Alternatives to Vancomycin for the Treatment of Methicillin-Resistant Staphylococcus aureus Infections

Antibiotic considerations in the treatment of multidrug-resistant (MDR) pathogens: a case-based review

The recent rise in antimicrobial resistance among health-care associated pathogens is a growing public health concern. According to the National Nosocomial Infections Surveillance System, rates of methicillin-resistant Staphylococcus aureus (MRSA) in intensive care units have nearly doubled over the last decade. Of equal importance, gram-negative agents such as Pseudomonas aeruginosa, Acinetobacter baumannii, and extended-spectrum beta lactamase-producing Enterobacteriaceae demonstrate increasing resistance to third-generation cephalosporins, fluoroquinolones, and, in some cases, carbapenems. As a consequence, hospitalists may find themselves utilizing new antibiotics in the treatment of bacterial infections. This case-based review will highlight 8 antibiotics that have emerging clinical indications in treating these multidrug-resistant (MDR) pathogens.

Multicenter, randomized study of the efficacy and safety of intravenous iclaprim in complicated skin and skin structure infections

Iclaprim is a novel antibacterial agent that is currently in development for the treatment of complicated skin and skin structure infections (cSSSI). Iclaprim specifically and selectively inhibits bacterial dihydrofolate reductase, a critical enzyme in the bacterial folate pathway, and exhibits an extended spectrum of activity against various resistant pathogens, including methicillin (meticillin)-resistant Staphylococcus aureus (MRSA). The objective of this randomized, double-blind phase II study was to compare the efficacy and safety of iclaprim to those of vancomycin in patients with cSSSI. Patients were randomized to receive 0.8 mg iclaprim/kg of body weight, 1.6 mg/kg iclaprim, or 1 g vancomycin twice a day for 10 days. Clinical cure rates for the 0.8- and 1.6-mg/kg-iclaprim treatment groups were comparable to that for the vancomycin treatment group (26/28 patients [92.9%], 28/31 patients [90.3%], and 26/28 patients [92.9%], respectively). Iclaprim also showed high microbiological eradication rates. Iclaprim exhibited an eradication rate of 80% and 72% versus 59% observed with vancomycin for S. aureus, the pathogen most frequently isolated at baseline. Five MRSA cases were observed, four in the 0.8-mg/kg-iclaprim arm and one in the vancomycin arm, and all were both clinically and microbiologically cured. Iclaprim exhibited a safety profile similar to that of vancomycin, an established drug for the treatment of cSSSI. Results from this study indicate that iclaprim is a promising new therapy for the treatment of cSSSI, in particular those caused by S. aureus, including MRSA.

In vitro activity of daptomycin against Staphylococci isolated from bacteremia and community-onset skin and soft tissue infections in France: data from two nationwide studies

Staphylococci are a leading cause of skin and soft tissue infections (SSTIs) and bacteremia in France, a country with a high prevalence of oxacillin resistance. We evaluated the in vitro activity of daptomycin compared with reference compounds against 445 Staphylococcus aureus and 53 coagulase-negative Staphylococci (CNS) collected during two large nationwide studies performed in 2006 and 2007. The percentage of oxacillin resistance among S. aureus was 13.6% (SSTIs) and 30.7% (bacteremia). Daptomycin showed lower MIC(90) levels compared to vancomycin, teicoplanin, and linezolid (0.19 mg/L vs. 2, 1.5, and 1 mg/L, respectively), irrespective of oxacillin susceptibility. Amongst the CNS, 64.2% of the isolates originated from clinical bacteremia were resistant to oxacillin and 24.5% to teicoplanin; all but one Staphylococci were susceptible to daptomycin (MIC = 1.5 mg/l). As with linezolid, daptomycin seems to constitute an alternative option to treat some staphylococcal infections in the French context of high oxacillin resistance prevalence and high glycopeptides MIC.

