Linezolid-resistant Staphylococcus aureus in two pediatric patients receiving low-dose linezolid therapy

Development and Validation of an HPLC-UV Method for Quantitation of Linezolid: Application to Resistance Study Using in vitro PK/PD Model

Background

Linezolid (LNZ), an oxazolidinone antibiotic, has 100% oral bioavailability and favorable activities against gram-positive pathogens. The in vitro PK/PD model was developed based on concentrations obtained with routine doses in humans can be used to guide dose optimization in the clinic.

Methods

In this study, we employed an in vitro PK/PD model to simulate the changes in the plasma concentration of linezolid in the human body against a clinical isolate of MRSA in vitro. A high-performance liquid chromatography (HPLC)-UV method was applied to measure the concentration of linezolid. Bacterial samples were collected at different times from the central compartment for count.

Results

The chromatographic separation was carried out with an AichromBond-AQC18 column(250mm×4.6mm, 5μm), using a mobile phase of water with 0.1% formic acid:acetonitrile 70:30 (v/v), followed by detection at 254 nm, and a single detection run was completed within 10 min. The method was validated by estimating the precision and accuracy for the inter- and intra-day analyses in the concentration range of 0.25-32 mg/L. The method was linear over the investigated range of 0.125-32 mg/L, with all correlation coefficients R² = 0.9999. The intra-day and inter-day precisions were within 7.598%, and the method recovery ranged from 90.912% to 106.459%. In vitro PK/PD model, both the absorption and elimination of linezolid being simulated can be precisely controlled by computer. In the control group, the bacterial reached 7.9 Log10CFU/mL in the first 48h and maintained until the end, indicating that the colonies grew well in vitro PK/PD model. In the linezolid 600 mg q12h administration group, the colony decreased to 2.39 Log10CFU/mL at 24h, showing a good bactericidal effect; however, the colonies resumed growth to the initial level in 48h, indicating an emergence of resistance.

Conclusion

We successfully established an in vitro infection PK/PD model and developed an HPLC-UV method to determine linezolid concentration for resistance investigation. The results suggest that the 600 mg q12h dosing regimen may no longer be applicable and requires optimization.

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.

Guía de consenso para el abordaje de la neumonía adquirida en la comunidad en el paciente anciano

La incidencia de la neumonía adquirida en la comunidad se incrementa con la edad y se asocia a una elevada morbimortalidad debido a los cambios fisiológicos asociados al envejecimiento y a una mayor presencia de enfermedades crónicas. Debido a la importancia que tiene desde un punto de epidemiológico y pronóstico, y a la enorme heterogeneidad descrita en el manejo clínico, creemos que existía la necesidad de realizar un documento de consenso específico para este perfil de paciente. El propósito de este fue realizar una revisión de las evidencias en relación con los factores de riesgo para la etiología, la presentación clínica, el manejo y el tratamiento de la neumonía adquirida en la comunidad en los ancianos con el fin de elaborar una serie de recomendaciones específicas basadas en el análisis crítico de la literatura. Este documento es fruto de la colaboración de diferentes especialistas en representación de la Sociedad Española de Medicina de Urgencias y Emergencias (SEMES), Sociedad Española de Geriatría y Gerontología (SEGG), Sociedad Española de Quimioterapia (SEQ), Sociedad Española de Medicina Interna (SEMI), Sociedad Española de Neumología y Cirugía Torácica (SEPAR), Sociedad Española de Hospitalización a Domicilio (SEHAD) y Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica (SEIMC).

Use of linezolid in children: an overview of recent advances

Linezolid is the first member of a new generation of antibiotics, the synthetic oxazolidinones, to become available, with a broad spectrum of in vitro activity against gram-positive organisms, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis and vancomycin-resistant E. faecium. Linezolid is showing great promise currently for the treatment of multiresistant gram-positive bacterial infections, especially complicated skin infections, catheter-induced bacteremia or nosocomial pneumonia both in the community and in a hospital setting, in children and in adults. Although most recent reports are favorable and anticipatory of a more extensive use of linezolid in appropriately selected pediatric population groups in the near future, following treatment failure of conventional antimicrobial agents, more clinical trials are, however, required to investigate the safety profile and tolerability of this new antibiotic in the pediatric population.

