Pharmacodynamics of Ceftazidime and Avibactam in Neutropenic Mice with Thigh or Lung Infection

Evolving resistance landscape in gram-negative pathogens: An update on β-lactam and β-lactam-inhibitor treatment combinations for carbapenem-resistant organisms

Antibiotic resistance has become a global threat as it is continuously growing due to the evolution of β-lactamases diminishing the activity of classic β-lactam (BL) antibiotics. Recent antibiotic discovery and development efforts have led to the availability of β-lactamase inhibitors (BLIs) with activity against extended-spectrum β-lactamases as well as Klebsiella pneumoniae carbapenemase (KPC)-producing carbapenem-resistant organisms (CRO). Nevertheless, there is still a lack of drugs that target metallo-β-lactamases (MBL), which hydrolyze carbapenems efficiently, and oxacillinases (OXA) often present in carbapenem-resistant Acinetobacter baumannii. This review aims to provide a snapshot of microbiology, pharmacology, and clinical data for currently available BL/BLI treatment options as well as agents in late stage development for CRO harboring various β-lactamases including MBL and OXA-enzymes.

Adequacy of the Dosing and Infusion Time of Ceftazidime/Avibactam for the Treatment of Gram-Negative Bacterial Infections: A PK/PD Simulation Study

Introduction

Recent studies suggested the potential benefits of extended infusion times to optimize the treatment efficacy of ceftazidime/avibactam, which indicated that the current pharmacokinetic/pharmacodynamic (PK/PD) target may not be sufficient, especially for severe infections. The purpose of this study is to assess the adequacy of dosing strategies and infusion durations of ceftazidime/avibactam when applying higher PK/PD targets.

Methods

This study utilized published PK parameters to conduct Monte Carlo simulations. Different dosages including the recommended regimen based on renal function were simulated and evaluated by the probability of target attainment (PTA) and cumulative fraction of response (CFR). Different PK/PD targets were set for ceftazidime and avibactam. MIC distributions from various sources were used to calculate the CFR.

Results

Multiple PK/PD targets have been set in this study, All recommended dosage could easily achieve the target of 50%fT ≥ MIC (ceftazidime) and 50%fT ≥ CT=1.0 mg/L (avibactam). However, for severe infection patients with normal renal function and augmented renal clearance at the recommended dosage (2000 mg/500 mg, every 8 hours), the infusion duration needs to be extended to 3 hours and 4 hours to achieve the targets of 100%fT ≥ MIC and 100%fT ≥ CT=1.0 mg/L. Only continuous infusion at higher dosages achieved 100%fT ≥ 4×MIC and 100%fT ≥ CT=4.0 mg/L targets to all currently recommended regimens. According to the varying MIC distributions, higher concentrations are needed for Pseudomonas aeruginosa, with the attainment rates vary across different regions.

Conclusion

The current recommended dosing regimen of ceftazidime/avibactam is insufficient for severe infection patients, and continuous infusion is suggested.

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.

What are the optimal pharmacokinetic/pharmacodynamic targets for β-lactamase inhibitors? A systematic review

BACKGROUND

Pharmacokinetic/pharmacodynamic (PK/PD) indices are widely used for the selection of optimum antibiotic doses. For β-lactam antibiotics, fT>MIC, best relates antibiotic exposure to efficacy and is widely used to guide the dosing of β-lactam/β-lactamase inhibitor (BLI) combinations, often without considering any PK/PD exposure requirements for BLIs.

OBJECTIVES

This systematic review aimed to describe the PK/PD exposure requirements of BLIs for optimal microbiological efficacy when used in combination with β-lactam antibiotics.

METHODS

Literature was searched online through PubMed, Embase, Web of Science, Scopus and Cochrane Library databases up to 5 June 2023. Studies that report the PK/PD index and threshold concentration of BLIs approved for clinical use were included. Narrative data synthesis was carried out to assimilate the available evidence.

RESULTS

Twenty-three studies were included. The PK/PD index that described the efficacy of BLIs was fT>CT for tazobactam, avibactam and clavulanic acid and fAUC0-24/MIC for relebactam and vaborbactam. The optimal magnitude of the PK/PD index is variable for each BLI based on the companion β-lactam antibiotics, type of bacteria and β-lactamase enzyme gene transcription levels.

CONCLUSIONS

The PK/PD index that describes the efficacy of BLIs and the exposure measure required for their efficacy is variable among inhibitors; as a result, it is difficult to make clear inference on what the optimum index is. Further PK/PD profiling of BLI, using preclinical infection models that simulate the anticipated mode(s) of clinical use, is warranted to streamline the exposure targets for use in the optimization of dosing regimens.

Molecular pharmacodynamics of meropenem for nosocomial pneumonia caused by Pseudomonas aeruginosa

Hospital-acquired pneumonia (HAP) is a leading cause of morbidity and mortality, commonly caused by Pseudomonas aeruginosa. Meropenem is a commonly used therapeutic agent, although emergent resistance occurs during treatment. We used a rabbit HAP infection model to assess the bacterial kill and resistance pharmacodynamics of meropenem. Meropenem 5 mg/kg administered subcutaneously (s.c.) q8h (±amikacin 3.33-5 mg/kg q8h administered intravenously[i.v.]) or meropenem 30 mg/kg s.c. q8h regimens were assessed in a rabbit lung infection model infected with P. aeruginosa, with bacterial quantification and phenotypic/genotypic characterization of emergent resistant isolates. The pharmacokinetic/pharmacodynamic output was fitted to a mathematical model, and human-like regimens were simulated to predict outcomes in a clinical context. Increasing meropenem monotherapy demonstrated a dose-response effect to bacterial kill and an inverted U relationship with emergent resistance. The addition of amikacin to meropenem suppressed the emergence of resistance. A network of porin loss, efflux upregulation, and increased expression of AmpC was identified as the mechanism of this emergent resistance. A bridging simulation using human pharmacokinetics identified meropenem 2 g i.v. q8h as the licensed clinical regimen most likely to suppress resistance. We demonstrate an innovative experimental platform to phenotypically and genotypically characterize bacterial emergent resistance pharmacodynamics in HAP. For meropenem, we have demonstrated the risk of resistance emergence during therapy and identified two mitigating strategies: (i) regimen intensification and (ii) use of combination therapy. This platform will allow pre-clinical assessment of emergent resistance risk during treatment of HAP for other antimicrobials, to allow construction of clinical regimens that mitigate this risk.IMPORTANCEThe emergence of antimicrobial resistance (AMR) during antimicrobial treatment for hospital-acquired pneumonia (HAP) is a well-documented problem (particularly in pneumonia caused by Pseudomonas aeruginosa) that contributes to the wider global antimicrobial resistance crisis. During drug development, regimens are typically determined by their sufficiency to achieve bactericidal effect. Prevention of the emergence of resistance pharmacodynamics is usually not characterized or used to determine the regimen. The innovative experimental platform described here allows characterization of the emergence of AMR during the treatment of HAP and the development of strategies to mitigate this. We have demonstrated this specifically for meropenem-a broad-spectrum antibiotic commonly used to treat HAP. We have characterized the antimicrobial resistance pharmacodynamics of meropenem when used to treat HAP, caused by initially meropenem-susceptible P. aeruginosa, phenotypically and genotypically. We have also shown that intensifying the regimen and using combination therapy are both strategies that can both treat HAP and suppress the emergence of resistance.

Ceftazidime-avibactam induced renal disorders: past and present

With the increasing prevalence of multidrug-resistant Gram-negative bacterial pathogens worldwide, antimicrobial resistance has become a significant public health concern. Ceftazidime-avibactam (CAZ-AVI) exhibited excellent in vitro activity against many carbapenemase-producing pathogens, and was widely used for the treatment of various complicated infections. CAZ-AVI is well tolerated across all dosing regimens, and its associated acute kidney injury (AKI) in phase II/III clinical trials is rare. However, recent real-world studies have demonstrated that CAZ-AVI associated AKI was more frequent in real-world than in phase II and III clinical trials, particularly in patients receiving concomitant nephrotoxic agents, with critically ill patients being at a higher risk. Herein, we reviewed the safety data related to renal impairment of CAZ-AVI, and discussed its pharmacokinetic/pharmacodynamic targets and dosage adjustment in patients with impaired renal function. This review aimed to emphasize the importance for healthcare professionals to be aware of this adverse event of CAZ-AVI and provide practical insights into the dosage optimization in critically ill patients with renal dysfunction.

Imipenem/funobactam (formerly XNW4107) in vivo pharmacodynamics against serine carbapenemase-producing Gram-negative bacteria: a novel modelling approach for time-dependent killing

BACKGROUND

Imipenem/funobactam (formerly XNW4107) is a novel β-lactam/β-lactamase inhibitor with activity against MDR Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacterales strains. Using a neutropenic murine thigh infection model, we aimed to determine the pharmacokinetic/pharmacodynamic (PK/PD) index, relative to funobactam exposure, that correlated most closely with the in vivo efficacy of imipenem/funobactam combination and the magnitude of index required for efficacy against serine carbapenemase-producing clinical strains.

METHODS

Dose-fractionation was conducted against three strains. Imipenem human-simulated regimen (HSR, 500 mg q6h 1 h infusion) efficacy in combination with escalating funobactam exposures against seven A. baumannii, four P. aeruginosa and four Klebsiella pneumoniae (imipenem/funobactam MICs 0.25-16 mg/L) was assessed as 24 h change in log10cfu/thigh.

