypes such as in vivo persistence, collateral sensitivity or cross-resistance. RM-seq will facilitate comprehensive detection, characterisation and surveillance of resistant bacterial populations ( https://github.com/rguerillot/RM-seq ).

Treatment strategies for persistent methicillin-resistant Staphylococcus aureus bacteraemia

WHAT IS KNOWN AND OBJECTIVE

Treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia is a long-standing challenge to health care, often complicated by metastatic infections, treatment failure and mortality. When MRSA bacteraemia persists despite adequate initial treatment, current Infectious Diseases Society of America guidelines recommend evaluation and removal of possible sources of infection. In addition, a change in therapy may be considered. The objective of this review was to explore the therapeutic options for the treatment of persistent MRSA bacteraemia.

METHODS

A literature search of PubMed, MEDLINE and Google Scholar was performed using the following search terms: [methicillin-resistant Staphylococcus aureus OR MRSA] AND [bacteraemia OR bloodstream infection] AND [persistent OR persistence OR refractory OR treatment failure OR salvage] AND treatment. We evaluated relevant, adult, English-language, peer-reviewed studies published between 1985 and May 2018. In vitro and animal studies were considered as supportive of in vivo data.

RESULTS AND DISCUSSION

Randomized, controlled trials are lacking. However, case series and case reports support multiple treatment options including high-dose daptomycin in combination with an antistaphylococcal β-lactam, ceftaroline, trimethoprim-sulfamethoxazole (TMP-SMX) or fosfomycin; ceftaroline alone or in combination with vancomycin or TMP-SMX; linezolid alone or in combination with a carbapenem, or telavancin.

WHAT IS NEW AND CONCLUSION

Given the heterogeneity of the data, a preferred regimen has not emerged. Prescribers must take into consideration recent exposure, source control, and available synergy and clinical data. Further comparative trials are needed to establish a preferred regimen and the creation of a universal treatment algorithm.

Comparison of Empiric Antibiotics for Acute Osteomyelitis in Children

OBJECTIVES

Broad-spectrum antibiotics are commonly used for the empiric treatment of acute hematogenous osteomyelitis and often target methicillin-resistant Staphylococcus aureus (MRSA) with medication-associated risk and unknown treatment benefit. We aimed to compare clinical outcomes among patients with osteomyelitis who did and did not receive initial antibiotics used to target MRSA.

METHODS

A retrospective cohort study of 974 hospitalized children 2 to 18 years old using the Pediatric Health Information System database, augmented with clinical data. Rates of hospital readmission, repeat MRI and 72-hour improvement in inflammatory markers were compared between treatment groups.

RESULTS

Repeat MRI within 7 and 180 days was more frequent among patients who received initial MRSA coverage versus methicillin-sensitive S aureus (MSSA)-only coverage (8.6% vs 4.1% within 7 days [P = .02] and 12% vs 5.8% within 180 days [P < .01], respectively). Ninety- and 180-day hospital readmission rates were similar between coverage groups (9.0% vs 8.7% [P = .87] and 10.9% vs 11.2% [P = .92], respectively). Patients with MRSA- and MSSA-only coverage had similar rates of 72-hour improvement in C-reactive protein values, but patients with MRSA coverage had a lower rate of 72-hour white blood cell count normalization compared with patients with MSSA-only coverage (4.2% vs 16.4%; P = .02).

CONCLUSIONS

In this study of children hospitalized with acute hematogenous osteomyelitis, early antibiotic treatment used to target MRSA was associated with a higher rate of repeat MRI compared with early antibiotic treatment used to target MSSA but not MRSA. Hospital readmission rates were similar for both treatment groups.

Daptomycin treatment in Gram-positive vascular graft infections

BACKGROUND

Daptomycin is a bactericidal antibiotic approved for the treatment of skin and soft tissue infections and right-side endocarditis. However, there is a lack of published data outlining its usefulness in vascular graft infections (VGI). The aim of this study was to describe the clinical experience of daptomycin use in the treatment of VGI caused by Gram-positive bacteria.

METHODS

This was a retrospective cohort study of patients diagnosed with VGI receiving daptomycin at a tertiary care hospital during the period January 2010 to December 2012.