Linezolid use in hospitalized children

We used the Pediatric Health Information System to evaluate linezolid use among hospitalized children. From 2003 to 2007, use increased 5-fold, including wide interhospital variation, then stabilized through 2011. Linezolid was responsible for 3% of total antibiotic expenditures. Children with respiratory, oncologic or transplant conditions were the most frequently treated with linezolid.

The emerging problem of linezolid-resistant Staphylococcus

The oxazolidinone antibiotic linezolid has demonstrated potent antimicrobial activity against Gram-positive bacterial pathogens, including methicillin-resistant staphylococci. This article systematically reviews the published literature for reports of linezolid-resistant Staphylococcus (LRS) infections to identify epidemiological, microbiological and clinical features for these infections. Linezolid remains active against >98% of Staphylococcus, with resistance identified in 0.05% of Staphylococcus aureus and 1.4% of coagulase-negative Staphylococcus (CoNS). In all reported cases, patients were treated with linezolid prior to isolation of LRS, with mean times of 20.0 ± 47.0 months for S. aureus and 11.0 ± 8.0 days for CoNS. The most common mechanisms for linezolid resistance were mutation (G2576T) to the 23S rRNA (63.5% of LRSA and 60.2% of LRCoNS) or the presence of a transmissible cfr ribosomal methyltransferase (54.5% of LRSA and 15.9% of LRCoNS). The emergence of linezolid resistance in Staphylococcus poses significant challenges to the clinical treatment of infections caused by these organisms, and in particular CoNS.

Resistance to linezolid caused by modifications at its binding site on the ribosome

Linezolid is an oxazolidinone antibiotic in clinical use for the treatment of serious infections of resistant Gram-positive bacteria. It inhibits protein synthesis by binding to the peptidyl transferase center on the ribosome. Almost all known resistance mechanisms involve small alterations to the linezolid binding site, so this review will therefore focus on the various changes that can adversely affect drug binding and confer resistance. High-resolution structures of linezolid bound to the 50S ribosomal subunit show that it binds in a deep cleft that is surrounded by 23S rRNA nucleotides. Mutation of 23S rRNA has for some time been established as a linezolid resistance mechanism. Although ribosomal proteins L3 and L4 are located further away from the bound drug, mutations in specific regions of these proteins are increasingly being associated with linezolid resistance. However, very little evidence has been presented to confirm this. Furthermore, recent findings on the Cfr methyltransferase underscore the modification of 23S rRNA as a highly effective and transferable form of linezolid resistance. On a positive note, detailed knowledge of the linezolid binding site has facilitated the design of a new generation of oxazolidinones that show improved properties against the known resistance mechanisms.

Clinical experience with linezolid in infants and children

The worldwide spread of multidrug-resistant organisms has required the development of new antimicrobials. Linezolid, the first oxazolidinone, has a broad spectrum of activity against Gram-positive bacteria, including resistant strains. Although approved by the Food and Drug Administration in 2002, the clinical experience with linezolid in the paediatric population is still limited, also given the fact that in most European countries the paediatric use of linezolid is off-label. In this paper we summarize the actual evidence on both licensed and off-label clinical uses of linezolid in children, including efficacy, safety and tolerability issues. Taking into account the potential bias in comparing heterogeneous clinical trials and reports, the available literature data suggest that linezolid is a safe and effective agent for the treatment of serious Gram-positive bacterial infections in neonates and children. At present, linezolid is reserved for those children who are intolerant to or fail conventional agents. A linezolid-containing regimen can be a valuable option for treating multidrug-resistant and extensively drug-resistant tuberculosis in children as well as disseminated non-tuberculous mycobacterial infections. Given the rare occurrence of serious side effects, careful monitoring of haematological parameters, possible drug interactions and neurological manifestations is recommended in linezolid-treated children, especially in case of prolonged treatments. Appropriate linezolid dosage and hospital infection control measures are essential to avoid the spread of linezolid resistance. Further studies are needed to establish novel paediatric indications for linezolid use and to assess the tolerability of long-term treatments.