RESULTS

Increased funobactam fractionation enhanced efficacy, indicating time-dependent killing. Changes in log10cfu/thigh versus %fT > MIC were poorly predictive of efficacy; bactericidal activity was observed at %fT > MIC = 0%. Across different threshold plasma funobactam concentrations (CTs), %fT > CT(1 mg/L) had the highest correlation with efficacy. Normalizing the %fT > CT = 1 mg/L index to the respective isolate imipenem/funobactam MIC ([%fT > CT]/MIC) allowed integration of the isolate's susceptibility, which further enhanced the correlation. Median (%fT > CT[1 mg/L])/MIC values associated with 1-log reductions were 9.82 and 9.90 for A. baumannii and P. aeruginosa, respectively. Median (%fT > CT[1 mg/L])/MIC associated with stasis was 55.73 for K. pneumoniae. Imipenem/funobactam 500/250 mg q6h 1 h infusion HSR produced >1-log kill against 6/7 A. baumannii, 4/4 P. aeruginosa and stasis against 4/4 K. pneumoniae.

CONCLUSIONS

Imipenem/funobactam showed potent in vivo efficacy against serine carbapenemase-producers. The novel PK/PD index (%fT > CT)/MIC appeared to best describe in vivo activity.

Plasma and intraperitoneal pharmacokinetics of ceftazidime/avibactam in peritoneal dialysis patients

OBJECTIVES

Peritonitis is a serious complication in patients undergoing automated peritoneal dialysis (APD) that increases morbidity and frequently disqualifies patients from the peritoneal dialysis programme. Ceftazidime/avibactam (CAZ/AVI) is a potential treatment option for APD patients with peritonitis caused by resistant Gram-negative bacteria, but limited data exist on systemic and target-site pharmacokinetics (PK) in patients undergoing APD. This study set out to investigate the PK of CAZ/AVI in plasma and peritoneal dialysate (PDS) of patients undergoing APD.

METHODS

A prospective, open-label PK study was conducted on eight patients undergoing APD. CAZ/AVI was administered as a single intravenous dose of 2 g/0.5 g over 120 minutes. APD cycles were initiated 15 hours after the study drug administration. Dense PDS and plasma sampling was performed for 24 hours after the start of administration. PK parameters were analysed with population PK modelling. Probability of target attainment (PTA) was simulated for different CAZ/AVI doses.

RESULTS

PK profiles of both drugs in plasma and PDS were similar, indicating that the two drugs are well suited for a fixed-dose combination. A two-compartment model best described the PK of both drugs. A single dose of 2 g/0.5 g CAZ/AVI led to concentrations that far exceeded the PK/PD targets of both drugs. In the Monte Carlo simulations, even the lowest dose (750/190 mg CAZ/AVI) achieved a PTA of >90% for MICs up to 8 mg/L (The European Committee on Antimicrobial Susceptibility Testing epidemiological cut-off value for Pseudomonas aeruginosa) in plasma and PDS.

DISCUSSION

On the basis of PTA simulations, a dose of 750/190 mg CAZ/AVI would be sufficient to treat plasma and peritoneal fluid infections in patients undergoing APD.

All Roads Lead to Rome: Enhancing the Probability of Target Attainment with Different Pharmacokinetic/Pharmacodynamic Modelling Approaches

In light of rising antimicrobial resistance and a decreasing number of antibiotics with novel modes of action, it is of utmost importance to accelerate development of novel treatment options. One aspect of acceleration is to understand pharmacokinetics (PK) and pharmacodynamics (PD) of drugs and to assess the probability of target attainment (PTA). Several in vitro and in vivo methods are deployed to determine these parameters, such as time-kill-curves, hollow-fiber infection models or animal models. However, to date the use of in silico methods to predict PK/PD and PTA is increasing. Since there is not just one way to perform the in silico analysis, we embarked on reviewing for which indications and how PK and PK/PD models as well as PTA analysis has been used to contribute to the understanding of the PK and PD of a drug. Therefore, we examined four recent examples in more detail, namely ceftazidime-avibactam, omadacycline, gepotidacin and zoliflodacin as well as cefiderocol. Whereas the first two compound classes mainly relied on the ‘classical’ development path and PK/PD was only deployed after approval, cefiderocol highly profited from in silico techniques that led to its approval. Finally, this review shall highlight current developments and possibilities to accelerate drug development, especially for anti-infectives.

The primary pharmacology of ceftazidime/avibactam: resistance in vitro

This article reviews resistance to ceftazidime/avibactam as an aspect of its primary pharmacology, linked thematically with recent reviews of the basic in vitro and in vivo translational biology of the combination (J Antimicrob Chemother 2022; 77: 2321-40 and 2341-52). In Enterobacterales or Pseudomonas aeruginosa, single-step exposures to 8×  MIC of ceftazidime/avibactam yielded frequencies of resistance from <∼0.5 × 10-9 to 2-8 × 10-9, depending on the host strain and the β-lactamase harboured. β-Lactamase structural gene mutations mostly affected the avibactam binding site through changes in the Ω-loop: e.g. Asp179Tyr (D179Y) in KPC-2. Other mutations included ones proposed to reduce the permeability to ceftazidime and/or avibactam through changes in outer membrane structure, up-regulated efflux, or both. The existence, or otherwise, of cross-resistance between ceftazidime/avibactam and other antibacterial agents was also reviewed as a key element of the preclinical primary pharmacology of the new agent. Cross-resistance between ceftazidime/avibactam and other β-lactam-based antibacterial agents was caused by MBLs. Mechanism-based cross-resistance was not observed between ceftazidime/avibactam and fluoroquinolones, aminoglycosides or colistin. A low level of general co-resistance to ceftazidime/avibactam was observed in MDR Enterobacterales and P. aeruginosa. For example, among 2821 MDR Klebsiella spp., 3.4% were resistant to ceftazidime/avibactam, in contrast to 0.07% of 8177 non-MDR isolates. Much of this was caused by possession of MBLs. Among 1151 MDR, XDR and pandrug-resistant isolates of P. aeruginosa from the USA, 11.1% were resistant to ceftazidime/avibactam, in contrast to 3.0% of 7452 unselected isolates. In this case, the decreased proportion susceptible was not due to MBLs.

Optimizing antibiotic dosing regimens for nosocomial pneumonia: a window of opportunity for pharmacokinetic and pharmacodynamic modeling

INTRODUCTION

Determining antibiotic exposure in the lung and the threshold(s) needed for effective antibacterial killing is paramount during development of new antibiotics for the treatment of nosocomial pneumonia, as these exposures directly affect clinical outcomes and resistance development. The use of pharmacokinetic and pharmacodynamic modeling is recommended by regulatory agencies to evaluate antibiotic pulmonary exposure and optimize dosage regimen selection. This process has been implemented in newer antibiotic development.

AREAS COVERED

This review will discuss the basis for conducting pharmacokinetic and pharmacodynamic studies to support dosage regimen selection and optimization for the treatment of nosocomial pneumonia. Pharmacokinetic/pharmacodynamic data that supported recent hospital-acquired bacterial pneumonia/ventilator-associated bacterial pneumonia indications for ceftolozane/tazobactam, ceftazidime/avibactam, imipenem/cilastatin/relebactam, and cefiderocol will be reviewed.

EXPERT OPINION

Optimal drug development requires the integration of preclinical pharmacodynamic studies, healthy volunteers and ideally patient bronchoalveolar lavage pharmacokinetic studies, Monte-Carlo simulation, and clinical trials. Currently, plasma exposure has been successfully used as a surrogate for lung exposure threshold. Future studies are needed to identify the value of lung pharmacodynamic thresholds in nosocomial pneumonia antibiotic dosage optimization.

Pharmacokinetic/Pharmacodynamic Index Linked to In Vivo Efficacy of the Ampicillin-Ceftriaxone Combination against Enterococcus faecalis

Combination therapy with ampicillin plus ceftriaxone (AMP+CRO) is the first-line therapy for treating severe infections due to Enterococcus faecalis. However, the pharmacokinetic/pharmacodynamic (PK/PD) index linked to the in vivo efficacy of the combination is not yet defined, hindering dose optimization in the clinic. Because classical PK/PD indices are not directly applicable to antimicrobial combinations, two novel indices were tested in the optimized murine model of infection by E. faecalis to delineate the potentiation of AMP by CRO: the time above the CRO threshold (T_>threshold) and the time above the AMP instantaneous MIC (T_>MICi). The potential clinical relevance was evaluated by simulating human doses of AMP and CRO. Hill's equation fitted well the exposure-response data in terms of T_>threshold, with a CRO threshold of 1 mg/L. The required exposures were 46%, 49%, and 52% for stasis and 1- and 2-log₁₀ killing, respectively. Human ceftriaxone doses of 2 g every 12 h (q12h) would reach the target in >90% of strains with thresholds ≤64 mg/L. The AMP T_>MICi index also fitted well, and the required exposures were 37%, 41%, and 46% for stasis and 1- and 2-log₁₀ killing, respectively. In humans, the addition of CRO would allow use of lower AMP doses to reach the same T_>MICi and to treat strains with higher MICs. This is the first report of the PK/PD indices and required magnitudes linked to AMP+CRO against E. faecalis; these results can be used as the basis to guide the design of clinical trials to improve combined therapy against enterococci.

Development of an optimized and practical pharmacokinetics/pharmacodynamics analysis method for aztreonam/nacubactam against carbapenemase-producing K. pneumoniae

BACKGROUND

Nacubactam, a new β-lactamase inhibitor with antibacterial activity, is being developed as a single drug to be co-administered with cefepime or aztreonam. However, determining pharmacokinetics/pharmacodynamics (PK/PD) parameters in β-lactam/β-lactamase inhibitor combinations remains challenging. We aimed to establish a practical PK/PD analysis method for aztreonam/nacubactam that incorporates instantaneous MIC (MICi).