RESULTS

Of a total 1066 consecutive patients who had undergone vascular grafts (VG), 25 were diagnosed with VGI. Fifteen of these patients (11 prosthetic VG, three autologous VG, one both types) received daptomycin (median dose 6.7mg/kg/day, range 4.1-7.1mg/kg/day; median age 69 years, range 45-83 years; 80% male). The infected bypass was removed in 13 cases. The most common reason for selecting daptomycin was kidney failure (53%). The Gram-positive organisms isolated were coagulase-negative Staphylococcus (n=10), Staphylococcus aureus (n=3) (two methicillin-resistant S. aureus), Enterococcus faecium (n=2), and Enterococcus faecalis (n=1). The mean follow-up was 69 months (interquartile range 48-72 months). Ten patients (66.7%) achieved complete healing of the VGI. A recurrence of the infection was observed in 100% of patients in whom the bypass was not removed. Among patients who did not achieve complete healing, one needed a supracondylar amputation and one died as a consequence of infection. Five patients received treatment with rifampicin in addition to daptomycin and they were all cured.

CONCLUSIONS

The use of daptomycin and surgery for Gram-positive VGI was effective and well tolerated, and this may be a good alternative for the treatment of VGI in patients with peripheral arterial disease in whom renal insufficiency is common.

Role of rifampin for the treatment of bacterial infections other than mycobacteriosis

OBJECTIVES

Rifampin was initially approved for the treatment of tuberculosis. Because of its low toxicity, broad-spectrum activity, and good bioavailability, rifampin is now commonly administered as combination antimicrobial therapy for the treatment of various infections caused by organisms other than mycobacteria. This review summarizes the most recent clinical studies on the use of rifampin combinations for treating four common non-mycobacterial infections: acute bacterial meningitis, infective endocarditis and bacteraemia, pneumonia, and biofilm-related infections.

METHODS

We performed a literature search of clinical studies published in English from January 2005 to June 2016 using the PubMed database with the search terms "rifampin" with "meningitis" or "infective endocarditis and bacteraemia" or "pneumonia" or "prosthetic joint infections.

RESULTS

Current evidence to support a rifampin combination therapy as a treatment for non-mycobacterial infections was largely based on in vitro/in vivo studies and non-comparable retrospective case series. Additionally, controlled clinical trials that directly compared outcomes resulting from rifampin treatment versus treatment without rifampin were limited.

CONCLUSIONS

Rifampin combination therapy appears promising for the treatment of non-mycobacterial infections. However, further definitive clinical trials are necessary to validate its use because the risk of adverse drug-drug interactions and of the emergence of rifampin resistance during treatment may outweigh the potential benefits.

Predicting effects of antibiotic combinations using MICs determined at pharmacokinetically derived concentration ratios: in vitro model studies with linezolid- and rifampicin-exposed Staphylococcus aureus

To predict the effects of combined use of antibiotics on their pharmacodynamics, the susceptibility of Staphylococcus aureus to linezolid-rifampicin combinations was tested at concentration ratios equal to the ratios of 24-area under the concentration-time curve (AUC₂₄) simulated in an in vitro dynamic model. The linezolid MICs in combination with rifampicin decreased 8- to 67-fold. The rifampicin MICs were similar with or without linezolid. The enhanced activity of linezolid combined with rifampicin increased the AUC₂₄/MIC ratios and provided more pronounced antibacterial effects compared with single treatments. The areas between the control growth and time-kill curves (ABBCs) determined in combined and single treatments with linezolid were plotted against AUC₂₄/MIC on the same graph (r² 0.94). These findings suggest that the effects of linezolid-rifampicin combinations can be predicted by AUC₂₄/MICs of linezolid using its MIC determined at pharmacokinetically derived linezolid-to-rifampicin concentration ratios.

