Pharmacodynamics of ceftaroline against Staphylococcus aureus studied in an in vitro pharmacokinetic model of infection

Safety and effectiveness of fifth generation cephalosporins for the treatment of methicillin-resistant staphylococcus aureus bloodstream infections: a narrative review exploring past, present, and future

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) is a major issue in healthcare, since it is often associated with endocarditis or deep site foci. Relevant morbidity and mortality associated with MRSA-BSIs forced the development of new antibiotic strategies; in particular, this review will focus the attention on fifth-generation cephalosporins (ceftaroline/ceftobiprole), that are the only ß-lactams active against MRSA.

AREAS COVERED

The review discusses the available randomized controlled trials and real-world observational studies conducted on safety and effectiveness of ceftaroline/ceftobiprole for the treatment of MRSA-BSIs. Finally, a proposal of MRSA-BSI treatment flowchart, based on fifth-generation cephalosporins, is described.

EXPERT OPINION

The use of anti-MRSA cephalosporins is an acceptable choice either in monotherapy or combination therapy for the treatment of MRSA-BSIs due to their relevant effectiveness and safety. Particularly, their use may be advisable in combination therapy in case of severe infections (including endocarditis or persistent bacteriemia) or in monotherapy in subjects at higher risk of drugs-induced toxicity with older regimens. On the contrary, caution should be taken in case of suspected/ascertained central nervous system infections due to inconsistent data regarding penetration of these drugs in cerebrospinal fluid and brain tissues.

Impact of Key Components of Intensified Ceftaroline Dosing on Pharmacokinetic/Pharmacodynamic Target Attainment

BACKGROUND AND OBJECTIVE

Ceftaroline fosamil is a β-lactam antibiotic approved as a 600 mg twice daily dose (≤1 h infusion, 'standard dosing') or a 600 mg thrice daily dose (2 h infusion) to treat complicated skin and soft tissue infections caused by Staphylococcus aureus (minimum inhibitory concentration [MIC] 2-4 mg/L). We sought to systematically evaluate the relative impact of the three key components of the intensified dosing regimen (i.e. shortened dosing interval, prolonged infusion duration and increased total daily dose [TDD]) on the pharmacokinetic/pharmacodynamic (PK/PD) target attainment given different grades of bacterial susceptibility.

METHODS

A population PK model was developed using data from 12 healthy volunteers (EudraCT-2012-005134-11) receiving standard or intensified dosing. PK/PD target attainment (ƒT>MIC = 35% and 100%) after 24 h was compared following systematically varied combinations of the (1) dosing interval (every 12 h [q12h]→ every 8 h [q8h]); (2) infusion duration (1 h→2 h); and (3) individual and total daily dose (400→900 mg, i.e. TDD 1200→1800 mg), as well as for varying susceptibility of S. aureus (MIC 0.032-8 mg/L).

RESULTS

A two-compartment model with linear elimination adequately described ceftaroline concentrations (n = 274). The relevance of the dosing components dosing interval/infusion duration/TDD for ƒT>MIC systematically changed with pathogen susceptibility. For susceptible pathogens with MIC ≤1 mg/L, shortened dosing intervals appeared as the main driver of the improved target attainment associated with the intensified dosing regimen, followed by increased TDD and infusion duration. For less susceptible pathogens, the advantage of q8h dosing and 2 h infusions declined, and increased TDD improved ƒT>MIC the most.

CONCLUSION

The analysis calls to mind consideration of dose increases when prolonging the infusion duration in the case of low bacterial susceptibility.

Systematic review of ceftaroline fosamil in the management of patients with methicillin-resistant Staphylococcus aureus pneumonia

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for an array of problematic community- and healthcare-acquired infections, including pneumonia, and is frequently associated with severe disease and high mortality rates. Standard recommended treatments for empiric and targeted coverage of suspected MRSA in patients with community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP), including ventilator-associated pneumonia (VAP), are vancomycin and linezolid. However, adverse events such as acute kidney injury and Clostridium difficile infection have been associated with these antibiotics. Ceftaroline fosamil is a β-lactam/extended-spectrum cephalosporin approved for the treatment of adults and children with CAP and complicated skin and soft tissue infections. Ceftaroline has in vitro activity against a range of common Gram-positive bacteria and is distinct among the β-lactams in retaining activity against MRSA. Due to the design of the pivotal randomised controlled trials of ceftaroline fosamil, outcomes in patients with MRSA CAP were not evaluated. However, various reports of real-world outcomes with ceftaroline fosamil for pneumonia caused by MRSA, including CAP and HAP/VAP, been published since its approval. A systematic literature review and qualitative analysis of relevant publications was undertaken to collate and summarise relevant published data on the efficacy and safety of ceftaroline fosamil in patients with MRSA pneumonia. While relatively few real-world outcomes studies are available, the available data suggest that ceftaroline fosamil is a possible alternative to linezolid and vancomycin for MRSA pneumonia. Specific scenarios in which ceftaroline fosamil might be considered include bacteraemia and complicating factors such as empyema.

Real-world experience of therapeutic drug monitoring and PK/PD achievement of ceftaroline administered by different infusion regimens in patients with confirmed infections caused by Gram-positive bacteria

BACKGROUND

Ceftaroline is a novel cephalosporin active against MDR Gram-positive (GP) bacteria. For β-lactam antibiotics, such as ceftaroline, prolonged infusions and therapeutic drug monitoring (TDM) are used for dosage optimization based on their pharmacokinetics/pharmacodynamics (PK/PD).

OBJECTIVES

To describe our experience with TDM and PK/PD target attainment of ceftaroline administered by intermittent and prolonged infusion in a cohort of patients with MDR-GP bacterial infections.

METHODS

Patients treated with ceftaroline administered by continuous (24 h), extended (3 h/6 h) and intermittent infusion (1 h) and undergoing TDM of plasma concentrations were included. A 100%fT>4×MIC was the pre-specified PK/PD target and 100%fT>10×MIC was considered overexposure. Dose recommendations were made based on TDM results and each patient's clinical condition.

RESULTS

Twelve patients [83.3% male, median age of 73 (38-83) years] were included. Nine patients (75%) achieved 100%fT>4×MIC, all under prolonged infusions. In one patient, the 100%fT was >10×MIC but no toxicity was observed. Based on TDM results, initial doses were recommended to be maintained in eight patients, decreased in three and increased in one.

CONCLUSIONS

The administration of ceftaroline by prolonged infusion together with TDM may be a useful strategy for achieving the desired PK/PD target in these patients. However, more studies evaluating the relationship between PK/PD attainment and clinical outcomes are needed.

Optimal drug therapy for Staphylococcus aureus bacteraemia in adults

PURPOSE OF REVIEW

Staphylococcus aureus is a significant human pathogen, causing a variety of infections, from skin and soft tissue infections to endocarditis, bone and joint infections and deep tissue abscesses. Mortality from S. aureus bacteraemia remains high, without major therapeutic advances in recent decades.

RECENT FINDINGS

In recent years, optimized dosing of antibiotics is increasingly being recognized as a cornerstone of management for severe infections including S. aureus bacteraemia. This comprehensive review details the pharmacokinetics/pharmacodynamics (PK/PD) targets for commonly used antistaphylococcal antibiotics and the doses predicted to achieve them in clinical practice. Recent advances in dosing of teicoplanin and use of cefazolin in CNS infections and findings from combination therapy studies are discussed. Drug exposure relationships related to toxicity are also detailed.

SUMMARY

This review details the different PK/PD targets for drugs used to treat S. aureus bacteraemia and how to apply them in various scenarios. The drug doses that achieve them, and the risks of toxicity are also provided.

Pharmacodynamics of Flucloxacillin in a Neutropenic Murine Thigh Infection Model: A Piece of the Puzzle towards Evidence-Based Dosing

For decades, flucloxacillin has been used to treat methicillin-susceptible Staphylococcus aureus (MSSA). Little is still known about its pharmacodynamics (PD). The present study aimed to determine the pharmacokinetic (PK)/PD index and the PD-index value minimally required for efficacy. MICs of 305 MSSA isolates were measured to determine the wild-type distribution. The PD of 8 S. aureus, 1 S. pyogenes, and 1 S. agalactiae isolates were evaluated in a neutropenic murine thigh infection model. Two S. aureus isolates were used in a dose-fractionation study and a dose−response analysis was performed additionally in the in vivo model. Data were analyzed with a population PK and sigmoid maximum effect model. The end of the wild-type distribution was 1 mg/L. The percentage of time the unbound concentration was above MIC (%fT > MIC) was best correlated with efficacy. For S. aureus, median %fT > 0.25 × MIC required for 1-log reduction was 15%. The value for S. pyogenes was 10%fT > MIC and for S. agalactiae 22%fT > 0.25xMIC for a 1-log reduction. The effect of flucloxacillin reached a 2-log reduction of S. aureus at 20%fT > 0.25xMIC and also for S. pyogenes and S. agalactiae, a reduction was reached. These data may serve to optimize dosing regimens currently used in humans.