Are we ready for novel detection methods to treat respiratory pathogens in hospital-acquired pneumonia?

Hospital-acquired pneumonia represents one of the most difficult treatment challenges in infectious diseases. Many studies suggest that the timely administration of appropriate, pathogen-directed therapy can be lifesaving. Because results of culture and antimicrobial susceptibility testing can take 48 h or longer, physicians currently rely on clinical, epidemiological, and demographic factors to assist with the choice of empiric therapy for antibiotic-resistant pathogens. At present, a number of rapid molecular tests are being developed that identify pathogens and the presence of genetic determinants of antimicrobial resistance (eg, GeneXpert [Cepheid], ResPlex [Qiagen], FilmArray [Idaho Technologies], and Microarray [Check-Points]). In this review, the potential impact that molecular diagnostics has to identify and characterize pathogens that cause hospital-acquired bacterial pneumonia at an early stage is examined. In addition, a perspective on a novel technology, polymerase chain reaction followed by electrospray ionization mass spectrometry, is presented, and its prospective use in the diagnosis of pneumonia is also discussed. The complexities of the pulmonary microbiome represent a novel challenge to clinicians, but many questions still remain even as these technologies improve.

Efficacy and safety of linezolid in immunocompromised children with cancer

BACKGROUND

The aim of this study was to determine the safety, tolerance and efficacy of linezolid for the treatment of infections from Gram-positive bacteria in immunocompromised children with cancer.

METHODS

This was a prospective non-comparative unblinded study in the Hematology/Oncology Unit over a two-year period, administering linezolid as monotherapy in children with cancer.

RESULTS

Seventeen children received linezolid (30 mg/kgr: 3 i.v. per day). Mean duration of linezolid administration was 12.2 days (range, 6-38 days), while the median age of the evaluable patients was 2.2 years (range, 6 months-11.2 years). Primary diagnosis was acute lymphoblastic leukemia (nine patients), brain tumor (three patients), multi-organ Langerhans cell histiocytosis (two patients), rhabdomyosarcoma, Burkitt's lymphoma and ovarian tumor (one patient each). All patients were in the midst of chemotherapy cycles. Ten out of 17 children had positive blood cultures (methicillin-resistant Staphylococcus aureus, four patients; vancomycin-resistant Enterococcus, three patients; penicillin-resistant Streptococcus pneumoniae, three patients), while seven of the 17 had fever and vancomycin-resistant Enterococcus in stool cultures. All patients were considered clinically cured after the end of the linezolid regimen (100% efficacy). The main adverse events were thrombocytopenia grade 1-3 and anemia grade 2-3 (four and two patients, respectively). Chemotherapy-induced myelotoxicity (six patients) was not worsened during linezolid therapy. No bleeding episodes were presented. Self-limited diarrhea grade 1-2 was presented in four patients (mean duration 2 days). The total adverse event rate was 23.5%; however, there was no premature cessation of linezolid in any patient.

CONCLUSIONS

Linezolid may be another effective and safe therapy to treat infections from resistant Gram-positive bacteria in immunocompromised children, even in young ages.

Clinical efficacy and tolerability of linezolid in pediatric patients: a systematic review

BACKGROUND

Linezolid is marketed for the treatment of severe, vancomycin-resistant infections with gram-positive bacteria in adults. Most information regarding the pharmacokinetic profile, efficacy, and tolerability of linezolid is derived from adult studies.

OBJECTIVE

The aim of this review was to summarize evidence regarding the use of linezolid in infants and children, focusing on the drug's clinical efficacy data and tolerability profile.