New Insight into Daptomycin Bioavailability and Localization in Staphylococcus aureus Biofilms by Dynamic Fluorescence Imaging

Staphylococcus aureus is one of the most frequent pathogens responsible for biofilm-associated infections (BAI), and the choice of antibiotics to treat these infections remains a challenge for the medical community. In particular, daptomycin has been reported to fail against implant-associated S. aureus infections in clinical practice, while its association with rifampin remains a good candidate for BAI treatment. To improve our understanding of such resistance/tolerance toward daptomycin, we took advantage of the dynamic fluorescence imaging tools (time-lapse imaging and fluorescence recovery after photobleaching [FRAP]) to locally and accurately assess the antibiotic diffusion reaction in methicillin-susceptible and methicillin-resistant S. aureus biofilms. To provide a realistic representation of daptomycin action, we optimized an in vitro model built on the basis of our recently published in vivo mouse model of prosthetic vascular graft infections. We demonstrated that at therapeutic concentrations, daptomycin was inefficient in eradicating biofilms, while the matrix was not a shield to antibiotic diffusion and to its interaction with its bacterial target. In the presence of rifampin, daptomycin was still present in the vicinity of the bacterial cells, allowing prevention of the emergence of rifampin-resistant mutants. Conclusions derived from this study strongly suggest that S. aureus biofilm resistance/tolerance toward daptomycin may be more likely to be related to a physiological change involving structural modifications of the membrane, which is a strain-dependent process.

Efficacy of Linezolid and Fosfomycin in Catheter-Related Biofilm Infection Caused by Methicillin-Resistant Staphylococcus aureus

As long-standing clinical problems, catheter-related infections and other chronic biofilm infections are more difficult to treat due to the high antibiotic resistance of biofilm. Therefore, new treatments are needed for more effective bacteria clearance. In this study, we evaluated the antibacterial activities of several common antibiotics alone and their combinations against biofilm-embedded methicillin-resistant staphylococcus aureus (MRSA) infections, both in vitro and in vivo. In brief, fosfomycin, levofloxacin, and rifampin alone or in combination with linezolid were tested in vitro against planktonic and biofilm-embedded MRSA infection in three MRSA stains. The synergistic effects between linezolid and the other three antibiotics were assessed by fractional inhibitory concentration index (FICI) and time-kill curves, where the combination of linezolid plus fosfomycin showed the best synergistic effect in all strains. For further evaluation in vivo, we applied the combination of linezolid and fosfomycin in a catheter-related biofilm rat model and found that viable bacteria counts in biofilm were significantly reduced after treatment (P < 0.05). In summary, we have shown here that the combination of linezolid and fosfomycin treatment had improved therapeutic effects on biofilm-embedded MRSA infection both in vitro and in vivo, which provided important basis for new clinical therapy development.

An update on surgical and antimicrobial therapy for acute periprosthetic joint infection: new challenges for the present and the future

Periprosthetic joint infection (PJI) is a devastating complication that can occur following any arthroplasty procedure. Approximately half of these infections develop within the first year after arthroplasty, mainly in the first 1 to 3 months. These infections are known as early PJI. It is widely accepted that many early PJIs can be successfully managed by debridement, irrigation, and prosthetic retention, followed by a course of biofilm-effective antibiotics (debridement, antibiotics, implant retention procedure), but candidate patients should meet the requirements set down in Zimmerli's algorithm. The best antibiotic regimen for acute PJI treated without implant removal remains uncertain. Rifampin-containing regimens, when feasible, are recommended in gram-positive infections, and fluoroquinolones in gram-negative cases. The duration, dosage, and administration route of antibiotics and the use of combined therapy are matters that requires further clarification, as the current level of evidence is low and most recommendations are based on experimental data, studies in small series, and expert experience.

New in vitro and in vivo models to evaluate antibiotic efficacy in Staphylococcus aureus prosthetic vascular graft infection

OBJECTIVE

Prosthetic vascular graft infection (PVGI) is an emerging disease, mostly caused by staphylococci, with limited data regarding efficacy of current antistaphylococcal agents. We aimed to assess the efficacy of different antibiotic regimens.

METHODS

Six different strains of MSSA and MRSA were used. We compared results of minimal biofilm inhibitory and eradicating concentrations (MBICs and MBECs) obtained with a Calgary Biofilm Pin Lid Device (CBPD) with those yielded by an original Dacron(®)-related minimal inhibitory and eradicating concentration measure model. We then used a murine model of Staphylococcus aureus vascular prosthetic material infection to evaluate efficacy of different antibiotic regimens: vancomycin and daptomycin combined or not with rifampicin for MRSA and the same groups with cloxacillin and cloxacillin combined with rifampicin for MSSA.