Ceftaroline Fosamil for Treatment of Pediatric Complicated Skin and Soft Tissue Infections and Community-Acquired Pneumonia

Community-acquired pneumonia (CAP)/community-acquired bacterial pneumonia (CABP) and complicated skin and soft tissue infection (cSSTI)/acute bacterial skin and skin structure infection (ABSSSI) represent major causes of morbidity and mortality in children. β-Lactams are the cornerstone of antibiotic treatment for many serious bacterial infections in children; however, most of these agents have no activity against methicillin-resistant Staphylococcus aureus (MRSA). Ceftaroline fosamil, a β-lactam with broad-spectrum in vitro activity against Gram-positive pathogens (including MRSA and multidrug-resistant Streptococcus pneumoniae) and common Gram-negative organisms, is approved in the European Union and the United States for children with CAP/CABP or cSSTI/ABSSSI. Ceftaroline fosamil has completed a pediatric investigation plan including safety, efficacy, and pharmacokinetic evaluations in patients with ages ranging from birth to 17 years. It has demonstrated similar clinical and microbiological efficacy to best available existing treatments in phase III-IV trials in patients aged ≥ 2 months to < 18 years with CABP or ABSSSI, with a safety profile consistent with the cephalosporin class. It is also approved in the European Union for neonates with CAP or cSSTI, and in the US for neonates with ABSSSI. Ceftaroline fosamil dosing for children (including renal function adjustments) is supported by pharmacokinetic/pharmacodynamic modeling and simulations in appropriate age groups, and includes the option of 5- to 60-min intravenous infusions for standard doses, and a high dose for cSSTI patients with MRSA isolates, with a ceftaroline minimum inhibitory concentration of 2-4 mg/L. Considered together, these data suggest ceftaroline fosamil may be beneficial in the management of CAP/CABP and cSSTI/ABSSSI in children.

Development and characterization of a new swine model of invasive pneumococcal pneumonia

Streptococcus pneumoniae is the most common microbial cause of community-acquired pneumonia. Currently, there are no available models of severe pneumococcal pneumonia in mechanically ventilated animals to mimic clinical conditions of critically ill patients. We studied endogenous pulmonary flora in 4 healthy pigs and in an additional 10 pigs in which we intra-bronchially instilled S. pneumoniae serotype 19 A, characterized by its resistance to penicillin, macrolides and tetracyclines. The pigs underwent ventilation for 72 h. All pigs that were not challenged with S. pneumoniae completed the 72-h study, whereas 30% of infected pigs did not. At 24 h, we clinically confirmed pneumonia in the infected pigs; upon necropsy, we sampled lung tissue for microbiological/histological confirmation of pneumococcal pneumonia. In control pigs, Streptococcus suis and Staphylococcus aureus were the most commonly encountered pathogens, and their lung tissue mean ± s.e.m. concentration was 7.94 ± 20 c.f.u./g. In infected pigs, S. pneumoniae was found in the lungs of all pigs (mean ± s.e.m. pulmonary concentration of 1.26 × 10⁵ ± 2 × 10² c.f.u./g). Bacteremia was found in 50% of infected pigs. Pneumococcal pneumonia was confirmed in all infected pigs at 24 h. Pneumonia was associated with thrombocytopenia, an increase in prothrombin time, cardiac output and vasopressor dependency index and a decrease in systemic vascular resistance. Upon necropsy, microbiological/histological pneumococcal pneumonia was confirmed in 8 of 10 pigs. We have therefore developed a novel model of penicillin- and macrolide-resistant pneumococcal pneumonia in mechanically ventilated pigs with bacteremia and severe hemodynamic compromise. The model could prove valuable for appraising the pathogenesis of pneumococcal pneumonia, the effects associated with macrolide resistance and the outcomes related to the use of new diagnostic strategies and antibiotic or complementary therapies.

Pharmacokinetic and Pharmacodynamic Target Attainment in Adult and Pediatric Patients Following Administration of Ceftaroline Fosamil as a 5-Minute Infusion

The key pharmacokinetic/pharmacodynamic (PK/PD) efficacy index for β-lactam antibiotics is the percentage of time that free drug concentrations exceed the minimum inhibitory concentration (MIC) of bacteria during each dosing interval (fT>MIC). Ceftaroline fosamil, the prodrug of the β-lactam ceftaroline, was initially approved for administration as 60-minute intravenous (IV) infusions. Population PK analyses comparing exposure and PK/PD target attainment for 5-minute and 60-minute IV infusions, described here, have supported ceftaroline fosamil labeling updates to include variable infusion durations of 5 to 60 minutes in adults and children aged ≥2 months. A 2-compartment disposition PK model for ceftaroline fosamil and ceftaroline was used to predict steady-state ceftaroline exposures (maximum plasma concentrations [Cmax,ss ] and area under the plasma concentration-time curve over 24 hours [AUCss,0-24 ]) and probability of target attainment in simulated adult and pediatric patients with various degrees of renal function receiving standard doses of ceftaroline fosamil as 5-minute or 60-minute IV infusions. Across age groups and renal function categories, median ceftaroline AUCss,0-24 values were similar for 5-minute and 60-minute infusions, whereas Cmax,ss was up to 42% higher for 5-minute infusions. Both infusion durations achieved >99% probability of target attainment based on PK/PD targets for Staphylococcus aureus (35% fT>MIC) and Streptococcus pneumoniae (44% fT>MIC) at European Committee on Antimicrobial Susceptibility Testing/Clinical and Laboratory Standards Institute MIC breakpoints (1 mg/L and 0.25/0.5 mg/L, respectively). These findings support administration of standard ceftaroline fosamil doses over 5 to 60 minutes for adults and children aged ≥2 months, providing added flexibility to clinicians and patients.

Comparing probability of target attainment against Staphylococcus aureus for ceftaroline fosamil, vancomycin, daptomycin, linezolid, and ceftriaxone in complicated skin and soft tissue infection using pharmacokinetic/pharmacodynamic models

For recently licensed antibiotics, such as the cephalosporin ceftaroline fosamil, probability of target attainment (PTA) curves, showing the percentage of patients reaching a predefined pharmacokinetic (PK)/pharmacodynamic (PD) target at different bacterial minimum inhibitory concentrations (MICs), have been used to support and justify dose recommendations across patient populations. However, information on PTA for older antibiotics is limited. A retrospective analysis was conducted to construct PTA curves for 4 antibiotics against Staphylococcus aureus in patients with complicated skin and soft tissue infections (cSSTIs). PK models for vancomycin, linezolid, daptomycin, and ceftriaxone were selected from the literature based on large numbers of subjects with covariates representative of patients in Europe and/or the United States. An existing model was available for ceftaroline fosamil. Standard and high-dosage regimens were used to compare the PTA of each antibiotic at MIC values 0.03 to 64 mg/L for a simulated set of patients with cSSTI caused by S. aureus. These were compared to proportions of S. aureus isolates at each MIC from global surveillance data. Ceftaroline achieved PTAs >99.9% for bacteriostatic and bactericidal targets at the MIC90 (1 mg/L), whereas the comparators failed to achieve PTAs >90%, at bacteriostatic or bactericidal targets, even when clinical doses were increased beyond those recommended. PTA analysis can be used to compare different drugs with the same simulated patient dataset, subject to availability of an appropriate PK model and robust exposure targets. This analysis shows that some antibiotics commonly used to treat cSSTIs may fail to reach high PTAs relative to contemporary MIC90 estimates.

Optimizing ceftaroline dosing in critically ill patients undergoing continuous renal replacement therapy

BACKGROUND AND OBJECTIVES

Currently, no dosing information exists for ceftaroline fosamil in patients undergoing continuous renal replacement therapy (CRRT). The objectives of this study are to characterize the pharmacokinetics of ceftaroline in critically ill patients undergoing CRRT modalities and to derive individualized dosing recommendations.

METHODS

This pharmacokinetic study aimed to enroll critically ill patients receiving ceftaroline fosamil and any CRRT modality from adult intensive care units. Selection of the specific CRRT modality and dosing regimen was based on clinical discretion. Pre-filter, post-filter, and ultrafiltrate samples were obtained before the administration of the fourth dose, after the completion of the infusion, and up to five additional time points post-infusion. Plasma concentrations were measured using a validated ultra-high performance liquid chromatography assay. Individual pharmacokinetic parameters were calculated using non-compartmental analysis.

