Efficacy of BAL5788, a prodrug of cephalosporin BAL9141, in a mouse model of acute pneumococcal pneumonia

Challenges for global antibiotic regimen planning and establishing antimicrobial resistance targets: implications for the WHO Essential Medicines List and AWaRe antibiotic book dosing

SUMMARYThe World Health Organisation's 2022 AWaRe Book provides guidance for the use of 39 antibiotics to treat 35 infections in primary healthcare and hospital facilities. We review the evidence underpinning suggested dosing regimens. Few (n = 18) population pharmacokinetic studies exist for key oral AWaRe antibiotics, largely conducted in homogenous and unrepresentative populations hindering robust estimates of drug exposures. Databases of minimum inhibitory concentration distributions are limited, especially for community pathogen-antibiotic combinations. Minimum inhibitory concentration data sources are not routinely reported and lack regional diversity and community representation. Of studies defining a pharmacodynamic target for ß-lactams (n = 80), 42 (52.5%) differed from traditionally accepted 30%-50% time above minimum inhibitory concentration targets. Heterogeneity in model systems and pharmacodynamic endpoints is common, and models generally use intravenous ß-lactams. One-size-fits-all pharmacodynamic targets are used for regimen planning despite complexity in drug-pathogen-disease combinations. We present solutions to enable the development of global evidence-based antibiotic dosing guidance that provides adequate treatment in the context of the increasing prevalence of antimicrobial resistance and, moreover, minimizes the emergence of resistance.

Protein-inspired antibiotics active against vancomycin- and daptomycin-resistant bacteria

The public health threat posed by a looming ‘post-antibiotic’ era necessitates new approaches to antibiotic discovery. Drug development has typically avoided exploitation of membrane-binding properties, in contrast to nature’s control of biological pathways via modulation of membrane-associated proteins and membrane lipid composition. Here, we describe the rejuvenation of the glycopeptide antibiotic vancomycin via selective targeting of bacterial membranes. Peptide libraries based on positively charged electrostatic effector sequences are ligated to N-terminal lipophilic membrane-insertive elements and then conjugated to vancomycin. These modified lipoglycopeptides, the ‘vancapticins’, possess enhanced membrane affinity and activity against methicillin-resistant Staphylococcus aureus (MRSA) and other Gram-positive bacteria, and retain activity against glycopeptide-resistant strains. Optimised antibiotics show in vivo efficacy in multiple models of bacterial infection. This membrane-targeting strategy has potential to ‘revitalise’ antibiotics that have lost effectiveness against recalcitrant bacteria, or enhance the activity of other intravenous-administered drugs that target membrane-associated receptors.

The antibiotic vancomycin inhibits bacterial cell wall synthesis by binding to a membrane-associated precursor. Here, Blaskovich et al. synthesize vancomycin derivatives containing lipophilic peptide moieties that enhance membrane affinity and in vivo activities against glycopeptide-resistant strains.

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 for the treatment of pneumonia: a European perspective

Ceftobiprole, a new broad spectrum, parenteral cephalosporin, exhibits potent in vitro activity against a number of Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus and penicillin-resistant Streptococcus pneumoniae, and Gram-negative pathogens associated with hospital-acquired pneumonia (HAP) and community-acquired pneumonia (CAP). Ceftobiprole has demonstrated noninferiority in two large-scale pivotal studies comparing it to ceftriaxone with or without linezolid in CAP, with clinical cure rates 86.6% versus 87.4%, or ceftazidime in HAP, with clinical cure rates of 77% versus 76%, respectively. However, ceftobiprole was inferior in the subgroup of patients undergoing mechanical ventilation. Ceftobiprole has so far demonstrated a good safety profile in preliminary studies, with similar tolerability to comparators. The most commonly observed adverse events of ceftobiprole included headache and gastrointestinal upset. It is the first cephalosporin monotherapy approved in the EU for the treatment of both CAP and HAP (excluding ventilator-associated pneumonia).

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.

Exposure to ceftobiprole is associated with microbiological eradication and clinical cure in patients with nosocomial pneumonia

The percentage of the dosing interval that the non-protein-bound plasma concentration is above the MIC (%fT>MIC) for cephalosporins has been shown to correlate with microbiological outcomes in preclinical studies. However, clinical data are scarce. Using data from a randomized double-blind phase 3 clinical trial, we explored the relationship of ceftobiprole exposure with microbiological and clinical outcomes in patients with nosocomial pneumonia. The individual ceftobiprole exposure was determined for different pharmacokinetic (PK)/pharmacodynamic (PD) indices using individual pharmacokinetic data and a previously published population model. The MICs used in the analysis were the highest MICs for any bacterium cultured at baseline or the end of treatment (EOT). Outcomes were microbiological cure at EOT and clinical cure at test of cure (TOC). Multiple logistic regression (MLR) and classification and regression tree (CART) analyses were applied to determine the relationships among exposure, patient characteristics, and outcomes. MLR indicated that the %fT>MIC of ceftobiprole was the best predictor for both microbiological eradication and clinical cure. CART analysis showed a breakpoint value of 51.1% (n = 159; P = 0.0024) for clinical cure, whereas it was 62.2% (n = 251; P < 0.0001) for microbiological eradication. Other factors also contributed, particularly to clinical outcome. These included the difference between VAP and non-VAP patients, systemic inflammatory response syndrome (SIRS), creatinine clearance, the use of anti-Pseudomonas combination therapy, and Acute Physiology and Chronic Health Evaluation II (APACHE-II) score. There is a strong correlation between microbiological eradication and clinical cure with exposure to ceftobiprole. The %fT>MIC required to result in a favorable clinical outcome is >51% of the dosing interval, which is in line with the values found for microbiological eradication, the comparator ceftazidime, and preclinical models.

Pharmacokinetic and pharmacodynamics evaluation of ceftobiprole medocaril for the treatment of hospital-acquired pneumonia

INTRODUCTION

Ceftobiprole is a cephalosporin with activity against methicillin-resistant Staphylococcus aureus, Enterobacteriaceae, and Pseudomonas aeruginosa with a promising role in the treatment of hospital-acquired pneumonia (HAP). Cure rates, however, with ceftobiprole at the doses studied may be inferior to conventional treatment in the ventilator-acquired subset of HAP.

