In vitro and in vivo properties of Ro 63-9141, a novel broad-spectrum cephalosporin with activity against methicillin-resistant staphylococci

Ceftobiprole mono-therapy versus combination or non-combination regimen of standard antibiotics for the treatment of complicated infections: A systematic review and meta-analysis

OBJECTIVE

Various bacteria produce complicated infections that are difficult to treat worldwide. Ceftobiprole is effective against resistant Gram-positive and Gram-negative bacteria.

METHODS

This review assessed effectiveness and safety of ceftobiprole monotherapy for severe infections. A systematic review and meta-analysis of randomized controlled trials comparing clinical cure, microbiological cure, and safety of ceftobiprole alone to a combination or non-combination antibiotic regimen was conducted. Until December 20, 2022, we searched a major databases.

RESULTS

This study includes 4168 patients from six trials. Ceftobiprole and comparator-received patients had similar clinical responses for all patient population. Also, the eradication rate of all organisms and specific pathogenic bacteria in microbiologically examined patients was comparable between the groups. Ceftobiprole induced more gastrointestinal side events than comparable drugs, mostly nausea [OR 1.91 (1.26-2.90), p=<0.01]. While skin-related adverse events were significantly associated with comparator antibiotics [6 trials, 4062 patients; OR 0.77 (0.60-0.99), p=0.03].

CONCLUSION

Ceftobiprole monotherapy is effective and safe for severe infections caused by Gram-positive or Gram-negative bacteria.

Cephalosporin resistance, tolerance, and approaches to improve their activities

Cephalosporins comprise a β-lactam antibiotic class whose first members were discovered in 1945 from the fungus Cephalosporium acremonium. Their clinical use for Gram-negative bacterial infections is widespread due to their ability to traverse outer membranes through porins to gain access to the periplasm and disrupt peptidoglycan synthesis. More recent members of the cephalosporin class are administered as last resort treatments for complicated urinary tract infections, MRSA, and other multi-drug resistant pathogens, such as Neisseria gonorrhoeae. Unfortunately, there has been a global increase in cephalosporin-resistant strains, heteroresistance to this drug class has been a topic of increasing concern, and tolerance and persistence are recognized as potential causes of cephalosporin treatment failure. In this review, we summarize the cephalosporin antibiotic class from discovery to their mechanisms of action, and discuss the causes of cephalosporin treatment failure, which include resistance, tolerance, and phenomena when those qualities are exhibited by only small subpopulations of bacterial cultures (heteroresistance and persistence). Further, we discuss how recent efforts with cephalosporin conjugates and combination treatments aim to reinvigorate this antibiotic class.

Antistaphylococcal discovery pipeline; where are we now?

The serious spread of antibiotic-resistant Staphylococcal aureus strains is alarming. This is reflected by the measures governments and health-related bodies are offering to ease antibiotic drug development. Finding new active agents, preferably with novel mechanism of action, or even finding new targets for drug development are essential. In this review, we summarize the current status of novel antistaphylococcal agents undergoing clinical trials. We mainly discuss antistaphylococcal small molecules and peptides in the text with a special focus on their chemistry, while antistaphylococcal immunotherapy (antibodies) are mentioned in a summative table. This review shall serve as a summary that influences future synthetic efforts in the antistaphyloccocals development field.

In Vitro Antibacterial Activity of Ceftobiprole and Comparator Compounds against Nation-Wide Bloodstream Isolates and Different Sequence Types of MRSA

Bloodstream infections by bacteria, especially multidrug-resistant bacteria, remain a worldwide public health concern. We evaluated the antibacterial activity of ceftobiprole and comparable drugs against different bloodstream isolates and different sequence types of methicillin-resistant Staphylococcus aureus (MRSA) in China. We found that MRSA, methicillin-susceptible Staphylococcus aureus (MSSA), and methicillin-susceptible coagulase-negative Staphylococcus (MSCNS) displayed ceftobiprole sensitivity rates of >95%, which are similar to the rates for linezolid, daptomycin, and vancomycin. Of the tested MRCNS strains, 90.4% were sensitive to ceftobiprole. The sensitivities of ST59, ST398, and ST22 MRSA to ceftobiprole were higher than that of ST239. Ceftobiprole's MIC50/90 value against Enterococcus faecalis was 0.25/2 mg/L, whereas Enterococcus faecium was completely resistant to this drug. Ceftobiprole exhibited no activity against ESBL-positive Enterobacterales, with resistance rates between 78.6% and 100%. For ESBL-negative Enterobacterales, excluding Klebsiella oxytoca, the sensitivity to ceftobiprole was comparable to that of ceftazidime, ceftriaxone, and cefepime. The MIC50/90 value of ceftobiprole against Pseudomonas aeruginosa was 2/16 mg/L, and for Acinetobacter baumannii, it was 32/>32 mg/L. Thus, ceftobiprole shows excellent antimicrobial activity against ESBL-negative Enterobacterales and Pseudomonas aeruginosa (comparable to that of ceftazidime, ceftriaxone, and cefepime); however, it is not effective against ESBL-positive Enterobacterales and Acinetobacter baumannii. These results provide important information to clinicians.

Real-life use of ceftobiprole for severe infections in a French intensive care unit

Ceftobiprole (CBP) is an anti-methicillin-resistant Staphylococcus aureus (MRSA) cephalosporin with a wide spectrum of activity. We aimed to describe our experience of real-life use of CBP for the treatment of severe infections of critically ill patients with multiple infected sites and related trough CBP concentrations. We performed a retrospective, observational, monocentric study in our intensive care unit (ICU) that included all patients treated with CBP for documented infections between January 2016 and December 2021. We collected demographic, clinical, and microbiological data. When available, we report the CBP trough concentrations. The primary endpoint was clinical cure at the end of treatment. The secondary endpoints were in-hospital mortality and documentation of the carriage of multidrug-resistant (MDR) bacteria not present before CBP treatment. Between January 2016 and December 2021, 47 patients were treated in the ICU with CBP. The main indication for treatment was pneumonia (51%) and most patients presented with associated bacteremia (72%). All infections were polymicrobial. A clinical cure was achieved for nearly 80% of the patients. Only five patients presented new carriage of MDR bacteria. In-hospital mortality was 32%. Out of 21 strains of Enterobacterales for which the MIC was available, 33% were considered to be resistant to CBP according to the EUCAST 2023 clinical breakpoint. Trough CBP concentrations were reported for 16 patients. In our real-life experience, treatment of ICU patients with CBP for polymicrobial severe infections resulted in most cases in a clinical cure. Monitoring of trough concentrations is critical, especially in cases of high MIC.

