The β-Lactams Strike Back: Ceftazidime-Avibactam

What's new in the treatment of multidrug-resistant gram-negative infections?

Eradicating multi-drug resistant (MDR) organisms has been a major challenge in healthcare settings worldwide. Newly approved drugs and those currently in the pipeline may have a promising solution to this issue. The purposes of this review are to describe the various resistance mechanisms of Gram-negative bacteria and to provide a summary of the current literature available on the newer agents, such as ceftazidime/avibactam, ceftolozane/tazobactam, meropenem/vaborbactam, and other emerging agents used for the treatment of MDR Gram-negative infections. Given that MDR organisms confer resistance to treatment by various methods, including enzymatic degradation, efflux pumps, and porin mutation, an understanding of mechanisms of bacterial resistance combined with information on newer antimicrobial agents against MDR Gram-negative bacteria will further assist clinicians in determining the best suitable therapy for the treatment of various complicated infections.

Antibacterial Activity of Human Simulated Epithelial Lining Fluid Concentrations of Ceftazidime-Avibactam Alone or in Combination with Amikacin Inhale (BAY41-6551) against Carbapenem-Resistant Pseudomonas aeruginosa and Klebsiella pneumoniae

The role of inhalational combination therapy when treating carbapenem-resistant Pseudomonas aeruginosa and Klebsiella pneumoniae with newer beta-lactam/beta-lactamase inhibitors has not been established. Using a 72-h in vitro pharmacodynamic chemostat model, we simulated the human exposures achieved in epithelial lining fluid (ELF) following intravenous treatment with ceftazidime-avibactam (CZA) 2.5 g every 8 h (q8h) alone and in combination with inhaled amikacin (AMK-I) 400 mg q12h, a reformulated aminoglycoside designed for inhalational administration, against three P. aeruginosa isolates (CZA [ceftazidime/avibactam] MICs, 4/4 to 8/4 μg/ml; AMK-I MICs, 8 to 64 μg/ml) and three K. pneumoniae isolates (CZA MICs, 1/4 to 8/4 μg/ml; AMK-I MICs, 32 to 64 μg/ml). Combination therapy resulted in a significant reduction in 72-h CFU compared with that of CZA monotherapy against two of three P. aeruginosa isolates (-4.14 log₁₀ CFU/ml, P = 0.027; -1.42 log₁₀ CFU/ml, P = 0.020; and -0.4 log₁₀ CFU/ml, P = 0.298) and two of three K. pneumoniae isolates (0.04 log₁₀ CFU/ml, P = 0.963; -4.34 log₁₀ CFU/ml, P < 0.001; and -2.34 log₁₀ CFU/ml, P = 0.021). When measured by the area under the bacterial growth curve (AUBC) over 72 h, significant reductions were observed in favor of the combination regimen against all six isolates tested. AMK-I combination therapy successfully suppressed CZA resistance development in one K. pneumoniae isolate harboring bla_KPC-3 that was observed during CZA monotherapy. These studies suggest a beneficial role for combination therapy with intravenous CZA and inhaled AMK when treating pneumonia caused by carbapenem-resistant Gram-negative bacteria.

In Vitro Activity of Ceftazidime-Avibactam against Isolates from Patients in a Phase 3 Clinical Trial for Treatment of Complicated Intra-abdominal Infections

The increasing prevalence of multidrug-resistant Gram-negative pathogens has generated a requirement for new treatment options. Avibactam, a novel non-β-lactam-β-lactamase inhibitor, restores the activity of ceftazidime against Ambler class A, C, and some class D β-lactamase-producing strains of Enterobacteriaceae and Pseudomonas aeruginosa The in vitro activities of ceftazidime-avibactam versus comparators were evaluated against 1,440 clinical isolates obtained in a phase 3 clinical trial in patients with complicated intra-abdominal infections (cIAI; ClinicalTrials.gov identifier NCT01499290). Overall, in vitro activities were determined for 803 Enterobacteriaceae, 70 P. aeruginosa, 304 Gram-positive aerobic, and 255 anaerobic isolates obtained from 1,066 randomized patients at baseline. Susceptibility was determined by broth microdilution. The most commonly isolated Gram-negative, Gram-positive, and anaerobic pathogens were Escherichia coli (n = 549), Streptococcus anginosus (n = 130), and Bacteroides fragilis (n = 96), respectively. Ceftazidime-avibactam was highly active against isolates of Enterobacteriaceae, with an overall MIC₉₀ of 0.25 mg/liter. In contrast, the MIC₉₀ for ceftazidime alone was 32 mg/liter. The MIC₉₀ value for ceftazidime-avibactam (4 mg/liter) was one dilution lower than that of ceftazidime alone (8 mg/liter) against isolates of Pseudomonas aeruginosa The ceftazidime-avibactam MIC₉₀ for 109 ceftazidime-nonsusceptible Enterobacteriaceae isolates was 2 mg/liter, and the MIC range for 6 ceftazidime-nonsusceptible P. aeruginosa isolates was 8 to 32 mg/liter. The MIC₉₀ values were within the range of susceptibility for the study drugs permitted per the protocol in the phase 3 study to provide coverage for aerobic Gram-positive and anaerobic pathogens. These findings demonstrate the in vitro activity of ceftazidime-avibactam against bacterial pathogens commonly observed in cIAI patients, including ceftazidime-nonsusceptible Enterobacteriaceae (This study has been registered at ClinicalTrials.gov under identifier NCT01499290.).