RESULTS

Four patients were enrolled to investigate the need for dosing adjustments. The average sieving coefficient for ceftaroline was 0.81 ± 0.1, indicating high filter efficiency. The average volume of distribution was 41.8 L (0.48 L/kg) and is within the previously reported range in patients with normal renal function. Non-renal clearance accounted for more than 50% of the total clearance observed in patients. The observed pharmacokinetic profiles suggest that the pharmacodynamic target for 2-log10  CFU reduction from baseline (%fT >1 mg/L of 50%) was met for each patient. Due to the impact of CRRT and non-renal clearance, dosing recommendations were derived for different ranges of effluent flow rates and adjusted body weights. For a patient with an adjusted body weight of 70 kg and receiving CRRT at an effluent flow rate of 3 L/h, a ceftaroline fosamil dosing regimen of 400 mg every 12 h is proposed.

CONCLUSION

Ceftaroline is cleared extensively in critically ill patients receiving CRRT and may impact pharmacodynamic target achievement. Dose adjustments should be based on the intensity of the CRRT regimen, patient weight, and the clinical status of the patient.

Susceptibility of clinical isolates of meticillin-resistant Staphylococcus aureus and phenotypic non-extended-spectrum β-lactamase-producing Klebsiella pneumoniae to ceftaroline in Taiwan: Results from Antimicrobial Testing Leadership and Surveillance (ATLAS) in 2012-2018 and Surveillance of Multicentre Antimicrobial Resistance in Taiwan (SMART) in 2018-2019

Data on ceftaroline (CPT) susceptibility amongst clinical isolates of meticillin-resistant Staphylococcus aureus (MRSA, n=1284) and phenotypic non-extended-spectrum β-lactamase-producing (non-ESBL-P) Klebsiella pneumoniae (n=466), obtained from the Antimicrobial Testing Leadership and Surveillance (ATLAS) programme from 2012 to 2018, and selected MRSA isolates from patients with bloodstream infections (BSIs) (n=95) from the Surveillance of Multicentre Antimicrobial Resistance in Taiwan (SMART) programme from 2018 to 2019 were analysed. The minimum inhibitory concentrations (MICs) of ATLAS isolates were determined using the broth microdilution method, whereas the MICs of SMART BSI-MRSA isolates were determined using the Etest and MicroScan system. The pharmacokinetic profiles and pharmacodynamic parameters of CPT were applied to explore the optimal dosage against infections caused by Taiwanese MRSA and K. pneumoniae isolates. Approximately 7.1% of ATLAS MRSA isolates were susceptible-dose dependent (S-DD) to CPT, and 19.7% of the non-ESBL-P K. pneumoniae isolates were not susceptible to CPT. Amongst the ATLAS MRSA isolates, the S-DD rates to CPT amongst isolates causing lower respiratory tract infections were 11.9% and 8.5% for isolates from intensive care units (ICUs) and general wards (GWs), and those causing skin and soft tissue infections (SSTIs) were 20% and 5.3% for isolates from ICUs and GWs, respectively (P=0.015). Of the SSTI MRSA isolates from GWs, 22.7% displayed vancomycin MICs >1 mg/L. Amongst 95 SMART BSI MRSA isolates, 28 (46.7%) isolates exhibited lower CPT MICs by the Etest compared with 60 isolates with CPT MICs of 1-2 mg/L by the MicroScan system. CPT 600 mg as a 2-h intravenous infusion every 8 h is suggested for treatment of infections caused by MRSA and phenotypic non-ESBL-P K. pneumoniae in Taiwan.

One Size Fits All? Application of Susceptible-Dose-Dependent Breakpoints to Pediatric Patients and Laboratory Reporting

The Clinical and Laboratory Standards Institute antimicrobial and antifungal standards define a susceptible-dose-dependent (SDD) category for certain organisms and drug combinations. Reporting MICs within the SDD category suggests that treatment success is likely with increased drug exposure. These breakpoints are based on pharmacokinetic, pharmacodynamic, and clinical outcome data from adults and not pediatric patients. This commentary aims to discuss the implications of reporting SDD interpretations for pediatric patients and recommends laboratory reporting comments.

Off-label use of ceftaroline fosamil: A systematic review

Ceftaroline fosamil is a fifth-generation cephalosporin with anti-methicillin-resistant Staphylococcus aureus (MRSA) activity. It has been approved by the EMA and FDA for the treatment of adults and children with community-acquired bacterial pneumonia (CABP) and acute bacterial skin and skin structure infections (ABSSSI). However, ceftaroline fosamil has a broad spectrum of activity, and a good safety and tolerability profile, so is frequently used off-label. The aim of this systematic review was to summarize the safety and efficacy of off-label use of ceftaroline. The review was conducted according to PRISMA guidelines. MEDLINE, EMBASE and CENTRAL databases (2010-2018) were searched using as the main term ceftaroline fosamil and its synonyms in combination with names of infectious diseases of interest. A total of 21 studies with 1901 patients were included: the most common off-label indications for ceftaroline use were bacteremia (n=595), endocarditis (n=171), osteoarticular infections (n=368), hospital-acquired pneumonia (n=115) and meningitis (n=23). The most common reasons for off-label use were persistent or recurrent infection after standard treatment or non-susceptibility to vancomycin and daptomycin. Clinical success was evaluated in 933 patients, and 724 (77%) of these reached this positive outcome. Incidence of adverse events (AEs) was reported in 11 studies. In 83 (9%) cases there were AEs related to the use of ceftaroline; the most common reported AEs were nausea, vomiting, diarrhea, rash and neutropenia. The review results show that ceftaroline may be used in clinical settings other than those currently approved; however, the use of ceftaroline in these contexts deserves further investigation.

Ceftaroline fosamil as a potential treatment option for Staphylococcus aureus community-acquired pneumonia in adults

Staphylococcus aureus (S. aureus), including methicillin-resistant S. aureus (MRSA), is an important aetiological cause of community-acquired pneumonia (CAP) and associated with significant morbidity and mortality. Empiric therapy for CAP frequently consists of β-lactam monotherapy or β-lactam/macrolide combination therapy. However, such agents are often ineffective against S. aureus and do not reflect the emergence and increasing prevalence of MRSA in the community setting. Ceftaroline fosamil is a fifth-generation parenteral cephalosporin with broad-spectrum activity against Gram-positive pathogens - such as S. aureus (including MRSA), Streptococcus pneumoniae and Streptococcus pyogenes - and typical Gram-negative pathogens, including Haemophilus influenzae and Moraxella catarrhalis. The approval of ceftaroline fosamil in the United States and Europe for the treatment of adults with moderate-to-severe CAP was based on two phase 3 trials (FOCUS 1 and 2), which demonstrated that ceftaroline fosamil was non-inferior to ceftriaxone, a standard empiric treatment for CAP, while exhibiting a comparable safety profile. Although head-to-head trials of ceftaroline fosamil versus comparators against MRSA CAP are lacking, the effectiveness of ceftaroline fosamil in subpopulations of patients not covered by phase 3 trials (e.g. those with MRSA CAP or severe renal impairment) has been demonstrated in the Clinical Assessment Program and Teflaro Utilization Registry (CAPTURE) study. As ineffective empiric therapy is associated with adverse outcomes, including mortality and increased costs, ceftaroline fosamil, with its extended spectrum of activity, is an attractive alternative to standard antibiotic CAP regimens.

Population Pharmacokinetic Modeling and Probability of Target Attainment Analyses in Asian Patients With Community-Acquired Pneumonia Treated With Ceftaroline Fosamil

Efficacy of ceftaroline fosamil, the prodrug of the active metabolite ceftaroline, was demonstrated in a phase 3 study of hospitalized Asian patients with Pneumonia Outcomes Research Team (PORT) risk class III-IV community-acquired pneumonia (NCT01371838). The objectives of the current analysis were to expand an existing ceftaroline and ceftaroline fosamil population pharmacokinetic (PK) model with data from this phase 3 study and a phase 1 study (NCT01458743) assessing ceftaroline PK in healthy Chinese volunteers and to evaluate the probability of PK/pharmacodynamic (PK/PD) target attainment (PTA) in Asian patients with community-acquired pneumonia (CAP) treated with ceftaroline fosamil. The ceftaroline plasma concentration-time course was simulated for 5000 Asian patients with CAP for different renal function subgroups using the final model. PTA was calculated for Streptococcus pneumoniae, Staphylococcus aureus, and non-extended-spectrum β-lactamase-producing Enterobacteriaceae. PTA was also evaluated for ceftaroline MIC90 values of isolates collected from Asia-Pacific surveillance studies (2012-2014) and for EUCAST and FDA/CLSI ceftaroline susceptibility break points. The final model reasonably described the ceftaroline PK. Race was not found to be a significant covariate impacting ceftaroline PK, suggesting similar ceftaroline PK in Asian and Western populations when corrected for body weight. High PTAs (90%-100%) were predicted for Asian patients with CAP treated with ceftaroline fosamil, covering MIC90 values of target CAP pathogens from the region. Similarly, >90% PTAs were predicted at EUCAST and FDA/CLSI clinical break points for these pathogens. These results support the use of the ceftaroline fosamil dosing regimens approved in Europe and the United States in Asian patients with PORT III-IV CAP.

