New ß-Lactam-ß-Lactamase Inhibitor Combinations.

The limited armamentarium against drug-resistant Gram-negative bacilli has led to the development of several novel ß-lactam-ß-lactamase inhibitor combinations (BLBLIs). In this review, we summarize their spectrum of in vitro activities, mechanisms of resistance, and pharmacokinetic-pharmacodynamic (PK-PD) characteristics. A summary of available clinical data is provided per drug. Four approved BLBLIs are discussed in detail. All are options for treating multidrug-resistant (MDR) Enterobacterales and Pseudomonas aeruginosa Ceftazidime-avibactam is a potential drug for treating Enterobacterales producing extended-spectrum ß-lactamase (ESBL), Klebsiella pneumoniae carbapenemase (KPC), AmpC, and some class D ß-lactamases (OXA-48) in addition to carbapenem-resistant Pseudomonas aeruginosa Ceftolozane-tazobactam is a treatment option mainly for carbapenem-resistant P. aeruginosa (non-carbapenemase producing), with some activity against ESBL-producing Enterobacterales Meropenem-vaborbactam has emerged as treatment option for Enterobacterales producing ESBL, KPC, or AmpC, with similar activity as meropenem against P. aeruginosa Imipenem-relebactam has documented activity against Enterobacterales producing ESBL, KPC, and AmpC, with the combination having some additional activity against P. aeruginosa relative to imipenem. None of these drugs present in vitro activity against Enterobacterales or P. aeruginosa producing metallo-ß-lactamase (MBL) or against carbapenemase-producing Acinetobacter baumannii Clinical data regarding the use of these drugs to treat MDR bacteria are limited and rely mostly on nonrandomized studies. An overview on eight BLBLIs in development is also provided. These drugs provide various levels of in vitro coverage of carbapenem-resistant Enterobacterales, with several drugs presenting in vitro activity against MBLs (cefepime-zidebactam, aztreonam-avibactam, meropenem-nacubactam, and cefepime-taniborbactam). Among these drugs, some also present in vitro activity against carbapenem-resistant P. aeruginosa (cefepime-zidebactam and cefepime-taniborbactam) and A. baumannii (cefepime-zidebactam and sulbactam-durlobactam).

Optimizing pharmacokinetics/pharmacodynamics of ß-lactam/ß-lactamase inhibitor combinations against high inocula of ESBL-producing bacteria.

OBJECTIVES: Reduced in vitro ß-lactam activity against a dense bacterial population is well recognized. It is commonly attributed to the presence of ß-lactamase(s) and it is unknown whether the inoculum effect could be diminished by a ß-lactamase inhibitor. We evaluated different ß-lactam/ß-lactamase inhibitor combinations in suppressing a high inoculum of ESBL-producing bacteria. METHODS: Three clinical isolates expressing representative ESBLs (CTX-M-15 and SHV-12) were examined. The impact of escalating ß-lactamase inhibitor (tazobactam or avibactam) concentrations on ß-lactam (piperacillin or ceftazidime) MIC reduction was characterized by an inhibitory sigmoid Emax model. The effect of various dosing regimens of ß-lactam/ß-lactamase inhibitor combinations was predicted using %T>MICi and selected exposures were experimentally validated in a hollow-fibre infection model over 120 h. The threshold exposure to suppress bacterial regrowth was identified using recursive partitioning. RESULTS: A concentration-dependent reduction in ß-lactam MIC was observed (r2 ≥0.93). Regrowth could be suppressed in all six experiments using %T>MICi ≥73.6%, but only one out of six experiments below the threshold (P = 0.015). The exposures to suppress regrowth might be attained using the clinical dose of avibactam, but a much higher dose than the standard dose would be needed for tazobactam. CONCLUSIONS: A dense population of ESBL-producing bacteria could be suppressed by an optimized dosing regimen of selected ß-lactam/ß-lactamase inhibitor combinations. The reversibility of enzyme inhibition could play an important role in diminishing the inoculum effect. In vivo investigations to validate these findings are warranted.

Optimal Piperacillin-Tazobactam Dosing Strategies against Extended-Spectrum-ß-Lactamase-Producing Enterobacteriaceae.