In vitro activity of cefepime/zidebactam (WCK 5222) against Gram-negative bacteria

Objectives

Diazabicyclooctanes (DBOs) inhibit class A, class C and some class D β-lactamases. A few also bind PBP2, conferring direct antibacterial activity and a β-lactamase-independent 'enhancer' effect, potentiating β-lactams targeting PBP3. We tested a novel DBO, zidebactam, combined with cefepime.

Methods

CLSI agar dilution MICs were determined with cefepime/zidebactam in a chequerboard format. Bactericidal activity was also measured.

Results

Zidebactam MICs were ≤2 mg/L (mostly 0.12-0.5 mg/L) for most Escherichia coli , Klebsiella , Citrobacter and Enterobacter spp., but were >32 mg/L for Proteeae, most Serratia and a few E. coli , Klebsiella and Enterobacter/Citrobacter . The antibacterial activity of zidebactam dominated chequerboard studies for Enterobacteriaceae, but potentiation of cefepime was apparent for zidebactam-resistant isolates with class A and C enzymes, illustrating β-lactamase inhibition. Overall, cefepime/zidebactam inhibited almost all Enterobacteriaceae with AmpC, ESBL, K1, KPC and OXA-48-like β-lactamases at 1 + 1 mg/L and also 29 of 35 isolates with metallo-carbapenemases, including several resistant to zidebactam alone. Zidebactam MICs for 36 of 50 Pseudomonas aeruginosa were 4-16 mg/L, and the majority of AmpC, metallo-β-lactamase-producing and cystic fibrosis isolates were susceptible to cefepime/zidebactam at 8 + 8 mg/L. Zidebactam MICs for Acinetobacter baumannii and Stenotrophomonas maltophilia were >32 mg/L; potentiation of cefepime was frequent for S. maltophilia , but minimal for A. baumannii . Kill curve results largely supported MICs.

Conclusions

Zidebactam represents a second triple-action DBO following RG6080, with lower MICs for Enterobacteriaceae and P. aeruginosa . Clinical evaluation of cefepime/zidebactam must critically evaluate the reliance that can be placed on this direct antibacterial activity and on the enhancer effect as well as β-lactamase inhibition.

Ceftazidime-avibactam: new rules for the game against multidrug-resistant gram-negative bacteria

The rapid spread of multidrug-resistant Gram-negative bacteria in hospital settings all over the world makes a demand for the new options to overcome antimicrobial resistance. Ceftazidime-avibactam is the first approved antibiotic that contains a new beta-lactamase inhibitor with unique properties. This review provides insight into the spectrum of activity, pharmacological characteristics, data on efficacy and safety of ceftazidime-avibactam obtained from the clinical trials and real clinical practice, as well as prospects for further studies and clinical application of this new antimicrobial agent.

Overcoming antibiotic resistance: Is siderophore Trojan horse conjugation an answer to evolving resistance in microbial pathogens?

Comparative study of siderophore biosynthesis pathway in pathogens provides potential targets for antibiotics and host drug delivery as a part of computationally feasible microbial therapy. Iron acquisition using siderophore models is an essential and well established model in all microorganisms and microbial infections a known to cause great havoc to both plant and animal. Rapid development of antibiotic resistance in bacterial as well as fungal pathogens has drawn us at a verge where one has to get rid of the traditional way of obstructing pathogen using single or multiple antibiotic/chemical inhibitors or drugs. 'Trojan horse' strategy is an answer to this imperative call where antibiotic are by far sneaked into the pathogenic cell via the siderophore receptors at cell and outer membrane. This antibiotic once gets inside, generates a 'black hole' scenario within the opportunistic pathogens via iron scarcity. For pathogens whose siderophore are not compatible to smuggle drug due to their complex conformation and stiff valence bonds, there is another approach. By means of the siderophore biosynthesis pathways, potential targets for inhibition of these siderophores in pathogenic bacteria could be achieved and thus control pathogenic virulence. Method to design artificial exogenous siderophores for pathogens that would compete and succeed the battle of intake is also covered with this review. These manipulated siderophore would enter pathogenic cell like any other siderophore but will not disperse iron due to which iron inadequacy and hence pathogens control be accomplished. The aim of this review is to offer strategies to overcome the microbial infections/pathogens using siderophore.

WCK 4234, a novel diazabicyclooctane potentiating carbapenems against Enterobacteriaceae, Pseudomonas and Acinetobacter with class A, C and D β-lactamases

Background

Several diazabicyclooctanes (DBOs) are under development as inhibitors of class A and C β-lactamases. Inhibition of OXA (class D) carbapenemases is variable, with those of Acinetobacter spp. remaining notably resistant. We describe a novel DBO, WCK 4234 (Wockhardt), with distinctive activity against OXA carbapenemases.