METHODS

A literature search was conducted of the Cochrane Library, EMBASE, and MEDLINE databases, from their inception through July 20, 2009, using the following terms: linezolid, newborn, infant, child, pediatrics, adolescent, human, clinical trial, and case report. Articles were excluded if they were redundant or not pertinent. (Articles that did not focus on the use of linezolid in children were considered not pertinent.) Bibliographies of all relevant articles were also evaluated.

RESULTS

Forty-seven publications regarding the use of linezolid in children were included in the review: 5 pharmacokinetic studies, 32 case reports, 6 randomized clinical trials (RCTs), 2 uncontrolled trials, 1 subanalysis of 2 published RCTs, and 1 subanalysis of published data about linezolid's tolerability. Pharmacokinetic data on linezolid use in children were derived from studies that enrolled 447 children. Plasma pharmacokinetics of linezolid in pediatric patients were found to be age dependent. Results from 6 vancomycinor cefadroxil-controlled RCTs (including 1480 children) evaluating linezolid treatment in children reported variable clinical cure rates, ranging from 75.0% to 93.2% in children with skin and skin-structure infections and from 77.5% to 90.0% in children with bacteremia or pneumonia. No significant difference in clinical cure rates between the linezolid group and the comparator group was observed in any study. The most frequently reported adverse events were diarrhea (from 3.1% to 16.8%), nausea and/or vomiting (from 2.9% to 11.9%), and thrombocytopenia (from 1.9% to 4.7%). To date, 3 cases of neuropathy have been described in children.

CONCLUSIONS

The reviewed pediatric studies in skin and skin-structure infections, bacteremia, or pneumonia found that linezolid was associated with high clinical cure rates (75.0%-93.2%) that did not differ significantly from those of vancomycin or cefadroxil. RCTs enrolling children with other types of infection (eg, osteomyelitis, endocarditis), as well as long-term studies, are needed to draw definitive conclusions about linezolid's efficacy and tolerability in pediatric patients. Careful monitoring for adverse events and possible linezolid resistance continues to be essential.

New therapeutic choices for infections caused by methicillin-resistant Staphylococcus aureus

In recent years, a marked increase in the incidence of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has occurred in many countries. This review addresses the effectiveness and limitations of drugs classically used for the treatment of MRSA, e.g. vancomycin, and also newer anti-MRSA antimicrobials, e.g. second-generation glycolipopeptides, tigecycline, and beta-lactams.

Activity of linezolid in an in vitro pharmacokinetic-pharmacodynamic model using different dosages and Staphylococcus aureus and Enterococcus faecalis strains with and without a hypermutator phenotype

The influence of antibiotic dosages and bacterial mutator phenotypes on the emergence of linezolid-resistant mutants was evaluated in an in vitro pharmacokinetic-pharmacodynamic model. A twice-daily 0.5-h infusion of a 200-, 600-, or 800-mg dose for 48 h was simulated against four strains (MIC, 2 microg/ml): Staphylococcus aureus RN4220 and its mutator derivative MutS2, Enterococcus faecalis ATCC 29212, and a mutator clinical strain of E. faecalis, Ef1497. The peak concentrations (4.38 to 4.79, 13.4 to 14.6, and 19.2 to 19.5 microg/ml) and half-lives at beta-phase (5.01 to 6.72 h) fit human plasma linezolid pharmacokinetics. Due to its bacteriostatic property, the cumulative percentages of the dosing interval during which the drug concentration exceeded the MIC (T > MIC), 66.6 and 69.1% of the dosing interval, were not significant, except for Ef1497, with an 800-mg dose and a T > MIC of 80.9%. At the standard 600-mg dosage, resistant mutants (2- to 8-fold MIC increases) were selected only with Ef1497. A lower, 200-mg dosage did not select resistant mutants of E. faecalis ATCC 29212, but a higher, 800-mg dosage against Ef1497 did not prevent their emergence. For the most resistant mutant (MIC, 16 microg/ml), characterization of 23S rRNA genes revealed the substitution A2453G in two of the four operons, which was previously described only in in vitro mutants of archaebacteria. Nevertheless, this mutant did not yield further mutants under 600- or 200-mg treatment. In conclusion, linezolid was consistently efficient against S. aureus strains. The emergence of resistant E. faecalis mutants was probably favored by the rapid decline of linezolid concentrations against a strong mutator, a phenotype less exceptional in E. faecalis than in S. aureus.