AREAS COVERED

Literature was sought using PubMed and through abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy (2006 - 2012) and the European Congress of Clinical Microbiology and Infectious Diseases (2007 - 2012). The authors used the search terms "ceftobiprole," "BAL9141," "RO63-9141," "BAL5788," and 'RO5788." The article discusses the activity, mechanism of action, pharmacokinetics (PK), pharmacodynamics (PD), and clinical trials of ceftobiprole in HAP. The article also provides discussion of how PK/PD parameters play a role in the outcome of HAP treatment and how dosing in ventilator-associated pneumonia (VAP) should be reconsidered in light of altered PK/PD.

EXPERT OPINION

In patients with normal PK and non-VAP, ceftobiprole is effective for the treatment of HAP in the recommended doses, ceftobiprole is unlikely to achieve the desired PD targets when PK parameters are altered in VAP (e.g., increased volume of distribution and clearance). In these settings, off-label use at higher doses may overcome these limitations; but in the presence of alternative therapies, it cannot be currently recommended.

Efficacy of ceftobiprole Medocaril against Enterococcus faecalis in a murine urinary tract infection model

We evaluated ceftobiprole against the well-characterized Enterococcus faecalis strain OG1RF (with and without the β-lactamase [Bla] plasmid pBEM10) in a murine urinary tract infection (UTI) model. Ceftobiprole was equally effective for Bla(+) and Bla(-) OG1 strains, while ampicillin was moderately to markedly (depending on the inoculum) less effective against Bla(+) than Bla(-) OG1 strains. These data illustrate an in vivo effect on ampicillin of Bla production by E. faecalis and the stability and efficacy of ceftobiprole in experimental UTI.

Evaluation of ceftobiprole activity against a variety of gram-negative pathogens, including Escherichia coli, Haemophilus influenzae (β-lactamase positive and β-lactamase negative), and Klebsiella pneumoniae, in a rabbit meningitis model

Ceftobiprole medocaril, a new cephalosporin, is highly active against a broad spectrum of Gram-positive and Gram-negative clinical pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant pneumococci. In this study, we tested ceftobiprole against various Gram-negative pathogens in a rabbit meningitis model and determined its penetration into the cerebrospinal fluid (CSF). In this animal model, ceftobiprole produced an antibacterial activity similar to that of cefepime against an Escherichia coli strain, a Klebsiella pneumoniae strain, and a β-lactamase-negative Haemophilus influenzae strain. Against a β-lactamase-positive H. influenzae strain, ceftobiprole was significantly superior. The penetration of ceftobiprole through inflamed meninges reached about 16% of serum levels compared to about 2% of serum levels through uninflamed meninges.

In vitro and in vivo intracellular killing effects of tigecycline against clinical nontyphoid Salmonella isolates using ceftriaxone as a comparator

Salmonella is an important, worldwide food-borne pathogen. Resistance to fluoroquinolones and cephalosporins has been increasingly reported, and new therapeutic agents are desperately needed. In this study, we evaluated the in vitro antimicrobial susceptibility of clinical nontyphoidal Salmonella isolates to tigecycline. Antibacterial activity of tigecycline, ceftriaxone, and ciprofloxacin were investigated by time-kill studies and the murine peritonitis model. The MIC₅₀/MIC₉₀ values of tigecycline, ceftriaxone, and ciprofloxacin against 76 Salmonella isolates were 0.25/0.5, 1/8, and 0.125/0.5 μg/ml, respectively. The intracellular inhibitory activity of tigecycline at 0.5 μg/ml (1 × MIC) against Salmonella isolates in human peripheral blood mononuclear cells was sustained for 24 h. In a mouse peritonitis model, tigecycline reduced the extracellular and intracellular bacterial counts from 10⁷ CFU/ml and 10⁵ CFU/ml, respectively, to an undetectable level within 96 h. The results were similar to those obtained with ceftriaxone. The survival rate of mice exposed to tigecycline after being infected by an inoculum of 1 × 10⁵ CFU was 80%, and that of mice exposed to ceftriaxone was 100%. When the inoculum was increased to 1.3 × 10⁶ CFU, the survival rate of mice treated by tigecycline was 20%, and that of mice exposed to ceftriaxone was 0% (P = 0.2). When a ceftriaxone- and ciprofloxacin-resistant but tigecycline-susceptible isolate was tested, mice treated by tigecycline had a higher survival rate than those treated by ceftriaxone (15/20 [75%] versus 6/20 [30%]; P = 0.011). Our results suggest that tigecycline is at least as effective as ceftriaxone for murine Salmonella infections and warrants further clinical investigations to delineate its potential against human Salmonella infections.

Resistance and the management of complicated skin and skin structure infections: the role of ceftobiprole

Antimicrobial resistant bacteria are an increasing concern due to the resulting increase in morbidity, mortality, and health-care costs associated with the administration of inadequate or delayed antimicrobial therapy. The implications of inadequate antimicrobial therapy in complicated skin and skin structure infections (cSSSIs) have gained more attention recently, most likely due to the recent emergence of community-acquired methicillin resistant Staphylococcus aureus (MRSA) and the already high prevalence of MRSA in the nosocomial setting. Due to the continuous threat of resistance arising and the limitations of currently available agents for the treatment of cSSSIs, it is necessary to develop new antimicrobials for this indication. Ceftobiprole medocaril, the prodrug of ceftobiprole, is a parental investigational cephalosporin for the treatment of cSSSIs displaying a wide-spectrum of activity against both Gram-positive and Gram-negative species, including MRSA. Ceftobiprole displays noncomplex linear pharmacokinetics, is eliminated primarily by glomerular filtration, and distributes to extracellular fluid. Additionally, it has been shown that the extent of distribution to the site of action with regard to cSSSIs, ie, the extracellular space fluid of subcutaneous adipose tissue and skeletal muscle, is expected to be efficacious, as free concentrations meet efficacy targets for most pathogens. Similar to other beta-lactams, it displays an excellent safety and tolerability profile with the primary adverse events being dysgeusia in healthy volunteers, resulting from the conversion of the prodrug to the active, and nausea in patients. Ceftobiprole has demonstrated noninferiority in two large-scale pivotal studies comparing it to vancomycin, clinical cure rates 93.3% vs 93.5%, respectively, or vancomycin plus ceftazidime, clinical cure rates 90.5% vs 90.2%, respectively. Given the pharmacokinetic and pharmacodynamic properties, ceftobiprole is a promising new agent for the treatment of cSSSIs and has the potential to be used as a single agent for empiric treatment.