Piperacillin-tazobactam has been proposed as an alternative to carbapenems for the treatment of infections caused by extended-spectrum-ß-lactamase (ESBL)-producing Enterobacteriaceae However, limited understanding of optimal dosing strategies for this combination may curtail its utility. In this study, we correlated various exposures of piperacillin-tazobactam to efficacy, using a modified pharmacokinetic/pharmacodynamic index. Using a clinical Klebsiella pneumoniae isolate expressing CTX-M-15, piperacillin MIC values were determined with increasing tazobactam concentrations and fitted to a sigmoid inhibitory maximum effect (Emax) model. A hollow-fiber infection model (HFIM) was used to evaluate the efficacy of escalating tazobactam dosing with a fixed piperacillin exposure. Simulated drug concentrations from the HFIM were incorporated in the Emax model to determine the percentage of free time above instantaneous MIC (%fT>MICi) associated with each experimental exposure. The target %fT>MICi associated with growth suppression was prospectively validated using an SHV-12-producing isolate of Escherichia coli and 2 other CTX-M-15-producing K. pneumoniae isolates. Based on our reference isolate, piperacillin-tazobactam exposures of %fT>MICi of ≥55.1% were associated with growth suppression. Despite underlying differences, these findings were consistent with prospective observations in 3 other clinical isolates. Our modeling approach can be applied relatively easily in the clinical setting, and it appeared to be robust in predicting the effectiveness of various piperacillin-tazobactam exposures. This modified pharmacokinetic/pharmacodynamic index could be used to characterize response to other ß-lactam/ß-lactamase inhibitor combinations.

Pharmacokinetics and Pharmacodynamics of Minocycline against Acinetobacter baumannii in a Neutropenic Murine Pneumonia Model.

Multidrug-resistant (MDR) Acinetobacter baumannii is increasingly more prevalent in nosocomial infections. Although in vitro susceptibility of A. baumannii to minocycline is promising, the in vivo efficacy of minocycline has not been well established. In this study, the in vivo activity of minocycline was evaluated in a neutropenic murine pneumonia model. Specifically, we investigated the relationship between minocycline exposure and bactericidal activity using five A. baumannii isolates with a broad range of susceptibility (MIC ranged from 0.25 mg/liter to 16 mg/liter). The pharmacokinetics of minocycline (single dose of 25 mg/kg of body weight, 50 mg/kg, 100 mg/kg, and a humanized regimen, given intraperitoneally) in serum and epithelial lining fluid (ELF) were characterized. Dose linearity was observed for doses up to 50 mg/kg and pulmonary penetration ratios (area under the concentration-time curve in ELF from 0 to 24 h [AUCELF,0-24]/area under the concentration time curve in serum from 0 to 24 h [AUCserum,0-24]) ranged from 2.5 to 2.8. Pharmacokinetic-pharmacodynamics (PK-PD) index values in ELF for various dose regimens against different A. baumannii isolates were calculated. The maximum efficacy at 24 h was approximately 1.5-log-unit reduction of pulmonary bacterial burdens from baseline. The AUC/MIC ratio was the PK-PD index most closely correlating to the bacterial burden (r2 = 0.81). The required AUCELF,0-24/MIC for maintaining stasis and achieving 1-log-unit reduction were 140 and 410, respectively. These findings could guide the treatment of infections caused by A. baumannii using minocycline in the future. Additional studies to examine resistance development during therapy are warranted.

Analytical and functional determination of polymyxin B protein binding in serum.

To enhance our understanding of the pharmacological properties of polymyxin B, serum protein binding for polymyxin B1, B2, and B3 and for isoleucine-polymyxin B1 was evaluated. Using equilibrium dialysis and ultrafiltration, comparable protein binding was found in all 4 components of polymyxin B (92% to 99%). Protein binding in human serum was further assessed using a functional assay, the results of which were in general agreement with previous findings (approximately 90%).

Dose selection for biological enzyme replacement therapy indicated for inborn errors of metabolism.