Methods

MICs of imipenem and meropenem were determined by CLSI agar dilution with WCK 4234 added at 4 or 8 mg/L. Test organisms were clinical Enterobacteriaceae, Acinetobacter baumannii and Pseudomonas aeruginosa with carbapenemases or carbapenem resistance via porin loss plus AmpC or ESBL activity. AmpC mutants were also tested.

Results

WCK 4234, which lacked direct antibacterial activity, strongly potentiated imipenem and meropenem against Enterobacteriaceae with OXA-48/OXA-181 or KPC enzymes, or with combinations of impermeability and AmpC or ESBL activity, with MICs reduced to ≤2 mg/L in almost all cases. Carbapenems likewise were potentiated against P. aeruginosa ( n  =   2) with OXA-181 enzyme, with MICs reduced from 64-128 to 2-8 mg/L and against A. baumannii with OXA carbapenemases, particularly OXA-23 or hyperproduced OXA-51, with MICs reduced to ≤2 mg/L for 9/10 acinetobacters with OXA-23 enzyme. Carbapenems were not potentiated against Enterobacteriaceae or non-fermenters with metallo-β-lactamases.

Conclusions

WCK 4234 distinctively overcame resistance mediated by OXA-type carbapenemases, including those of A. baumannii . It behaved similarly to other DBOs against strains with KPC carbapenemases or combinations of impermeability and ESBL or AmpC activity.

Compatibility of Ceftazidime-Avibactam, Ceftolozane-Tazobactam, and Piperacillin-Tazobactam with Vancomycin in Dextrose 5% in Water

Objectives: The compatibility of vancomycin with existing and novel β-lactam/β-lactamase inhibitors at clinically relevant concentrations in 5% dextrose in water has not been fully explored to date. Methods: Vancomycin concentrations tested ranged from 5 to 20 mg/mL. Ceftazidime-avibactam was tested at 8, 20, and 40 mg/mL, ceftolozane-tazobactam at 15 mg/mL, and piperacillin-tazobactam at 28 mg/mL. Compatibility of drug admixtures were tested via both simulated and actual y-site infusion. For the simulated y-site compatibility assessment, 1:1 mixtures of each respective drug were analyzed over 24 hours. Actual y-site infusion followed a 4-hour extended-infusion protocol, with aliquots tested hourly for 4 hours. At all time points, the compatibility of each admixture was determined using 6 different methods: visual, microscopic, Tyndall beam, nephelometric, pH, and microbiologic bioassay assessment. If any admixture failed any one of these 6 assays, it was considered incompatible. Any combination deemed incompatible was filtered through a 0.22 μm filter and reanalyzed to assess impact of particle size. Results: There were no differences in compatibility categorizations between simulated and actual y-site infusion. There were no changes in compatibility over the time course of any experiment. Ceftazidime-avibactam at 8 mg/mL was incompatible with vancomycin at 5 mg/mL. The maximum compatible vancomycin concentrations were 5 mg/mL and 10 mg/mL with 20 and 40 mg/mL of ceftazidime-avibactam, respectively. Ceftolozane-tazobactam 15 mg/mL was compatible with vancomycin concentrations up to 10 mg/mL. The maximum compatible vancomycin concentration with piperacillin-tazobactam 28 mg/mL was 5 mg/mL. None of the β-lactam/β-lactamase inhibitors tested were compatible with 15 or 20 mg/mL of vancomycin. None of the admixtures considered incompatible by other methods displayed any decrease in antimicrobial activity as assessed by bioassay. After filtration, all admixtures originally deemed incompatible maintained their visual turbidity and microscopic particulate matter. Conclusions: Ceftazidime-avibactam prepared at the lowest concentration recommended in the package insert is incompatible with vancomycin. Ceftolozane-tazobactam did not display incompatibility until vancomycin concentrations above 10 mg/mL were tested. Piperacillin-tazobactam at a typical extended-infusion concentration is compatible with vancomycin in D5W. To our knowledge, this is the first study to assess compatibility of antibiotic admixtures via direct measurement of antimicrobial activity. The lack of any decrement in antibacterial activity of any apparently incompatible admixture and maintenance of incompatibility after passage through a 0.22 μm filter may suggest a lack of clinically relevant adverse effects when co-administered. Future compatibility studies should incorporate appropriate methods to accurately assess both efficacy and safety of co-administered drug products.

Pharmacokinetics and Dialytic Clearance of Ceftazidime-Avibactam in a Critically Ill Patient on Continuous Venovenous Hemofiltration