Ceftobiprole: A novel, broad-spectrum cephalosporin with activity against methicillin-resistant Staphylococcus aureus

PURPOSE

The pharmacology, antimicrobial activity, pharmacokinetics, pharmacodynamics, clinical efficacy, safety, and place in therapy of ceftobiprole are reviewed.

SUMMARY

Ceftobiprole, a novel, broad-spectrum, parenteral cephalosporin, inhibits the cell-wall synthesis of penicillin-binding proteins (PBPs) PBP2a and PBP2x, responsible for the resistance in staphylococci and pneumococci, respectively. Ceftobiprole has good activity against gram-positive aerobes and anaerobes, and its activity against gram-negative aerobes and anaerobes is species dependent. Ceftobiprole is relatively inactive against Acinetobacter species. Its ability to bind relevant PBPs of resistant gram-positive and gram-negative bacteria indicates its potential use in the treatment of hospital-acquired pneumonia and complicated skin and skin-structure infections (cSSSIs). Ceftobiprole is primarily excreted unchanged by the kidneys and exhibits linear pharmacokinetics. The half-life of the drug is approximately 3-4 hours. It exhibits minimal plasma protein binding (16%). Ceftobiprole does not inhibit the cytochrome P-450 isoenzyme system, so the possibility of drug-drug interactions is low. The drug has not been approved for use in the United States but has been approved in Canada and elsewhere. Ceftobiprole is currently undergoing Phase III clinical trials and has demonstrated activity against methicillin-resistant Staphylococcus aureus, penicillin-resistant Streptococcus pneumoniae, and Pseudomonas aeruginosa. Completed Phase III trials used i.v. dosages of 500 mg every 8-12 hours. The most commonly observed adverse effects of ceftobiprole included headache and gastrointestinal upset.

CONCLUSION

Ceftobiprole is a novel, broad-spectrum, parenteral cephalosporin undergoing Phase III clinical trials. Its broad spectrum of activity makes it a candidate for monotherapy of cSSSIs and pneumonias that have required combination therapy in the past.

CEM-101, a novel fluoroketolide: antimicrobial activity against a diverse collection of Gram-positive and Gram-negative bacteria

CEM-101 is a novel fluoroketolide with reported high potency against diverse groups of Gram-positive (Micrococcus spp., viridans group streptococci, Corynebacterium spp. Listeria monocytogenes, Clostridium spp., etc.) and Gram-negative bacteria (Neisseria gonorrhoeae, Campylobacter jejuni, Helicobacter pylori, Bacteroides fragilis, Shigella spp., etc.), including mycoplasma and ureaplasma, as well as bacteria commonly associated with community-acquired respiratory tract infections and skin and skin structure infections. In this study, CEM-101 and comparator antimicrobials were tested against a collection of very low prevalence aerobic and anaerobic bacteria collected via the SENTRY Antimicrobial Surveillance Program platform. CEM-101 was highly active against all Gram-positive organisms (MIC(50), 0.015 microg/mL) as compared with telithromycin (MIC(50), 0.06 microg/mL), clarithromycin (MIC(50), 0.12 microg/mL), and erythromycin (MIC(50), 0.25 microg/mL). Among Gram-negative pathogens, CEM-101 also displayed a high potency against most strains (MIC(50), 4 microg/mL) but was found to be equivalent or less active when compared with other antimicrobials tested with MIC(50) values ranging from < or =0.12 microg/mL for levofloxacin to 8 microg/mL for telithromycin. Among the strict anaerobic species, CEM-101 activity mirrored that of the aerobic species: high activity against the Gram-positive anaerobes (MIC(50) results ranging from < or =0.03 microg/mL to 0.12 microg/mL) and equivalent or less susceptible against Gram-negative anaerobes. Our in vitro antimicrobial susceptibility results for CEM-101 demonstrate better activity compared with other MLS(B) class agents among a diverse group of uncommonly isolated bacterial pathogens; these results provide an impetus for possible expanded indications during Phase 2 and 3 clinical trials.

Emerging agents to combat complicated and resistant infections: focus on ceftobiprole

Antimicrobial resistance is a global concern. Over the past few years, considerable efforts and resources have been expended to detect, monitor, and understand at the basic level the many different facets of emerging and increasing resistance. Development of new antimicrobial agents has been matched by the development of new mechanisms of resistance by bacteria. Current antibiotics act at a variety of sites within the target bacteria, including the cross-linking enzymes in the cell wall, various ribosomal enzymes, nucleic acid polymerases, and folate synthesis. Ceftobiprole is a novel parenteral cephalosporin with high affinity for most penicillin-binding proteins, including the mecA product penicillin-binding protein 2a, rendering it active against methicillin-resistant staphylococci. Its in vitro activity against staphylococci and multiresistant pneumococci, combined with its Gram-negative spectrum comparable to that of other extended-spectrum cephalosporins, its stability against a wide range of beta-lactamases, and its pharmacokinetic and safety profiles make ceftobiprole an attractive and well tolerated new antimicrobial agent. The US Food and Drug Administration granted ceftobiprole medocaril fast-track status in 2003 for the treatment of complicated skin infections and skin structure infections due to methicillin-resistant staphylococci, and subsequently extended this to treatment of hospital-acquired pneumonia, including ventilator-associated pneumonia due to suspected or proven methicillin-resistant Staphylococcus aureus.