Ceftobiprole Medocaril Is an Effective Post-Exposure Treatment in the Fischer 344 Rat Model of Pneumonic Tularemia

Francisella tularensis subspecies tularensis is a category-A biothreat agent that can cause lethal tularemia. Ceftobiprole medocaril is being explored as a medical countermeasure for the treatment of pneumonic tularemia. The efficacy of ceftobiprole medocaril against inhalational tularemia was evaluated in the Fischer 344 rat model of infection. The dose was expected to be effective against F. tularensis isolates with ceftobiprole minimum inhibitory concentrations ≤0.5 µg/mL. Animals treated with ceftobiprole medocaril exhibited a 92% survival rate 31 days post-challenge, identical to the survival of levofloxacin-treated rats. By comparison, rats receiving placebo experienced 100% mortality. Terminally collected blood, liver, lung, and spleen samples confirmed disseminated F. tularensis infections in most animals that died prior to completing treatments (placebo animals and a rat treated with ceftobiprole medocaril), although levels of bacteria detected in the placebo samples were significantly elevated compared to the ceftobiprole-medocaril-treated group geometric mean. Furthermore, no evidence of infection was detected in any rat that completed ceftobiprole medocaril or levofloxacin treatment and survived to the end of the post-treatment observation period. Overall, survival rates, body weights, and bacterial burdens consistently demonstrated that treatment with ceftobiprole medocaril is efficacious against otherwise fatal cases of pneumonic tularemia in the rat model.

Antibiotics and Bacterial Resistance-A Short Story of an Endless Arms Race

Despite the undisputed development of medicine, antibiotics still serve as first-choice drugs for patients with infectious disorders. The widespread use of antibiotics results from a wide spectrum of their actions encompassing mechanisms responsible for: the inhibition of bacterial cell wall biosynthesis, the disruption of cell membrane integrity, the suppression of nucleic acids and/or proteins synthesis, as well as disturbances of metabolic processes. However, the widespread availability of antibiotics, accompanied by their overprescription, acts as a double-edged sword, since the overuse and/or misuse of antibiotics leads to a growing number of multidrug-resistant microbes. This, in turn, has recently emerged as a global public health challenge facing both clinicians and their patients. In addition to intrinsic resistance, bacteria can acquire resistance to particular antimicrobial agents through the transfer of genetic material conferring resistance. Amongst the most common bacterial resistance strategies are: drug target site changes, increased cell wall permeability to antibiotics, antibiotic inactivation, and efflux pumps. A better understanding of the interplay between the mechanisms of antibiotic actions and bacterial defense strategies against particular antimicrobial agents is crucial for developing new drugs or drug combinations. Herein, we provide a brief overview of the current nanomedicine-based strategies that aim to improve the efficacy of antibiotics.

Synergistic Combinations of FDA-Approved Drugs with Ceftobiprole against Methicillin-Resistant Staphylococcus aureus

New strategies are urgently needed to address the public health threat of antimicrobial resistance. Synergistic agent combinations provide one possible pathway toward addressing this need and are also of fundamental mechanistic interest. Effective methods for comprehensively identifying synergistic agent combinations are required for such efforts. In this study, an FDA-approved drug library was screened against methicillin-resistant Staphylococcus aureus (MRSA) (ATCC 43300) in the absence and presence of sub-MIC levels of ceftobiprole, a PBP2a-targeted anti-MRSA β-lactam. This screening identified numerous potential synergistic agent combinations, which were then confirmed and characterized for synergy using checkerboard analyses. The initial group of synergistic agents (sum of the minimum fractional inhibitory concentration ∑FIC_min ≤0.5) were all β-lactamase-resistant β-lactams (cloxacillin, dicloxacillin, flucloxacillin, oxacillin, nafcillin, and cefotaxime). Cloxacillin-the agent with the greatest synergy with ceftobiprole-is also highly synergistic with ceftaroline, another PBP2a-targeted β-lactam. Further follow-up studies revealed a range of ceftobiprole synergies with other β-lactams, including with imipenem, meropenem, piperacillin, tazobactam, and cefoxitin. Interestingly, given that essentially all other ceftobiprole-β-lactam combinations showed synergy, ceftaroline and ceftobiprole showed no synergy. Modest to no synergy (0.5 < ∑FIC_min ≤ 1.0) was observed for several non-β-lactam agents, including vancomycin, daptomycin, balofloxacin, and floxuridine. Mupirocin had antagonistic activity with ceftobiprole. Flucloxacillin appeared particularly promising, with both a low intrinsic MIC and good synergy with ceftobiprole. That so many β-lactam combinations with ceftobiprole show synergy suggests that β-lactam combinations can generally increase β-lactam effectiveness and may also be useful in reducing resistance emergence and spread in MRSA. IMPORTANCE Antimicrobial resistance represents a serious threat to public health. Antibacterial agent combinations provide a potential approach to combating this problem, and synergistic agent combinations-in which each agent enhances the antimicrobial activity of the other-are particularly valuable in this regard. Ceftobiprole is a late-generation β-lactam antibiotic developed for MRSA infections. Resistance has emerged to ceftobiprole, jeopardizing this agent's effectiveness. To identify synergistic agent combinations with ceftobiprole, an FDA-approved drug library was screened for potential synergistic combinations with ceftobiprole. This screening and follow-up studies identified numerous β-lactams with ceftobiprole synergy.

Susceptibility of Ceftobiprole against Gram-positive and Gram-negative Clinical Isolates from 2019 from different European territories

BACKGROUND

Ceftobiprole is approved for use in treatment of hospital-associated and community-acquired pneumonia in 16 different European countries and is currently undergoing clinical trials in the USA.

METHODS

Isolates were collected from hospital laboratories from 16 European countries during 2019 as part of an ongoing post-marketing surveillance study. MICs were determined using EUCAST broth microdilution methodology and interpreted using 2020 EUCAST breakpoints.

RESULTS

Ceftobiprole was active (MIC, ≤2 mg/L) against 100% and 99.3% of methicillin-susceptible Staphylococcus aureus and MRSA isolates collected in 2019. Against S. pneumoniae, ceftobiprole was active (MIC, ≤0.5 mg/L) against 98.4% of isolates. Overall, 77.4% of Enterobacterales were susceptible though isolate numbers in certain countries were notably low. In addition, based on non-species related PK/PD breakpoints, 69.7% of Pseudomonas aeruginosa isolates were susceptible to ceftobiprole. Analysis of data by geographical regions showed that susceptibility to ceftobiprole by region or country was not significantly varied though MRSA, S. pneumoniae, Enterobacterales and P. aeruginosa. Isolates from Italy had lower susceptibilities to ceftobiprole: 98% of MRSA, 94% of S. pneumoniae and 61% of Enterobacterales isolates were susceptible to ceftobiprole.

CONCLUSIONS

The data for ceftobiprole for isolates from 2019 are encouragingly very similar to studies performed on isolates from earlier years showing that susceptibility to ceftobiprole has not changed and importantly that resistance emergence remains low throughout Europe.

Current pharmacotherapy for methicillin-resistant Staphylococcus aureus (MRSA) pneumonia

INTRODUCTION

Currently, several antibiotics are active against methicillin-resistant Staphylococcus aureus (MRSA) and can be used for the treatment of pneumonia. They show great variability in terms of antibiotic class, indication, pharmacodynamic/pharmacokinetic properties, type of available formulations, spectrum of activity against bacteria other than MRSA, and toxicity profile.

AREAS COVERED

In this narrative review, the authors discuss the characteristics of currently available agents for the treatment of MRSA pneumonia.