Ceftazidime-avibactam administered at 1.25 g every 8 h was used to treat multidrug-resistant Pseudomonas aeruginosa bacteremia in a critically ill patient on continuous venovenous hemofiltration (CVVH). Prefiltration plasma drug concentrations of ceftazidime and avibactam were measured at 0, 1, 2, 4, 6, and 8 h along with postfiltration and ultrafiltrate concentrations at h 2 and h 6. Plasma pharmacokinetic parameters of ceftazidime and avibactam, respectively, were as follows: maximum plasma concentration (C_max), 61.10 and 14.54 mg/liter; minimum plasma concentration (C_min), 31.96 and 8.45 mg/liter; half-life (t_1/2), 6.07 and 6.78 h; apparent volume of distribution at the steady state (V_ss), 27.23 and 30.81 liters; total clearance at the steady state (CL_ss), 2.87 and 2.95 liters/h; area under the concentration-time curve from 0 to 8 h (AUC_0-8), 347.87 and 85.69 mg · h/liter. Concentrations of ceftazidime in plasma exceeded the ceftazidime-avibactam MIC (6 mg/liter) throughout the 8-h dosing interval. Mean CVVH extraction ratios for ceftazidime and avibactam were 14.44% and 11.53%, respectively, and mean sieving coefficients were 0.96 and 0.93, respectively. The calculated mean clearance of ceftazidime by CVVH was 1.64 liters/h and for avibactam was 1.59 liters/h, representing 57.1% of the total clearance of ceftazidime and 54.3% of the total clearance of avibactam. Further data that include multiple patients and dialysis modes are needed to verify the optimal ceftazidime-avibactam dosing strategy during critical illness and CVVH.

Pharmacodynamic and pharmacokinetic considerations in the treatment of critically Ill patients infected with carbapenem-resistant Enterobacteriaceae

Carbapenem-Resistant Enterobacteriaceae (CRE) are an emerging healthcare crisis. Infections due to CRE are associated with high morbidity and mortality, especially in critically ill patients. Due to the multi-drug resistant nature of these infections only limited treatment options are available. Antimicrobials that have been described for the treatment of CRE infections include carbapenems, polymyxins, fosfomycin, tigecycline, aminoglycosides, and ceftazidime-avibactam. Given the limited treatment options it is imperative the pharmacokinetic and pharmacodynamics (PK-PD) characteristics of these agents are considered to optimize treatment regimens. This review will focus on the PK-PD challenges of the current treatment options for CRE infections.

Cephem Potentiation by Inactivation of Nonessential Genes Involved in Cell Wall Biogenesis of β-Lactamase-Producing Escherichia coli

Reversal of antimicrobial resistance is an appealing and largely unexplored strategy in drug discovery. The objective of this study was to identify potential targets for "helper" drugs reversing cephem resistance in Escherichia coli strains producing β-lactamases. A CMY-2-encoding plasmid was transferred by conjugation to seven isogenic deletion mutants exhibiting cephem hypersusceptibility. The effect of each mutation was evaluated by comparing the MICs in the wild type and the mutant harboring the same plasmid. Mutation of two genes encoding proteins involved in cell wall biosynthesis, dapF and mrcB, restored susceptibility to cefoxitin (FOX) and reduced the MICs of cefotaxime and ceftazidime, respectively, from the resistant to the intermediate category according to clinical breakpoints. The same mutants harboring a CTX-M-1-encoding plasmid fell into the intermediate or susceptible category for all three drugs. Individual deletion of dapF and mrcB in a clinical isolate of CTX-M-15-producing E. coli sequence type 131 (ST131) resulted in partial reversal of ceftazidime and cefepime resistance but did not reduce MICs below susceptibility breakpoints. Growth curve analysis indicated no fitness cost in a ΔmrcB mutant, whereas a ΔdapF mutant had a 3-fold longer lag phase than the wild type, suggesting that drugs targeting DapF may display antimicrobial activity, in addition to synergizing with selected cephems. DapF appeared to be a potential FOX helper drug target candidate, since dapF inactivation resulted in synergistic potentiation of FOX in the genetic backgrounds tested. The study showed that individual inactivation of two nonessential genes involved in cell wall biogenesis potentiates cephem activity according to drug- and strain-specific patterns.

A review on cell wall synthesis inhibitors with an emphasis on glycopeptide antibiotics

Cell wall biosynthesis inhibitors (CBIs) have historically been one of the most effective classes of antibiotics. They are the most extensively used class of antibiotics and their importance is exemplified by the β-lactams and glycopeptide antibiotics. However, this class of antibiotics has not received impunity from resistance development. In the wake of this predicament, this review presents the progress of CBIs, especially glycopeptide derivatives as antibiotics to confront antibacterial resistance. The various strategies used for the development of CBIs, their clinical status and possible directions in which this field can evolve have also been discussed.

Evaluation of Genotypic and Phenotypic Methods to Detect Carbapenemase Production in Gram-Negative Bacilli

BACKGROUND

Carbapenemase-producing gram-negative bacteria (CP-GNB) are an urgent and expanding public health threat. Rapid and accurate identification of these organisms facilitates infection prevention efforts in healthcare facilities. The objective of our study was to evaluate methods to detect and identify CP-GNB.

METHODS

We examined 189 carbapenem-resistant GNB(CR-GNB), including Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii complex, using 3 different methods: 2 methods to screen isolates of GNB for carbapenemase production [the carbapenem inactivation method (CIM) and 2 chromogenic agars] and a molecular method (Cepheid GeneXpert Carba-R) to identify the mechanism of carbapenem resistance and the associated resistance genes (bla_KPC, bla_NDM, bla_IMP, bla_OXA-48-like, and bla_VIM).