Severe invasive community-associated methicillin-resistant Staphylococcus aureus infections in previously healthy children

OBJECTIVE

An increase in community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections has been reported in the literature. Most severe, life-threatening infections were previously thought to be associated with chronically ill or frail patients. Our pediatric intensive care unit (PICU) has seen a recent dramatic increase in primary, severe invasive CA-MRSA infections in healthy children.

DESIGN/SETTING

A retrospective chart review of all previously healthy patients admitted to our 19-bed combined medical-surgical PICU with a primary diagnosis of severe invasive, culture-proven CA-MRSA disease during the past 6 years.

RESULTS

Eleven previously healthy patients were admitted to our PICU with severe, primary, invasive CA-MRSA infections from March 2006 through September 2007, in contrast to no patients meeting these criteria in the preceding 5 years. The mortality rate was 27%, compared with an overall PICU mortality rate during the study period of <7%. The mean PICU length of stay of these patients was 14.9 days, compared with an average PICU length of stay of 2.4 days. Despite initiation of treatment with vancomycin at admission to the PICU in all but one case, patients took a mean of 5.7 days to convert to negative blood cultures. Eight patients had bacteremia longer than 4 days. Six of the patients developed bilateral necrotizing pneumonia requiring prolonged mechanical ventilation.

CONCLUSIONS

Severe CA-MRSA infections in healthy children are increasing at an alarming rate in our institution. This acute rise in incidence, coupled with an alarmingly high associated mortality rate, raises important questions about the initial empirical antibiotic therapy we use in caring for patients presenting with suspected life-threatening CA-MRSA disease. Vancomycin monotherapy may not be adequate treatment for severe CA-MRSA infections.

Early appropriate parenteral antimicrobial treatment of complicated skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus

BACKGROUND

Complicated skin and soft tissue infections (cSSTIs) are a major clinical problem, in part because of the increasing resistance of infecting bacteria to our current antibiotic therapies. Prompt appropriate treatment of infections in hospitalized patients reduces the mortality rate. Furthermore, appropriate and timely antibiotic therapy improves outcomes for cSSTIs caused by methicillin-resistant Staphylococcus aureus (MRSA). This review delineates factors to consider in the choice of initial antibiotic treatment for cSSTIs and describes the antimicrobial agents available or under clinical development for the treatment of cSSTIs caused by MRSA.

METHODS

Review of the pertinent literature and recommendations.

RESULTS

The choice of antimicrobial agent for empiric treatment of cSSTIs should be guided by the site and type of infection, the presence of an immunocompromised state or neutropenia, and risk factors for hospital-acquired MRSA (HA-MRSA) or community-associated MRSA (CA-MRSA) infection. Most CA-MRSA strains remain susceptible to ciprofloxacin, clindamycin, gentamicin, and trimethoprim/sulfamethoxazole, although resistance to clindamycin can emerge during treatment. Of the agents available for the treatment of HA-MRSA cSSTIs, vancomycin has been the reference standard, but clinical failures have been reported increasingly. Alternative agents for HA-MRSA include linezolid, which has been well-studied for treatment of cSSTIs, as well as daptomycin and tigecycline. A number of antibiotic agents are undergoing clinical trials or are under development for the treatment of cSSTIs caused by MRSA.

CONCLUSIONS

Severe and progressive cSSTIs should be treated promptly with appropriate antibiotic agents. The choice of agent should be guided by a number of factors, including suspected CA-MRSA or HA-MRSA infection. Available agents should be evaluated carefully for efficacy in the treatment of MRSA cSSTIs.

Iclaprim: a novel dihydrofolate reductase inhibitor for skin and soft tissue infections

Antibiotic resistance is an ever-increasing concern in the treatment of severe skin and skin-structure infections, pneumonia, bacteremia and other serious infections caused by methicillin-resistant Staphylococcus aureus, vancomycin-resistant S. aureus, group A Streptococcus and vancomycin-resistant Enterococcus. In this review, we summarize the current status of both US FDA-approved and investigational agents aimed at this group of pathogens. We also describe, in detail, the chemistry, mechanism of action, pharmacokinetic properties and spectrum of microbiological activity of iclaprim, a novel dihydrofolate reductase inhibitor recently awarded fast-track approval status by the FDA. Finally, we review the clinical efficacy of iclaprim compared with linezolid for skin and skin-structure infections as demonstrated in Phase III randomized, controlled trials, and comment on its potential role in the treatment of other severe infections with drug-resistant Gram-positive pathogens.