METHODS

Based on chequerboard MIC measurements, MICi of aztreonam against carbapenemase-producing Klebsiella pneumoniae in the presence of nacubactam was simulated.

RESULTS

The mean change in the bacterial count of thigh-infected mice in an in vivo PD study was plotted based on %fT>MICi and analysed using the inhibitory effect sigmoid Imax model. fT>MICi calculated from the PK experiments showed a high correlation with the in vivo bactericidal effect, suggesting that fT>MICi is the optimal PK/PD parameter for aztreonam/nacubactam. The target values of fT>MICi achieving growth inhibition, 1 log10 kill and 2 log10 kill, were 22, 38% and 75%, respectively.

CONCLUSIONS

The PK/PD analysis method proposed in this study is promising for determining practical PK/PD parameters in combination therapy. In addition, this is the first report of aztreonam/nacubactam showing a potent in vivo therapeutic effect against NDM-producing K. pneumoniae.

Ceftazidime-Avibactam Treatment for Severe Post-Neurosurgical Meningitis and Abscess Caused by Extended-Spectrum β-Lactamase Escherichia coli in a Pediatric Patient: A Case Report

Post-neurosurgical infections caused by multidrug-resistant Enterobacterales are difficult to treat due to limited therapeutic options. Ceftazidime-avibactam (CAZ-AVI), a combination of cephalosporin and a novel β-lactamase inhibitor, has exhibited potential activity against multi/extensive drug-resistant (MDR/XDR) gram-negative bacilli. Several reports have described the successful treatment of central infections caused by MDR/XDR Pseudomonas aeruginosa or Enterobacterales. However, data on the efficacy and effective drug distribution of CAZ-AVI in the central nervous system (CNS), particularly in children, are lacking. We report a case of a 4-year-old girl with post-neurosurgical meningitis and abscess caused by extended-spectrum β-lactamase-producing Escherichia coli successfully treated with CAZ-AVI. CAZ-AVI therapeutic drug monitoring was performed to evaluate its efficacy and effective drug distribution in the CNS. We measured CAZ (15.6, 7.1, and 3.5 μg/mL) and AVI (4.0, 2.1, and 1.2 μg/mL) in cerebrospinal fluid (CSF) samples obtained 3, 5, and 7 h after the administration of the 15th CAZ-AVI dose (2.5 g, q8h, iv), respectively. We also measured CAZ (57.0 and 25.8 μg/mL) and AVI (11.3 and 4.5 μg/mL) in serum samples obtained 3 and 5 h after the administration, respectively. CAZ-AVI achieved an adequate CSF concentration throughout the drug interval. Our case provides evidence for using CAZ-AVI to treat CNS infections.

Synergy between Mecillinam and Ceftazidime/Avibactam or Avibactam against Multi-Drug-Resistant Carbapenemase-Producing Escherichia coli and Klebsiella pneumoniae

Background: Carbapenemase-producing Klebsiella pneumoniae and Escherichia coli have become a significant global health challenge. This has created an urgent need for new treatment modalities. We evaluated the efficacy of mecillinam in combination with either avibactam or ceftazidime/avibactam against carbapenemase-producing clinical isolates. Materials and methods: Nineteen MDR clinical isolates of K. pneumoniae and E. coli were selected for the presence of blaKPC, blaNDM, blaOXA or blaIMP based on whole-genome sequencing and phenotypic susceptibility testing. We tested the synergy between mecillinam and avibactam or ceftazidime/avibactam. We used time−kill studies in vitro and a mouse peritonitis/sepsis model to confirm the synergistic effect. We investigated avibactam’s impact on mecillinam´s affinity for penicillin-binding proteins with a Bocillin assay, and cell changes with phase-contrast and confocal laser scanning microscopy. Results: Mecillinam combined with ceftazidime/avibactam or avibactam substantially reduced MICs (from up to >256 µg/mL to <0.0016 µg/mL) for 17/18 strains. Significant log-CFU reductions were confirmed in time−kill and in vivo experiments. The Bocillin assay did not reveal changes. Conclusion: Mecillinam in combination with avibactam or ceftazidime/avibactam has a notable effect on most types of CPEs, both in vitro and in vivo. The mecillinam/avibactam combination treatment could be a new efficient antibiotic treatment against multi-drug-resistant carbapenemase-producing Gram-negative pathogens.

Variability of murine bacterial pneumonia models used to evaluate antimicrobial agents

Antimicrobial resistance has become one of the greatest threats to human health, and new antibacterial treatments are urgently needed. As a tool to develop novel therapies, animal models are essential to bridge the gap between preclinical and clinical research. However, despite common usage of in vivo models that mimic clinical infection, translational challenges remain high. Standardization of in vivo models is deemed necessary to improve the robustness and reproducibility of preclinical studies and thus translational research. The European Innovative Medicines Initiative (IMI)-funded “Collaboration for prevention and treatment of MDR bacterial infections” (COMBINE) consortium, aims to develop a standardized, quality-controlled murine pneumonia model for preclinical efficacy testing of novel anti-infective candidates and to improve tools for the translation of preclinical data to the clinic. In this review of murine pneumonia model data published in the last 10 years, we present our findings of considerable variability in the protocols employed for testing the efficacy of antimicrobial compounds using this in vivo model. Based on specific inclusion criteria, fifty-three studies focusing on antimicrobial assessment against Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii were reviewed in detail. The data revealed marked differences in the experimental design of the murine pneumonia models employed in the literature. Notably, several differences were observed in variables that are expected to impact the obtained results, such as the immune status of the animals, the age, infection route and sample processing, highlighting the necessity of a standardized model.

Therapeutic Drug Monitoring of Ceftazidime-Avibactam Concentrations in Carbapenem-Resistant K. pneumoniae-Infected Patients With Different Kidney Statuses

Aims: Carbapenem-resistant K. pneumoniae (CRKP) is the most common carbapenem-resistant Enterobacteriaceae with high mortality. Ceftazidime-avibactam (CAZ-AVI) has exhibited excellent in vitro activity in vivo against CRKP. However, the efficacy of CAZ-AVI in KPC-producing CRKP-infected patients with different kidney statuses varies, such as renal insufficiency, normal renal function, and augmented renal clearance (ARC). We explored the use of therapeutic drug monitoring (TDM) to evaluate the concentration and efficacy of CAZ-AVI in CRKP-infected patients with different kidney statuses.

Methods: Serum concentrations for CAZ and AVI were determined by the high-performance liquid chromatography method. Bacterial identification, routine susceptibility testing, renal function index, and others were performed in standard protocols in the hospital’s clinical laboratories.

Results: In the two patients with ARC, in case 1, CAZ-AVI 2.5g q6h was used with good efficacy, and the concentrations were up to the pharmacokinetics/pharmacodynamics targets. In Case 2, 2.5 g q8h was used with invalid effectiveness, and AVI C_min was only 0.797 mg/l, which is lower than the PK/PD target. Case 3 was renal insufficiency using CAZ-AVI 1.25 q8h, and case 4 was normal renal function using 2.5 g q8h. Their concentrations were both up to the PK/PD targets.

Conclusion: TDM results demonstrated that CAZ-AVI steady-state plasma concentration varies among patients with different kidney statuses, providing evidence for the utility of TDM of CAZ-AVI in individualized drug dose adjustment. ARC patients may need more CAZ-AVI daily doses than the standard dose.

New Perspectives on Antimicrobial Agents: Imipenem-Relebactam

Imipenem (IMI)/cilastatin/relebactam (REL) (I/R) is a novel β-lactam/β-lactamase inhibitor combination with expanded microbiologic activity against carbapenem-resistant non-Morganellaceae Enterobacterales (CR-NME) and difficult-to-treat (DTR) Pseudomonas aeruginosa. Relebactam, a bicyclic diazabicyclooctane, has no direct antimicrobial activity but provides reliable inhibition of many Ambler class A and class C enzymes. It is currently approved for the treatment of adult patients with hospital-acquired bacterial pneumonia and ventilator-associated bacterial pneumonia (HABP/VABP) and those with complicated urinary tract infections (cUTIs) and complicated intra-abdominal infections (cIAIs) when limited or no alternative treatments are available. Given the number of recently approved β-lactams with expanded activity against highly resistant Gram-negative pathogens, this review summarizes the published literature on I/R, with a focus on its similar and distinguishing characteristics relative to those of other recently approved agents. Overall, available data support its use for the treatment of patients with HABP/VABP, cUTI, and cIAI due to CR-NME and DTR P. aeruginosa. Data indicate that I/R retains some activity against CR-NME and DTR P. aeruginosa isolates that are resistant to the newer β-lactams and vice versa, suggesting that susceptibility testing be performed for all the newer agents to determine optimal treatment options for patients with CR-NME and DTR P. aeruginosa infections. Further comparative PK/PD and clinical studies are warranted to determine the optimal role of I/R, alone and in combination, for the treatment of patients with highly resistant Gram-negative infections. Until further data are available, I/R is a potential treatment for patients with CR-NME and DTR P. aeruginosa infections when the benefits outweigh the risks.