In vivo activity of ceftobiprole in murine skin infections due to Staphylococcus aureus and Pseudomonas aeruginosa

Ceftobiprole, a broad-spectrum cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA) (P. Hebeisen et al., Antimicrob. Agents Chemother. 45:825-836, 2001), was evaluated in a subcutaneous skin infection model with Staphylococcus aureus Smith OC 4172 (methicillin-susceptible S. aureus [MSSA]), S. aureus OC 8525 (MRSA), Pseudomonas aeruginosa OC 4351 (having an inducible AmpC beta-lactamase), and P. aeruginosa OC 4354 (overproducing AmpC beta-lactamase). In the MSSA and MRSA infection models, ceftobiprole, administered as the prodrug ceftobiprole medocaril, was more effective in reducing CFU/g skin (P < 0.001) than were cefazolin, vancomycin, or linezolid based on the dose-response profiles. Skin lesion volumes in MSSA-infected animals treated with ceftobiprole were 19 to 29% lower than those for cefazolin-, vancomycin-, or linezolid-treated animals (P < 0.001). In MRSA infections, lesion size in ceftobiprole-treated mice was 34% less than that with cefazolin or linezolid treatment (P < 0.001). Against P. aeruginosa, ceftobiprole at similar doses was as effective as meropenem-cilastatin in reductions of CFU/g skin, despite 8- and 32-fold-lower MICs for meropenem; both treatments were more effective than was cefepime (P < 0.001) against the inducible and overproducing AmpC beta-lactamase strains of P. aeruginosa. Ceftobiprole was similar to meropenem-cilastatin and 47 to 54% more effective than cefepime (P < 0.01) in reducing the size of the lesion caused by either strain of P. aeruginosa in this study. These studies indicate that ceftobiprole is effective in reducing both bacterial load and lesion volume associated with infections due to MSSA, MRSA, and P. aeruginosa in this murine model of skin and soft tissue infection.

Ceftobiprole: a new beta-lactam antibiotic

The increasing threat of antimicrobial resistance in general, and that of methicillin-resistant Staphylococcus aureus (MRSA) in particular, is raising significant medical, economical and public health challenges worldwide, both within hospitals and throughout the community. These considerations, along with the extensive time and costs associated with the development and approval of new therapeutic agents, represent some of the major reasons why understanding the advantages and limitations of new antibiotics, ensuring their judicious use and maximising their active shelf life should become global priorities. On March 18, 2008, the Food and Drug Administration issued an approvable letter for ceftobiprole, a broad-spectrum beta-lactam antibiotic active against MRSA and other clinically relevant Gram-positive and Gram-negative pathogens. Ceftobiprole is currently available only for parenteral administration, and besides its remarkable antimicrobial spectrum, this antibiotic possesses additional desirable characteristics, such as low propensity to select for resistance, efficacy in animal models of disease and good safety profile. Furthermore, in recently completed clinical trials, ceftobiprole demonstrated non-inferiority to comparator compounds such as vancomycin, and emerged as a promising clinical option of monotherapy for the treatment of complicated skin and skin structure infections and community-acquired pneumonia. Here, we discuss some of the most important clinically relevant findings on ceftobiprole obtained from in vitro studies, animal models of disease and recently completed phase III clinical trials.

Ceftobiprole: a novel cephalosporin with activity against Gram-positive and Gram-negative pathogens, including methicillin-resistant Staphylococcus aureus (MRSA)

Ceftobiprole is a novel broad-spectrum cephalosporin with activity against a wide range of Gram-positive and Gram-negative bacteria, including several resistant species such as methicillin-resistant Staphylococcus aureus and penicillin-resistant Streptococcus pneumoniae. Ceftobiprole is administered intravenously as the prodrug ceftobiprole medocaril, which is almost immediately converted to the active form. It is currently under review by the US Food and Drug Administration (FDA) and is approved in Canada under the trade name Zeftera. The pharmacokinetics of ceftobiprole are non-complex as it displays a two-compartment model, dose proportionality, linear plasma protein binding and negligible accumulation. The volume of distribution is approximately equal to the extracellular fluid volume and it is cleared primarily by glomerular filtration, resulting in a half-life of approximately 3-4h. Ceftobiprole displays a low plasma protein binding of approximately 22%. The efficacy of ceftobiprole was demonstrated in two pivotal studies in patients with complicated skin and skin-structure infections (cSSSIs) that compared ceftobiprole with vancomycin in Gram-positive infections in one study and ceftobiprole with vancomycin plus ceftazidime in Gram-positive and Gram-negative infections in the other. The clinical cure rates were similar for ceftobiprole vs. comparator treatments: 93.3% vs. 93.5% with vancomycin only and 90.5% vs. 90.2% with vancomycin plus ceftazidime. The pharmacokinetic/pharmacodynamic profile supports the use of ceftobiprole to treat a wide range of cSSSIs.

In vivo pharmacodynamics of ceftobiprole against multiple bacterial pathogens in murine thigh and lung infection models

Ceftobiprole medocaril is the parenteral prodrug of ceftobiprole, a novel pyrrolidinone broad-spectrum cephalosporin with in vitro and in vivo bactericidal activities against methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant Streptococcus pneumoniae (PRSP). We have used murine thigh and lung infection models in neutropenic and normal mice to characterize the in vivo pharmacokinetic (PK)-pharmacodynamic (PD) activities of ceftobiprole against multiple strains of S. aureus (including MRSA), S. pneumoniae (including PRSP), and gram-negative bacilli. Serum levels of ceftobiprole following the administration of multiple doses were determined by a microbiological assay. In vivo bactericidal activities and postantibiotic effects (PAEs) of ceftobiprole against MRSA and PRSP strains were determined from serial CFU/thigh values following single doses of ceftobiprole (40 and 160 mg/kg of body weight). Dose fractionation studies were used to determine which PK-PD index correlated best with activity. Magnitudes of the PK-PD indices were calculated from MICs and PK parameters. A sigmoid dose-response model was used to estimate the dose (mg/kg/24 h) required to achieve a static and 2-log(10) kill effects over 24 h. PK results showed area under the concentration-time curve/dose values of 1.8 to 2.8 and half-lives of 0.29 to 0.51 h. MICs ranged from 0.015 to 2 microg/ml. Ceftobiprole demonstrated time-dependent killing; its in vivo PAEs varied from 3.8 h to 4.8 h for MRSA and from 0 to 0.8 h for PRSP. The time above MIC (T > MIC) correlated best with efficacy for both MRSA and PRSP. The T > MIC values required for the static doses were significantly longer (P < 0.001) for Enterobacteriaceae (36 to 45%) than for S. aureus (14 to 28%) and S. pneumoniae (15 to 22%). The drug showed activities in the lung model similar to those in the thigh model. The presence of neutrophils significantly enhanced the activity of ceftobiprole against S. pneumoniae but only slightly against Klebsiella pneumoniae. Based on its PD profile, ceftobiprole is a promising new beta-lactam agent with activity against gram-negative and gram-positive organisms including MRSA and PRSP.