RESULTS

We demonstrated that classical measures of MBICs and MBECs obtained with a CPBD could overestimate the decrease in antibiotic susceptibility in material-related infections and that the nature of the support used might influence the measure of biofilm susceptibility, since results yielded by our Dacron(®)-related minimal eradicating assay were lower than those found with a plastic device. In our in vivo model, we showed that daptomycin was significantly more bactericidal than comparators for some strains of MRSA or MSSA but not for all. For the majority of strains, it was as efficient as comparators. The addition of rifampicin to daptomycin did not enhance daptomycin efficacy.

CONCLUSIONS

Despite the heterogeneity of results according to bacterial strains, these innovative models represent an option to better evaluate the in vitro efficacy of antibiotics on Dacron(®)-related biofilm S. aureus infections, and to screen different antibiotic regimens in a mouse model of PVGIs.

Should daptomycin-rifampin combinations for MSSA/MRSA isolates be avoided because of antagonism?

PURPOSE

There is increasing clinical evidence from observational studies, that combination therapy of daptomycin with rifampin is a valuable treatment option for biofilm-associated difficult to treat Staphylococcus aureus infections such as osteomyelitis, prosthetic joint infection and endocarditis. However, two studies analyzing a limited number of S. aureus isolates reported an antagonism of those two drugs questioning the benefit of this combination.

METHODS

To estimate the frequency of this possible antagonism, we performed in vitro checkerboard assays on 58 consecutive clinical isolates of S. aureus (MSSA n = 9, MRSA n = 49). We determined the fractional inhibitory concentration index (FICI) and the susceptible breakpoint index (SBPI). All isolates were characterized by a microprobe array detecting 336 different genes/alleles to ensure their non-clonal origin.

RESULTS

For all isolates, the FICI was between 1.00 and 1.25 indicating additive effects for the daptomycin/rifampin combination. Neither antagonism nor synergism as defined by the FICI was found for any of the isolates.

CONCLUSION

Based on these data, there is no evidence to advise against the daptomycin/rifampin combination therapy.

Towards a definition of daptomycin optimal dose: Lessons learned from experimental and clinical data

Daptomycin exhibits excellent antibacterial activity against a wide range of Gram-positive bacteria. The on-label standard daily doses for daptomycin are 4 mg/kg for skin infections and 6 mg/kg for bacteraemia or right-sided endocarditis. Daptomycin bactericidal activity is predominantly concentration-dependent and by considering the values of pharmacokinetic targets established by several authors as well as the peak and trough concentrations of daptomycin obtained at various daily dosages, it appears that these targets can easily be reached with a dose of 6 mg/kg but only for a minimum inhibitory concentration (MIC) at 0.1 mg/L, and that for increasing MICs (e.g. 0.5 mg/L or 1 mg/L) these targets may only be attained with higher dosages (i.e. ≥10 mg/kg). High-dose (HD) daptomycin therapy has also been proven to be effective for reducing the risk of selection of daptomycin-resistant strains. Given the concentration-dependent bactericidal activity of daptomycin, the absence of a dose-toxicity relationship and the need to prevent the selection of resistant strains, we propose to consider for staphylococcal (i) skin and soft-tissue infections, daily doses of daptomycin of 6 mg/kg (new standard dose) and (ii) endocarditis or bacteraemia including those associated with intravascular catheter and implant-related infections, ≥10 mg/kg (HD) when the MIC is unknown or >0.25 mg/L, and 6-10 mg/kg (intermediate doses) when the MIC is ≤0.25 mg/L. For severe and deep-seated enterococcal infections, we propose high (≥10 mg/kg) daily doses of daptomycin in combination with another active agent, especially a β-lactam.

3D printed bioceramics for dual antibiotic delivery to treat implant-associated bone infection