The primary pharmacology of ceftazidime/avibactam: in vivo translational biology and pharmacokinetics/pharmacodynamics (PK/PD)

This review describes the translational in vivo and non-clinical pharmacokinetics/pharmacodynamics (PK/PD) research that supported clinical trialling and subsequently licensing approval of ceftazidime/avibactam, a new β-lactam/β-lactamase inhibitor combination aimed at the treatment of infections by Enterobacterales and Pseudomonas aeruginosa. The review thematically follows on from the co-published article, Nichols et al. (J Antimicrob Chemother 2022; dkac171). Avibactam protected ceftazidime in animal models of infection with ceftazidime-resistant, β-lactamase-producing bacteria. For example, a single subcutaneous dose of ceftazidime at 1024 mg/kg yielded little effect on the growth of ceftazidime-resistant, blaKPC-2-carrying Klebsiella pneumoniae in the thighs of neutropenic mice (final counts of 4 × 108 to 8 × 108 cfu/thigh). In contrast, co-administration of avibactam in a 4:1 ratio (ceftazidime:avibactam) was bactericidal in the same model (final counts of 2 × 104 to 3 × 104 cfu/thigh). In a rat abdominal abscess model, therapy with ceftazidime or ceftazidime/avibactam (4:1 w/w) against blaKPC-2-positive K. pneumoniae resulted in 9.3 versus 3.3 log cfu/abscess, respectively, after 52 h. With respect to PK/PD, in Monte Carlo simulations, attainment of unbound drug exposure targets (ceftazidime fT>8 mg/L and avibactam fT>1 mg/L, each for 50% of the dosing interval) for the labelled dose of ceftazidime/avibactam (2 and 0.5 g, respectively, q8h by 2 h IV infusion), including dose adjustments for patients with impaired renal function, ranged between 94.8% and 99.6% of patients, depending on the infection modelled.

The primary pharmacology of ceftazidime/avibactam: in vitro translational biology

Previous reviews of ceftazidime/avibactam have focused on in vitro molecular enzymology and microbiology or the clinically associated properties of the combination. Here we take a different approach. We initiate a series of linked reviews that analyse research on the combination that built the primary pharmacology data required to support the clinical and business risk decisions to perform randomized controlled Phase 3 clinical trials, and the additional microbiological research that was added to the above, and the safety and chemical manufacturing and controls data, that constituted successful regulatory licensing applications for ceftazidime/avibactam in multiple countries, including the USA and the EU. The aim of the series is to provide both a source of reference for clinicians and microbiologists to be able to use ceftazidime/avibactam to its best advantage for patients, but also a case study of bringing a novel β-lactamase inhibitor (in combination with an established β-lactam) through the microbiological aspects of clinical development and regulatory applications, updated finally with a review of resistance occurring in patients under treatment. This first article reviews the biochemistry, structural biology and basic microbiology of the combination, showing that avibactam inhibits the great majority of serine-dependent β-lactamases in Enterobacterales and Pseudomonas aeruginosa to restore the in vitro antibacterial activity of ceftazidime. Translation to efficacy against infections in vivo is reviewed in the second co-published article, Nichols et al. (J Antimicrob Chemother 2022; dkac172).

Rapid, simple, and economical LC-MS/MS method for simultaneous determination of ceftazidime and avibactam in human plasma and its application in therapeutic drug monitoring

WHAT IS KNOWN AND OBJECTIVE

Carbapenem-resistant Gram-negative bacterial pathogens continue to threaten public health. Avibactam (AVI), a novel non-β-lactam β-lactamase inhibitor, has been approved for use with ceftazidime (CAZ) mainly against carbapenem-resistant Enterobacteriaceae. Therapeutic drug monitoring (TDM) is urgently needed to optimize dosage regimens to maximize efficacy, minimize toxicity, and delay the emergence of resistance. This study aims to develop and validate a rapid, simple, and economical LC-MS/MS method for simultaneous determination of CAZ/AVI in human plasma.

METHODS

Samples were processed by simple protein precipitation, and gradient elution strategy was applied to separate CAZ and AVI on a reverse-phase C18 column; with subsequent detection by the mass spectrometer in a positive and negative ion switching mode. Plasma samples from patients were analysed.

RESULTS AND DISCUSSION

A 4-min run of LC-MS/MS was developed. The precision, trueness, matrix effect, extraction recovery, carry-over, dilution integrity, and stability were all acceptable for a bioanalytical method. The method was successfully applied to the determination of CAZ and AVI in patients, and a considerable PK variability of CAZ/AVI was observed among patients.

WHAT IS NEW AND CONCLUSION

A robust, rapid, simple, and economical LC-MS/MS method for the simultaneous determination of CAZ and AVI was developed. The considerable PK variability of CAZ/AVI among patients demonstrates the clinical significance of TDM.

Pharmacodynamic Thresholds for Beta-Lactam Antibiotics: A Story of Mouse Versus Man

Beta-lactams remain a critical member of our antibiotic armamentarium and are among the most commonly prescribed antibiotic classes in the inpatient setting. For these agents, the percentage of time that the free concentration remains above the minimum inhibitory concentration (%fT > MIC) of the pathogen has been shown to be the best predictor of antibacterial killing effects. However, debate remains about the quantity of fT > MIC exposure needed for successful clinical response. While pre-clinical animal based studies, such as the neutropenic thigh infection model, have been widely used to support dosing regimen selection for clinical development and susceptibility breakpoint evaluation, pharmacodynamic based studies in human patients are used validate exposures needed in the clinic and for guidance during therapeutic drug monitoring (TDM). For the majority of studied beta-lactams, pre-clinical animal studies routinely demonstrated the fT > MIC should exceed approximately 40–70% fT > MIC to achieve 1 log reductions in colony forming units. In contrast, clinical studies tend to suggest higher exposures may be needed, but tremendous variability exists study to study. Herein, we will review and critique pre-clinical versus human-based pharmacodynamic studies aimed at determining beta-lactam exposure thresholds, so as to determine which targets may be best suited for optimal dosage selection, TDM, and for susceptibility breakpoint determination. Based on our review of murine and clinical literature on beta-lactam pharmacodynamic thresholds, murine based targets specific to each antibiotic are most useful during dosage regimen development and susceptibility breakpoint assessment, while a range of exposures between 50 and 100% fT > MIC are reasonable to define the beta-lactam TDM therapeutic window for most infections.

Pharmacokinetic/pharmacodynamic simulations of cost-effective dosage regimens of ceftolozane/tazobactam and ceftazidime/avibactam in patients with renal impairment

The pharmacokinetics of ceftolozane/tazobactam (TOL/TAZ) and ceftazidime/avibactam (CEF/AVI) is influenced by renal function. Application of recommended dosages in patients with renal impairment require to use fractions of the full dose, as only one dosage is available for both antibiotics. The objective of this study was to evaluate the adequacy of alternative dosage regimens based on the full dose. We performed pharmacokinetic/pharmacodynamic (PK/PD) simulations of recommended and alternative dosage regimens in patients with various degrees of renal impairment, by using the Pmetrics program. Alternative regimens included longer dosage interval and prolonged infusions of the full dose for both drugs. Probabilities of target attainment (PTA) were assessed considering PK/PD targets defined for cephalosporins and beta-lactamase inhibitors as well as MIC breakpoints. The risk of overexposure was also assessed. Results showed that alternative dosage regimens based on a full dose of TOL/TAZ and CEF/AVI administered every 12 or 24h were associated with PTA similar to that of recommended dosages, especially when administered as prolonged infusion. The alternative dosage regimens were not associated with overexposure in most cases. In addition, those regimens could reduce dosing errors, drug cost and nurse labor. Clinical investigation of those alternative dosage regimens would be required before implementation.

Dose optimisation of antibiotics used for meningitis

PURPOSE OF REVIEW

Central nervous system (CNS) infections such as ventriculitis and meningitis are associated with significant morbidity and mortality. In part, this may be due to increased difficulties in achieving a therapeutic antibiotic concentration at the site of infection due to both the pharmacokinetic (PK) changes observed during critical illness and the reduced antibiotic penetration through the blood brain barrier. This paper reviews the pharmacodynamics (PD) and CNS PKs of antibiotics used for Gram-negative bacterial CNS infections to provide clinicians with practical dosing advice.

RECENT FINDINGS

Recent PK studies have shown that currently used intravenous antibiotic dosing regimens may not achieve a therapeutic exposure within the CNS, even for reportedly 'susceptible' bacteria per the current clinical meningitis breakpoints. Limited data exist for new β-lactam antibiotic/β-lactamase inhibitor combinations, which may be required for multidrug resistant infections. Intraventricular antibiotic administration, although not a new concept, has further evidence demonstrating improved patient outcomes compared with intravenous therapy alone, despite the ongoing paucity of PK studies guiding dosing recommendations.

SUMMARY

Clinicians should obtain the bacterial minimum inhibitory concentration when treating patients with CNS Gram-negative bacterial infections and consider the underlying PK/PD principles when prescribing antibiotics. Therapeutic drug monitoring, where available, should be considered to guide dosing. Intraventricular therapy should also be considered for patients with ventricular drains to optimise clinical outcomes.

Preclinical Pharmacokinetic/Pharmacodynamic Studies and Clinical Trials in the Drug Development Process of EMA-Approved Antibacterial Agents: A Review

Development of new antibacterial agents is necessary as drug-resistant bacteria are a threat to global health. In Europe, the European Medicines Agency has been guiding this development process for more than two decades. We investigated preclinical and clinical pre-approval studies to illuminate the current authorization process with emphasis on pharmacokinetic/pharmacodynamic approaches and clinical phases. All centrally authorized systemic antibacterial and antimycobacterial drugs within the European Union were included without any time restriction. Additionally, US Food and Drug Administration-approved antibiotics of the previous 3 years, which were not yet approved by the European Medicines Agency, were included. We focused on preclinical pharmacokinetic/pharmacodynamic studies and phase II and phase III clinical trials. Furthermore, we looked at the recommended dosing regimens and approved indications. In this review, we designed tree diagrams as a new means of illustrating the development process of antibiotics to relate pharmacokinetic/pharmacodynamic phase II and III studies to approved indications. We included 23 (European Medicines Agency, 18; US Food and Drug Administration, 5) antimicrobial agents. Tetracyclines, carbapenems, and cephalosporins were the leading classes. The recommended dosing intervals were significantly shorter in time- vs exposure-dependent drugs (median 8 vs 12, p = 0.006). The majority of approved indications (i.e., acute bacterial skin and soft-tissue infection, community-acquired pneumonia, complicated intra-abdominal infection, complicated urinary tract infection, and complicated skin and soft-tissue infection) used non-inferiority trials. Phase II and III clinical trials investigating community-acquired pneumonia involved the fewest patients. Some promising drugs were marketed in recent years; the individual steps to their authorizations are illuminated. We confirmed the relevance of preclinical pharmacokinetic/pharmacodynamic studies in dosing optimization and decision making in antimicrobial drug development. Non-inferiority clinical trials predominated.