EXPERT OPINION

The availability of different agents with anti-MRSA activity, and approved for the treatment of pneumonia can allow a personalized approach for any given patient based on the severity of the disease, the setting of occurrence, the patient's baseline risk of toxicity and drug interactions, and the possibility of oral therapy whenever early discharge or outpatient treatment are possible. Although some gray areas still remain, like the lack of high certainty evidence on the efficacy of some old agents and on the precise role of companion agents with toxin inhibitory activity in the case of necrotizing pneumonia, the frequent availability of different treatment choices, each with peculiar characteristics, is already allowing an important step toward a precision medicine approach for the treatment of MRSA pneumonia.

Surveillance of ceftobiprole against Gram-positive and Gram-negative clinical isolates from 2018 from different European territories

OBJECTIVES

Ceftobiprole is approved for the treatment of hospital-acquired and community-acquired pneumonia in 17 different European countries and is currently undergoing clinical trials in the USA.

METHODS

In this study, isolates were collected from hospital laboratories from 15 European countries during 2018 as part of an ongoing post-marketing surveillance study. Minimum inhibitory concentrations (MICs) were determined using European Committee on Antimicrobial Susceptibility Testing (EUCAST) broth microdilution methodology and were interpreted using 2019 EUCAST breakpoints.

RESULTS

Ceftobiprole was active (MIC, ≤2 mg/L) against 100% and 98.9% of methicillin-susceptible Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) from 2018, respectively. Only six MRSA isolates (1.1%) were resistant to ceftobiprole and originated from four countries. Against Streptococcus pneumoniae, ceftobiprole was active (MIC, ≤0.5 mg/L) against 98.7% of isolates. Overall, 75.6% of Enterobacterales were susceptible, although isolate numbers in certain countries were notably low. In addition, based on non-species-related pharmacokinetic/pharmacodynamic breakpoints, 63.2% of Pseudomonas aeruginosa isolates were susceptible to ceftobiprole.

CONCLUSION

Data for ceftobiprole for isolates from 2018 are very similar to studies performed on isolates from earlier years, showing that susceptibility to ceftobiprole has remained high.

Efficacy and safety of ceftobiprole in patients aged 65 years or older: a post hoc analysis of three Phase III studies

Aim: To evaluate the efficacy and safety of ceftobiprole in patients aged ≥65 years. Materials & methods: We conducted a post hoc analysis of three randomized, double-blind, Phase III studies in patients with acute bacterial skin and skin structure infections, community-acquired pneumonia and hospital-acquired pneumonia. Results: Findings for patients aged ≥65 years (n = 633) were consistent with those for the overall study populations, although a trend toward improved outcomes was reported in some subgroups, for example, patients aged ≥75 years with community-acquired pneumonia were more likely to achieve an early clinical response with ceftobiprole than comparator (treatment difference 16.3% [95% CI:1.8-30.8]). The safety profile was similar between treatment groups in all studies. Conclusion: This analysis further supports the efficacy and safety of ceftobiprole in older patients with acute bacterial skin and skin structure infections or pneumonia. Clinicaltrials.gov trial identifiers: NCT03137173, NCT00326287, NCT00210964, NCT00229008.

Development of TLC Chromatographic-Densitometric Procedure for Qualitative and Quantitative Analysis of Ceftobiprole

Currently, there is still a need for broad-spectrum antibiotics. The new cephalosporin antibiotics include, among others, ceftobiprole, a fifth-generation gram-positive cephalosporin, active against Staphylococcus aureus methicillin agonist (MRSA). The main focus of the work was to optimize the conditions of ceftobiprole qualitative determination and to validate the developed procedure according to ICH guidelines. As a result of the optimization process, HPTLC Cellulose chromatographic plates as a stationary phase and a mixture consisting of ethanol:2-propanol: glacial acetic acid: water (4:4:1:3, v/v/v/v) as a mobile phase were chosen. The densitometric detection was carried out at maximum absorbance of ceftobiprole (λ = 232 nm). Next, the validation process of the developed procedure was carried out. The relative standard deviation (RSD) for precision was less than 1.65%, which proves the high compatibility of the results, as well as the LOD = 0.0257 µg/spot and LOQ = 0.0779 µg/spot values, which also confirm the high sensitivity of the procedure. The usefulness of the developed method for the stability studies of ceftobiprole was analyzed. Study was carried out under stress conditions, i.e., acid and alkaline environments, exposure to radiation imitating sunlight and high temperature (40–60 °C). It was found that cefotbiprole is unstable in an alkaline environment and during exposure to UV-VIS radiation. Moreover, the lipophilicity parameter, as a main physicochemical property of the biologically active compound, was determined using experimental and computational methods.

Spotlight on New Antibiotics for the Treatment of Pneumonia

In the last years, the presence of multidrug-resistant (MDR) Gram-negative (like Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii) and Gram-positive bacteria (mostly methicillin-resistant Staphylococcus aureus) was worldwide reported, limiting the options for an effective antibiotic therapy. For these reasons, inappropriate antimicrobial therapy and delayed prescription can lead to an unfavorable outcome, especially in patients with pneumonia. New antibiotics approved belong to classes of antimicrobials, like beta-lactams with or without beta-lactamase inhibitors, aminoglycosides, oxazolidinones, quinolones, and tetracyclines, or based on new mechanisms of action. These new compounds show many advantages, including a broad spectrum of activity against MDR pathogens, good lung penetration, safety and tolerability, and finally the possibility of intravenous and/or oral formulations. However, the new antibiotics under development represent an important possible armamentarium against difficult-to-treat strains. The safety and clinical efficacy of these future drugs should be tested in clinical practice. In this review, there are reported characteristics of newly approved antibiotics that represent potential future options for the treatment of respiratory tract infections, including those caused by multidrug-resistant bacteria. Finally, the characteristics of the drugs under development are briefly reported.

Emerging Strategies to Combat β-Lactamase Producing ESKAPE Pathogens

Since the discovery of penicillin by Alexander Fleming in 1929 as a therapeutic agent against staphylococci, β-lactam antibiotics (BLAs) remained the most successful antibiotic classes against the majority of bacterial strains, reaching a percentage of 65% of all medical prescriptions. Unfortunately, the emergence and diversification of β-lactamases pose indefinite health issues, limiting the clinical effectiveness of all current BLAs. One solution is to develop β-lactamase inhibitors (BLIs) capable of restoring the activity of β-lactam drugs. In this review, we will briefly present the older and new BLAs classes, their mechanisms of action, and an update of the BLIs capable of restoring the activity of β-lactam drugs against ESKAPE (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) pathogens. Subsequently, we will discuss several promising alternative approaches such as bacteriophages, antimicrobial peptides, nanoparticles, CRISPR (clustered regularly interspaced short palindromic repeats) cas technology, or vaccination developed to limit antimicrobial resistance in this endless fight against Gram-negative pathogens.