Surgical implant-associated bone infections (osteomyelitis) have severe clinical and socioeconomic consequences. Treatment of chronic bone infections often involves antibiotics given systemically and locally to the affected site in poly (methyl methacrylate) (PMMA) bone cement. Given the high antibiotic concentrations required to affect bacteria in biofilm, local delivery is important to achieve high doses at the infection site. PMMA is not suitable to locally-deliver some biofilm-specific antibiotics, including rifampin, due to interference with PMMA polymerisation. To examine the efficacy of localised, combinational antibiotic delivery compared to PMMA standards, we fabricated rifampin- and vancomycin-laden calcium phosphate scaffolds (CPS) by three-dimensional (3D) printing to treat an implant-associated Staphylococcus aureus bone infection in a murine model. All vancomycin- and rifampin-laden CPS treatments significantly reduced the bacterial burden compared with vancomycin-laden PMMA. The bones were bacteria culture negative in 50 % of the mice that received sustained release vancomycin- and rifampin-laden CPS. In contrast, 100 % of the bones treated with vancomycin monotherapy using PMMA or CPS were culture positive. Yet, the monotherapy CPS significantly reduced the bacterial metabolic load following revision compared to PMMA. Biofilm persisted on the fixation hardware, but the infection-induced bone destruction was significantly reduced by local rifampin delivery. These data demonstrate that, despite the challenging implant-retaining infection model, co-delivery of rifampin and vancomycin from 3D printed CPS, which is not possible with PMMA, significantly improved the outcomes of implant-associated osteomyelitis. However, biofilm persistence on the fixation hardware reaffirms the importance of implant exchange or other biofilm eradication strategies to complement local antibiotics.

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.

Impact of the combination of daptomycin and trimethoprim-sulfamethoxazole on clinical outcomes in methicillin-resistant Staphylococcus aureus infections

Complicated Staphylococcus aureus infections, including bacteremia, are often associated with treatment failures, prolonged hospital stays, and the emergence of resistance to primary and even secondary therapies. Daptomycin is commonly used as salvage therapy after vancomycin failure for the treatment of methicillin-resistant S. aureus (MRSA) infections. Unfortunately, the emergence of daptomycin resistance, especially in deep-seated infections, has been reported, prompting the need for alternative or combination therapy. Numerous antibiotic combinations with daptomycin have been investigated clinically and in vitro. Of interest, the combination of daptomycin and trimethoprim-sulfamethoxazole (TMP-SMX) has proved to be rapidly bactericidal in vitro to strains that are both susceptible and nonsusceptible to daptomycin. However, to date, there is limited clinical evidence supporting the use of this combination. This was a multicenter, retrospective case series of patients treated with the combination of daptomycin and TMP-SMX for at least 72 h. The objective of this study was to describe the safety and effectiveness of this regimen in clinical practice. The most commonly stated reason that TMP-SMX was added to daptomycin was persistent bacteremia and/or progressive signs and symptoms of infection. After the initiation of combination therapy, the median time to clearance of bacteremia was 2.5 days. Microbiological eradication was demonstrated in 24 out of 28 patients, and in vitro synergy was demonstrated in 17 of the 17 recovered isolates. Further research with this combination is necessary to describe the optimal role and its impact on patient outcomes.

Evaluation of High-Dose Daptomycin Versus Vancomycin Alone or Combined with Clarithromycin or Rifampin Against Staphylococcus aureus and S. epidermidis in a Novel In Vitro PK/PD Model of Bacterial Biofilm

INTRODUCTION

Medical device infections are associated with significant morbidity and mortality. These difficult-to-treat infections often result in antibiotic failure and resistance. Combination therapy is often required, however, the most optimal combination is unknown. We evaluated the in vitro activity of daptomycin (DAP) or vancomycin (VAN) alone and in combination with rifampin (RIF) or clarithromycin (CLA) against strains of Staphylococcus aureus and S. epidermidis grown in biofilm on 3 prosthetic device materials.

METHODS

One methicillin-resistant S. aureus (MRSA R5266), one heteroresistant vancomycin-intermediate S. aureus (hVISA R3640), and one methicillin-resistant S. epidermidis (MRSE R461) strain was evaluated in a CDC biofilm reactor with titanium, Teflon®, and steel coupons. Regimens simulated included DAP 10 mg/kg/day, and VAN 1 g q12h alone or in combination with RIF 600 mg q24h or CLA 250 mg q12h. Additional regimens including DAP 12 mg/kg/day or VAN ± RIF 450 mg q12h were evaluated against the hVISA strain.

RESULTS

DAP + RIF or VAN + RIF demonstrated enhanced activity against R3640 in embedded biofilm (EB) cells in all materials versus DAP or VAN alone (P ≤ 0.040). Only DAP + RIF demonstrated sustained bactericidal activity (≥3.80 log10 CFU/cm2 reduction from baseline) against EB and planktonic cells of R5266 and EB cells of R461 in all 3 materials. Of interest, CLA did not appear to enhance DAP or VAN killing activities, and the addition of RIF prevented the emergence of resistance to DAP or VAN in all organisms.