RESULTS

The CIM was a simple and inexpensive phenotypic screen to differentiate between CR-GNB and CP-GNB, with improved analytical performance characteristics and inter-reader correlation compared to the modified Hodge test. Both chromogenic agars evaluated (HardyCHROM CRE and chromID CARBA) were able to support growth of most of the organisms tested, including isolates possessing the bla_OXA-48-like gene. However, these media had a low analytical specificity for carbapenemase production, with breakthrough of CR-GNB that did not produce a carbapenemase. The Xpert Carba-R assay was rapid and easy to perform, and demonstrated 100% positive and negative agreement for characterization of genetic determinants of carbapenem resistance.

CONCLUSIONS

Screening by CIM followed by the Xpert Carba-R PCR is an accurate method for detecting and characterizing CP-GNB, including Enterobacteriaceae, P. aeruginosa, and A. baumannii complex.

Ceftazidime-avibactam (CTZ-AVI) as a treatment for hospitalized adult patients with complicated intra-abdominal infections

Avibactam, a novel β-lactamase inhibitor, has recently been co-formulated with ceftazidime and approved for use in patients with complicated intra-abdominal and urinary tract infections, where no better treatment alternative exists. The basis for its FDA approval has been the extensive clinical experience with ceftazidime and the demonstration in vitro and in animal models that the addition of avibactam reverses resistance to ceftazidime in extended-spectrum β-lactamase and some carbapenemase-producing Enterobacteriaceae. Early clinical data are promising, with efficacy demonstrated in patients with complicated intra-abdominal and urinary tract infections. This review will summarize the in vitro, animal and clinical data available on this agent to date.

Updates in the Management of Cephalosporin-Resistant Gram-Negative Bacteria

Resistance to cephalosporins is now common among Gram-negative bacterial infections, including those caused by the Enterobacteriaceae and Pseudomonas aeruginosa, posing a major threat to public health. As resistance to the traditional drugs of choice for these infections, carbapenems, has also become increasingly common, interest in cefepime and piperacillin-tazobactam as carbapenem-sparing alternatives has increased. Additionally, the availability of the novel β-lactam-β-lactamase inhibitor combinations ceftolozane-tazobactam and ceftazidime-avibactam has added to the antimicrobial armamentarium available to treat these multidrug-resistant infections. Here, we review the recent literature on the use of carbapenem-sparing alternatives and highlight the potential utility of novel antimicrobials.

Effect of β-Lactamase inhibitors on in vitro activity of β-Lactam antibiotics against Burkholderia cepacia complex species

BACKGROUND

Bacteria belonging to the Burkholderia cepacia complex (Bcc) are an important cause of chronic respiratory tract infections in cystic fibrosis patients. Intrinsic resistance to a wide range of antimicrobial agents, including a variety of β-lactam antibiotics, is frequently observed in Bcc strains. Resistance to β-lactams is most commonly mediated by efflux pumps, alterations in penicillin-binding proteins or the expression of β-lactamases. β-lactamase inhibitors are able to restore the in vitro activity of β-lactam molecules against a variety of Gram-negative species, but the effect of these inhibitors on the activity of β-lactam treatment against Bcc species is still poorly investigated.

METHODS

In the present study, the susceptibility of a panel of Bcc strains was determined towards the β-lactam antibiotics ceftazidime, meropenem, amoxicillin, cefoxitin, cefepime and aztreonam; alone or in combination with a β-lactamase inhibitor (clavulanic acid, sulbactam, tazobactam and avibactam). Consequently, β-lactamase activity was determined for active β-lactam/β-lactamase inhibitor combinations.

RESULTS

Clavulanic acid had no effect on minimum inhibitory concentrations, but addition of sulbactam, tazobactam or avibactam to ceftazidime, amoxicillin, cefoxitin, cefepime or aztreonam leads to increased susceptibility (at least 4-fold MIC-decrease) in some Bcc strains. The effect of β-lactamase inhibitors on β-lactamase activity is both strain- and/or antibiotic-dependent, and other mechanisms of β-lactam resistance (besides production of β-lactamases) appear to be important.

CONCLUSIONS

Considerable differences in susceptibility of Bcc strains to β-lactam antibiotics were observed. Results obtained in the present study suggest that resistance of Bcc strains against β-lactam antibiotics is mediated by both β-lactamases and non-β-lactamase-mediated resistance mechanisms.

Ceftazidime-avibactam for the treatment of complicated intra-abdominal infections

INTRODUCTION

The treatment of complicated intra-abdominal infections (cIAI) is increasingly challenging due to increased resistance of Gram-negative organisms. These multidrug resistant organisms lead to an increase in morbidity and mortality. This has led to renewed interest in use of older β-lactam antibiotics in combination with newer β-lactamase inhibitors. Ceftazidime-avibactam is one of the newest such combination antibiotics, which has been released for treatment of complicated intra-abdominal infections in combination with metronidazole. Areas covered: In this drug evaluation manuscript cIAI along with the chemistry, pharmacodynamics, pharmacokinetics, metabolism and clinical study results of ceftazidime-avibactam are reviewed. Expert opinion: The role of ceftazidime-avibactam in combination with metronidazole in the treatment of cIAI is still to be defined. Patients with cIAI known to be infected with Klebsiella pneumoniae carbapenemase-producing Enterobacteriaceae would be clear candidates for treatment with this agent, as would patients infected with more common types of extended-spectrum β-lactamase producing Gram-negative pathogens if a carbapenem alternative were desired. At present, it is difficult to establish a clear group of patients with cIAI for whom initial empiric therapy with this agent would be warranted.