Comparative severity of pediatric osteomyelitis attributable to methicillin-resistant versus methicillin-sensitive Staphylococcus aureus

BACKGROUND

Staphylococcus aureus remains the most common etiology of hematogenous osteomyelitis in children. Recently emerged virulent strains of methicillin-resistant S. aureus (MRSA) strains now predominate. It remains uncertain whether these pathogens cause a measurably more severe illness than methicillin-sensitive strains.

METHODS

We reviewed records of 97 pediatric patients with hematogenous osteomyelitis of varying etiologies to determine whether there were significant differences among the groups in terms of predetermined measures of disease severity. These measures included degree and duration of elevated temperature, acute-phase reactants, length of hospitalization, the number of surgical procedures required, and long-term sequelae.

RESULTS

Differences in the clinical course of illness were observed. Patients with MRSA had a significant increase in degree and duration of elevated temperature (P = 0.0001 for both), acute-phase reactant measures (white blood cell count, P = 0.0001; C-reactive protein, P = 0.0058; erythrocyte sedimentation rate, P = 0.0046), initial length of hospital stay (P = 0.0001), and surgical interventions (all procedures, P = 0.0001; therapeutic procedures, only P = 0.0002) as compared with patients with osteomyelitis caused by other bacterial pathogens and culture-negative osteomyelitis. A similar general pattern was observed when the analysis was restricted to culture-positive staphylococcal cases only.

CONCLUSIONS

Our results support the hypothesis that MRSA produces more severe bone infection and is likely to require more aggressive surgical and medical management.

New trends in pharmacogenomic strategies against resistance development in microbial infections

This review summarizes some of the new trends in the fight against drug resistant bacteria. We review Gram-positive (e.g., S.aureus) and Gram-negative (e.g., Pseudomonas aeruginosa, Helicobacter pylori) bacteria, the current antibiotic resistance situation, as well as resistance spread and some recently discovered resistance mechanisms, such as those based on integrons and complex transposons. We then summarize several current routes to identify new drugs such as cationic antimicrobial peptides, novel acyldepsipeptides, RNA aptamers and lipopeptides. New drug strategies to treat resistant pathogens include eliciting growth in dormant bacteria, or a new way to attack efflux systems. Typical approaches from pharmacogenomics combined with systems biology and bioinformatics support these routes (simulations, metagenomics and metabolic network modeling), as well as the patient treatment (e.g., haplotyping and immune response).

Management and Treatment Considerations for Infections Caused by Methicillin-Resistant Staphylococcus aureus

Infections caused by methicillin-resistant Staphylococcus aureus have been documented since the 1960s. Four decades later, this microorganism has evolved from a pathogen found primarily in the health care environment to a major pathogen of community-acquired infections. Interestingly, the community-acquired methicillin-resistant Staphylococcus aureus isolates tend to be genetically distinct from their health-care–acquired relatives, have a propensity to be more virulent, yet be susceptible to more antibiotics. Furthermore, infections caused in the pediatric population have a susceptibility pattern that differs from those found in adults. With an increase in infections caused by methicillin-resistant Staphylococcus aureus, empiric therapy should contain an agent with activity against this microorganism. Currently several options exist for the treatment of skin and skin structure infections, yet very few options are available for the treatment of more invasive diseases caused by methicillin-resistant Staphylococcus aureus. This article will review the history of methicillin-resistant Staphylococcus aureus, Staphylococcus aureus economic considerations, and the current plus future treatment options for these infections.