This paper summarizes key features of the dose-finding strategies used in the development of 11 approved new molecular entities that are first-in-class enzyme replacement therapy (ERT), with a goal to gain insight into the dose exploration approaches to inform efficient dose-finding in future development of biological products for Inborn Errors of Metabolism (IEM). Dose exploration should preferably begin in in vitro studies, followed by testing multiple doses in an appropriate animal disease model, when available, which can provide important information for dose assessment in humans. Performing adequate dose-finding in early phase clinical studies in a well-defined study population, including pediatric subjects, is generally critical to inform dose selection for pivotal trials; alternatively, additional dose exploration can be incorporated as part of a pivotal trial. Two important considerations for successful dose selection include (1) identifying appropriate disease-specific endpoints, including pharmacodynamic (PD) end points and intermediate clinical end points or clinical end points, and (2) designing a study with adequate treatment durations for evaluating these end points. Appropriately selected PD biomarkers is useful for dose selection, and early development of these biomarkers can facilitate the overall clinical development program. Optimization of ERT doses, as well as evaluations of patient intrinsic factors and/or immune tolerance strategies may be necessary to overcome antibody responses or increase efficacy in IEM.

What the Clinical Microbiologist Should Know About Pharmacokinetics/Pharmacodynamics in the Era of Emerging Multidrug Resistance: Focusing on ß-Lactam/ß-Lactamase Inhibitor Combinations.

As a class, ß-lactamase inhibitors have proved successful in extending the clinical utility of ß-lactam antibiotics by circumventing ß-lactamase-mediated resistance. However, the rapid evolution of these ß-lactamases calls for a critical reevaluation of the relationships between susceptibility, drug exposures, and bacterial response. The existing paradigm for in vitro susceptibility testing and development of ß-lactam/ß-lactamase inhibitor combinations may not optimally facilitate clinical use. Thus, alternative approaches for pairing these combinations and evaluating in vitro susceptibility are needed to provide better guidance to clinicians.

Corrigendum to "In Vivo Resistance to Ceftolozane/Tazobactam in Pseudomonas aeruginosa Arising by AmpC- and Non-AmpC-Mediated Pathways".

[This corrects the article DOI: 10.1155/2018/9095203.].

Prevalence of extended-spectrum beta-lactamase and carbapenemase-producing bloodstream isolates of Klebsiella pneumoniae in a tertiary care hospital.

To improve prescribing of empiric therapy, the local molecular epidemiology of extended-spectrum beta-lactamases (ESBLs) and Klebsiella pneumoniae carbapenemases (KPCs) in bloodstream isolates of K. pneumoniae were evaluated. Isolates resistant to third generation cephalosporins were screened phenotypically for ESBLs and carbapenemases, and subsequently confirmed by PCR for the presence of ESBL (blaTEM, blaSHV and blaCTX-M) and carbapenemase (blaKPC, blaVIM, blaNDM and blaOXA-48) genes. Hydrolytic activity (functional gene expression) was quantified using a nitrocefin degradation assay and correlated to ceftazidime or meropenem MIC. Clonality was assessed by repetitive element-based PCR. Beta-lactamases were functionally expressed in 13 isolates (15.5%); 7 (53.8%) harboured blaCTX-M-15 and 6 (46.2%) carried the blaKPC-2 gene. Correlation of hydrolytic activity to MIC yielded a coefficient of 98% for isolates expressing ESBLs alone and 56% for carbapenemase producers. Four unique ESBL-expressing clones and five carbapenem-resistant clones were identified. All 13 resistant isolates were susceptible to ceftazidime/avibactam (MIC ≤ 8/4 mg/L).

In Vivo Resistance to Ceftolozane/Tazobactam in Pseudomonas aeruginosa Arising by AmpC- and Non-AmpC-Mediated Pathways.

Two pairs of ceftolozane/tazobactam susceptible/resistant P. aeruginosa were isolated from 2 patients after exposure to ß-lactams. The genetic basis of ceftolozane/tazobactam resistance was evaluated, and ß-lactam-resistant mechanisms were assessed by phenotypic assays. Whole genome sequencing identified mutations in AmpC including the mutation (V213A) and a deletion of 7 amino acids (P210-G216) in the Ω-loop. Phenotypic assays showed that ceftolozane/tazobactam resistance in the strain with AmpCV213A variant was associated with increased ß-lactamase hydrolysis activity. On the other hand, the deletion of 7 amino acids in the Ω-loop of AmpC did not display enhanced ß-lactamase activity. Resistance to ceftolozane/tazobactam in P. aeruginosa is associated with changes in AmpC; however, the apparent loss of ß-lactamase activity in AmpC∆7 suggests that non-AmpC mechanisms could play an important role in resistance to ß-lactam/ß-lactamase inhibitor combinations.