Linezolid

THE MOST RECENT DATA FROM THE National Institute of Child Health and Human Development Neonatal Research Network revealed that in late-onset sepsis events in very low birth weight neonates proven by blood culture, 70 percent were caused by Gram-positive organisms. Coagulase-negative staphylococci accounted for 68 percent of these Gram-positive infections, and Staphylococcus aureus, Enterococcus species, and Group B Streptococcus were isolated in the remainder.1Staphylococcus epidermidis continues to be the most common coagulase-negative Staphylococcus species isolated in culture, and S. capitis, S. warneri, S. haemolyticus and S. hominis have also been implicated in neonatal infection.

The efficacy and safety of daptomycin vs. vancomycin for the treatment of cellulitis and erysipelas

BACKGROUND

Results from previous trials suggest that daptomycin may result in faster clinical improvement than penicillinase-resistant penicillins or vancomycin for patients with complicated skin and skin structure infections.

OBJECTIVE

The objective was to evaluate whether daptomycin treatment of cellulitis or erysipelas would result in faster resolution compared with vancomycin.

DESIGN

The study was a prospective, evaluator-blinded, multi-centre trial. Patients were randomised to receive daptomycin 4 mg/kg once daily or vancomycin according to standard of care for 7-14 days.

PATIENTS

Adults diagnosed with cellulitis or erysipelas requiring hospitalisation and intravenous antibiotic therapy were eligible for enrolment.

RESULTS

The clinical success rates were 94.0% for daptomycin and 90.2% for vancomycin (95% confidence interval for the difference, -6.7%, 14.3%). There were no statistically significant differences between treatment arms in the time to resolution or improvement in any of the predefined clinical end-points. Both daptomycin and vancomycin were well tolerated.

CONCLUSIONS

There was no difference in the rate of resolution of cellulitis or erysipelas among patients treated with daptomycin or vancomycin. Daptomycin 4 mg/kg once daily appeared to be effective and safe for treating cellulitis or erysipelas.

Treatment strategies for methicillin-resistant Staphylococcus aureus infections in pediatrics

Staphylococcus aureus is an important pathogen that frequently causes clinical disease in children. A wide array of illnesses can be caused by this common pathogen ranging from non-invasive skin infections to severe, life-threatening sepsis. Additionally, as antibacterials have been used to eradicate S. aureus, it has developed resistance to these important therapeutic agents. Methicillin-resistant S. aureus (MRSA) has become an increasing problem in pediatric patients over the past decade. In this review, we discuss the epidemiology, pathogenesis, and treatment options available in treating MRSA infections in children. Specifically, we address the importance of abscess drainage in the treatment of skin and soft tissue infections, the most common clinical manifestation of MRSA infections, and highlight the various agents that are available for treating this common infection. In severe, life-threatening invasive MRSA infections the primary therapeutic option is vancomycin. In cases of MRSA toxic shock syndrome the addition of clindamycin is necessary. In other invasive MRSA infections, such as pneumonia and musculoskeletal infections, the empiric treatment of choice is clindamycin. Finally, newer agents and additional treatment options are discussed.

Review of the guidelines for complicated skin and soft tissue infections and intra-abdominal infections--are they applicable today?