Review of Ceftazidime-Avibactam for the Treatment of Infections Caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes a range of serious infections that are often challenging to treat, as this pathogen can express multiple resistance mechanisms, including multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes. Ceftazidime–avibactam is a combination antimicrobial agent comprising ceftazidime, a third-generation semisynthetic cephalosporin, and avibactam, a novel non-β-lactam β-lactamase inhibitor. This review explores the potential role of ceftazidime–avibactam for the treatment of P. aeruginosa infections. Ceftazidime–avibactam has good in vitro activity against P. aeruginosa relative to comparator β-lactam agents and fluoroquinolones, comparable to amikacin and ceftolozane–tazobactam. In Phase 3 clinical trials, ceftazidime–avibactam has generally demonstrated similar clinical and microbiological outcomes to comparators in patients with complicated intra-abdominal infections, complicated urinary tract infections or hospital-acquired/ventilator-associated pneumonia caused by P. aeruginosa. Although real-world data are limited, favourable outcomes with ceftazidime–avibactam treatment have been reported in some patients with MDR and XDR P. aeruginosa infections. Thus, ceftazidime–avibactam may have a potentially important role in the management of serious and complicated P. aeruginosa infections, including those caused by MDR and XDR strains.

Pharmacokinetic/pharmacodynamic analysis of oral fosfomycin against Enterobacterales, Pseudomonas aeruginosa and Enterococcus spp. in an in vitro bladder infection model: impact on clinical breakpoints

OBJECTIVES

Fosfomycin is an established treatment for uncomplicated urinary tract infections (UTIs), yet evidence supporting susceptibility breakpoints is limited. We examine the UTI susceptibility criteria.

METHODS

Fosfomycin susceptibility, heteroresistance and in vitro growth in a bladder infection model, after a single 3 g dose of oral fosfomycin, were bridged to human pharmacokinetics with pharmacokinetic/pharmacodynamic and Monte Carlo analyses. Data from common uropathogens (24 Escherichia coli, 20 Klebsiella pneumoniae, 4 Enterobacter cloacae, 14 Pseudomonas aeruginosa, 8 Enterococcus faecalis and 8 Enterococcus faecium) were compared and analysed to ascertain species-specific PTA.

RESULTS

Glucose-6-phosphate (G6P) increased MICs of E. coli, K. pneumoniae and E. cloacae (median 2-fold dilutions 3-5), but not of P. aeruginosa and Enterococcus. Atypical E. coli lacking G6P potentiation were killed in the bladder infection model despite high MICs (32-128 mg/L). Fosfomycin heteroresistance was uncommon in E. coli (MIC > 2 mg/L) but was detected in the majority of K. pneumoniae (MIC > 1 mg/L) and P. aeruginosa (MIC >8 mg/L). For these species, baseline heteroresistance was a strong predictor for treatment failure in the model. No heteroresistance was found in Enterococcus. The fAUC/MIC targets for stasis were 1935, 3393, 9968, 2738 and 283 for typical E. coli, K. pneumoniae, E. cloacae, P. aeruginosa and E. faecalis, respectively (synthetic human urine medium alone promoted a 1 log10 kill in E. faecium). A >95% PTA for stasis was only found at MIC ≤ epidemiological cut-off (ECOFF) for E. coli (4 mg/L). For other species, PTAs were low for WT populations.

CONCLUSIONS

With the exception of E. coli, fosfomycin is a poor target for other uropathogen species. A reduction in oral fosfomycin UTI breakpoints is supported.

Aztreonam/avibactam effect on pharmacodynamic indices for mutant selection of Escherichia coli and Klebsiella pneumoniae harbouring serine- and New Delhi metallo-β-lactamases

OBJECTIVES

Ceftazidime/avibactam is not active against MBL-producing bacteria. Combining ceftazidime/avibactam or avibactam with aztreonam can counter the resistance of MBL-producing Enterobacterales. The aim of this study was to evaluate whether the addition of avibactam could reduce or close the mutant selection window (MSW) of aztreonam in Escherichia coli and Klebsiella pneumoniae harbouring MBLs; MSW is a pharmacodynamic (PD) parameter for the selection of emergent resistant mutants.

METHODS

In vitro susceptibility of 19 clinical isolates to ceftazidime/avibactam, aztreonam alone, and in co-administration (aztreonam/ceftazidime/avibactam and aztreonam/avibactam) was determined, as well as the mutant prevention concentration (MPC). The fraction of time within 24 h that the free drug concentration was within the MSW (fTMSW) and the fraction of time that the free drug concentration was above the MPC (fT>MPC) in both plasma and epithelial lining fluid (ELF) were determined from simulations of 10 000 profiles. The joint PTA was used to derive a joint cumulative fraction of response (CFR).

RESULTS

All isolates were resistant to ceftazidime/avibactam or aztreonam. Combining aztreonam and avibactam or ceftazidime/avibactam resulted in synergistic bactericidal activities against all isolates. Synergism was primarily due to the aztreonam/avibactam combination. For aztreonam/avibactam dosing regimens evaluated in clinical trials, fT>MPC values were >90% and >80%, whereas fTMSW measures were <10% and <20% in plasma and ELF, respectively. The CFR was 100% for aztreonam/avibactam against the collection of clinical isolates.

CONCLUSIONS

Effective antimicrobial combination optimized the PD parameters measuring selection for emergent mutants by increasing fT>MPC and reducing fTMSW.

Pharmacokinetics of Non-β-Lactam β-Lactamase Inhibitors

The growing emergence of drug-resistant bacterial strains is an issue to treat severe infections, and many efforts have identified new pharmacological agents. The inhibitors of β-lactamases (BLI) have gained a prominent role in the safeguard of beta-lactams. In the last years, new β-lactam-BLI combinations have been registered or are still under clinical evaluation, demonstrating their effectiveness to treat complicated infections. It is also noteworthy that the pharmacokinetics of BLIs partly matches that of β-lactams companions, meaning that some clinical situations, as well as renal impairment and renal replacement therapies, may alter the disposition of both drugs. Common pharmacokinetic characteristics, linear pharmacokinetics across a wide range of doses, and known pharmacokinetic/pharmacodynamic parameters may guide modifications of dosing regimens for both β-lactams and BLIs. However, comorbidities (i.e., burns, diabetes, cancer) and severe changes in individual pathological conditions (i.e., acute renal impairment, sepsis) could make dose adaptation difficult, because the impact of those factors on BLI pharmacokinetics is partly known. Therapeutic drug monitoring protocols may overcome those issues and offer strategies to personalize drug doses in the intensive care setting. Further prospective clinical trials are warranted to improve the use of BLIs and their β-lactam companions in severe and complicated infections.

Efficacy of single and multiple oral doses of fosfomycin against Pseudomonas aeruginosa urinary tract infections in a dynamic in vitro bladder infection model

OBJECTIVES

We used a dynamic bladder infection in vitro model with synthetic human urine (SHU) to examine fosfomycin exposures to effectively kill, or prevent emergence of resistance, among Pseudomonas aeruginosa isolates.

METHODS

Dynamic urinary fosfomycin concentrations after 3 g oral fosfomycin were simulated, comparing single and multiple (daily for 7 days) doses. Pharmacodynamic response of 16 P. aeruginosa (MIC range 1 to >1024 mg/L) were examined. Baseline disc diffusion susceptibility, broth microdilution MIC and detection of heteroresistance were assessed. Pathogen kill and emergence of resistance over 72 h following a single dose, and over 216 h following daily dosing for 7 days, were investigated. The fAUC0-24/MIC associated with stasis and 1, 2 and 3 log10 kill were determined.

RESULTS

Pre-exposure high-level resistant (HLR) subpopulations were detected in 11/16 isolates after drug-free incubation in the bladder infection model. Five of 16 isolates had >2 log10 kill after single dose, reducing to 2/16 after seven doses. Post-exposure HLR amplification occurred in 8/16 isolates following a single dose and in 11/16 isolates after seven doses. Baseline MIC ≥8 mg/L with an HLR subpopulation predicted post-exposure emergence of resistance following the multiple doses. A PK/PD target of fAUC0-24/MIC >5000 was associated with 3 log10 kill at 72 h and 7 day-stasis.

CONCLUSIONS

Simulated treatment of P. aeruginosa urinary tract infections with oral fosfomycin was ineffective, despite exposure to high urinary concentrations and repeated daily doses for 7 days. Emergence of resistance was observed in the majority of isolates and worsened following prolonged therapy. Detection of a baseline resistant subpopulation predicted treatment failure.