Establishment of a Simple and Quick Method for Detecting Extended-Spectrum β-Lactamase (ESBL) Genes in Bacteria

Extended-spectrum β-lactamase (ESBL) genes that render bacteria resistant to antibiotics are commonly detected using phenotype testing, which is time consuming and not sufficiently accurate. To establish a better method, we used phenotype testing to identify ESBL-positive bacterial strains and conducted PCR to screen for TEM (named after the patient Temoneira who provided the first sample), sulfhydryl reagent variable (SHV), cefotaxime (CTX)-M-1, and CTX-M-9, the 4 most common ESBL types and subtypes. We then performed multiplex PCR with 1 primer containing a biotin and hybridized the PCR products with gene-specific probes that were coupled with microbeads and coated with a specific fluorescence. The hybrids were linked to streptavidin-R-phycoerythrins (SA-PEs) and run through a flow cytometer, which sorted the fluorescently dyed microbeads and quantified the PEs. The results from single PCR, multiplex PCR, and cytometry were consistent with each other. We used this method to test 169 clinical specimens that had been determined for phenotypes and found 154 positive for genotypes, including 30 of the 45 samples that were negative for phenotypes. The CTX-M genotype tests alone, counting both positive and negative cases, showed 99.41% (168/169) consistency with the ESBL phenotype test. Thus, we have established a multiplex-PCR system as a simple and quick method that is high throughput and accurate for detecting 4 common ESBL types and subtypes.

Bacterial fatty acid metabolism in modern antibiotic discovery

Bacterial fatty acid synthesis is essential for many pathogens and different from the mammalian counterpart. These features make bacterial fatty acid synthesis a desirable target for antibiotic discovery. The structural divergence of the conserved enzymes and the presence of different isozymes catalyzing the same reactions in the pathway make bacterial fatty acid synthesis a narrow spectrum target rather than the traditional broad spectrum target. Furthermore, bacterial fatty acid synthesis inhibitors are single-targeting, rather than multi-targeting like traditional monotherapeutic, broad-spectrum antibiotics. The single-targeting nature of bacterial fatty acid synthesis inhibitors makes overcoming fast-developing, target-based resistance a necessary consideration for antibiotic development. Target-based resistance can be overcome through multi-targeting inhibitors, a cocktail of single-targeting inhibitors, or by making the single targeting inhibitor sufficiently high affinity through a pathogen selective approach such that target-based mutants are still susceptible to therapeutic concentrations of drug. Many of the pathogens requiring new antibiotic treatment options encode for essential bacterial fatty acid synthesis enzymes. This review will evaluate the most promising targets in bacterial fatty acid metabolism for antibiotic therapeutics development and review the potential and challenges in advancing each of these targets to the clinic and circumventing target-based resistance. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.

Managing Pseudomonas aeruginosa respiratory infections in cystic fibrosis

PURPOSE OF REVIEW

The current guidelines and recent clinical research in the management of Pseudomonas aeruginosa respiratory infections in cystic fibrosis (CF) are reviewed. Areas where further research is required will also be highlighted.

RECENT FINDINGS

P. aeruginosa is a key respiratory pathogen in CF. Inhaled tobramycin or colistin is recommended for early eradication to prevent establishment of chronic infection. Other antibiotic options are currently being investigated. The long-term success of eradication strategies is also now being assessed. The use of inhaled antibiotics in the management of chronic P. aeruginosa infection is an area of active investigation. Acute pulmonary exacerbations are still a major cause of morbidity and mortality. Guidelines continue to recommend combination intravenous therapy but further research is required to clarify the advantage of this approach. Multidrug resistance is common and potentially more effective antipseudomonal antibiotics may soon become available.

SUMMARY

The management of P. aeruginosa respiratory infection in CF remains a challenging area, especially in the setting of multidrug resistance. The role of inhaled antibiotics continues to be expanded. Further research is required in the key areas of eradication and management of chronic infection and acute pulmonary exacerbations to identify those treatments that optimize long-term, clinical benefits.

Spotlight on ceftazidime/avibactam: a new option for MDR Gram-negative infections

During the last decade infections caused by MDR Gram-negative bacteria (GNB) have become increasingly prevalent. Because of their high morbidity and mortality rates, these infections constitute a serious threat to public health worldwide. Ceftazidime/avibactam is a new approved agent combining ceftazidime and a novel β-lactamase inhibitor with activity against various β-lactamases produced by MDR GNB. Avibactam has a spectrum of inhibition of class A and C β-lactamases, including ESBLs, AmpC and Klebsiella pneumoniae carbapenemase (KPC) enzymes. Thus, combination with this inhibitor expands ceftazidime's spectrum of activity to MDR Enterobacteriaceae and Pseudomonas aeruginosa strains. In Phase II clinical trials of patients with complicated intra-abdominal infections and complicated urinary tract infections ceftazidime/avibactam exhibited clinical efficacy comparable to those of meropenem and imipenem/cilastatin, respectively. A Phase III clinical trial confirmed the efficacy of ceftazidime/avibactam in patients with MDR Enterobacteriaceae and P. aeruginosa infections. Microbiological surveillance studies, in vivo animal models of infection and pharmacokinetic/pharmacodynamic target attainment analyses are also discussed, to assess the potential role of this new drug in the treatment of infections caused by MDR GNB.