New cephalosporins for the treatment of pneumonia in internal medicine wards

The burden of hospital admission for pneumonia in internal medicine wards may not be underestimated; otherwise, cases of pneumonia are a frequent indication for antimicrobial prescriptions. Community- and hospital-acquired pneumonia are characterized by high healthcare costs, morbidity and non-negligible rates of fatality. The overcoming prevalence of resistant gram-negative and positive bacteria (e.g., methicillin-resistant Staphylococcus aureus, penicillin and ceftriaxone-resistant Streptococcus pneumoniae, extended-spectrum β-lactamases and carbapenemases producing Enterobacteriaceae) has made the most of the first-line agents ineffective for treating lower respiratory tract infections. A broad-spectrum of activity, favourable pulmonary penetration, harmlessness and avoiding in some cases a combination therapy, characterise new cephalosporins such as ceftolozane/tazobactam, ceftobiprole, ceftazidime/avibactam and ceftaroline. We aimed to summarise the role and place in therapy of new cephalosporins in community- and hospital-acquired pneumonia within the setting of internal medicine wards. The "universal pneumonia antibiotic strategy" is no longer acceptable for treating lung infections. Antimicrobial therapy should be individualized considering local antimicrobial resistance and epidemiology, the stage of the illness and potential host factors predisposing to a high risk for specific pathogens.

Ceftobiprole Activity against Bacteria from Skin and Skin Structure Infections in the United States from 2016 through 2018

Ceftobiprole medocaril is an advanced-generation cephalosporin prodrug that has qualified infectious disease product status granted by the US FDA and is currently being evaluated in phase 3 clinical trials in patients with acute bacterial skin and skin structure infections (ABSSSIs) and in patients with Staphylococcus aureus bacteremia. In this study, the activity of ceftobiprole and comparators was evaluated against more than 7,300 clinical isolates collected in the United States from 2016 through 2018 from patients with skin and skin structure infections. The major species/pathogen groups were S. aureus (53%), Enterobacterales (23%), Pseudomonas aeruginosa (7%), beta-hemolytic streptococci (6%), Enterococcus spp. (4%), and coagulase-negative staphylococci (2%). Ceftobiprole was highly active against S. aureus (MIC_50/90, 0.5/1 mg/liter; 99.7% susceptible by EUCAST criteria; 42% methicillin-resistant S. aureus [MRSA]). Ceftobiprole also exhibited potent activity against other Gram-positive cocci. The overall susceptibility of Enterobacterales to ceftobiprole was 84.8% (>99.0% susceptible for isolate subsets that exhibited a non-extended-spectrum β-lactamase [ESBL] phenotype). A total of 74.4% of P. aeruginosa, 100% of beta-hemolytic streptococci and coagulase-negative staphylococci, and 99.6% of Enterococcus faecalis isolates were inhibited by ceftobiprole at ≤4 mg/liter. As expected, ceftobiprole was largely inactive against Enterobacterales that contained ESBL genes and Enterococcus faecium Overall, ceftobiprole was highly active against most clinical isolates from the major Gram-positive and Gram-negative skin and skin structure pathogen groups collected at U.S. medical centers participating in the SENTRY Antimicrobial Surveillance Program during 2016 to 2018. The broad-spectrum activity of ceftobiprole, including potent activity against MRSA, supports its further evaluation for a potential ABSSSI indication.

Structural Insights into Ceftobiprole Inhibition of Pseudomonas aeruginosa Penicillin-Binding Protein 3

Ceftobiprole is an advanced-generation broad-spectrum cephalosporin antibiotic with potent and rapid bactericidal activity against Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus, as well as susceptible Gram-negative pathogens, including Pseudomonas sp. pathogens. In the case of Pseudomonas aeruginosa, ceftobiprole acts by inhibiting P. aeruginosa penicillin-binding protein 3 (PBP3). Structural studies were pursued to elucidate the molecular details of this PBP inhibition. The crystal structure of the His-tagged PBP3-ceftobiprole complex revealed a covalent bond between the ligand and the catalytic residue S294. Ceftobiprole binding leads to large active site changes near binding sites for the pyrrolidinone and pyrrolidine rings. The S528 to L536 region adopts a conformation previously not observed in PBP3, including partial unwinding of the α11 helix. These molecular insights can lead to a deeper understanding of β-lactam-PBP interactions that result in major changes in protein structure, as well as suggesting how to fine-tune current inhibitors and to develop novel inhibitors of this PBP.

Penicillin binding protein 2a: An overview and a medicinal chemistry perspective

Antimicrobial resistance is an imminent threat worldwide. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the "superbug" family, manifesting resistance through the production of a penicillin binding protein, PBP2a, an enzyme that provides its transpeptidase activity to allow cell wall biosynthesis. PBP2a's low affinity to most β-lactams, confers resistance to MRSA against numerous members of this class of antibiotics. An Achilles' heel of MRSA, PBP2a represents a substantial target to design novel antibiotics to tackle MRSA threat via inhibition of the bacterial cell wall biosynthesis. In this review we bring into focus the PBP2a enzyme and examine the various aspects related to its role in conferring resistance to MRSA strains. Moreover, we discuss several antibiotics and antimicrobial agents designed to target PBP2a and their therapeutic potential to meet such a grave threat. In conclusion, we consider future perspectives for targeting MRSA infections.

Ceftobiprole: drug evaluation and place in therapy

Introduction: Ceftobiprole is a fifth-generation cephalosporin with a broad spectrum of antimicrobial activity, including also methicillin-resistant Staphylococcus aureus (MRSA). Ceftobiprole is approved for the treatment of community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP), excluding ventilator-associated pneumonia, in several European and non-European countries. Areas covered: In this narrative review, we discuss the current place in therapy of ceftobiprole, both within and outside approved indications. An inductive MEDLINE/PubMed search of the available literature was conducted. Expert opinion: There are three main reasons which render ceftobiprole an attractive option for the empirical and targeted treatment of CAP and HAP: (i) its broad spectrum of activity; (ii) its activity against MRSA; (iii) its good safety profile. For these indications, ceftobiprole should be employed thoughtfully, in those scenarios in which its intrinsic advantages could be maximized. The use of ceftobiprole outside approved indications could be justified in specific scenarios, such as when other approved alternatives are ineffective, when the risk of toxicity due to other agents is unacceptable, and for salvage therapy. In the near future, ongoing phase 3 studies and further observational experiences could both enlarge the current panel of approved indications and enrich our knowledge on the use of ceftobiprole for off-label indications.

New Antibiotics for Pneumonia

Delayed antimicrobial prescriptions and inappropriate treatment can lead to poor outcomes in pneumonia. In nosocomial infections, especially in countries reporting high rates of antimicrobial resistance, the presence of multidrug-resistant gram-negative and gam-positive bacteria can limit options for adequate antimicrobial treatment. New antibiotics, belonging to known classes of antimicrobials or characterized by novel mechanisms of actions, have recently been approved or are under development. Advantages of the new compounds include enhanced spectrum of activity against resistant bacteria, high lung penetration, good tolerability, and possibility for intravenous to oral sequential therapy. This article reviews characteristics of newly approved and investigational compounds.

Early improvement in severely ill patients with pneumonia treated with ceftobiprole: a retrospective analysis of two major trials

BACKGROUND

Patients with pneumonia who are elderly or severely ill are at a particularly high risk of mortality. This post hoc retrospective analysis of data from two Phase III studies evaluated early improvement outcomes in subgroups of high-risk patients with community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP, excluding ventilator-associated pneumonia [VAP]).