Community-Associated Methicillin-Resistant Staphylococcus aureus in the Pediatric Population

PURPOSE

To review the epidemiology and prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), define the differences between community-acquired and hospital-acquired strains, highlight the advantages and disadvantages of antibiotics commonly used to treat infections caused by this pathogen, and identify strategies to limit the spread of this organism and prevent future outbreaks.

DATA

Literature was accessed through MEDLINE using the search terms community-acquired methicillin-resistant Staphylococcus aureus, community-associated methicillin-resistant Staphylococcus aureus, CA-MRSA, pediatrics, and children. Articles evaluated were published in the English language and limited to human studies. References of literature identified by initial search techniques were reviewed for additional relevant articles.

DATA SYNTHESIS

Community-associated methicillin-resistant Staphylococcus aureus has become a prominent pathogen in pediatric patients in the last ten years. Its increasing prevalence has been reported throughout the United States, and it is the cause of over one half of all skin and soft tissue infections seen in many hospitals and emergency departments. The risk factors for infection with this pathogen differ from those associated with hospital-acquired strains. Mild to moderate infections can generally be treated with oral antibiotics, while more serious infections may require parenteral therapy. Sulfamethoxazole/trimethoprim and clindamycin are the preferred oral agents due to their efficacy, tolerability, well established side effect profiles, and cost. Vancomycin is the standard of care for parenteral therapy, although clindamycin is an acceptable parenteral alternative. More costly agents such as linezolid, daptomycin, and quinupristin/dalfopristin should be reserved for patients with severe infections, multiple allergies, or in strains with unusual resistance patterns. The best way to prevent and control outbreaks is to maintain standard infection control procedures including excellent hand hygiene.

CONCLUSIONS

CA-MRSA is a serious and frequently seen pathogen. Proper antibiotic selection that takes into account patient factors, disease severity, ease of administration, and cost is necessary to maximize favorable patient outcomes.

Current and novel antibiotics against resistant Gram-positive bacteria

The challenge posed by resistance among Gram-positive bacteria, epitomized by methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE) and vancomycin-intermediate and -resistant S. aureus (VISA and VRSA) is being met by a new generation of antimicrobials. This review focuses on the new β-lactams with activity against MRSA (ceftobiprole and ceftaroline) and on the new glycopeptides (oritavancin, dalbavancin, and telavancin). It will also consider the role of vancomycin in an era of existing alternatives such as linezolid, daptomycin and tigecycline. Finally, compounds in early development are described, such as iclaprim, friulimicin, and retapamulin, among others.

Resistance profiles in surgical-site infection

Surgical-site infections (SSIs) remain a common complication, affecting some 5% of patients undergoing surgical procedures and can sometimes present a major challenge after surgery with life-threatening septic illness. The appearance of organisms that are often resistant to common antibiotic treatment is of great concern. Staphylococcus aureus is the organism most commonly recovered from infected surgical wounds, and usually contaminates wounds from the patients own skin. SSIs occur despite appropriate skin disinfection, sterilization of instruments, use of gown and gloves, appropriate sterile technique and prophylactic antimicrobials. In fact, it is difficult to maintain a sterile field over time, and most wounds become contaminated throughout the course of surgery. Methicillin-resistant S. aureus (MRSA) first arose in the hospital setting, but have more recently evolved in the community. Such community-acquired MRSA are genetically different and seem to be even more virulent owing to genes that encode virulence factors, such as staphylococcal cassette chromosome mec type IV and Panton-Valentine leukocidin. The purpose of this review is to summarize characteristics of frequently isolated bacterial strains from SSIs. The focus will be on Gram-positive organisms because of their increasing prevalence in SSIs and their high potential to develop resistance against several antibiotic agents, including vancomycin.

Community-associated methicillin-resistant Staphylococcus aureus

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged over the last decade across the United States and the world, becoming a major pathogen in many types of community-acquired infections. Although most commonly associated with minor skin and soft tissue infections, such as furuncles, CA-MRSA also can cause necrotizing fasciitis, pyomyositis, osteoarticular infections, and community-acquired pneumonia. This article discusses the epidemiology, diagnosis, and management of these infections from the perspective of the emergency physician.