Pseudomonas aeruginosa Ventilator-Associated Pneumonia Rabbit Model for Preclinical Drug Development

Development and validation of large animal models of Pseudomonas aeruginosa ventilator-associated pneumonia are needed for testing new drug candidates in a manner that mimics how they will be used clinically. We developed a new model in which rabbits were ventilated with low tidal volume and challenged with P. aeruginosa to recapitulate hallmark clinical features of acute respiratory distress syndrome (ARDS): acute lung injury and inflammation, progressive decrease in arterial oxygen partial pressure to fractional inspired oxygen PaO₂:FiO₂, leukopenia, neutropenia, thrombocytopenia, hyperlactatemia, severe hypotension, bacterial dissemination from lung to other organs, multiorgan dysfunction, and ultimately death. We evaluated the predictive power of this rabbit model for antibiotic efficacy testing by determining whether a humanized dosing regimen of meropenem, a potent antipseudomonal β-lactam antibiotic, when administered with or without intensive care unit (ICU)-supportive care (fluid challenge and norepinephrine), could halt or reverse natural disease progression. Our humanized meropenem dosing regimen produced a plasma concentration-time profile in the rabbit model similar to those reported in patients with ventilator-associated bacterial pneumonia. In this rabbit model, treatment with humanized meropenem and ICU-supportive care achieved the highest level of survival, halted the worsening of ARDS biomarkers, and reversed lethal hypotension, although treatment with humanized meropenem alone also conferred some protection compared to treatment with placebo (saline) alone or placebo plus ICU-supportive care. In conclusion, this rabbit model could help predict whether an antibiotic will be efficacious for the treatment of human ventilator-associated pneumonia.

Evaluation of the post-antibiotic effect in vivo for the combination of a β-lactam antibiotic and a β-lactamase inhibitor: ceftazidime-avibactam in neutropenic mouse thigh and lung infections

The post-antibiotic effect (PAE) of ceftazidime-avibactam in vivo was evaluated using models of thigh- and lung-infection with Pseudomonas aeruginosa in neutropenic mice. In thigh-infected mice, the PAE was negative (-2.18 to -0.11 h) for three of four strains: caused by a 'burst' of rapid bacterial growth after the drug concentrations had fallen below their pre-specified target values. With lung infection, PAE was positive, and longer for target drug concentrations in ELF (>2 h) than plasma (1.69-1.88 h). The time to the start of regrowth was quantified as a new parameter, PAE_R, which was positive (0.35-1.00 h) in both thigh- and lung-infected mice. In the context that measurements of the PAE of β-lactam/β-lactamase inhibitor combinations in vivo have not previously been reported, it is noted that the negative values were consistent with previous measurements of the PAE of ceftazidime-avibactam in vitro and of ceftazidime alone in vivo.

Intrapulmonary Pharmacokinetics of Cefepime and Enmetazobactam in Healthy Volunteers: Towards New Treatments for Nosocomial Pneumonia

Cefepime-enmetazobactam is a novel β-lactam-β-lactamase inhibitor combination with broad-spectrum antimicrobial activity against a range of multidrug-resistant Enterobacteriaceae This agent is being developed for a range of serious hospital infections. An understanding of the extent of partitioning of β-lactam-β-lactamase inhibitor combinations into the human lung is required to better understand the potential role of cefepime-enmetazobactam for the treatment of nosocomial pneumonia. A total of 20 healthy volunteers were used to study the intrapulmonary pharmacokinetics of a regimen of 2 g cefepime-1 g enmetazobactam every 8 h intravenously (2 g/1 g q8h i.v.). Each volunteer contributed multiple plasma samples and a single epithelial lining fluid (ELF) sample, obtained by bronchoalveolar lavage. Concentrations of cefepime and enmetazobactam were quantified using liquid chromatography-tandem mass spectrometry. The pharmacokinetic data were modeled using a population methodology, and Monte Carlo simulations were performed to assess the attainment of pharmacodynamic targets defined in preclinical models. The concentration-time profiles of both agents in plasma and ELF were similar. The mean ± standard deviation percentage of partitioning of total drug concentrations of cefepime and enmetazobactam between plasma and ELF was 60.59% ± 28.62% and 53.03% ± 21.05%, respectively. Using pharmacodynamic targets for cefepime of greater than the MIC and free enmetazobactam concentrations of >2 mg/liter in ELF of 20% of the dosing interval, a regimen of cefepime-enmetazobactam of 2 g/0.5 g q8h i.v. infused over 2 h resulted in a probability of target attainment of ≥90% for Enterobacteriaceae with cefepime-enmetazobactam MICs of ≤8 mg/liter. This result provides a rationale to further consider cefepime-enmetazobactam for the treatment of nosocomial pneumonia caused by multidrug-resistant Enterobacteriaceae.

Pharmacodynamics of the Novel Metallo-β-Lactamase Inhibitor ANT2681 in Combination with Meropenem for the Treatment of Infections Caused by NDM-Producing Enterobacteriaceae

Enterobacteriaceae that produce metallo-β-lactamases (MBLs) are an emerging threat to public health. The metallo-β-lactamase inhibitor (MBLi) ANT2681 inhibits the enzymatic activity of MBLs through interaction with the dinuclear zinc ion cluster present in the active site that is common to these enzymes. ANT2681 is being codeveloped, with meropenem as the partner β-lactam, as a novel combination therapy for infections caused by MBL-producing bacteria. The pharmacokinetics/pharmacodynamics of meropenem-ANT2681 were studied in a murine neutropenic thigh model of NDM-producing Enterobacteriaceae Dose-ranging studies were performed with both meropenem and ANT2681. Dose fractionation experiments were performed to identify the relevant pharmacodynamic index of ANT2681 when coadministered with meropenem. A background of meropenem at 50 mg/kg of body weight every 4 h (q4h) subcutaneously (s.c.) had minimal antibacterial effect. On this background, half-maximal effect was observed with an ANT2681 dose of 89 mg/kg q4h intravenously (i.v.). The dose fractionation study showed that area under the concentration-time curve (AUC) was the relevant pharmacodynamic index for the inhibitor. The magnitude of the meropenem-ANT2681 exposure required to achieve stasis was explored using 5 NDM-producing strains. A 3-dimensional surface fitted to the pharmacodynamic data from the 5 strains suggested that stasis was achieved with an fT > potentiated meropenem MIC of 40% and ANT2681 AUC of 700 mg · h/liter. These data and analyses provide the underpinning evidence for the combined use of meropenem and ANT2681 for clinical infections.

Using Therapeutic Drug Monitoring to Treat KPC-Producing Klebsiella pneumoniae Central Nervous System Infection With Ceftazidime/Avibactam

This report describes the treatment of Klebsiella pneumoniae carbapenemase (KPC)–3–producing multidrug-resistant K. pneumoniae with ceftazidime/avibactam (CAZ-AVI) in a patient who developed postneurosurgical meningitis and bacteremia. Therapeutic drug monitoring of cerebrospinal fluid and blood samples demonstrated CAZ-AVI concentration levels 20-fold greater than the minimum inhibitory concentration in the first 60 minutes postinfusion, providing evidence for the utility of CAZ-AVI in treating KPC–Klebsiella pneumoniae central nervous system infections.

Monitoring Ceftazidime-Avibactam and Aztreonam Concentrations in the Treatment of a Bloodstream Infection Caused by a Multidrug-Resistant Enterobacter sp. Carrying Both Klebsiella pneumoniae Carbapenemase-4 and New Delhi Metallo-β-Lactamase-1

In an infection with an Enterobacter sp. isolate producing Klebsiella pneumoniae Carbapenemase-4 and New Delhi Metallo-β-Lactamase-1 in the United States, recognition of the molecular basis of carbapenem resistance allowed for successful treatment by combining ceftazidime-avibactam and aztreonam. Antimicrobial synergy testing and therapeutic drug monitoring assessed treatment adequacy.

Pharmacologic optimization of antibiotics for Gram-negative infections

PURPOSE OF REVIEW

Antimicrobial resistance among Gram-negative organisms is a rapidly escalating global challenge. Pharmacologic dose optimization based on pharmacokinetic/pharmacodynamic principles is essential for managing Gram-negative infections. High-risk patient populations may receive nonoptimized antimicrobial dosing because pf physiologic changes in acute illness and/or medical interventions. The purpose of this review is to discuss opportunities for pharmacologic optimization of new agents and highlight patient populations that are often associated with poor drug exposure profiles.

RECENT FINDINGS

Dose optimization of the novel β-lactam-β-lactamase inhibitor combinations has been evaluated through optimizing exposure at the site of infection, evaluating target attainment of both the β-lactam and the β-lactamase-inhibitor in critically ill patients, and evaluating drug exposure to prevent the development of resistance. Plazomicin, a novel aminoglycoside, has pharmacodynamic optimization potential via therapeutic drug monitoring and nomogram-based dosing. Recent studies have evaluated the adequacy of dosing in varying degrees of renal function specifically acute kidney injury, continuous renal replacement therapy (CRRT), and augmented renal clearance (ARC).

SUMMARY

The application of fundamental pharmacokinetic/pharmacodynamic principles is required to optimize new antimicrobials in the treatment of serious Gram-negative infections. Exposure at the site of infection, pharmacokinetics in critically ill patients, and exposures to prevent resistance are all considerations to improve microbiologic and clinical outcomes. Therapeutic drug monitoring may be needed for high-risk patients.