Efficacies of ceftobiprole medocaril and comparators in a rabbit model of osteomyelitis due to methicillin-resistant Staphylococcus aureus

The pharmacokinetics and distribution into bone tissue of ceftobiprole in uninfected New Zealand White rabbits were determined after subcutaneous administration of the prodrug ceftobiprole medocaril. Serum exposure (maximum concentration of the drug in serum, trough concentration, area under the concentration-time curve) to ceftobiprole at 20 and 80 mg/kg was dose proportional, and there was no accumulation of ceftobiprole following repeated (every 6 h [q6h]) injections of the antibiotic. Ceftobiprole titers in the tibial matrix and marrow were 3.2 +/- 1.3 microg/g and 11.2 +/- 6.5 microg/g, respectively, in uninfected animals treated with 20 mg/kg of the antibiotic and 13.4 +/- 7.3 microg/g and 66.3 +/- 43.2 microg/g, respectively, in uninfected animals treated with 80 mg/kg of the antibiotic. No differences in ceftobiprole titers were observed between right and left tibiae for either bone matrix or marrow. The efficacies of 4 weeks of treatment with ceftobiprole (40 mg/kg administered subcutaneously [s.c.] q6h), vancomycin (30 mg/kg administered s.c. q12h), or linezolid (60 mg/kg administered orally q8h) were compared, using a rabbit model of methicillin-resistant Staphylococcus aureus tibial osteomyelitis. After treatment with ceftobiprole, the bacterial titers in all infected left tibiae from evaluable rabbits were below the level of detection, whereas only 73% of infected left tibiae from vancomycin- or linezolid-treated animals had bacterial titers below the level of detection; the mean titers of ceftobiprole were 3 to 5 times higher in infected left tibiae than in uninfected right tibiae. These results indicate that ceftobiprole provided effective parenteral treatment of osteomyelitis in this rabbit model.

Pharmacodynamic characterization of ceftobiprole in experimental pneumonia caused by phenotypically diverse Staphylococcus aureus strains

Ceftobiprole (BPR) is an investigational cephalosporin with activity against Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) strains. The pharmacodynamic (PD) profile of BPR against S. aureus strains with a variety of susceptibility phenotypes in an immunocompromised murine pneumonia model was characterized. The BPR MICs of the test isolates ranged from 0.25 to 2 mug/ml. Pharmacokinetic (PK) studies were conducted with infected neutropenic BALB/c mice; and the BPR concentrations were measured in plasma, epithelial lining fluid (ELF), and lung tissue. PD studies with these mice were undertaken with eight S. aureus isolates (two methicillin-susceptible S. aureus strains, three hospital-acquired MRSA strains, and three community-acquired MRSA strains). Subcutaneous BPR doses of 2 to 125 mg/kg of body weight/day were administered, and the change in the number of log(10) CFU/ml in lungs was evaluated after 24 h of therapy. The PD profile was characterized by using the free drug exposures (f) determined from the following parameters: the percentage of time that the concentration was greater than the MIC (T > MIC), the maximum concentration in serum/MIC, and the area under the concentration-time curve/MIC. The BPR PK parameters were linear over the dose range studied in plasma, and the ELF concentrations ranged from 60 to 94% of the free plasma concentration. fT > MIC was the parameter that best correlated with efficacy against a diverse array of S. aureus isolates in this murine pneumonia model. The 80% effective dose (ED(80)), ED(50), and stasis exposures appeared to be similar among the isolates studied. BPR exerted maximal antibacterial effects when fT > MIC ranged from 6 to 22%, regardless of the phenotypic profile of resistance to beta-lactam, fluoroquinolone, erythromycin, clindamycin, or tetracycline antibiotics.

Multidrug-resistant Streptococcus pneumoniae infections: current and future therapeutic options

Antibacterial resistance in Streptococcus pneumoniae is increasing worldwide, affecting principally beta-lactams and macrolides (prevalence ranging between approximately 1% and 90% depending on the geographical area). Fluoroquinolone resistance has also started to emerge in countries with high level of antibacterial resistance and consumption. Of more concern, 40% of pneumococci display multi-drug resistant phenotypes, again with highly variable prevalence among countries. Infections caused by resistant pneumococci can still be treated using first-line antibacterials (beta-lactams), provided the dosage is optimised to cover less susceptible strains. Macrolides can no longer be used as monotherapy, but are combined with beta-lactams to cover intracellular bacteria. Ketolides could be an alternative, but toxicity issues have recently restricted the use of telithromycin in the US. The so-called respiratory fluoroquinolones offer the advantages of easy administration and a spectrum covering extracellular and intracellular pathogens. However, their broad spectrum raises questions regarding the global risk of resistance selection and their safety profile is far from optimal for wide use in the community. For multi-drug resistant pneumococci, ketolides and fluoroquinolones could be considered. A large number of drugs with activity against these multi-drug resistant strains (cephalosporins, carbapenems, glycopeptides, lipopeptides, ketolides, lincosamides, oxazolidinones, glycylcyclines, quinolones, deformylase inhibitors) are currently in development. Most of them are only new derivatives in existing classes, with improved intrinsic activity or lower susceptibility to resistance mechanisms. Except for the new fluoroquinolones, these agents are also primarily targeted towards methicillin-resistant Staphylococcus aureus infections; therefore, demonstration of their clinical efficacy in the management of pneumococcal infections is still awaited.