Difficult-to-treat infections in surgical patients, such as serious skin and soft tissue infections (SSTIs) and complicated intra-abdominal infections (cIAIs), are the cause of significant morbidity and mortality, and carry an economic burden. These surgical site infections are typically polymicrobial infections caused by a plethora of pathogens, which include difficult-to-treat organisms and multiresistant Gram-positive and Gram-negative strains. Optimal management of SSTIs and cIAIs must take into account the presence of resistant pathogens, and depends on the administration of appropriate antimicrobial therapy (i.e. the correct spectrum, route and dose in a timely fashion for a sufficient duration as well as the timely implementation of source control measures). Treatment recommendations from the Infectious Diseases Society of America and the Surgical Infection Society are available for guidance in the management of both of these infections, yet the increased global prevalence of multidrug-resistant pathogens has complicated the antibiotic selection process. Several pathogens of concern include methicillin-resistant Staphylococcus aureus, responsible for problematic postoperative infections, especially in patients with SSTIs, extended-spectrum beta-lactamase-producing Gram-negative bacteria, including CTX-M-type-producing Escherichia coli strains, and multidrug-resistant strains of Bacteroides fragilis. New empirical regimens, taking advantage of potent broad-spectrum antibiotic options, may be needed for the treatment of certain high-risk patients with surgical site infections.

Crystal structure of the oxazolidinone antibiotic linezolid bound to the 50S ribosomal subunit

The oxazolidinone antibacterials target the 50S subunit of prokaryotic ribosomes. To gain insight into their mechanism of action, the crystal structure of the canonical oxazolidinone, linezolid, has been determined bound to the Haloarcula marismortui 50S subunit. Linezolid binds the 50S A-site, near the catalytic center, which suggests that inhibition involves competition with incoming A-site substrates. These results provide a structural basis for the discovery of improved oxazolidinones active against emerging drug-resistant clinical strains.

R chi-01, a new family of oxazolidinones that overcome ribosome-based linezolid resistance

New and improved antibiotics are urgently needed to combat the ever-increasing number of multidrug-resistant bacteria. In this study, we characterized several members of a new oxazolidinone family, R chi-01. This antibiotic family is distinguished by having in vitro and in vivo activity against hospital-acquired, as well as community-acquired, pathogens. We compared the 50S ribosome binding affinity of this family to that of the only marketed oxazolidinone antibiotic, linezolid, using chloramphenicol and puromycin competition binding assays. The competition assays demonstrated that several members of the R chi-01 family displace, more effectively than linezolid, compounds known to bind to the ribosomal A site. We also monitored binding by assessing whether R chi-01 compounds protect U2585 (Escherichia coli numbering), a nucleotide that influences peptide bond formation and peptide release, from chemical modification by carbodiimide. The R chi-01 oxazolidinones were able to inhibit translation of ribosomes isolated from linezolid-resistant Staphylococcus aureus at submicromolar concentrations. This improved binding corresponds to greater antibacterial activity against linezolid-resistant enterococci. Consistent with their ribosomal A-site targeting and greater potency, the R chi-01 compounds promote nonsense suppression and frameshifting to a greater extent than linezolid. Importantly, the gain in potency does not impact prokaryotic specificity as, like linezolid, the members of the R chi-01 family show translation 50% inhibitory concentrations that are at least 100-fold higher for eukaryotic than for prokaryotic ribosomes. This new family of oxazolidinones distinguishes itself from linezolid by having greater intrinsic activity against linezolid-resistant isolates and may therefore offer clinicians an alternative to overcome linezolid resistance. A member of the R chi-01 family of compounds is currently undergoing clinical trials.

An infection with linezolid-resistant S. aureus in a patient with left ventricular assist system

We report an infection with a linezolid-resistant S. aureus in a patient with a left ventricular assist system. Linezolid should be used with caution when invasive devices or foreign materials are in place or therapeutic courses last longer than 14 d. Previous cases of linezolid-resistant S. aureus are summarized.

Combating resistance in a challenging, changing environment

The prevalence of antimicrobial resistance for both Gram-positive and Gram-negative pathogens is escalating worldwide. Outbreaks of community- and hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) are being reported more frequently. Although antimicrobial resistance is well recognised as a global problem, decisions about appropriate intervention and treatment should be made at the level of the local hospital or healthcare system. Thus, local surveillance to identify prevalent pathogens, detect bacterial resistance and identify particular strains is necessary for selecting optimal treatment regimens. In addition, bactericidal antimicrobial agents with novel mechanisms of action and activity against multidrug-resistant bacteria, together with improved infection control measures, are needed to address this growing medical problem more effectively.