Ceftaroline fosamil doses and breakpoints for Staphylococcus aureus in complicated skin and soft tissue infections

Objectives

To describe the pharmacokinetic/pharmacodynamic (PK/PD) modelling and microbiological data that were used to support the recent European approval of ceftaroline fosamil 600 mg q8h by 2 h intravenous (iv) infusion for patients with complicated skin and soft tissue infections (cSSTIs) caused by Staphylococcus aureus with ceftaroline MICs of 2 or 4 mg/L, and the associated EUCAST MIC breakpoint update for q8h dosing (intermediate = 2 mg/L and resistant >2 mg/L).

Methods

A population PK model for ceftaroline and ceftaroline fosamil was developed using PK data from 21 clinical studies. The final model was used to simulate PTA in patients with cSSTI receiving ceftaroline fosamil 600 mg q12h by 1 h iv infusion or 600 mg q8h by 2 h iv infusion. PTA was calculated by MIC for S. aureus PK/PD targets derived from preclinical studies (27% fT>MIC for stasis, 31% fT>MIC for 1 log10 kill and 35% fT>MIC for 2 log10 kill) and compared with S. aureus ceftaroline MIC distributions from a 2013 global surveillance study.

Results

The final population PK model based on 951 subjects adequately described ceftaroline and ceftaroline fosamil PK. High PTA (>90%) was predicted for the ceftaroline fosamil 600 mg q12h dosage regimen against S. aureus isolates with ceftaroline MICs ≤2 mg/L. Greater than 90% PTA was predicted for the ceftaroline fosamil 600 mg q8h dosage regimen against S. aureus with ceftaroline MICs ≤4 mg/L.

Conclusions

The approved ceftaroline fosamil dosage regimens for adults and adolescents with cSSTI achieve high PTA against S. aureus at the associated EUCAST breakpoints.

Mechanisms of action and antimicrobial activity of ceftobiprole

Ceftobiprole, a novel last generation parenteral cephalosporin, has an extended spectrum of activity, notably against methicillin-resistant Staphylococcus aureus (MRSA), ampicillin-susceptible enterococci, penicillin-resistant pneumococci, Enterobacterales and susceptible Pseudomonas aeruginosa. It exerts an inhibitory action on essential peptidoglycan transpeptidases, interfering with cell wall synthesis. The inhibitory action of ceftobiprole through binding to abnormal PBPs like PBP2a in methicillin-resistant staphylococci and PBP2b and PBP2x in the case of β-lactam-resistant pneumococci, ultimately leads to rapid bacterial cell death. In the case of Enterobacterales, ceftobiprole retains activity against narrow spectrum β-lactamases but is hydrolysed by their extended-spectrum counterparts, overexpressed Amp C, and carbapenemases. It is also affected by certain efflux pumps from P. aeruginosa. For anaerobic bacteria, ceftobiprole is active against Gram-positive Clostridioides difficile and Peptococcus spp. and Gram-negative Fusobacterium nucleatum but not against Bacteroides group or other anaerobic Gram-negatives. In in vitro studies, a low propensity to select for resistant subpopulations has been demonstrated. Currently, ceftobiprole is approved for the treatment of community-acquired pneumonia and hospital-acquired pneumonia with the exception of ventilator-associated pneumonia. Ceftobiprole's place in therapy appears to lie mainly in its combined activity against Gram-positive organisms, such as S. aureus and S. pneumoniae alongside that against Gram-negative organisms such as P. aeruginosa.

Pharmacokinetics of single-dose ceftaroline fosamil in children with cystic fibrosis

BACKGROUND

Single-dose pharmacokinetics (PK) and safety of ceftaroline fosamil with population pharmacokinetic/pharmacodynamic (PK/PD) modeling for staphylococcal pneumonia was performed in children with CF.

METHODS

Subjects between 6 and 18 years old were evaluated in this phase 1, open-label, single-dose, prospective study using 10 mg/kg (up to 600 mg). Non-compartmental analysis and population-based PK analyses with Monte Carlo simulation (for doses 8-20 mg/kg every 8 h, infused over 1-4 h) were conducted.

RESULTS

A total of 20 subjects were enrolled. The median age and weight were 12 yr (range 6.3-17.4) and 38.7 kg (range 17.8-94.3), respectively. A 3-compartment linear model incorporating age and weight provided the best fit for the data. Comparing children 6 to <12 years to those 12 to <18 years, the mean posthoc Bayesian parameter estimates for total volume of distribution (VT ) were 0.32 ± 0.05 L/kg versus 0.32 ± 0.04 L/kg, P = 0.7; and total Clearance (CLT ), 0.50 ± 0.10 L/h/kg versus 0.30 ± 0.07 L/h/kg, P = 0.001. Using susceptibility data from pediatric MRSA lower respiratory tract isolates, 8 mg/kg (maximum of 1000 mg per dose) infused over 1 h every 8 h achieved free-drug plasma concentrations above the minimum inhibitory concentration for ≥60% of the dosing interval in at least 95% of virtual subjects.

CONCLUSIONS

Since children with CF have increased ceftaroline CL compared with published data from non-CF children; greater dosages may be required in children with CF to achieve adequate exposure in the treatment of MRSA pneumonia. Pharmacodynamic-based dosing predicts that dosing should also be based on the patient's MRSA MIC.

Ceftaroline efficacy against high-MIC clinical Staphylococcus aureus isolates in an in vitro hollow-fibre infection model

Objectives

The current CLSI and EUCAST clinical susceptible breakpoint for 600 mg q12h dosing of ceftaroline (active metabolite of ceftaroline fosamil) for Staphylococcus aureus is ≤1 mg/L. Efficacy data for S. aureus infections with ceftaroline MIC ≥2 mg/L are limited. This study was designed to generate in-depth pharmacokinetic/pharmacodynamics (PK/PD) understanding of S. aureus isolates inhibited by ≥ 2 mg/L ceftaroline using an in vitro hollow-fibre infection model (HFIM).

Methods

The PK/PD target of ceftaroline was investigated against 12 diverse characterized clinical MRSA isolates with ceftaroline MICs of 2 or 4 mg/L using q8h dosing for 24 h. These isolates carried substitutions in the penicillin-binding domain (PBD) and/or the non-PBD. Additionally, PD responses of mutants with ceftaroline MICs ranging from 2 to 32 mg/L were evaluated against the mean 600 mg q8h human-simulated dose over 72 h.

Results

The mean stasis, 1 log10-kill and 2 log10-kill PK/PD targets were 29%, 32% and 35% f T>MIC, respectively. In addition, these data suggest that the PK/PD target for MRSA is not impacted by the presence of substitutions in the non-PBD commonly found in isolates with ceftaroline MIC values of ≤ 2 mg/L. HFIM studies with 600 mg q8h dosing demonstrated a sustained long-term bacterial suppression for isolates with ceftaroline MICs of 2 and 4 mg/L.

Conclusions

Overall, efficacy was demonstrated against a diverse collection of clinical isolates using HFIM indicating the utility of 600 mg ceftaroline fosamil for S. aureus isolates with MIC ≤4 mg/L using q8h dosing.

Pharmacodynamics of minocycline against Acinetobacter baumannii studied in a pharmacokinetic model of infection

Minocycline (MNO) is an old antibiotic that may have an important role in the treatment of multidrug-resistant Gram-negative bacterial infections as the burden of such infections increases. In this study, a single-compartment dilutional pharmacokinetic model was used to determine the relationship between MNO exposure and antibacterial effect, including the risk of resistance emergence, against strains of Acinetobacter baumannii. The mean ± standard deviation area under the unbound drug concentration-time curve to minimum inhibitory concentration ratio (fAUC/MIC) associated with a 24-h bacteriostatic effect was 16.4 ± 2.6 and with a -1 log reduction in bacterial load at 24 h was 23.3 ± 3.7. None of the strains reached a -2 log reduction over 48 h. Changes in population profiles were noted for two of the three strains studied, especially at fAUC/MIC ratios of >5-15. A reasonable translational pharmacodynamic target for MNO against A. baumannii could be an fAUC/MIC of 20-25. However, if maximum standard 24-h doses of intravenous MNO are used (400 mg/day), many strains would be exposed to MNO concentrations likely to change population profiles and associated with the emergence of resistance. Either MNO combination therapy or an increased MNO dose (>400 mg/day) should be considered when treating A. baumannii infections.