In-vitro profile of a new beta-lactam, ceftobiprole, with activity against methicillin-resistant Staphylococcus aureus

Ceftobiprole is a novel, broad-spectrum cephalosporin with in-vitro activity against common Gram-positive and Gram-negative organisms. It forms a stable inhibitory complex with Staphylococcus aureus penicillin-binding protein (PBP) 2' (2a), resulting in enhanced activity against methicillin-resistant S. aureus (MRSA). In recent studies of methicillin-susceptible S. aureus, the ceftobiprole MIC(90) value was most frequently < or =1.0 mg/L (MIC range < or =0.25-1.0 mg/L). For MRSA, MIC(90) values were generally 2.0 mg/L (MIC range < or =0.06-4.0 mg/L). MICs for all streptococcal species, except penicillin-resistant Streptococcus viridans but including penicillin-resistant Streptococcus pneumoniae, ranged from < or =0.008 to 2.0 mg/L. Ceftobiprole is active against Enterococcus faecalis (MIC(90) = 4 mg/L), but not generally active against Enterococcus faecium (MIC(90) > 16 mg/L). Ceftobiprole displayed bactericidal activity against Gram-negative pathogens comparable to that of cefepime, ceftazidime or piperacillin-tazobactam in early studies. However, recent data show activity against Pseudomonas aeruginosa similar to that of cefepime but less than that of ceftazidime. Ceftobiprole, like cefepime, is stable in the presence of most class A non-extended spectrum beta-lactamases and inducible class C beta-lactamases. Ceftobiprole is a poor inducer of AmpC beta-lactamase and a poor substrate for hydrolysis by AmpC beta-lactamase. Studies of ceftobiprole in several animal models have demonstrated potent in-vivo efficacy against infections caused by MRSA, including strains intermediately resistant to vancomycin. It was also efficacious in murine infections caused by Gram-negative bacteria with MIC values < or =2 mg/L. The broad spectrum of activity demonstrated by ceftobiprole in vitro and in vivo suggests that it may have potential for empirical treatment of suspected Gram-negative and Gram-positive infections, including those caused by MRSA.

Results of a double-blind, randomized trial of ceftobiprole treatment of complicated skin and skin structure infections caused by gram-positive bacteria

Ceftobiprole is the first broad-spectrum cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA) to be assessed in late-stage clinical trials. As a pivotal step in the clinical development of ceftobiprole, a multicenter, global, randomized, double-blind trial was conducted to compare the efficacy of ceftobiprole to that of vancomycin in patients with complicated skin and skin structure infections (cSSSIs) caused by gram-positive bacteria. The primary objective was to assess noninferiority on the basis of the cure rates 7 to 14 days after the completion of therapy in patients administered ceftobiprole 500 mg every 12 h or vancomycin 1 g every 12 h. Of 784 patients randomized, 282 receiving ceftobiprole and 277 receiving vancomycin were clinically evaluable. Of these patients, 93.3% treated with ceftobiprole and 93.5% treated with vancomycin were cured (95% confidence interval of difference, -4.4%, 3.9%). The cure rates for patients with MRSA infections were 91.8% (56/61) with ceftobiprole treatment and 90.0% (54/60) with vancomycin treatment (95% confidence interval of difference, -8.4%, 12.1%). At least one adverse event (AE) was reported by 52% of the ceftobiprole-treated patients and 51% of the vancomycin-treated patients. The most common AEs reported by the ceftobiprole-treated patients were nausea (14%) and taste disturbance (8%). Discontinuation of the study drug because of treatment-emergent AEs occurred in 4% (n = 17) of the ceftobiprole-treated patients and 6% (n = 22) of the vancomycin-treated patients. The results of this trial support the use of ceftobiprole as an effective and well-tolerated treatment option for patients with cSSSIs caused by a spectrum of gram-positive bacteria.

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.

Anti-MRSA beta-lactams in development, with a focus on ceftobiprole: the first anti-MRSA beta-lactam to demonstrate clinical efficacy

Ceftobiprole is the first of the investigational beta-lactam antibiotics with in vitro activity against methicillin-resistant staphylococci to reach and complete Phase III therapeutic trials. Its antibacterial spectrum includes methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecalis, penicillin-resistant streptococci and many Gram-negative pathogens. It has demonstrated in vivo activity against many experimental infections caused by these pathogens. Ceftobiprole has completed Phase III clinical trials for complicated skin and skin structure infections, is being studied in Phase III pneumonia trials and has demonstrated non-inferiority compared with vancomycin in a Phase III complicated skin and skin structure infections trial, resulting in > 90% clinical cures of infections caused by MRSA. Other anti-MRSA beta-lactams in therapeutic clinical trials include the carbapenem CS-023/RO-4908463 and the cephalosporin ceftaroline (PPI-0903). The future of all of these agents will depend on their clinical efficacy, safety and their ability to be accepted as beta-lactams for the reliable treatment of a broad spectrum of infections, including those caused by MRSA.

Probability of target attainment for ceftobiprole as derived from a population pharmacokinetic analysis of 150 subjects

Ceftobiprole is a broad-spectrum cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA) that is undergoing phase III trials for the treatment of complicated skin and skin structure infections and nosocomial pneumonia. The objectives were to describe the pharmacodynamic profiles of ceftobiprole given at 500 mg intravenously (i.v.) every 8 h (q8h) (2-h infusion) and 500 mg i.v. every 12 h (q12h) (1-h infusion) to determine the overall probability of target attainment (PTA) by weighting for the expected distributions of renal function in the populations of interests, to determine the PTA against representative pathogens encountered in clinical trials, and to determine the optimal renal dose adjustment for ceftobiprole at 500 mg i.v. q8h (2-h infusion). Data for a total of 150 subjects in phase I/II trials were analyzed by using the population pharmacokinetic modeling program BigNPOD (nonparametric optimal design). Monte Carlo simulation was performed with the ADAPT II program to estimate the PTA at which the free drug concentrations exceed the MIC for 30 to 60% of the dosing interval (30 to 60% fT > MIC). For ceftobiprole at 500 mg i.v. q12h, the probabilities of achieving 30% and 50% fT > MIC exceeded 90% for MICs < or =2 mg/liter and < or =1 mg/liter, respectively, For ceftobiprole at 500 mg i.v. q8h, the probabilities of achieving 40 and 60% fT > MIC exceeded 90% for MICs < or =4 mg/liter and < or =2 mg/liter, respectively. For ceftobiprole at both 500 mg i.v. q12h and 500 mg i.v. q8h, the probability of achieving a nearly bactericidal effect (50% fT > MIC) exceeded 90% for methicillin-susceptible S. aureus and MRSA. For gram-negative pathogens, the PTA for achieving a nearly maximal bactericidal effect (60% fT > MIC) for ceftobiprole at 500 mg i.v. q8h exceeded 90% for non-AmpC-producing gram-negative organisms. Ceftobiprole at 500 mg i.v. q12h, for patients who had a creatinine clearance rate of < or =50 ml/min, was identified as the most appropriate treatment regimen for patients who require renal dose adjustment for mild to moderate renal impairment.