METHODS

One study included hospitalised CAP patients randomised to ceftobiprole or ceftriaxone ± linezolid treatment. The other study included HAP patients, who were randomised to ceftobiprole or ceftazidime plus linezolid treatment. The primary outcome was rate of early clinical response (Day 3 in CAP and Day 4 in HAP patients). Additional outcome measures included clinical cure at a test-of-cure visit, 30-day all-cause mortality and safety.

RESULTS

The overall high-risk group comprised 398 CAP patients and 307 HAP patients with risk factors present at baseline. The rate of early response was numerically higher in ceftobiprole-treated patients vs comparator-treated patients in the following high-risk groups: CAP patients aged ≥75 years (16.3% difference, 95% confidence interval [CI]: 1.8, 30.8); CAP patients with COPD (20.1% difference, 95% CI: 8.8, 31.1); all high-risk HAP patients (12.5% difference, 95% CI: 3.5, 21.4); HAP patients with >10 baseline comorbidities (15.3% difference, 95% CI: 0.3, 30.4).

CONCLUSIONS

Previous studies show that ceftobiprole is an efficacious therapy for patients with pneumonia who are at high risk of poor outcomes. This post hoc analysis provides preliminary evidence that ceftobiprole treatment may have advantages over other antibiotics in terms of achieving early improvement in high-risk patients with HAP (excluding VAP) and in some subgroups of high-risk CAP patients.

TRIAL REGISTRATION

NCT00210964 : registered September 21, 2005; NCT00229008 : registered September 29, 2005; NCT00326287 : registered May 16, 2006.

PES Pathogens in Severe Community-Acquired Pneumonia

Worldwide, there is growing concern about the burden of pneumonia. Severe community-acquired pneumonia (CAP) is frequently complicated by pulmonary and extra-pulmonary complications, including sepsis, septic shock, acute respiratory distress syndrome, and acute cardiac events, resulting in significantly increased intensive care admission rates and mortality rates. Streptococcus pneumoniae (Pneumococcus) remains the most common causative pathogen in CAP. However, several bacteria and respiratory viruses are responsible, and approximately 6% of cases are due to the so-called PES (Pseudomonas aeruginosa, extended-spectrum β-lactamase Enterobacteriaceae, and methicillin-resistant Staphylococcus aureus) pathogens. Of these, P. aeruginosa and methicillin-resistant Staphylococcus aureus are the most frequently reported and require different antibiotic therapy to that for typical CAP. It is therefore important to recognize the risk factors for these pathogens to improve the outcomes in patients with CAP.

Ceftobiprole for the treatment of pneumonia

Ceftobiprole is a fifth-generation cephalosporin with potent antimicrobial activity against Gram positive and Gram-negative bacteria. It has been approved in major European countries for the treatment of community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP), excluding ventilator-associated pneumonia (VAP). Ceftobiprole is currently in a phase 3 clinical program for registration in the U.S. In 2015, it was designated as an infectious disease product qualified for the treatment of lung and skin infections by the FDA. The efficacy of ceftobiprole in pneumonia has been demonstrated in two-phase III clinical trials conducted in patients with CAP and HAP. The recommended dose in the adult with pneumonia is 500 mg every 8 h infused in 2 h; in case of renal failure, the regimen of administration must be adjusted according to the patient's renal function. It is not necessary to adjust the dose according to gender, age, body weight or liver failure. In case of hyperfiltration, an extension to 4 h infusion of the 500mg TID is required.

Structural and kinetic analyses of penicillin-binding protein 4 (PBP4)-mediated antibiotic resistance in Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) causes serious community-acquired and nosocomial infections worldwide. MRSA strains are resistant to a variety of antibiotics, including the classic penicillin and cephalosporin classes of β-lactams, making them intractable to treatment. Although β-lactam resistance in MRSA has been ascribed to the acquisition and activity of penicillin-binding protein 2a (PBP2a, encoded by mecA), it has recently been observed that resistance can also be mediated by penicillin-binding protein 4 (PBP4). Previously, we have shown that broad-spectrum β-lactam resistance can arise following serial passaging of a mecA-negative COL strain of S. aureus, creating the CRB strain. This strain has two missense mutations in pbp4 and a mutation in the pbp4 promoter, both of which play an instrumental role in β-lactam resistance. To better understand PBP4's role in resistance, here we have characterized its kinetics and structure with clinically relevant β-lactam antibiotics. We present the first crystallographic PBP4 structures of apo and acyl-enzyme intermediate forms complexed with three late-generation β-lactam antibiotics: ceftobiprole, ceftaroline, and nafcillin. In parallel, we characterized the structural and kinetic effects of the PBP4 mutations present in the CRB strain. Localized within the transpeptidase active-site cleft, the two substitutions appear to have different effects depending on the drug. With ceftobiprole, the missense mutations impaired the K_m value 150-fold, decreasing the proportion of inhibited PBP4. However, ceftaroline resistance appeared to be mediated by other factors, possibly including mutation of the pbp4 promoter. Our findings provide evidence that S. aureus CRB has at least two PBP4-mediated resistance mechanisms.

Susceptibility to ceftobiprole of respiratory-tract pathogens collected in the United Kingdom and Ireland during 2014-2015

Purpose

Lower respiratory tract infections (LRTIs) can cause significant morbidity and mortality and are becoming increasingly difficult to treat because of the growing prevalence of resistance to conventional antimicrobial agents. This study aimed to assess the current in vitro susceptibility of respiratory tract pathogens collected from the UK and Ireland to ceftobiprole, an advanced-generation cephalosporin, as compared with other antibiotics.

Methods

Pathogens isolated from patients with LRTIs were analyzed as part of the British Society for Antimicrobial Chemotherapy Antimicrobial Resistance Surveillance Programme during 2014–2015. Antibiotic susceptibility was evaluated using European Committee on Antimicrobial Susceptibility Testing breakpoints, including the ceftobiprole pharmacokinetic/pharmacodynamic non-species-specific breakpoint when species-specific breakpoints were not available.

Results

One thousand one hundred and sixty-eight isolates from community-onset LRTIs and 1,264 isolates from hospital-onset LRTIs were analyzed. The ceftobiprole susceptibility rate was 99.8% (428/429) for Streptococcus pneumoniae, 100% (502/502) for Haemophilus influenzae, and 99.6% (236/237) for Moraxella catarrhalis. All Staphylococcus aureus isolates, including methicillin-susceptible S. aureus (MSSA; N=181) and methicillin-resistant S. aureus (MRSA; N=35), were susceptible to ceftobiprole. Overall, ceftobiprole susceptibility was observed in 88.1% (215/244) of Escherichia coli isolates, 83.4% (156/187) of Klebsiella pneumoniae isolates and 86.7% (98/113) of Enterobacter spp. isolates.

Conclusion

Ceftobiprole had in vitro activity against all S. aureus (both MSSA and MRSA) isolates, and almost all S. pneumoniae isolates, as well as against Gram-negative bacteria associated with community-onset or hospital-onset LRTIs. Based on this analysis, ceftobiprole is a good treatment option when broad-spectrum antibiotic coverage is needed for LRTIs.