Ceftaroline Fosamil: A Review in Complicated Skin and Soft Tissue Infections and Community-Acquired Pneumonia

Intravenous ceftaroline fosamil (Zinforo™), a prodrug that is rapidly converted to its active metabolite ceftaroline, is approved for use in adults and children (from 2 months of age) with complicated skin and soft tissue infections (cSSTIs) or community-acquired pneumonia (CAP). In several multinational trials, ceftaroline fosamil was an effective and generally well tolerated treatment in adult and paediatric patients with cSSTIs or CAP. In the phase 3 CANVAS trials, ceftaroline fosamil treatment was noninferior to vancomycin plus aztreonam in adults with cSSTIs. Based on a meta-analysis of three similarly designed, phase 3 trials (FOCUS 1, FOCUS 2 and an Asian trial), ceftaroline fosamil treatment was superior to ceftriaxone in adults with CAP of Pneumonia Outcomes Research Teams (PORT) risk class III or IV. Ceftaroline fosamil was also associated with high clinical cure rates in hospitalized children (aged 2 months to 17 years) with cSSTIs or CAP. With its broad spectrum of in vitro activity against clinically relevant Gram-positive [including methicillin-resistant Staphylococcus aureus (MRSA) and drug-resistant Streptococcus pneumoniae isolates] and Gram-negative pathogens implicated in cSSTIs and CAP, ceftaroline fosamil is an important treatment option for cSSTI and CAP in adults and children from the age of 2 months.

Penetration of Ceftaroline into the Epithelial Lining Fluid of Healthy Adult Subjects

Ceftaroline, the active metabolite of the prodrug ceftaroline fosamil, is a cephalosporin with bactericidal activity against Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA). This study aimed to (i) evaluate ceftaroline concentrations in human plasma and epithelial lining fluid (ELF) and (ii) develop a population pharmacokinetic (PK) model for plasma and ELF to be used in PK/pharmacodynamic (PD) target attainment simulations. Ceftaroline concentrations in ELF and plasma at steady state (day 4) were measured in healthy adult subjects for two dosages: 600 mg every 12 h (q12h) and 600 mg every 8 h (q8h). Both were well tolerated with no serious adverse events. The penetration of free ceftaroline into ELF, assuming 20% protein binding in plasma and no protein binding in ELF, was ≈23%. The population PK model utilized a two-compartment model for both ceftaroline fosamil and ceftaroline. Goodness-of-fit criteria revealed the model was consistent with observed data and no systematic bias remained. At 600 mg q12h and a MIC of 1 mg/liter, 98.1% of simulated patients would be expected to achieve a target free drug concentration above the MIC (fT>MIC) in plasma of 42%, and in ELF 81.7% would be expected to achieve a target fT>MIC of 17%; at 600 mg q8h, 100% were predicted to achieve an fT>MIC in plasma of 42% and 94.7% to achieve an fT>MIC of 17% in ELF. The literature and data suggest the 600 mg q12h dose is adequate for MICs of ≤1 mg/liter. There is a need for clinical data in patients with MRSA pneumonia and data to correlate PK/PD relationships in ELF with clinical outcomes.

Single- and Repeated-Dose Pharmacokinetics of Ceftaroline in Plasma and Soft Tissues of Healthy Volunteers for Two Different Dosing Regimens of Ceftaroline Fosamil

Ceftaroline fosamil (CPT-F) is currently approved for use for the treatment of complicated skin and soft tissue infections and community-acquired pneumonia at 600 mg twice daily (q12h), but other dosing regimens are under evaluation. To date, very limited data on the soft tissue pharmacokinetics (PK) of the active compound, ceftaroline (CPT), are available. CPT concentrations in the plasma, muscle, and subcutis of 12 male healthy volunteers were measured by microdialysis after single and repeated intravenous administration of 600 mg CPT-F q12h or three times daily (q8h) in two groups of 6 subjects each. Relevant PK and PK/pharmacodynamic (PD) parameters were calculated and compared between groups. In plasma, the area under the concentration-time curve (AUC) from 0 to 24 h for total CPT and the cumulative percentage of the dosing interval during which the free drug concentrations exceeded the MIC (fTMIC) for unbound CPT for the currently established threshold of 1 mg/liter were significantly higher in the group receiving CPT-F q8h. Exposure to free drug in soft tissues was higher in the group receiving CPT-F q8h, but high interindividual variability in relevant PK parameters was observed. The mean ratios of the AUC from time zero to the end of the dosing interval (AUC0-τ) for free CPT in soft tissues and the AUC0-τ for the calculated free fraction in plasma at steady state ranged from 0.66 to 0.75. Administration of CPT-F q8h led to higher levels of drug exposure in all investigated compartments. When MIC values above 1 mg/liter were assumed, the calculated fTMIC after dosing q12h was markedly lower than that after dosing q8h. The clinical implications of these differences are discussed in light of recently completed clinical phase III and PK/PD studies.

Bacteremia due to Methicillin-Resistant Staphylococcus aureus: New Therapeutic Approaches

This article reviews recent clinical evidence for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. Vancomycin remains the initial antibiotic of choice for the treatment of patients with MRSA bacteremia and endocarditis due to isolates with vancomycin minimum inhibitory concentration ≤2 μg/mL, whereas daptomycin is an effective alternative, and ceftaroline seems promising. Treatment options for persistent MRSA bacteremia or bacteremia due to vancomycin-intermediate or vancomycin-resistant strains include daptomycin, ceftaroline, and combination therapies. There is a critical need for high-level evidence from clinical trials to allow optimally informed decisions in the treatment of MRSA bacteremia and endocarditis.

Differences in the pharmacodynamics of ceftaroline against different species of Enterobacteriaceae studied in an in vitro pharmacokinetic model of infection

OBJECTIVES

Dose-ranging experiments were performed to study the pharmacodynamics of ceftaroline against Enterobacteriaceae.

METHODS

A range of fT>MIC values (0%-100%) were simulated over 96 h using a single-compartment dilutional in vitro pharmacokinetic model using Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Citrobacter koseri and Serratia marcescens (n = 16). Antibacterial effect was assessed by change in viable count and population profiles by growth on ceftaroline MIC ×2, ×4 and ×8 agar plates. The fT>MIC (%) was related to antibacterial effect using a sigmoid Emax model.

RESULTS

The 24 h bacteriostatic effect fT>MIC was 39.7% ± 15.7% and 43.2% ± 15.6% for a -1 log drop for all strains. E. coli required lower exposures than K. pneumoniae, i.e. 24 h fT>MIC for a -3 log drop in viable count was 40.0% ± 9.6% and 84.8% ± 15.2% for K. pneumoniae. Similarly at 96 h, fT>MIC was >100% for K. pneumoniae (for four of five strains), 27.2%-66.2% for E. coli and 16.2%-86.6% for P. mirabilis. Strain-to-strain variation within species in the fT>MIC for static and cidal effect was marked; the 24 h bacteriostatic range was 14.1%-73.4% for P. mirabilis, 34.2%-44.6% for E. coli and 42.2%-62.5% for K. pneumoniae. Changes in ceftaroline population analysis profiles were observed with E. coli, K. pneumoniae and C. koseri, especially at fT>MIC values just below the bacteriostatic effect exposures.

CONCLUSIONS

The pharmacodynamics of ceftaroline against the species within the Enterobacteriaceae group are different. K. pneumoniae requires higher drug exposures than E. coli, and P. mirabilis strains are highly variable, which may have important clinical correlates. Translational extrapolations from preclinical observations using E. coli to other Enterobacteriaceae species may not be optimal.

Potential of Staphylococcus aureus isolates carrying different PBP2a alleles to develop resistance to ceftaroline

OBJECTIVES

Infections caused by MRSA continue to cause significant morbidity worldwide. Ceftaroline (the active metabolite of the prodrug ceftaroline fosamil) is a cephalosporin that possesses activity against MRSA due to its having high affinity for PBP2a while maintaining activity against the other essential PBPs. PBP2a sequence variations, including some outside of the transpeptidase binding pocket, impact ceftaroline susceptibility. This study evaluated the potential of ceftaroline to select for resistant Staphylococcus aureus clones in isolates containing a variety of PBP2a alleles and with a range of ceftaroline MIC values from different MLST lineages.

METHODS

Direct resistance selection experiments were performed by plating 20 S. aureus isolates (18 MRSA and 2 MSSA) on agar plates containing increasing concentrations of ceftaroline. Colonies that emerged were tested by standard broth microdilution for changes in ceftaroline susceptibility and genetically characterized.

RESULTS

The frequency of spontaneous resistance to ceftaroline was low for all isolates and, although resistant variants were not obtained on plates containing ≥4-fold the MIC of ceftaroline, six MRSA isolates had a small number of colonies emerge on plates containing 2-fold the MIC of ceftaroline and had a 2- to 8-fold elevation of the ceftaroline MIC, while also impacting the MIC of methicillin compared with the parental isolate. Additional PBP2a mutations located in the ceftaroline-binding pocket, Y446N or A601S, were observed in several of the resistant isolates.

CONCLUSIONS

These studies demonstrate that there is a low risk of generating ceftaroline-resistant MRSA isolates, which appears independent of any pre-existing variation in the PBP2a protein sequence or initial ceftaroline MIC.