Addition of rifampin to standard therapy for treatment of native valve infective endocarditis caused by Staphylococcus aureus

Staphylococcus aureus is a common cause of native valve infective endocarditis (IE). Rifampin is often added to traditional therapy for the management of serious S. aureus infections. There are no large, prospective studies documenting the safety and efficacy of adjunctive therapy with rifampin for treatment of native valve S. aureus IE. We reviewed all cases of definite native valve S. aureus IE confirmed by modified Duke criteria in a large urban hospital between 1 January 2004 and 31 December 2005. A retrospective cohort analysis was used to assess the impact of the addition of rifampin to standard therapy. There were 42 cases of S. aureus IE treated with the addition of rifampin and 42 controls. Cases received a median of 20 days of rifampin (range, 14 to 48 days). Rifampin-resistant S. aureus isolates developed in nine cases who received rifampin before clearance of bacteremia (56%), while significant hepatic transaminase elevations also occurred in nine cases, all of whom had hepatitis C infection. Unrecognized significant drug-drug interactions with rifampin occurred frequently (52%). Cases were more likely to have a longer duration of bacteremia (5.2 versus 2.1 days; P < 0.001) and were less likely to survive (79% versus 95%; P = 0.048) than controls. Our results suggest that the potential for hepatotoxicity, drug-drug interactions, and the emergence of resistant S. aureus isolates warrants a careful risk-benefit assessment before adding rifampin to standard antibiotic treatment of native valve S. aureus IE until further clinical studies are performed.

New antibacterial agents for treating infections caused by multi-drug resistant Gram-negative bacteria

BACKGROUND

Infections caused by multi-drug resistant (MDR) Gram-negative bacteria represent an ever-growing area of unmet medical need. To address this need, it is imperative that novel classes of antibiotics demonstrating activity against bacterial strains resistant to established antibiotics are introduced into the clinic.

OBJECTIVES

To examine the current status of the Gram-negative antibacterial pipeline, ranging from the more advanced preclinical candidates to drugs recently launched, and look to the future of anti-Gram-negative drug development.

METHODS

Information was compiled from scientific and patent literature, conference proceedings and company publications/websites.

RESULTS/CONCLUSIONS

None of the antibacterial agents currently in clinical trials that encompass Gram-negative bacteria in their spectrum of activity possess sufficiently novel modes of action to circumvent extant antibiotic resistance mechanisms. Furthermore, although some interesting anti-Gram-negative drug candidates are nearing the beginning of clinical trials, they are limited in number and, even in the best-case scenario, many years away from the clinic.

Therapy-refractory Panton Valentine Leukocidin-positive community-acquired methicillin-sensitive Staphylococcus aureus sepsis with progressive metastatic soft tissue infection: a case report

We report a case of fulminant multiple organ failure including the Acute Respiratory Distress Syndrome (ARDS), haemodynamic, and renal failure due to community-acquired methicillin-sensitive Panton Valentine Leukocidin (PVL) positive spa-type 284 (ST121) Staphylococcus aureus septic shock. The patient's first clinical symptom was necrotizing pneumonia. Despite organism-sensitive triple antibiotic therapy with linezolid, imipenem and clindamycin from the first day of treatment, progressive abscess formation in multiple skeletal muscles was observed. As a result, repeated surgical interventions became necessary. Due to progressive soft tissue infection, the anti-microbial therapy was changed to a combination of clindamycin and daptomycin. Continued surgical and antimicrobial therapy finally led to a stabilisation of the patients' condition. The clinical course of our patient underlines the existence of a "PVL-syndrome" which is independent of in vitro Staphylococcus aureus susceptibility. The PVL-syndrome should not only be considered in patients with soft tissue or bone infection, but also in patients with pneumonia. Such a condition, which may easily be mistaken for uncomplicated pneumonia, should be treated early, aggressively and over a long period of time in order to avoid relapsing infection.