Comparative activity of ceftobiprole against coagulase-negative staphylococci from the BSAC Bacteraemia Surveillance Programme, 2013-2015

Coagulase-negative staphylococci (CoNS) are a significant cause of bacteraemia, the treatment of which is becoming increasingly complex due to the emergence of multidrug-resistant strains. This study aimed to evaluate the in vitro activity of ceftobiprole, an advanced-generation cephalosporin, as compared with other antimicrobial agents against CoNS from patients with bacteraemia. As part of the British Society for Antimicrobial Chemotherapy (BSAC) Bacteraemia Surveillance Programme, 650 blood isolates of CoNS were obtained from patients with bacteraemia at 74 centres throughout the UK and Ireland for the years 2013–2015. Minimum inhibitory concentrations (MICs) of ceftobiprole and other antimicrobial agents were determined using the BSAC agar dilution method. Susceptibility was assessed by European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. The majority of the isolates (63.2%) were Staphylococcus epidermidis. Overall, methicillin resistance, as determined by oxacillin susceptibility testing, was observed in 64.2% of isolates. The MIC_50/90 of ceftobiprole was 1/2 mg/L, and 100% of CoNS isolates were inhibited at the EUCAST ceftobiprole non-species-specific pharmacokinetic/pharmacodynamic breakpoint of 4 mg/L. Only one isolate was resistant to vancomycin. Overall rates of resistance to ciprofloxacin, clindamycin, erythromycin and teicoplanin were 50.5, 25.1, 68.2 and 20.9%, respectively. In S. epidermidis, resistance to oxacillin was associated with increased resistance to other antimicrobials. Ceftobiprole demonstrated in vitro activity against all CoNS species isolated from patients with bacteraemia and was active against species resistant to other antistaphylococcal antimicrobials. The collection of clinical data regarding the efficacy of ceftobiprole in treating CoNS bacteraemia is warranted.

Pharmacokinetics and Target Attainment of Ceftobiprole in Asian and Non-Asian Subjects

Ceftobiprole is a broad-spectrum cephalosporin. The objective of this study was to test the hypothesis that the pharmacokinetics (PK) and exposure of ceftobiprole in Asian subjects are similar to those in non-Asian subjects. Three approaches were followed. The first compared the individual PK estimates between the 2 subgroups derived from a population PK model previously built. Next, it was determined whether "Asian subject" was a significant covariate. Finally, a pharmacodynamic analysis was performed by comparing measures of exposure and target attainment. No significant differences were found between PK parameter estimates for Asian and non-Asian subjects, with median values (range) for clearance of 4.82 L/h (2.12-10.47) and 4.97 L/h (0.493-20.6), respectively (P = .736). "Asian subject" was not a significant covariate in the population PK model. There were no significant differences between the measures of exposure. The geometric mean ratio for the fAUC was 1.022 (90%CI, 0.91-1.15), indicating bioequivalence. Taking a target of 60% coverage of the dose interval, more than 90% of the population in both subgroups was adequately exposed. This analysis demonstrated that there are no PK or pharmacodynamic differences between Asian and non-Asian subjects for a ceftobiprole dose of 500 mg every 8 hours as a 2-hour infusion.

Pharmacokinetic drug evaluation of ceftobiprole for the treatment of MRSA

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA), while decreasing in overall incidence, is still a prominent concern world-wide. New agents coming to market in the last 10 years allow practitioners to optimize treatment for MRSA infections. Ceftobiprole is a cephalosporin agent with MRSA activity, currently approved in selected countries for the treatment of community-acquired pneumonia and hospital-acquired pneumonia. Areas covered: Relevant literature regarding spectrum of activity, pharmacokinetics, pharmacodynamics, and clinical trials will be discussed. Expert opinion: Ceftobiprole is an addition to a growing number of antimicrobials with activity against MRSA. Concern for appropriate dosing in critically ill patients remains due to its ineffectiveness for the treatment of ventilator-associated pneumonia (VAP). While ceftobiprole has activity against gram-negative organisms, the allowance for use of an additional agent for gram-negative infections in clinical trials limits recommendations for monotherapy for empirical treatment of HAP. Ceftobiprole's place in therapy will lie in its activity against gram positive organisms, such as Streptococcus spp. and Staphylococcus spp.

β-Lactams and β-Lactamase Inhibitors: An Overview

β-Lactams are the most widely used class of antibiotics. Since the discovery of benzylpenicillin in the 1920s, thousands of new penicillin derivatives and related β-lactam classes of cephalosporins, cephamycins, monobactams, and carbapenems have been discovered. Each new class of β-lactam has been developed either to increase the spectrum of activity to include additional bacterial species or to address specific resistance mechanisms that have arisen in the targeted bacterial population. Resistance to β-lactams is primarily because of bacterially produced β-lactamase enzymes that hydrolyze the β-lactam ring, thereby inactivating the drug. The newest effort to circumvent resistance is the development of novel broad-spectrum β-lactamase inhibitors that work against many problematic β-lactamases, including cephalosporinases and serine-based carbapenemases, which severely limit therapeutic options. This work provides a comprehensive overview of β-lactam antibiotics that are currently in use, as well as a look ahead to several new compounds that are in the development pipeline.

Structure-Activity Relationship for the 4(3H)-Quinazolinone Antibacterials

We recently reported on the discovery of a novel antibacterial (2) with a 4(3H)-quinazolinone core. This discovery was made by in silico screening of 1.2 million compounds for binding to a penicillin-binding protein and the subsequent demonstration of antibacterial activity against Staphylococcus aureus. The first structure–activity relationship for this antibacterial scaffold is explored in this report with evaluation of 77 variants of the structural class. Eleven promising compounds were further evaluated for in vitro toxicity, pharmacokinetics, and efficacy in a mouse peritonitis model of infection, which led to the discovery of compound 27. This new quinazolinone has potent activity against methicillin-resistant (MRSA) strains, low clearance, oral bioavailability and shows efficacy in a mouse neutropenic thigh infection model.

Glycosyltransferases and Transpeptidases/Penicillin-Binding Proteins: Valuable Targets for New Antibacterials

Peptidoglycan (PG) is an essential macromolecular sacculus surrounding most bacteria. It is assembled by the glycosyltransferase (GT) and transpeptidase (TP) activities of multimodular penicillin-binding proteins (PBPs) within multiprotein complex machineries. Both activities are essential for the synthesis of a functional stress-bearing PG shell. Although good progress has been made in terms of the functional and structural understanding of GT, finding a clinically useful antibiotic against them has been challenging until now. In contrast, the TP/PBP module has been successfully targeted by β-lactam derivatives, but the extensive use of these antibiotics has selected resistant bacterial strains that employ a wide variety of mechanisms to escape the lethal action of these antibiotics. In addition to traditional β-lactams, other classes of molecules (non-β-lactams) that inhibit PBPs are now emerging, opening new perspectives for tackling the resistance problem while taking advantage of these valuable targets, for which a wealth of structural and functional knowledge has been accumulated. The overall evidence shows that PBPs are part of multiprotein machineries whose activities are modulated by cofactors. Perturbation of these systems could lead to lethal effects. Developing screening strategies to take advantage of these mechanisms could lead to new inhibitors of PG assembly. In this paper, we present a general background on the GTs and TPs/PBPs, a survey of recent issues of bacterial resistance and a review of recent works describing new inhibitors of these enzymes.