Pharmacokinetic and Pharmacodynamic Analyses of Ceftaroline in Adults with Cystic Fibrosis

STUDY OBJECTIVE

To evaluate the pharmacokinetics and pharmacodynamics of ceftaroline in adults with cystic fibrosis (CF).

DESIGN

Open-label, single-center, prospective study.

SETTING

University-affiliated teaching institution.

PATIENTS

Eight patients with a diagnosis of CF and a history of methicillin-resistant Staphylococcus aureus who were treated with ceftaroline between November 2013 and September 2014.

INTERVENTION

All patients received at least three doses of intravenous ceftaroline 600 mg every 12 hours, administered as a 60-minute infusion, to achieve steady-state concentrations before blood sample collection. After an interim analysis of the first four patients' pharmacokinetic data, the remaining four patients received a change in dosage of ceftaroline to 600 mg every 8 hours.

MEASUREMENTS AND MAIN RESULTS

Patients' blood samples were collected at two time points, 2 and 6 hours after infusion initiation, after administration of at least three doses of ceftaroline. Serum ceftaroline concentrations were determined by using a validated mass spectrometry, with a lower limit of detection of 20 ng/ml. These ceftaroline concentrations were used to estimate patient-specific pharmacokinetic parameters, and 10,000-patient Monte Carlo simulations were performed to determine the pharmacodynamic probability of target attainment (PTA) for ceftaroline in adults with CF. A PTA of 90% or higher for the desired pharmacodynamic target was considered adequate. The PTA for 60% or higher of the dosing interval during which free (unbound) drug concentrations exceed the minimum inhibitory concentration (%fT > MIC) was simulated for various MICs. Compared with values previously reported in other populations, the volume of distribution was increased in the study patients, and the estimated half-life was shorter. Monte Carlo simulations revealed that a dose of ceftaroline 600 mg every 8 hours, infused over 60 minutes, maintained a higher than 90% PTA for %fT > MIC of 60% or higher for an MIC at the susceptibility breakpoint of 1 mg/L.

CONCLUSION

The pharmacokinetics of ceftaroline is altered in adults with CF, which suggests the need for modified dosing in this patient population to achieve adequate %fT > MIC. A dosage of intravenous ceftaroline 600 mg every 8 hours administered as a 60-minute infusion should be considered to achieve 60% fT > MIC.

In vitro activity of ceftaroline against bacterial pathogens isolated from skin and soft tissue infections in Europe, Russia and Turkey in 2012: results from the Assessing Worldwide Antimicrobial Resistance Evaluation (AWARE) surveillance programme

OBJECTIVES

The objective of this study was to analyse antimicrobial susceptibility testing data generated by the Assessing Worldwide Antimicrobial Resistance Evaluation (AWARE) global surveillance programme for pathogens causing skin and soft tissue infections (SSTIs) in European countries in 2012.

METHODS

Confirmation of pathogen identity by MALDI-TOF and antimicrobial susceptibility testing following the CLSI broth microdilution method were performed by a central laboratory.

RESULTS

Using CLSI breakpoint criteria, ceftaroline was active against MSSA (n = 1116; MIC90, 0.25 mg/L; 99.8% susceptible), MRSA (n = 1467; MIC90, 1 mg/L; 92.2% susceptible) and Streptococcus pyogenes (n = 312; MIC90, 0.008 mg/L; 100% susceptible). By CLSI interpretative criteria, two S. aureus isolates (2/2583, 0.08%) were ceftaroline resistant (MIC, ≥4 mg/L) and 114 isolates (114/2583, 4.4%) were ceftaroline intermediate (2 mg/L). By EUCAST interpretative criteria (MIC, >1 mg/L), 4.5% (116/2583) of S. aureus isolates were ceftaroline resistant. Most ceftaroline-non-susceptible isolates (81.0%, 94/116) were from Russia, Turkey, Italy and Hungary. Ceftaroline susceptibility was equal to or exceeded 99% for S. aureus isolates submitted by 7 of 17 countries. Against Escherichia coli (n = 349), Klebsiella pneumoniae (n = 215), Klebsiella oxytoca (n = 74) and Proteus mirabilis (n = 121), ceftaroline activity was dependent upon ESBL production. For ESBL-negative E. coli, K. pneumoniae, K. oxytoca and P. mirabilis, 87.5% (MIC90, 1 mg/L), 92.3% (MIC90, 0.5 mg/L), 93.2% (MIC90, 0.5 mg/L) and 85.1% (MIC90, 2 mg/L) of isolates were susceptible to ceftaroline, respectively.

CONCLUSIONS

Ceftaroline demonstrated potent in vitro activity against a contemporary collection of bacterial pathogens from patients with SSTIs in European countries, Russia and Turkey. Surveillance programmes such as AWARE are essential to global efforts to improve antimicrobial stewardship.

Suppression of Emergence of Resistance in Pathogenic Bacteria: Keeping Our Powder Dry, Part 1

We are in a crisis of bacterial resistance. For economic reasons, most pharmaceutical companies are abandoning antimicrobial discovery efforts, while, in health care itself, infection control and antibiotic stewardship programs have generally failed to prevent the spread of drug-resistant bacteria. At this point, what can be done? The first step has been taken. Governments and international bodies have declared there is a worldwide crisis in antibiotic drug resistance. As discovery efforts begin anew, what more can be done to protect newly developing agents and improve the use of new drugs to suppress resistance emergence? A neglected path has been the use of recent knowledge regarding antibiotic dosing as single agents and in combination to minimize resistance emergence, while also providing sufficient early bacterial kill. In this review, we look at the data for resistance suppression. Approaches include increasing the intensity of therapy to suppress resistant subpopulations; developing concepts of clinical breakpoints to include issues surrounding suppression of resistance; and paying attention to the duration of therapy, which is another important issue for resistance suppression. New understanding of optimizing combination therapy is of interest for difficult-to-treat pathogens like Pseudomonas aeruginosa, Acinetobacter spp., and multidrug-resistant (MDR) Enterobacteriaceae. These lessons need to be applied to our old drugs to preserve them as well and need to be put into national and international antibiotic resistance strategies. As importantly, from a regulatory perspective, new chemical entities should have a corresponding resistance suppression plan at the time of regulatory review. In this way, we can make the best of our current situation and improve future prospects.

Susceptibility testing challenges with ceftaroline, MRSA and a 1 mg/L breakpoint

OBJECTIVES

A 1 mg/L susceptibility breakpoint for ceftaroline and staphylococci is universally agreed; EUCAST counts MIC >1 mg/L as resistant whereas CLSI and FDA count 2 mg/L as intermediate and >2 mg/L as resistant. We investigated whether routine diagnostic tests reliably distinguish MICs of 1 versus 2 mg/L.

METHODS

Thirty-five UK laboratories collected Staphylococcus aureus isolates and performed tests with 5 μg (as EUCAST) or 30 μg (as CLSI) discs and either confluent growth on Mueller-Hinton agar (as EUCAST and CLSI) or semi-confluent growth on Iso-Sensitest agar (as BSAC). They also ran Etests for MRSA. Reference MICs were determined centrally by CLSI and BSAC agar dilution.

RESULTS

We obtained paired local disc and central MIC results for 1607 S. aureus (33% MRSA). EUCAST's zone breakpoint recognized 56% of isolates found resistant in MIC tests, but the positive predictive value (PPV) for resistance was 11.0%; corresponding proportions by CLSI testing were 28.0% and 13.4%. The BSAC disc method detected 25% of resistant isolates, with a PPV of 18.2%. Essential agreement, ±1 dilution, of local Etests and central agar MICs was >95%, but only 20% of the isolates found non-susceptible by agar dilution were found non-susceptible by Etest and vice versa. Review for isolates with the modal MIC (0.25 mg/L) indicated that the same laboratories reported large or small zones irrespective of disc and method, implying systematic bias.

CONCLUSIONS

MRSA with ceftaroline MICs of 1 and 2 mg/L were poorly discriminated by routine methods. Solutions lie in greater standardization, automation or dosages justifying a higher breakpoint.