Recent Advances in the Rational Design and Optimization of Antibacterial Agents

This review discusses next-generation antibacterial agents developed using rational, or targeted, drug design strategies. The focus of this review is on small-molecule compounds that have been designed to bypass developing bacterial resistance, improve the antibacterial spectrum of activity, and/or to optimize other properties, including physicochemical and pharmacokinetic properties. Agents are discussed that affect known antibacterial targets, such as the bacterial ribosome, nucleic acid binding proteins, and proteins involved in cell-wall biosynthesis; as well as some affecting novel bacterial targets which do not have currently marketed agents. The discussion of the agents focuses on the rational design strategies employed and the synthetic medicinal chemistry and structure-based design techniques utilized by the scientists involved in the discoveries, including such methods as ligand- and structure-based strategies, structure-activity relationship (SAR) expansion strategies, and novel synthetic organic chemistry methods. As such, the discussion is limited to small-molecule therapeutics that have confirmed macromolecular targets and encompasses only a fraction of all antibacterial agents recently approved or in late-stage clinical trials. The antibacterial agents selected have been recently approved for use on the U.S. or European markets or have shown promising results in phase 2 or phase 3 U.S.

CLINICAL TRIALS

[Rational antibiotic treatment of mediastinitis]

Mediastinitis occurs as a severe complication of thoracic and cardiac surgical interventions and is the result of traumatic esophageal perforation, conducted infections or as a result of lymphogenic and hematogenic spread of specific infective pathogens. Treatment must as a rule be accompanied by antibiotics, whereby knowledge of the spectrum of pathogens depending on the pathogenesis is indispensable for successful antibiotic therapy. Polymicrobial infections with a high proportion of anaerobes are found in conducted infections of the mediastinum and after esophageal perforation. After cardiac surgery Staphylococci are the dominant pathogens and a nasal colonization with Staphylococcus aureus seems to be a predisposing risk factor. Fungi are the predominant pathogens in immunocompromised patients with consumptive underlying illnesses and can cause acute or chronic forms with granulomatous inflammation. Resistant pathogens are increasingly being found in high-risk patient cohorts, which must be considered for a calculated therapy. For calculated antibiotic therapy the administration of broad spectrum antibiotics, mostly beta-lactams alone or combined with metronidazole is the therapy of choice for both Gram-positive and Gram-negative bacteria inclusive of anaerobes. For patients at risk, additional antibiotic classes with a spectrum against methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant Enterococcus (VRE) can be administered. Increasing rates of multidrug-resistant Gram-negative bacteria (e.g. Enterobacteriaceae) and non-fermenting bacteria (e.g. Pseudomonas and Acinetobacter) in individual cases necessitates the use of polymyxins (e.g. colistin), new tetracyclines (e.g. glycylglycines) and newly developed combinations of beta-lactams and beta-lactam inhibitors. For treatment of fungal infections (e.g. Candida, Aspergillus and Histoplasma) established and novel azoles, amphotericin B and echinocandins seem to be successful; however, detection of Candida, particularly in mixed infections does not always necessitate treatment. Mediastinitis is still a severe infectious disease with a high mortality, which necessitates an early and broad spectrum antibiotic therapy; however, with respect to optimal duration of therapy and selection of antibiotics, data from good quality comparative studies are lacking.

Critical evaluation of ceftolozane-tazobactam for complicated urinary tract and intra-abdominal infections

The rise in resistant Gram-negative pathogens continues to challenge clinicians treating infections. These resistant infections have inspired the development of new antimicrobial agents, including ceftolozane-tazobactam, a novel β-lactam/β-lactamase inhibitor combination approved by the US Food and Drug Administration for the treatment of complicated urinary tract infections (cUTIs) and complicated intra-abdominal infections (cIAIs) in combination with metronidazole. Ceftolozane exhibits bactericidal activity by inhibiting penicillin-binding proteins (PBPs), with high affinity for PBP1b, PBP1c, and PBP3. The addition of tazobactam protects ceftolozane from hydrolysis by irreversibly binding to some β-lactamase enzymes. Ceftolozane-tazobactam is active against a wide range of Gram-negative pathogens, including extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and multidrug-resistant (MDR) Pseudomonas aeruginosa, several streptococcal species, and Bacteroides fragilis. When anaerobic coverage is needed, it should be used in combination with metronidazole. Ceftolozane demonstrates linear pharmacokinetics, low protein binding, and minimal accumulation with repeated dosing. The major pharmacokinetic/pharmacodynamic index for ceftolozane is the percentage of the dosing interval in which the plasma free drug concentration remains higher than the minimum inhibitory concentration (%T.MIC). Phase III clinical trials for the treatment of cUTIs and cIAIs have been completed, showing that it is an effective and safe alternative for the treatment of these infections. The approved dose for cUTIs and cIAIs is 1.5 g (1 g ceftolozane and 500 mg tazobactam) infused over 1 hour every 8 hours. A higher 3 g dose is currently in Phase III trials for the treatment of ventilated nosocomial pneumonia. Dosage adjustments are necessary for patients with moderate-to-severe renal impairment. Current data suggest that ceftolozane-tazobactam is a promising carbapenem-sparing alternative agent for the treatment of cUTIs and cIAIs, including those caused by ESBL-producing Enterobacteriaceae and MDR P. aeruginosa.