CONCLUSION

Using an in vitro bacterial biofilm model containing three common prosthetic device materials, DAP + RIF and VAN + RIF were the most effective regimens. DAP + RIF displayed the greatest activity and represents a promising combination to evaluate for treatment of biofilm-associated staphylococcal infections.

Treatment options for methicillin-resistant Staphylococcus aureus (MRSA) infection: Where are we now?

Methicillin-resistant Staphylococcus aureus (MRSA) infection continues to be a substantial global problem with significant associated morbidity and mortality. This review summarises the discussions that took place at the 4th MRSA Consensus Conference in relation to the current treatment options for serious MRSA infections and how to optimise whichever therapy is embarked upon. It highlights the many challenges faced by both the laboratory and clinicians in the diagnosis and treatment of MRSA infections.

Prosthetic joint infection

Prosthetic joint infection (PJI) is a tremendous burden for individual patients as well as the global health care industry. While a small minority of joint arthroplasties will become infected, appropriate recognition and management are critical to preserve or restore adequate function and prevent excess morbidity. In this review, we describe the reported risk factors for and clinical manifestations of PJI. We discuss the pathogenesis of PJI and the numerous microorganisms that can cause this devastating infection. The recently proposed consensus definitions of PJI and approaches to accurate diagnosis are reviewed in detail. An overview of the treatment and prevention of this challenging condition is provided.

Treatment of infections due to resistant Staphylococcus aureus

This chapter reviews data on the treatment of infections caused by drug-resistant Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA). This review covers findings reported in the English language medical literature up to January of 2013. Despite the emergence of resistant and multidrug-resistant S. aureus, we have seven effective drugs in clinical use for which little resistance has been observed: vancomycin, quinupristin-dalfopristin, linezolid, tigecycline, telavancin, ceftaroline, and daptomycin. However, vancomycin is less effective for infections with MRSA isolates that have a higher MIC within the susceptible range. Linezolid is probably the drug of choice for the treatment of complicated MRSA skin and soft tissue infections (SSTIs); whether it is drug of choice in pneumonia remains debatable. Daptomycin has shown to be non-inferior to either vancomycin or β-lactams in the treatment of staphylococcal SSTIs, bacteremia, and right-sided endocarditis. Tigecycline was also non-inferior to comparator drugs in the treatment of SSTIs, but there is controversy about whether it is less effective than other therapeutic options in the treatment of more serious infections. Telavancin has been shown to be non-inferior to vancomycin in the treatment of SSTIs and pneumonia, but has greater nephrotoxicity. Ceftaroline is a broad-spectrum cephalosporin with activity against MRSA; it is non-inferior to vancomycin in the treatment of SSTIs. Clindamycin, trimethoprim-sulfamethoxazole, doxycycline, rifampin, moxifloxacin, and minocycline are oral anti-staphylococcal agents that may have utility in the treatment of SSTIs and osteomyelitis, but the clinical data for their efficacy is limited. There are also several drugs with broad-spectrum activity against Gm-positive organisms that have reached the phase II and III stages of clinical testing that will hopefully be approved for clinical use in the upcoming years: oritavancin, dalbavancin, omadacycline, tedizolid, delafloxacin, and JNJ-Q2. Thus, there are currently many effective drugs to treat resistant S. aureus infections and many promising agents in the pipeline. Nevertheless, S. aureus remains a formidable adversary, and despite our deep bullpen of potential therapies, there are still frequent treatment failures and unfortunate clinical outcomes. The following discussion summarizes the clinical challenges presented by MRSA, the clinical experience with our current anti-MRSA antibiotics, and the gaps in our knowledge on how to use these agents to most effectively combat MRSA infections.

Establishment of a new methicillin resistant Staphylococcus aureus animal model of osteomyelitis

PURPOSE

The increase in methicillin-resistant Staphylococcus aureus (MRSA) infections is currently a major health care problem. Vancomycin is still often the first-line anti-microbiological agent for treating such infections; however, a recent decline in efficacy of vancomycin in MRSA infections has raised concerns and accelerated the search for new antibiotics. The aim of this study was to establish a MRSA peri-implant osteomyelitis animal model for future testing of new anti-microbiological agents under typical MRSA infection conditions.