A critical review on the clinical pharmacokinetics, pharmacodynamics, and clinical trials of ceftaroline

Only a parenteral formulation of ceftaroline is commercially available, and the prodrug, ceftaroline fosamil, is hydrolyzed quickly and completely upon intravenous administration. Ceftaroline is relatively minimally bound to plasma proteins (15-28 %), with a volume of distribution of 30-40 L. Ceftaroline undergoes minimal metabolism and does not appear to be a cytochrome P450 substrate. Its renal clearance (e.g. 4-7 L/h after multiple dosing) approximates glomerular filtration rate, with a terminal half-life of ~2.6 h in healthy subjects. The pharmacokinetics of ceftaroline have been described thoroughly in clinical investigations primarily conducted by the manufacturer. Despite its indications for treating skin and skin structure infections (SSSI) or community-acquired pneumonia (CAP), some studies that contributed data to the final drug labelling were conducted only in healthy volunteers. A significant amount of data have been contributed by the drug maker, and the overall quality of the pharmacodynamics and clinical data, based on our critical analysis provided in this review, is strong. Ceftaroline can be considered as a therapeutic alternative for complicated SSSI and CAP (Pneumonia Outcome Research Team Class III-IV). The current dosing regimen of ceftaroline 600 mg intravenously every 12 h appears sufficient to establish pharmacokinetic-pharmacodynamic relationships and achieve optimal clinical efficacy. More clinical studies are needed to define the place of ceftaroline in therapy for SSSI, CAP, and other indications such as osteomyelitis, endocarditis, and other types of pneumonia. Moreover, continued development in population modelling incorporating more patient-specific data would allow further analysis to identify intrinsic and extrinsic factors that influence the pharmacokinetics of ceftaroline in humans.

Molecular characterization of MRSA isolates bracketing the current EUCAST ceftaroline-susceptible breakpoint for Staphylococcus aureus: the role of PBP2a in the activity of ceftaroline

OBJECTIVES

The objectives of this study were to characterize contemporary MRSA isolates and understand the prevalence and impact of sequence variability in PBP2a on ceftaroline susceptibility.

METHODS

A total of 184 MRSA isolates collected from 28 countries were collected and characterized.

RESULTS

WT PBP2a proteins were found in MRSA distributed evenly over the ceftaroline MIC range of 0.5-2 mg/L (n=56). PBP2a variations found in 124 isolates fell into two categories: (i) 12 isolates contained a substitution in the transpeptidase pocket located in the penicillin-binding domain and exhibited significantly decreased ceftaroline susceptibility (typically 8 mg/L); and (ii) isolates with substitutions in the non-penicillin-binding domain (nPBD) in a region proposed to be functionally important for cell wall biogenesis. The majority (71%) of isolates containing only nPBD variations were inhibited by 2 mg/L ceftaroline, 23% by ≤1 mg/L and 6% by 4 mg/L. These data suggest that the WT MRSA distribution extends beyond the current EUCAST and CLSI susceptible breakpoints and includes isolates inhibited by 2 mg/L ceftaroline. SCCmec type IV was the predominant type in the ceftaroline-susceptible population (68%), whereas it only represented 6% of the non-susceptible population. The variations of MLST lineages were fewer among the non-susceptible group.

CONCLUSIONS

This study suggests that MRSA populations with a WT PBP2a and those with nPBD variations overlap significantly and that PBP2a sequence-independent factors contribute to ceftaroline susceptibility. Whereas characterization of isolates with a ceftaroline MIC of 2 mg/L enriched for isolates with nPBD variations, it was not a discrete population. In contrast, the rare isolates containing a substitution in the transpeptidase-binding pocket were readily differentiated.

Pharmacokinetics of ceftaroline in normal body weight and obese (classes I, II, and III) healthy adult subjects

The pharmacokinetic profile of ceftaroline has not been well characterized in obese adults. The purpose of this study was to evaluate the pharmacokinetics of ceftaroline in 32 healthy adult volunteers aged 18 to 50 years in the normal, overweight, and obese body size ranges. Subjects were evenly assigned to 1 of 4 groups based on their body mass index (BMI) and total body weight (TBW) (ranges, 22.1 to 63.5 kg/m(2) and 50.1 to 179.5 kg, respectively). Subjects in the lower-TBW groups were matched by age, sex, race/ethnicity, and serum creatinine to the upper-BMI groups. Serial plasma and urine samples were collected over 12 h after the start of the infusion, and the concentrations of ceftaroline fosamil (prodrug), ceftaroline, and ceftaroline M-1 (inactive metabolite) were assayed. Noncompartmental and population pharmacokinetic analyses were used to evaluate the data. The mean plasma ceftaroline maximum concentration and area under the curve were ca. 30% lower in subjects with a BMI of ≥40 kg/m(2) compared to those <30 kg/m(2). A five-compartment pharmacokinetic model with zero-order infusion and first-order elimination optimally described the plasma concentration-time profiles of the prodrug and ceftaroline. Estimated creatinine clearance (eCLCR) and TBW best explained ceftaroline clearance and volume of distribution, respectively. Although lower ceftaroline plasma concentrations were observed in obese subjects, Monte Carlo simulations suggest the probability of target attainment is ≥90% when the MIC is ≤1 μg/ml irrespective of TBW or eCLCR. No dosage adjustment for ceftaroline appears to be necessary based on TBW alone in adults with comparable eCLCR. Confirmation of these findings in infected obese patients is necessary to validate these findings in healthy volunteers. (This study has been registered at ClinicalTrials.gov under registration no. NCT01648127.).

The Tipper-Strominger Hypothesis and Triggering of Allostery in Penicillin-Binding Protein 2a of Methicillin-Resistant Staphylococcus aureus (MRSA)

The transpeptidases involved in the synthesis of the bacterial cell wall (also known as penicillin-binding proteins, PBPs) have evolved to bind the acyl-D-Ala-D-Ala segment of the stem peptide of the nascent peptidoglycan for the physiologically important cross-linking of the cell wall. The Tipper-Strominger hypothesis stipulates that β-lactam antibiotics mimic the acyl-D-Ala-D-Ala moiety of the stem and, thus, are recognized by the PBPs with bactericidal consequences. We document that this mimicry exists also at the allosteric site of PBP2a of methicillin-resistant Staphylococcus aureus (MRSA). Interactions of different classes of β-lactam antibiotics, as mimics of the acyl-D-Ala-D-Ala moiety at the allosteric site, lead to a conformational change, across a distance of 60 Å to the active site. We directly visualize this change using an environmentally sensitive fluorescent probe affixed to the protein loops that frame the active site. This conformational mobility, documented in real time, allows antibiotic access to the active site of PBP2a. Furthermore, we document that this allosteric trigger enables synergy between two different β-lactam antibiotics, wherein occupancy at the allosteric site by one facilitates occupancy by a second at the transpeptidase catalytic site, thus lowering the minimal-inhibitory concentration. This synergy has important implications for the mitigation of facile emergence of resistance to these antibiotics by MRSA.

Pre-Use Susceptibility to Ceftaroline in Clinical Staphylococcus aureus Isolates from Germany: Is There a Non-Susceptible Pool to be Selected?

Ceftaroline is a new cephalosporin active against Methicillin-resistant Staphylococcus aureus (MRSA). Based on a representative collection of clinical S. aureus isolates from Germany, supplemented with isolates of clonal lineages ST228 and ST239, we demonstrate the in-vitro susceptibility towards ceftaroline prior to its introduction into clinical use for a total of 219 isolates. Susceptibility testing was performed by broth microdilution, disc diffusion and Etest, respectively. Results were interpreted according to EUCAST guidelines and showed considerable variance in dependence on clonal affiliation of the isolates tested. Among isolates of widespread hospital-associated lineages we found a high proportion of clinical isolates with MICs close to the EUCAST breakpoint (MIC50/90 1.0/1.5 mg/L); currently, interpretation of these "borderline" MICs is complicated by a lack of concordant susceptibility testing methods and reasonable breakpoint determination. Isolates of clonal lineages ST228 and ST239 demonstrated increased MIC50/90 values of 2.5/3.33 mg/L. Sequencing of mecA revealed no association of resistance to a specific mecA polymorphism, but rather reveals two regions in the non-penicillin-binding domain of PbP2a which displayed different combinations of mutations putatively involved in resistance development. This study provides national baseline data to (i) adjust susceptibility testing methods and current breakpoints to clinical and epidemiological requirements, (ii) evaluate current breakpoints with respect to therapeutic outcome and (iii) monitor further resistance evolution.

Ceftaroline in the management of complicated skin and soft tissue infections and community acquired pneumonia

Ceftaroline is a new parenteral cephalosporin approved by the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) for the treatment of complicated skin and soft tissue infections (cSSTIs) including those due to methicillin-resistant Staphylococcus aureus (MRSA), and community-acquired pneumonia (CAP). Ceftaroline has broad-spectrum activity against gram-positive and gram-negative bacteria and exerts its bactericidal effects by binding to penicillin-binding proteins (PBPs), resulting in inhibition of bacterial cell wall synthesis. It binds to PBP 2a of MRSA with high affinity and also binds to all six PBPs in Streptococcus pneumoniae. In in vitro studies, ceftaroline demonstrated potent activity against Staphylococcus aureus (including MRSA and vancomycin-intermediate isolates), Streptococcus pneumoniae (including multidrug resistant isolates), Haemophilus influenzae, Moraxella catarrhalis, and many common gram-negative pathogens, excluding extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae and Pseudomonas aeruginosa. In Phase II and Phase III clinical trials, ceftaroline was noninferior to its comparator agents and demonstrated high clinical cure rates in the treatment of cSSTIs and CAP. It demonstrated favorable outcomes in patients treated for both regulatory-approved indications and unlicensed indications in a retrospective analysis. Ceftaroline is a safe and effective option for treatment in specific patient populations in which its efficacy and safety have been proven. This article reviews the challenges in the treatment of cSSTI and CAP, ceftaroline and its microbiology, pharmacology, efficacy, and safety data which support its use in treatment of cSSTIs and CAP.