Ceftobiprole medocaril (BAL5788) treatment of experimental Haemophilus influenzae, Enterobacter cloacae, and Klebsiella pneumoniae murine pneumonia

Ceftobiprole (BAL9141) is an investigational cephalosporin active against methicillin- and vancomycin-resistant staphylococci administered as a water-soluble prodrug, ceftobiprole medocaril (BAL5788). Using an immunocompetent murine pneumonia model of Haemophilus influenzae, Enterobacter cloacae, or extended-spectrum beta-lactamase (ESBL) nonproducing or producing Klebsiella pneumoniae pneumonia, we compared results of treatment with ceftobiprole medocaril (71 mg/kg, sc, qid), ceftriaxone (50 mg/kg, im, bid), or cefepime (50 mg/kg, ip, q.i.d.). Results were expressed as median and 25th to 75th percentile log10 colony forming units per gram of lung tissue. Ceftobiprole, ceftriaxone, and cefepime were each more active than was no treatment and were equally active for treatment of experimental H. influenzae, E. cloacae, or ESBL-nonproducing K. pneumoniae pneumonia. For ESBL-producing K. pneumoniae, no differences were detected between no treatment and treatment with ceftobiprole, ceftriaxone, or cefepime. Ceftobiprole is active against H. influenzae, E. cloacae, and ESBL-nonproducing K. pneumoniae in an immunocompetent experimental murine pneumonia model.

Activities of ceftobiprole, a novel broad-spectrum cephalosporin, against Haemophilus influenzae and Moraxella catarrhalis

Ceftobiprole, a broad-spectrum pyrrolidinone-3-ylidenemethyl cephem currently in phase III clinical trials, had MICs between 0.008 microg/ml and 8.0 microg/ml for 321 clinical isolates of Haemophilus influenzae and between < or =0.004 microg/ml and 1.0 microg/ml for 49 clinical isolates of Moraxella catarrhalis. Ceftobiprole MIC(50) and MIC(90) values for H. influenzae were 0.06 microg/ml and 0.25 microg/ml for beta-lactamase-positive strains (n = 262), 0.03 microg/ml and 0.25 microg/ml for beta-lactamase-negative strains (n = 40), and 0.5 microg/ml and 2.0 microg/ml for beta-lactamase-negative ampicillin-resistant strains (n = 19), respectively. Ceftobiprole MIC(50) and MIC(90) values for beta-lactamase-positive M. catarrhalis strains (n = 40) were 0.12 microg/ml and 0.5 microg/ml, respectively, whereas the ceftobiprole MIC range for beta-lactamase-negative M. catarrhalis strains (n = 9) was < or =0.004 to 0.03 microg/ml. Ceftriaxone MICs usually were generally at least twofold lower than those of ceftobiprole, whereas amoxicillin-clavulanate MICs usually were higher than those of ceftobiprole. Azithromycin and telithromycin had unimodal MIC distributions against H. influenzae, with MIC(90) values of azithromycin and telithromycin of 2 microg/ml and 4 microg/ml, respectively. Except for selected quinolone-nonsusceptible H. influenzae strains, moxifloxacin proved highly active, with MIC(90) values of 0.12 microg/ml. Time-kill analyses showed that ceftobiprole, ceftriaxone, cefpodoxime, amoxicillin-clavulanate, azithromycin, telithromycin, and moxifloxacin were bactericidal at 2x MIC by 24 h against all 10 H. influenzae strains surveyed. Only modest increases in MICs were found for H. influenzae or M. catarrhalis clones after 50 serial passages in the presence of subinhibitory concentrations of ceftobiprole, and single-passage selection showed that the selection frequency of H. influenzae or M. catarrhalis clones with elevated ceftobiprole MICs is quite low.

Investigational new drugs for the treatment of resistant pneumococcal infections

Antibiotic resistance in Streptococcus pneumoniae is not only increasing with penicillin but also with other antimicrobial classes including the macrolides, tetracyclines and sulfonamides. This trend with antibiotic resistance has highlighted the need for the further development of new anti-infectives for the treatment of pneumococcal infections, particularly against multi-drug resistant pneumococci. Several new drugs with anti-pneumococcal activity are at various stages of development and will be discussed in this review. Two new cephalosporins with activity against S. pneumoniae include ceftobiprole and RWJ-54428. Faropenem is in a new class of beta-lactam antibiotics called the penems. Structurally, the penems are a hybrid between the penicillins and cephalosporins. Sitafloxacin and garenoxacin are two new quinolones that are likely to have a role in treating pneumococcal infections. Oritavancin and dalbavancin are glycopeptides with activity against methicillin-resistant S. aureus and vancomycin-resistant Enterococcus spp. as well as multi-drug resistant pneumococci. Tigecycline is the first drug in a new class of anti-infectives called the glycycyclines that has activity against penicillin-resistant pneumococci.