Ceftobiprole medocaril in the treatment of hospital-acquired pneumonia

Ceftobiprole medocaril is a fifth-generation cephalosporin approved in Europe as single-agent therapy for hospital-acquired pneumonia (HAP), excluding ventilator-associated pneumonia (VAP). It is rapidly converted to the active metabolite ceftobiprole following intravenous administration. Ceftobiprole has a broad spectrum of activity, notably against methicillin-resistant Staphylococcus aureus, ampicillin-susceptible enterococci, penicillin-resistant pneumococci and Enterobacteriaceae not producing extended-spectrum β-lactamase. Ceftobiprole is primarily excreted renally by glomerular filtration, with minimal propensity for interaction with co-administered drugs. Normal dose is ceftobiprole 500 mg, administered by 2-h intravenous infusion every 8 h, with dose adjustment according to renal function. In a pivotal Phase III trial in patients with HAP, ceftobiprole monotherapy was as efficacious as ceftazidime/linezolid for clinical and microbiological cure and was noninferior to ceftazidime/linezolid in the subgroup of patients with HAP excluding VAP. Ceftobiprole and ceftazidime/linezolid were similarly well tolerated. Ceftobiprole is an efficacious and well-tolerated option for empirical treatment of patients with HAP (excluding VAP).

Ceftobiprole medocaril: a review of its use in patients with hospital- or community-acquired pneumonia

Ceftobiprole, the active metabolite of the prodrug ceftobiprole medocaril (Zevtera(®)), is a new generation broad-spectrum intravenous cephalosporin with activity against methicillin-resistant Staphylococcus aureus. Ceftobiprole exhibits potent in vitro activity against a number of Gram-positive and Gram-negative pathogens associated with hospital-acquired pneumonia (HAP) and community-acquired pneumonia (CAP). It is the first cephalosporin monotherapy approved in the EU for the treatment of both HAP (excluding ventilator associated-pneumonia [VAP]) and CAP. In phase III trials, ceftobiprole medocaril was noninferior, in terms of clinical cure rates at the test-of-cure visit, to ceftazidime plus linezolid in patients with HAP and to ceftriaxone ± linezolid in patients with CAP severe enough to require hospitalization. In patients with HAP, noninferiority of ceftobiprole medocaril to ceftazidime plus linezolid was not demonstrated in a subset of patients with VAP. In patients with CAP, ceftobiprole medocaril was effective in those at risk for poor outcomes (pneumonia severity index ≥91, Pneumonia Patient Outcomes Research Team score IV-V or bacteraemic pneumonia). In the phase III trials, ceftobiprole medocaril was generally well tolerated, with ≈10 % of patients discontinuing the treatment because of adverse events. The most common treatment-related adverse events occurring in ceftobiprole recipients in the trials in patients with HAP or CAP included nausea, diarrhoea, infusion site reactions, vomiting, hepatic enzyme elevations and hyponatraemia. Therefore, ceftobiprole medocaril monotherapy offers a simplified option for the initial empirical treatment of patients with HAP (excluding VAP) and in those with CAP requiring hospitalization.

The evolving role of chemical synthesis in antibacterial drug discovery

The discovery and implementation of antibiotics in the early twentieth century transformed human health and wellbeing. Chemical synthesis enabled the development of the first antibacterial substances, organoarsenicals and sulfa drugs, but these were soon outshone by a host of more powerful and vastly more complex antibiotics from nature: penicillin, streptomycin, tetracycline, and erythromycin, among others. These primary defences are now significantly less effective as an unavoidable consequence of rapid evolution of resistance within pathogenic bacteria, made worse by widespread misuse of antibiotics. For decades medicinal chemists replenished the arsenal of antibiotics by semisynthetic and to a lesser degree fully synthetic routes, but economic factors have led to a subsidence of this effort, which places society on the precipice of a disaster. We believe that the strategic application of modern chemical synthesis to antibacterial drug discovery must play a critical role if a crisis of global proportions is to be averted.

Penicillin-binding protein 2a of methicillin-resistant Staphylococcus aureus

High-level resistance to β-lactam antibiotics in methicillin-resistant Staphylococcus aureus (MRSA) is due to expression of penicillin-binding protein 2a (PBP2a), a transpeptidase that catalyzes cell-wall crosslinking in the face of the challenge by β-lactam antibiotics. The activity of this protein is regulated by allostery at a site 60 Å distant from the active site, where crosslinking of cell wall takes place. This review discusses the state of knowledge on this important enzyme of cell-wall biosynthesis in MRSA.

In silico study on Penicillin derivatives and Cephalosporins for upper respiratory tract bacterial pathogens

Upper respiratory tract infection (URTI) is an acute infection which involves the upper respiratory tract: nose, sinuses, tonsils and pharynx. URT infections are caused mainly by pathogenic bacteria like Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus. Conventionally, β-lactam antibiotics are used to treat URT infections. Penicillin binding proteins (PBPs) catalyze the cell wall synthesis in bacteria. β-Lactam antibiotics like Penicillin, Cephalosporins, Carbapenems and Monobactams inhibit bacterial cell wall synthesis by binding with PBPs. Pathogenic bacteria have efficiently evolved to resist these β-lactam antibiotics. New generation antibiotics are capable of inhibiting the action of PBP due to its new and peculiar structure. New generation antibiotics and Penicillin derivatives are selected in this study and virtually compared on the basis of interaction studies. 3-Dimensional (3D) interaction studies between Lactivicin, Cefuroxime, Cefadroxil, Ceftaroline, Ceftobiprole and Penicillin derivatives with PBPs of the above-mentioned bacteria are carried out. The aim of this study was to suggest a potent new generation molecule for further modification to increase the efficacy of the drug for the URTI.

Ceftobiprole activity against over 60,000 clinical bacterial pathogens isolated in Europe, Turkey, and Israel from 2005 to 2010