Ceftaroline fosamil salvage therapy: an option for reduced-vancomycin-susceptible MRSA bacteraemia

OBJECTIVES

To examine the activity of ceftaroline against reduced-vancomycin-susceptible MRSA isolates.

METHODS

One-hundred and three MRSA blood culture isolates (predominantly ST239-MRSA-III), with varying vancomycin phenotypes, had their ceftaroline MICs determined by broth microdilution and MIC Evaluator strip (Oxoid-Thermo Fisher). Statistical analyses were performed that examined relationships with vancomycin and daptomycin MICs. Mutations in mecA were also examined.

RESULTS

All 103 isolates (including 60 heteroresistant vancomycin-intermediate Staphylococcus aureus/vancomycin-intermediate S. aureus) were susceptible to ceftaroline, with one isolate displaying heteroresistance that may be related to a mecA mutation. Higher ceftaroline MICs were associated with vancomycin-susceptible S. aureus isolates.

CONCLUSIONS

This study highlights that ceftaroline fosamil is an option for salvage therapy based on in vitro activity.

Ceftaroline: clinical and microbiology experience with focus on methicillin-resistant Staphylococcus aureus after regulatory approval in the USA

Ceftaroline fosamil was approved in 2010 by the United States Food and Drug Administration (USA-FDA) for the treatment of patients with acute bacterial skin and skin structure infections (ABSSSIs) and community-acquired bacterial pneumonia (CABP). After approval, several studies and case reports have described the postmarketing clinical experience with ceftaroline in ABSSSIs and CABP and in patients with invasive methicillin-resistant Staphylococcus aureus (MRSA) infections, many of whom had failed prior antibiotics. Successful clinical outcomes observed among the majority of these patients were supported by preapproval and postapproval in vitro surveillance of ceftaroline activity using breakpoint criteria that have been harmonized between the USA-FDA and CLSI. MIC90 values/percentage of strains susceptible to ceftaroline has remained stable over the period 2009-2012. Taken together, these postapproval studies support the use of ceftaroline for ABSSSI as well as CABP. Importantly, these data also suggest that ceftaroline can be effective in patients with serious invasive MRSA infections who have failed other therapies.

In vitro activity of human-simulated epithelial lining fluid exposures of ceftaroline, ceftriaxone, and vancomycin against methicillin-susceptible and -resistant Staphylococcus aureus

Staphylococcus aureus, including methicillin-susceptible (MSSA) and -resistant (MRSA) strains, is an important pathogen of bacterial pneumonia. As antibiotic concentrations at the site of infection are responsible for killing, we investigated the activity of human-simulated epithelial lining fluid (ELF) exposures of three antibiotics (ceftaroline, ceftriaxone, and vancomycin) commonly used for treatment of S. aureus pneumonia. An in vitro pharmacodynamic model was used to simulate ELF exposures of vancomycin (1 g every 12 h [q12h]), ceftaroline (600 mg q12h and q8h), and ceftriaxone (2 g q24h and q12h). Four S. aureus isolates (2 MSSA and 2 MRSA) were evaluated over 72 h with a starting inoculum of ∼ 10(6) CFU/ml. Time-kill curves were constructed, and microbiological response (change in log10 CFU/ml from 0 h and the area under the bacterial killing and regrowth curve [AUBC]) was assessed in duplicate. The change in 72-h log10 CFU/ml was largest for ceftaroline q8h (reductions of >3 log10 CFU/ml against all strains). This regimen also achieved the lowest AUBC against all organisms (P < 0.05). Vancomycin produced reliable bacterial reductions of 0.9 to 3.3 log10 CFU/ml, while the activity of ceftaroline q12h was more variable (reductions of 0.2 to 2.3 log10 CFU/ml against 3 of 4 strains). Both regimens of ceftriaxone were poorly active against MSSA tested (0.1 reduction to a 1.8-log10 CFU/ml increase). Against these S. aureus isolates, ELF exposures of ceftaroline 600 mg q8h exhibited improved antibacterial activity compared with ceftaroline 600 mg q12h and vancomycin, and therefore, this q8h regimen deserves further evaluation for the treatment of bacterial pneumonia. These data also suggest that ceftriaxone should be avoided for S. aureus pneumonia.

Pharmacokinetic and pharmacodynamic evaluation of ceftaroline fosamil

INTRODUCTION

Ceftaroline fosamil is a 5th generation cephalosporin with an in vitro spectrum of activity including Streptococcus agalactiae, penicillin- and cephalosporin-resistant S. pneumoniae, S. pyogenes, methicillin-susceptible S. aureus and methicillin-resistant S. aureus, Haemophilus influenzae, Klebsiella oxytoca, K. pneumoniae and Moraxella catarrhalis. It is currently approved by the FDA for the treatment of acute bacterial skin and skin structure infections (ABSSSI) and community-acquired bacterial pneumonia (CABP) in adults.

AREAS COVERED

This review covers the mechanism of action; bacterial resistance; pharmacokinetic characteristics in various patient populations; pharmacodynamic data in animal and in vitro models as well as human studies; efficacy observed in clinical trials for ABSSSI and CABP; and adverse effects.

EXPERT OPINION

Ceftaroline provides in vitro bactericidal activity against methicillin-, vancomycin-, daptomycin-, and linezolid-resistant Gram-positive organisms and select Gram-negative pathogens. The pharmacodynamics of ceftaroline is similar to other β-lactam agents. Ceftaroline exhibits a favorable adverse effect profile and is generally well tolerated. There is little data on clinical success of ceftaroline in patients with bacteremia or endocarditis other than what has been published in a small series of case reports. Randomized-control studies are needed to establish clinical outcomes and safety in these patient populations.

Comparison of in vivo and in vitro pharmacodynamics of a humanized regimen of 600 milligrams of Ceftaroline Fosamil every 12 hours against Staphylococcus aureus at initial inocula of 106 and 108 CFU per milliliter

In light of the in vivo/in vitro discordance among beta-lactams against Gram-negative pathogens, we compared the in vivo pharmacodynamics of humanized ceftaroline against 9 Staphylococcus aureus strains (MICs of 0.13 to 1 mg/liter) from published in vitro studies using standard and high inocula in the murine thigh infection model. Consistent with the in vitro findings, mean reductions of ≥1 log10 CFU were observed for ceftaroline against all strains using both standard and high inocula. These results suggest in vivo/in vitro concordance with no observed inoculum effect.

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

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

Ceftaroline activity against bacterial organisms isolated from acute bacterial skin and skin structure infections in United States medical centers (2009-2011)

Ceftaroline, the active metabolite of the prodrug ceftaroline fosamil, is a new cephalosporin with bactericidal activity against resistant Gram-positive organisms including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant strains of Streptococcus pneumoniae, and commonly isolated Gram-negative organisms, including ceftriaxone-susceptible Enterobacteriaceae. We evaluated the in vitro activity of ceftaroline and selected comparator agents against bacterial isolates collected from patients with acute bacterial skin and skin structure infections (ABSSSIs) in the USA. A total of 6222 isolates were collected from 67 medical centers distributed across all nine USA census regions between 2009 and 2011 and tested for susceptibility by reference broth microdilution methods. Ceftaroline was very active against S. aureus (MIC50/90, 0.5/1 μg/mL; 99.6% susceptible), including MRSA (MIC50/90, 0.5/1 μg/mL; 99.1% susceptible). Against β-hemolytic streptococci, the activity of ceftaroline (MIC50/90, ≤0.015/0.03 μg/mL; 100.0% susceptible) was comparable to that of both penicillin (MIC50/90, ≤0.06/≤0.06 μg/mL; 100.0% susceptible) and ceftriaxone (MIC50/90, ≤0.25/≤0.25 μg/mL; 100.0% susceptible). Ceftaroline was also highly active against viridans group streptococci (MIC50/90, 0.03/0.06 μg/mL). Similar to ceftriaxone and ceftazidime, ceftaroline was active against wild-type strains of Escherichia coli (MIC50/90, 0.12/0.25 μg/mL; 94.0% susceptible) and Klebsiella pneumoniae (MIC50/90, 0.12/0.25 μg/mL; 96.8% susceptible); however, the ceftaroline activity was compromised among strains with an extended-spectrum β-lactamase-phenotype (MIC50/90, >32/>32 μg/mL for both E. coli and K. pneumoniae). In summary, ceftaroline showed potent activity against a large contemporary collection (6222) of bacterial isolates associated with ABSSSI in the USA.