Antistaphylococcal activity of ceftobiprole, a new broad-spectrum cephalosporin

Ceftobiprole (formerly BAL9141), the active component of the prodrug BAL5788 (ceftobiprole medocaril), is a novel cephalosporin with expanded activity against gram-positive bacteria. Among 152 Staphylococcus aureus isolates, including 5 vancomycin-intermediate and 2 vancomycin-resistant strains, MIC(50) and MIC(90) values for ceftobiprole were each 0.5 microg/ml against methicillin-susceptible strains and 2 mug/ml against methicillin-resistant strains. Against 151 coagulase-negative staphylococci (including 4 vancomycin-intermediate strains), MIC(50) and MIC(90) values were, respectively, 0.125 microg/ml and 1 microg/ml against methicillin-susceptible and 1 microg/ml and 2 microg/ml against methicillin-resistant strains. Teicoplanin was less active than vancomycin against coagulase-negative strains. Linezolid, quinupristin-dalfopristin, and daptomycin were active against all strains, whereas increased MICs for amoxicillin-clavulanate, cefazolin, minocycline, gentamicin, trimethoprim-sulfamethoxazole, levofloxacin, rifampin, mupirocin, fusidic acid, and fosfomycin were sometimes observed. At 2x MIC, ceftobiprole was bactericidal against 11 of 12 test strains by 24 h. Prolonged serial passage in the presence of subinhibitory concentrations of ceftobiprole failed to select for clones with MICs >4 times those of the parents; the maximum MIC achieved for ceftobiprole after 50 passages (in 1 of 10 strains) was 8 mug/ml. Single-passage selections showed very low frequencies of resistance to ceftobiprole irrespective of genotype or phenotype; the maximal ceftobiprole MIC of recovered clones was 8 mug/ml.

Intensive therapy with ceftobiprole medocaril of experimental foreign-body infection by methicillin-resistant Staphylococcus aureus

The therapeutic activity of ceftobiprole medocaril, the water-soluble prodrug of ceftobiprole, was compared to that of vancomycin in a rat tissue cage model of chronic methicillin-resistant Staphylococcus aureus (MRSA) foreign-body infection. The MICs and MBCs of ceftobiprole and vancomycin in Mueller-Hinton broth for strain MRGR3 were 1 and 4 and 1 and 2 microg/ml, respectively. In vitro elimination rates of strain MRGR3 of 4 and 8 microg/ml of ceftobiprole or vancomycin were equivalent. After 2 weeks of infection, mean +/- standard error of the mean viable counts of strain MRGR3 were 6.83 +/- 0.11 log CFU/ml of tissue cage fluid (n = 87). High-dose regimens of ceftobiprole medocaril (equivalent to 150 mg/kg of ceftobiprole) or 50 mg/kg vancomycin produced nearly identical average peak and trough levels of ceftobiprole and vancomycin in tissue cage fluid, which exceeded the MBC of either antibiotic towards strain MRGR3 for > or =75% of each dosing interval. After 7 days of therapy with ceftobiprole medocaril or vancomycin, average counts of MRGR3 decreased significantly (P < 0.02) by 0.68 +/- 0.28 (n = 29) and 0.88 +/- 0.22 (n = 28) log CFU/ml of tissue cage fluid, respectively, compared with cages of untreated animals, but were not significantly different from each other. No resistant mutants were detected on ceftobiprole-supplemented agar following therapy with this cephalosporin. The in vivo activity of ceftobiprole medocaril against chronic MRSA foreign-body infections was equivalent to that of vancomycin and did not lead to the emergence of resistant subpopulations.

Antipneumococcal activity of ceftobiprole, a novel broad-spectrum cephalosporin

Ceftobiprole (previously known as BAL9141), an anti-methicillin-resistant Staphylococcus aureus cephalosporin, was very highly active against a panel of 299 drug-susceptible and -resistant pneumococci, with MIC(50) and MIC(90) values (microg/ml) of 0.016 and 0.016 (penicillin susceptible), 0.06 and 0.5 (penicillin intermediate), and 0.5 and 1.0 (penicillin resistant). Ceftobiprole, imipenem, and ertapenem had lower MICs against all pneumococcal strains than amoxicillin, cefepime, ceftriaxone, cefotaxime, cefuroxime, or cefdinir. Macrolide and penicillin G MICs generally varied in parallel, whereas fluoroquinolone MICs did not correlate with penicillin or macrolide susceptibility or resistance. All strains were susceptible to linezolid, quinupristin-dalfopristin, daptomycin, vancomycin, and teicoplanin. Time-kill analyses showed that at 1x and 2x the MIC, ceftobiprole was bactericidal against 10/12 and 11/12 strains, respectively. Levofloxacin, moxifloxacin, vancomycin, and teicoplanin were each bactericidal against 10 to 12 strains at 2x the MIC. Azithromycin and clarithromycin were slowly bactericidal, and telithromycin was bactericidal against only 5/12 strains at 2x the MIC. Linezolid was mainly bacteriostatic, whereas quinupristin-dalfopristin and daptomycin showed marked killing at early time periods. Prolonged serial passage in the presence of subinhibitory concentrations of ceftobiprole failed to yield mutants with high MICs towards this cephalosporin, and single-passage selection showed very low frequencies of spontaneous mutants with breakthrough MICs towards ceftobiprole.

Evaluation of ceftobiprole in a rabbit model of aortic valve endocarditis due to methicillin-resistant and vancomycin-intermediate Staphylococcus aureus

Ceftobiprole is a novel broad-spectrum cephalosporin that binds with high affinity to PBP 2a, the methicillin-resistance determinant of staphylococci, and is active against methicillin- and vancomycin-resistant Staphylococcus aureus. Ceftobiprole was compared to vancomycin in a rabbit model of methicillin-resistant S. aureus aortic valve endocarditis. Ceftobiprole and vancomycin were equally effective against endocarditis caused by methicillin-resistant S. aureus strain 76, whereas ceftobiprole was more effective than vancomycin against the vancomycin-intermediate S. aureus strain HIP5836. The activity of ceftobiprole against drug-resistant strains of S. aureus warrants its further clinical development.

Methicillin-Resistant Staphylococcus aureus: An Evolutionary, Epidemiologic, and Therapeutic Odyssey

Methicillin-resistant Staphylococcus aureus, first identified just over 4 decades ago, has undergone rapid evolutionary changes and epidemiologic expansion. It has spread beyond the confines of health care facilities, emerging anew in the community, where it is rapidly becoming a dominant pathogen. This has led to an important change in the choice of antibiotics in the management of community-acquired infections and has also led to the development of novel antimicrobials.