Investigational treatments for postoperative surgical site infections

Surgical site infections rank third among nosocomial infections, representing a global threat, associated with the emergence of multi-drug-resistant bacteria. The pharmaceutical industry has recently curtailed developmental programmes; however, the need for new compounds is extremely important. This article reviews new antimicrobials and immunointerventional targets for their potential to treat surgical site infections in comparison with recently licensed compounds. Daptomycin, dalbavancin, oritavancin, telavancin, iclaprim and ranbezolid seem to be promising agents against infections caused by Gram-positive pathogens and effectively address the present problems of multi-resistance in Gram-positive infections. Peptide deformylase inhibitors and immunostimulating agents open new perspectives in this field; however, very few compounds targeting Gram-negative problematic pathogens are in the pipeline of the future. Tigecycline (recently marketed) ceftobiprole, ceftaroline and doripenem seem to possess an extended anti-Gram-positive and -negative spectrum. Among these compounds, only doripenem demonstrates activity against Pseudomonas aeruginosa, for which there is a clear unmet need for new compounds, focusing on new targets.

Pharmacokinetic/pharmacodynamic factors influencing emergence of resistance to linezolid in an in vitro model

Emerging resistance threatens the usefulness of linezolid for the treatment of severe infections caused by multidrug-resistant gram-positive bacteria. Optimal pharmacokinetic (PK)/pharmacodynamic (PD) indices have been described for the antimicrobial efficacy of linezolid (area under the concentration-time curve over 24 h at steady state divided by the MIC, >100; the cumulative percentage of a 24-h period that the drug concentration exceeds the MIC under steady-state PK conditions, >85). The aim of this study was to investigate the influence of these PK/PD indices on the development of resistance to linezolid by using an in vitro PK/PD model. Four dosage regimens were simulated over 72 h (two intermittent bolus regimens of 600 mg every 12 h [q12h] and 120 mg q12h and two continuous-infusion regimens of 120 mg/24 h and 30 mg/24 h) against four reference strains: methicillin-resistant Staphylococcus aureus (MRSA), heteroresistant vancomycin-intermediate S. aureus (hVISA), vancomycin-intermediate S. aureus (VISA), and vancomycin-resistant Enterococcus faecium (VRE). Linezolid concentrations were measured by high-performance liquid chromatography. Changes in susceptibility were characterized by pre- and posttreatment MIC measurements and population analysis profiles (PAPs). The linezolid concentrations that were achieved closely matched those that were targeted. The simulation with 600 mg q12h provided a >3-log10 reduction in the number of CFU/ml for all four strains, as did the 120-mg-q12h regimen for hVISA and VISA and the 30-mg/24-h continuous infusion for VRE and VISA. After 72 h of exposure to the 120-mg/24-h continuous-infusion simulation, the area under the PAP curve for all strains increased substantially (40 to 178%); increases in the MICs for the MRSA and hVISA strains were observed. The results demonstrate that PK/PD considerations are important in optimizing both antibacterial activity and the development of resistance to linezolid. The potential for resistance development appears to be higher when a constant concentration is maintained in the vicinity of the MIC of the bacteria.

Nadifloxacin: a quinolone for topical treatment of skin infections and potential for systemic use of its active isomer, WCK 771

Nadifloxacin is a potent, broad-spectrum, quinolone agent approved for topical use in acne vulgaris and skin infections in Japan. As exposure of pathogenic and colonising bacteria to antibiotics results in drug resistance, it is not desirable to use an important, broad-spectrum antibiotic, which belongs to a class of agents widely used systemically to treat a wide variety of infections, as a topically applied preparation. On this basis, nadifloxacin is not a good option for topical treatment of acne when other effective non-antibiotic treatments are available. Nadifloxacin has potential as a topical agent for short-term treatment of skin infections. The arginine salt of its (-)-(S)-isomer is being developed as a parenteral agent based on its potency against methicillin and quinolone-resistant Staphylococcus aureus.