Ceftobiprole medocaril is a newly approved drug in Europe for the treatment of hospital-acquired pneumonia (HAP) (excluding patients with ventilator-associated pneumonia but including ventilated HAP patients) and community-acquired pneumonia in adults. The aim of this study was to evaluate the in vitro antimicrobial activity of ceftobiprole against prevalent Gram-positive and -negative pathogens isolated in Europe, Turkey, and Israel during 2005 through 2010. A total of 60,084 consecutive, nonduplicate isolates from a wide variety of infections were collected from 33 medical centers. Species identification was confirmed, and all isolates were susceptibility tested using reference broth microdilution methods. Ceftobiprole had high activity against methicillin-susceptible Staphylococcus aureus (MSSA) (100.0% susceptible), methicillin-susceptible coagulase-negative staphylococci (CoNS), beta-hemolytic streptococci, and Streptococcus pneumoniae (99.3% susceptible), with MIC90 values of 0.25, 0.12, ≤ 0.06, and 0.5 μg/ml, respectively. Ceftobiprole was active against methicillin-resistant S. aureus (MRSA) (98.3% susceptible) and methicillin-resistant CoNS, having a MIC90 of 2 μg/ml. Ceftobiprole was active against Enterococcus faecalis (MIC50/90, 0.5/4 μg/ml) but not against most Enterococcus faecium isolates. Ceftobiprole was very potent against the majority of Enterobacteriaceae (87.3% susceptible), with >80% inhibited at ≤ 0.12 μg/ml. The potency of ceftobiprole against Pseudomonas aeruginosa (MIC50/90, 2/>8 μg/ml; 64.6% at MIC values of ≤ 4 μg/ml) was similar to that of ceftazidime (MIC50/90, 2/>16 μg/ml; 75.4% susceptible), but limited activity was observed against Acinetobacter spp. and Stenotrophomonas maltophilia. High activity was also observed against all Haemophilus influenzae (MIC90, ≤ 0.06 μg/ml) and Moraxella catarrhalis (MIC50/90, ≤ 0.06/0.25 μg/ml) isolates. Ceftobiprole demonstrated a wide spectrum of antimicrobial activity against this very large longitudinal sample of contemporary pathogens.

Treatment ofPseudomonas aeruginosainfection in critically ill patients

Critically ill patients are on the increase in the present clinical setting. Aging of our population and increasingly aggressive medical and therapeutic interventions, including implanted foreign bodies, organ transplantation and advances in the chemotherapy of malignant diseases, have created a cohort of particularly vulnerable patients. Pseudomonas aeruginosa is one of the leading gram-negative organisms associated with nosocomial infections. This organism is frequently feared because it causes severe hospital-acquired infections, especially in immunocompromised hosts, and is often antibiotic resistant, complicating the choice of therapy. The epidemiology, microbiology, mechanisms of resistance and currently available and future treatment options for the most relevant infections caused by P. aeruginosa are reviewed.

Natural product and natural product derived drugs in clinical trials

The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.

Activity of ceftobiprole against methicillin-resistant Staphylococcus aureus strains with reduced susceptibility to daptomycin, linezolid or vancomycin, and strains with defined SCCmec types

Ceftobiprole is a broad-spectrum cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative pathogens including Pseudomonas aeruginosa. The aim of this study was to evaluate the activity of ceftobiprole against MRSA isolates with decreased susceptibility to daptomycin, linezolid or vancomycin as well as isolates from staphylococcal chromosome cassette mec (SCCmec) types I, II, III and IV. Overall, ceftobiprole demonstrated high potency against the 216 isolates tested, with MIC50 and MIC90 values (minimum inhibitory concentrations required to inhibit 50% and 90% of the isolates, respectively) of 1mg/L and 2mg/L (97.2% susceptible). The MIC90 for ceftobiprole was 2mg/L against the linezolid-non-susceptible, daptomycin-non-susceptible and vancomycin-intermediate (VISA and hVISA) subsets and was 1mg/L against the vancomycin-resistant (VRSA) strains. The MIC50/90 values for ceftobiprole were 2/4, 1/2, 2/2 and 1/1mg/L against SCCmec types I, II, III and IV, respectively. SCCmec type I strains had the highest MICs, with six strains exhibiting a ceftobiprole MIC of 4mg/L and 15 strains at 2mg/L. Ceftobiprole demonstrated potent activity against MRSA, including subsets of isolates with reduced susceptibility to daptomycin, linezolid and vancomycin. The activity of ceftobiprole against these resistant phenotypes indicates that it may have clinical utility in the treatment of infections caused by multidrug-resistant S. aureus and across strains from prevalent SCCmec types.

Application of pharmacokinetic/pharmacodynamic modelling and simulation for the prediction of target attainment of ceftobiprole against meticillin-resistant Staphylococcus aureus using minimum inhibitory concentration and time-kill curve based approaches

The purpose of this report was to compare two different methods for dose optimisation of antimicrobials. The probability of target attainment (PTA) was calculated using Monte Carlo simulation to predict the PK/PD target of fT>MIC or modelling and simulation of time-kill curve data. Ceftobiprole, the paradigm compound, activity against two MRSA strains was determined, ATCC 33591 (MIC=2mg/L) and a clinical isolate (MIC=1mg/L). A two-subpopulation model accounting for drug degradation during the experiment adequately fit the time-kill curve data (concentration range 0.25-16× MIC). The PTA was calculated for plasma, skeletal muscle and subcutaneous adipose tissue based on data from a microdialysis study in healthy volunteers. A two-compartment model with distribution factors to account for differences between free serum and tissue interstitial space fluid concentration appropriately fit the pharmacokinetic data. Pharmacodynamic endpoints of fT>MIC of 30% or 40% and 1- or 2-log kill were used. The PTA was >90% in all tissues based on the PK/PD endpoint of fT>MIC >40%. The PTAs based on a 1- or 2-log kill from the time-kill experiments were lower than those calculated based on fT>MIC. The PTA of a 1-log kill was >90% for both MRSA isolates for plasma and skeletal muscle but was slightly below 90% for subcutaneous adipose tissue (both isolates ca. 88%). The results support a dosing regimen of 500mg three times daily as a 2-h intravenous infusion. This dose should be confirmed as additional pharmacokinetic data from various patient populations become available.

Ceftobiprole medocaril is an effective treatment against methicillin-resistant Staphylococcus aureus (MRSA) mediastinitis in a rat model

Methicillin-resistant Staphylococcus aureus (MRSA) mediastinitis after median sternotomy is a major complication of cardiac surgery with significant morbidity and mortality rates. We evaluated the efficacy of ceftobiprole medocaril in a new rat model of mediastinitis and compared it to vancomycin. The model was induced in 92 rats. Infection was induced immediately after median sternotomy by the injection of MRSA (strain 3020, 1 × 10(7) cfu/rat) into the sternal bone. After 24 h, rats (groups of 6-8) were treated intraperitoneally for 5 days or 14 days by either: (i) saline (control, q8h), (ii) ceftobiprole medocaril (70 or 100 mg/kg, q8h), or (iii) vancomycin (50 mg/kg, q12h). Efficacy was determined by a reduction in bacterial cfu in the sternum and spleen tissues. Comparisons were performed using the Mann-Whitney test. A 5-day treatment course of ceftobiprole at both doses tested lead to a significant reduction in MRSA load in the sternum (p < 0.01) as compared to the control group and compared to 5-day vancomycin treatment, which lead to a non-significant reduction (p = 0.07). Longer treatment (14 days) with ceftobiprole lead to a complete clearance of MRSA from the sternum, similarly to vancomycin. Ceftobiprole also showed a significant effect on eliminating MRSA dissemination to the spleen compared to saline-treated rats. Ceftobiprole was effective in treating MRSA mediastinitis in the rat model. In the 5-day course, ceftobiprole showed a significant reduction in sternal MRSA counts and was superior to vancomycin. After 14 days, both ceftobiprole and vancomycin showed clearance of MRSA from the sternum in more than 50 % of rats and almost complete clearance in the remainder.