Pharmacodynamics of Cefepime Combined with the Novel Extended-Spectrum-β-Lactamase (ESBL) Inhibitor Enmetazobactam for Murine Pneumonia Caused by ESBL-Producing Klebsiella pneumoniae

Klebsiella pneumoniae strains that produce extended-spectrum beta lactamases (ESBLs) are a persistent public health threat. There are relatively few therapeutic options, and there is undue reliance on carbapenems. Alternative therapeutic options are urgently required. A combination of cefepime and the novel beta lactamase inhibitor enmetazobactam is being developed for the treatment of serious infections caused by ESBL-producing organisms. The pharmacokinetics-pharmacodynamics (PK-PD) of cefepime-enmetazobactam against ESBL-producing K. pneumoniae was studied in a neutropenic murine pneumonia model. Dose-ranging studies were performed. Dose fractionation studies were performed to define the relevant PD index for the inhibitor. The partitioning of cefepime and enmetazobactam into the lung was determined by comparing the area under the concentration-time curve (AUC) in plasma and epithelial lining fluid. The magnitude of drug exposure for cefepime-enmetazobactam required for logarithmic killing in the lung was defined using 3 ESBL-producing strains. Cefepime, given as 100 mg/kg of body weight every 8 h intravenously (q8h i.v.), had minimal antimicrobial effect. When this background regimen of cefepime was combined with enmetazobactam, a half-maximal effect was induced with enmetazobactam at 4.71 mg/kg q8h i.v. The dose fractionation study suggested both fT > threshold and fAUC:MIC are relevant PD indices. The AUC_ELF:AUC_plasma ratio for cefepime and enmetazobactam was 73.4% and 61.5%, respectively. A ≥2-log kill in the lung was achieved with a plasma and ELF cefepime fT > MIC of ≥20% and enmetazobactam fT > 2 mg/liter of ≥20% of the dosing interval. These data and analyses provide the underpinning evidence for the combined use of cefepime and enmetazobactam for nosocomial pneumonia.

Considerations in the Selection of Renal Dosage Adjustments for Patients with Serious Infections and Lessons Learned from the Development of Ceftazidime-Avibactam

An extensive clinical development program (comprising two phase 2 and five phase 3 trials) has demonstrated the efficacy and safety of ceftazidime-avibactam in the treatment of adults with complicated intra-abdominal infection (cIAI), complicated urinary tract infection (cUTI), and hospital-acquired pneumonia (HAP), including ventilator-associated pneumonia (VAP). During the phase 3 clinical program, updated population pharmacokinetic (PK) modeling and Monte Carlo simulations using clinical PK data supported modified ceftazidime-avibactam dosage adjustments for patients with moderate or severe renal impairment (comprising a 50% increase in total daily dose compared with the original dosage adjustments) to reduce the risk of subtherapeutic drug exposures in the event of rapidly improving renal function. The modified dosage adjustments were included in the ceftazidime-avibactam labeling information at the time of initial approval and were subsequently evaluated in the final phase 3 trial (in patients with HAP, including VAP), providing supportive data for the approved U.S. and European ceftazidime-avibactam dosage regimens across renal function categories. This review describes the analyses supporting the ceftazidime-avibactam dosage adjustments for renal impairment and discusses the wider implications and benefits of using modeling and simulation to support dosage regimen optimization based on emerging clinical evidence.

Avibactam Sensitizes Carbapenem-Resistant NDM-1-Producing Klebsiella pneumoniae to Innate Immune Clearance

Infections caused by New Delhi metallo-β-lactamase (NDM)–producing strains of multidrug-resistant Klebsiella pneumoniae are a global public health threat lacking reliable therapies. NDM is impervious to all existing β-lactamase inhibitor (BLI) drugs, including the non–β-lactam BLI avibactam (AVI). Though lacking direct activity against NDMs, AVI can interact with penicillin-binding protein 2 in a manner that may influence cell wall dynamics. We found that exposure of NDM-1–producing K. pneumoniae to AVI led to striking bactericidal interactions with human cathelicidin antimicrobial peptide LL-37, a frontline component of host innate immunity. Moreover, AVI markedly sensitized NDM-1–producing K. pneumoniae to killing by freshly isolated human neutrophils, platelets, and serum when complement was active. Finally, AVI monotherapy reduced lung counts of NDM-1–producing K. pneumoniae in a murine pulmonary challenge model. AVI sensitizes NDM-1–producing K. pneumoniae to innate immune clearance in ways that are not appreciated by standard antibiotic testing and that merit further study.

Selecting the dosage of ceftazidime-avibactam in the perfect storm of nosocomial pneumonia

PURPOSE

Ceftazidime-avibactam is a novel β-lactam/β-lactamase inhibitor combination recently approved in Europe and the USA for the treatment of adults with hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP), among other indications. In the phase III REPROVE trial (NCT01808092), ceftazidime-avibactam demonstrated non-inferiority to meropenem for the treatment of patients with nosocomial pneumonia (NP), including VAP. As ceftazidime-avibactam was not studied in patients with NP prior to REPROVE, selecting an appropriate dosage regimen in the "perfect storm" of NP required careful consideration of potential determinants and confounders of response specific to the NP patient population.

METHODS

This review describes the series of preclinical studies and pharmacokinetic/pharmacodynamic (PK/PD) analyses that supported ceftazidime-avibactam dosage selection for patients with NP/VAP (2000/500 mg by 2-h intravenous infusion every 8 h, adjusted for renal function). In parallel, important considerations for antibiotic dosage selection in patients with NP are highlighted, including adequate drug penetration into the lungs, the suitability of murine-derived plasma PK/PD targets, evaluation of MIC distributions against clinical bacterial isolates from patients with NP, and consideration of PK in patients with NP, who are often critically ill. These analyses also supported the European approval of ceftazidime-avibactam for adults with HAP, including VAP, before the completion of REPROVE.

CONCLUSIONS

This work serves as a successful practical example of dosage design for a new antibacterial drug therapy in the indication of NP, including VAP, where previous drug therapies have failed, possibly as a result of evaluation of too few variables, thereby limiting the accuracy of pharmacodynamic predictions.

Steady-State Ceftazidime-Avibactam Serum Concentrations and Dosing Recommendations in a Critically Ill Patient Being Treated for Pseudomonas aeruginosa Pneumonia and Undergoing Continuous Venovenous Hemodiafiltration

Ceftazidime-avibactam (CAZ-AVI) is a novel intravenous β-lactam/β-lactamase inhibitor combination used in the treatment of multidrug-resistant (MDR) gram-negative infections. Although renal dosing recommendations exist for the medication, limited data are available for dosing in patients receiving continuous renal replacement therapy. In this report, we describe a case in which CAZ-AVI 2.5 g was administered as a 2-hour infusion every 8 hours to a 50-year-old critically ill patient with MDR Pseudomonas aeruginosa (CAZ-AVI minimum inhibitory concentration [MIC] 8 μg/ml) pneumonia who was also receiving continuous venovenous hemodiafiltration (CVVHDF). Total serum concentrations of both ceftazidime and avibactam were measured at ~0.5, 2, 4, and 6 hours after completion of the 2-hour infusion of the 11th dose of CAZ-AVI. Ceftazidime pharmacokinetic parameters were as follows: maximum serum concentration (C_max ) 152.39 μg/ml, half-life 5.17 hours, volume of distribution at steady state (Vd_ss ) 11.51 L, clearance 1.54 L/hour, and area under the concentration-time curve (AUC) 1295.38 hour•μg/ml. This regimen achieved free ceftazidime serum concentrations more than 4 times the MIC for 100% of the dosing interval. Avibactam pharmacokinetic parameters were as follows: C_max 35.83 μg/ml, half-life 5.92 hours, Vd_ss 12.44 L, clearance 1.45 L/hour, and AUC 343.44 hour•μg/ml, which achieved free avibactam concentrations above 1 μg/ml for 100% of the dosing interval. Higher CAZ-AVI dosing is critical in the treatment of pneumonia due to limited ceftazidime penetration into epithelial lining fluid; however, epithelial lining fluid drug concentrations were not collected or measured. Based on this case report and the available evidence, a dose of CAZ-AVI 2.5 g infused over 2 hours every 8 hours appears to be appropriate for critically ill patients who are being treated for pneumonia and are receiving CVVHDF.

Epidemiology and Treatment of Multidrug-Resistant and Extensively Drug-Resistant Pseudomonas aeruginosa Infections

In recent years, the worldwide spread of the so-called high-risk clones of multidrug-resistant or extensively drug-resistant (MDR/XDR) Pseudomonas aeruginosa has become a public health threat. This article reviews their mechanisms of resistance, epidemiology, and clinical impact and current and upcoming therapeutic options. In vitro and in vivo treatment studies and pharmacokinetic and pharmacodynamic (PK/PD) models are discussed. Polymyxins are reviewed as an important therapeutic option, outlining dosage, pharmacokinetics and pharmacodynamics, and their clinical efficacy against MDR/XDR P. aeruginosa infections. Their narrow therapeutic window and potential for combination therapy are also discussed. Other "old" antimicrobials, such as certain β-lactams, aminoglycosides, and fosfomycin, are reviewed here. New antipseudomonals, as well as those in the pipeline, are also reviewed. Ceftolozane-tazobactam has clinical activity against a significant percentage of MDR/XDR P. aeruginosa strains, and its microbiological and clinical data, as well as recommendations for improving its use against these bacteria, are described, as are those for ceftazidime-avibactam, which has better activity against MDR/XDR P. aeruginosa, especially strains with certain specific mechanisms of resistance. A section is devoted to reviewing upcoming active drugs such as imipenem-relebactam, cefepime-zidebactam, cefiderocol, and murepavadin. Finally, other therapeutic strategies, such as use of vaccines, antibodies, bacteriocins, anti-quorum sensing, and bacteriophages, are described as future options.