METHODS

Eighteen randomised NZW-rabbits underwent a standardised surgical procedure with the insertion of a femoral bone implant. Animals were then divided into group 1 (MRSA inoculation, no antibiotics; M/N), group 2 (MRSA inoculation, Vancomyin; M/V), and group 3 (no MRSA inoculation, no antibiotics; N/N). The primary study outcome parameters were animal leucocyte count, animal weight, and animal body temperature at one, seven, and 42 days after surgery. Additionally, a histo-morphometrical score was established and adjusted to a modified histological Smeltzer score.

RESULTS

Macroscopic and histo-morphometrical findings showed a peri-implant osteomyelitis in group 1 with both increased acute and chronic infection parameters in M/N, as compared to M/V and N/N, indicating that vancomycin treatment prevented typical morphological changes of MRSA peri-implant osteomyelitis. Similarly, there was a reduction in animal weight and increase in leucocyte count and body temperature in group 1 (each p < 0.005). Vancomycin treatment again resulted in significantly reduced leucocyte count and body temperature, and increased animal body weight.

CONCLUSIONS

Here we have established a peri-implant MRSA osteomyelitis model that successfully combined clinical and laboratory outcome parameters of infection with histo-morphometrical results; this model appears to be valuable for future experimental use and therapeutic monitoring of new anti-microbiological MRSA drugs.

Current pharmacotherapy options for osteomyelitis: convergences, divergences and lessons to be drawn

INTRODUCTION

Antibiotic therapy of osteomyelitis is complex and requires a multidisciplinary approach including surgeons and infectious diseases specialists. However, it suffers from a lack of high-quality clinical studies indicating the superiority of one type of therapy over another. Knowing the antibiotics and their main characteristics is important to guide the choice of treatment for patients with osteomyelitis.

AREAS COVERED

The aim of the present article is to review the systemic curative antibiotic therapy of osteomyelitis in adults with a focus on new agents. Diabetic foot osteomyelitis will be briefly discussed separately. A literature search of the PubMed database using the term 'osteomyelitis' alone and in combination with 'hematogenous', 'vertebral', 'biofilm', 'diabetic foot', 'trauma', 'antibiotic' 'daptomycin', 'telavancin', 'tigecycline', 'linezolid', 'ertapenem', 'ceftobiprole' and 'ceftaroline' was carried out.

EXPERT OPINION

Antibiotic treatment of acute and chronic osteomyelitis should be considered as two distinct entities with regard to the choice of the most appropriate antibiotics and the need for surgery. Among the most recently available antibiotics, ertapenem and daptomycin are promising agents for the treatment of osteomyelitis due to resistant bacteria.

Daptomycin: the role of high-dose and combination therapy for Gram-positive infections

Daptomycin, a cyclic lipopeptide with rapid bactericidal activity, is approved at doses of 4 mg/kg and 6 mg/kg for the treatment of its respective indications [i.e. complicated skin and soft-tissue infections (cSSTIs) caused by Gram-positive bacteria; and Staphylococcus aureus bacteraemia associated with right-sided infective endocarditis (RIE) or cSSTIs, or RIE due to S. aureus]. Higher doses and combination therapy strategies have been investigated in some difficult-to-treat infections in order to: enhance clinical success rates; treat pathogens that may be non-susceptible to standard doses; and minimise the risk of resistance development in patients, particularly those who may need an extended treatment duration, who may have had suboptimal surgical management and/or who may have not responded to prior antibiotic therapy. Although clinical trial data of daptomycin doses >6 mg/kg and of daptomycin in combination with other antibiotics are limited, clinical experience reported to date suggests that daptomycin is effective and well tolerated at higher doses and in combination. In this review, the rationale both for high-dose and combination therapy strategies with daptomycin is explored and the available evidence is presented by indication and evaluated from a clinical perspective. Safety and efficacy are discussed from prospective and retrospective clinical studies, together with case reports for a variety of infections, including bacteraemia, endocarditis, cSSTIs and osteomyelitis, and expert recommendations are provided in summary of the evidence. The use of high-dose daptomycin, alone or in combination, may be useful for difficult-to-treat Gram-positive infections and further evaluation of these strategies is warranted.