In Vivo Pharmacodynamic Study of Cefiderocol, a Novel Parenteral Siderophore Cephalosporin, in Murine Thigh and Lung Infection Models

The pharmacokinetic (PK) and pharmacodynamic (PD) parameters which correlated with the in vivo efficacy of cefiderocol were evaluated using neutropenic murine thigh and lung infection models in which the infections were caused by a variety of Gram-negative bacilli. The dose fractionation study using the thigh infection model in which the infection was caused by Pseudomonas aeruginosa showed that the cumulative percentage of a 24-h period that the free drug concentration in plasma exceeds the MIC (%fT>MIC) rather than the free peak level divided by the MIC (fCmax/MIC) and the area under the free concentration-time curve over 24 h divided by the MIC (fAUC/MIC) was the PK/PD parameter that best correlated with efficacy. The study with multiple carbapenem-resistant strains revealed that the %fT>MIC determined in iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB) better reflected the in vivo efficacy of cefiderocol than the %fT>MIC determined in cation-adjusted Mueller-Hinton broth (CAMHB). The mean %fT>MIC of cefiderocol required for a 1-log10 reduction against 10 strains of Enterobacteriaceae and 3 strains of Pseudomonas aeruginosa in the thigh infection models were 73.3% and 77.2%, respectively. The mean %fT>MIC for Enterobacteriaceae, P. aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia in the lung infection model were 64.4%, 70.3%, 88.1%, and 53.9%, respectively. These results indicate that cefiderocol has potent efficacy against Gram-negative bacilli, including carbapenem-resistant strains, irrespective of the bacterial species, in neutropenic thigh and lung infection models and that the in vivo efficacy correlated with the in vitro MIC under iron-deficient conditions.

A translational pharmacokinetic/pharmacodynamic model to characterize bacterial kill in the presence of imipenem-relebactam

OBJECTIVES

Relebactam is a small molecule β-lactamase inhibitor under clinical investigation for use as a fixed-dose combination with imipenem/cilastatin. Here we present a translational pharmacokinetic/pharmacodynamic mathematical model to support optimal dose selection of relebactam.

METHODS

Data derived from in vitro checkerboard and hollow fiber infection studies of imipenem-resistant strains of Pseudomonas aeruginosa were incorporated into the model. The model integrates the effect of relebactam concentration on imipenem susceptibility in a semi-mechanistic manner using the checkerboard data and characterizes the bacterial time-kill profiles from the hollow fiber infection model data.

RESULTS

Simulations demonstrated that the ratio of the area under the concentration-time curve for free drug to the minimum inhibitory concentration (fAUC/MIC) was the pharmacokinetic driver for relebactam, with a target fAUC/MIC=7.5 associated with 2-log kill. At a clinical dose of 250mg relebactam, greater than 2-log reductions in bacterial load are projected for imipenem-resistant strains with an imipenem/relebactam MIC≤4μg/mL.

CONCLUSIONS

The study confirms that the pharmacokinetic/pharmacodynamic driver for relebactam is fAUC/MIC, that an fAUC/MIC ratio of 7.5 is associated with 2-log kill in vitro, and that a 250mg clinical dose of relebactam achieves this target value when delivered in combination with imipenem/cilastatin.

Pharmacokinetics-pharmacodynamics of β-lactamase inhibitors: are we missing the target?

Introduction: β-lactamase production in Gram-negative bacteria is a leading cause of antimicrobial resistance. β-lactamase inhibitors are therapeutic agents used in combination with a partner antimicrobial to overcome the production of these enzymes and restore antimicrobial activity. To address the ongoing threat of multi-drug resistant bacteria, a recent wave of β-lactamase inhibitor development has occurred. Emphasis on the pharmacokinetics and pharmacodynamics of these agents is needed to optimize their clinical impact. Areas covered: This review will describe methods currently used to define the pharmacokinetics/pharmacodynamics of β-lactamase inhibitors. Minimal focus will be on the structure and mechanism of β-lactamase inhibitors. Emphasis will be placed on the use of specific thresholds to normalize β-lactamase inhibitor exposure. In vitro and in vivo pharmacokinetic/pharmacodynamic data specific to FDA approved and pipeline β-lactamase inhibitors will be explored. Expert opinion: Describing the exposure-response relationship of β-lactamase inhibitors is an ongoing challenge due to the dynamic relationship of the β-lactamase inhibitor with the active partner compound. Pharmacokinetic/pharmacodynamic indices and target exposures lack generalizability, as they are often specific to the infecting organism and/or β-lactamase, rather than β-lactamase inhibitor class. Selected dosage regimens of new agents should be validated via the use of population target attainment analyses.

New antibiotics for ventilator-associated pneumonia

PURPOSE OF REVIEW

Ventilator-associated pneumonia (VAP) caused by multidrug-resistant (MDR) bacteria represents a global emerging problem. Delayed prescription of an adequate treatment for VAP has been associated with higher morbidity and mortality. New molecules have been developed to face the need of compounds that are active against resistant Gram-positive and Gram-negative pathogens. The aim of this review is to summarize the current scenario of new therapeutic options for the treatment of VAP.

RECENT FINDINGS

A number of new antibiotics with activity against MDR have been recently approved for the treatment of VAP, and other agents are under investigation. In this review, the authors summarize the current therapeutic options for the treatment of VAP that showed promising implications for clinical practice, including new compounds belonging to old antibiotic classes (e.g., ceftolozane/tazobactam, ceftazidime/avibactam meropenem/vaborbactam, imipenem/relebactam, tedizolid, cefiderocol, eravacycline, and plazomicin) and novel chemical classes, such as murepavadin. Nebulized antibiotics that are currently in development for the treatment of pneumonia in mechanically ventilated patients are also presented.

SUMMARY

Newly approved and investigational drugs for the treatment of VAP are expected to offer many advantages for the management of patients with respiratory infections caused by MDR. Promising characteristics of new compounds include high activity against both methicillin-resistant Staphylococcus aureus and MDR Gram-negative bacteria and a favorable safety profile.

A mathematical model-based analysis of the time-kill kinetics of ceftazidime/avibactam against Pseudomonas aeruginosa

Objectives

To characterize quantitatively the effect of avibactam in potentiating ceftazidime against MDR Pseudomonas aeruginosa by developing a mathematical model to describe the bacterial response to constant concentration time-kill information and validating it using both constant and time-varying concentration-effect data from in vitro and in vivo infection systems.

Methods

The time course of the bacterial population dynamics in the presence of static concentrations of ceftazidime and avibactam was modelled using a two-state pharmacokinetic/pharmacodynamic (PK/PD) model, consisting of active and resting states, to account for bactericidal activities, bacteria-mediated ceftazidime degradation and inhibition of degradation by avibactam. Ceftazidime's effect on the bacterial population was described as an enhancement of the death rate of the active population, with the effect of avibactam being to increase ceftazidime potency. Model validation was performed by comparing simulated time courses of bacterial responses with those from in vitro and in vivo experimental exposures of ceftazidime and avibactam that represented those predicted in an average patient dosed with 2 g/0.5 g ceftazidime/avibactam administered every 8 h as 2 h infusions.

Results

The two-state model successfully described the bacterial population dynamics, ceftazidime degradation and its inhibition by avibactam. For external validation, the model correctly predicted the bacterial response of P. aeruginosa isolates evaluated in in vitro hollow-fibre and in vivo neutropenic mouse thigh and lung infection models.

Conclusions

The PK/PD model and modelled strains successfully replicated the spread in activity when compared with a large selection of P. aeruginosa strains reported in the literature.

In Vitro Pharmacodynamics of a Novel Ceftibuten-Clavulanate Combination Antibiotic against Enterobacteriaceae

A novel antibiotic combination of the oral cephalosporin ceftibuten (CTB) and the β-lactamase inhibitor clavulanate (CLA) is currently in development for urinary tract infections, including those caused by extended-spectrum-β-lactamase (ESBL)-producing organisms. This study aimed to identify the pharmacodynamic index and magnitude of this index for CLA, when combined with a fixed CTB exposure (∼59% free time above the CTB-CLA MIC) against ESBL-producing Escherichia coli and Klebsiella pneumoniae (CTB-CLA MICs of 0.25/0.125 to 1/0.5 μg/ml) using the in vitro chemostat model. Dose fractionation studies identified the time that free CLA concentrations remained above a threshold concentration (fT>threshold) to be the best pharmacodynamic index (R ² = 0.85) compared with the free area under the curve (AUC)/threshold ratio (R ² = 0.62) and free maximum concentration/threshold ratio (R ² = 0.37). For E. coli isolates, stasis and 1-log₁₀ CFU reductions were achieved at 30.9 and 47.9% fT>CTB concentrations of the 2:1 CTB-CLA MIC (fT>MIC here), respectively. For K. pneumoniae isolates, stasis and 1-log₁₀ CFU reductions were achieved at 51.9 and 92.0% fT>MIC, respectively. These data inform exposure requirements for CLA combined with CTB for optimizing pharmacodynamics against Enterobacteriaceae and should be useful in designing dosage regimens for this combination antibiotic.

Resistenze antibiotiche e nuove molecole: qual è lo scenario attuale?

Antibiotic resistance and new drugs in urologic setting: what we need to know? Urinary tract infections (UTIs) are among the most frequent infectious diseases, and represent an important public health problem with a substantial economic burden. In recent years the chemoresistance of the main uropathogens has significantly increased worldwide. Extended spectrum beta-lactamase (ESBL) production and multi-drug resistant (MDR) clones of Escherichia coli and Klebsiella pneumoniae are limiting available treatment options. Carbapenems and aminoglycosides are still effective in complicated UTI. New beta-lactam combinations such as ceftolozane-tazobactam and ceftazidime-avibactam may be highly useful in treating severe infections while contributing to the carbapenem sparing strategy. For uncomplicated UTI, within older antibiotics, fosfomycin trometamol may be considered a first-choice drug since it is still retaining a good activity against MDR uropathogens. On the other hand, there are extensive data showing that the administration of antimicrobials according to pharmacokinetic/pharmacodynamic (PK/PD) parameters improves the possibility of a positive clinical outcome, particularly in severely ill patients. Evidence is growing that when PK/PD parameters are used to target not only clinical cure. This article discusses the PK/PD characteristics of antimicrobial agents for the treatment of UTIs, and the pharmacological and therapeutic strategies for limiting or preventing bacterial resistance.