Clinical and laboratory considerations for the rapid detection of carbapenem-resistant Enterobacteriaceae

Carbapenem resistance among the Enterobacteriaceae has become a significant clinical and public health dilemma. Rapid administration of effective antimicrobials and implementation of supplemental infection control practices is required to both improve patient outcomes and limit the spread of these highly resistant organisms. However, carbapenem-resistant Enterobacteriaceae (CRE)-infected patients are predominantly identified by routine culture methods, which take days to perform. Rapid genomic and phenotypic methods are currently available to accelerate the identification of carbapenemase-producing CRE. Effective use of these technologies is reliant on close collaboration between clinical microbiology, infection prevention, antimicrobial stewardship and infectious diseases specialists. This review discusses the performance characteristics of these technologies to date, and describes strategies for their optimal implementation.

Insights into Newer Antimicrobial Agents Against Gram-negative Bacteria

Currently, drug resistance, especially against cephalosporins and carbapenems, among gram-negative bacteria is an important challenge, which is further enhanced by the limited availability of drugs against these bugs. There are certain antibiotics (colistin, fosfomycin, temocillin, and rifampicin) that have been revived from the past to tackle the menace of superbugs, including members of Enterobacteriaceae, Acinetobacter species, and Pseudomonas species. Very few newer antibiotics have been added to the pool of existing drugs. There are still many antibiotics that are passing through various phases of clinical trials. The initiative of Infectious Disease Society of America to develop 10 novel antibiotics against gram-negative bacilli by 2020 is a step to fill the gap of limited availability of drugs. This review aims to provide insights into the current and newer drugs in pipeline for the treatment of gram-negative bacteria and also discusses the major challenging issues for their management.

Ceftazidime-Avibactam: A Novel Cephalosporin/β-Lactamase Inhibitor Combination for the Treatment of Resistant Gram-negative Organisms

PURPOSE

Multidrug-resistant gram-negative bacterial infections have emerged as a major threat in hospitalized patients. Treatment options are often inadequate and, as a result, these infections are associated with high mortality. A cephalosporin and a novel synthetic non-β-lactam, β-lactamase inhibitor, ceftazidime-avibactam, is approved for the treatment of serious infections caused by resistant gram-negative bacteria. This article reviews the spectrum of activity, clinical pharmacology, pharmacodynamic and pharmacokinetic properties, clinical efficacy and tolerability, and dosing and administration of ceftazidime-avibactam.

METHODS

Searches of MEDLINE and International Pharmaceutical Abstracts from 1980 to September 2015 were conducted by using the search terms ceftazidime, avibactam, and ceftazidime-avibactam. Abstracts from Infectious Disease Week (2014-2015), the Interscience Conference on Antimicrobial Agents and Chemotherapy (2014-2015), and the European Congress of Clinical Microbiology and Infectious Diseases were also searched.

FINDINGS

Ceftazidime, a third-generation cephalosporin, when combined with avibactam has a significant improvement in its activity against β-lactamase-producing gram-negative pathogens, including extended-spectrum β-lactamases, AmpC β-lactamases, Klebsiella pneumoniae carbapenemase-producing Enterobacteriaceae, and multidrug-resistant Pseudomonas aeruginosa. Data from 2 Phase II and 1 Phase III clinical trial are available. In the Phase II trial of patients with complicated intra-abdominal infections, ceftazidime-avibactam produced clinical cure rates comparable to meropenem (91.2% vs 93.4%). Similarly, patients receiving ceftazidime-avibactam in a Phase II study of complicated urinary tract infections had clinical and microbiologic response rates similar to those receiving imipenem-cilastatin (70.4% and 71.4% microbiologic success rates, respectively). A Phase III trial compared ceftazidime-avibactam to best available therapy for the treatment of ceftazidime-resistant organisms. Clinical response and microbiological response for ceftazidime-avibactam versus best available therapy was comparable (90.9% and 91.2% clinical response, respectively); (81.8% and 63.5% microbiological response, respectively).

IMPLICATIONS

Currently, ceftazidime-avibactam is approved for the indications of complicated intra-abdominal infections (with metronidazole) and complicated urinary tract infections. Clinical trials published to date on this antimicrobial agent have shown its excellent safety and tolerability. This new combination agent has a role, but its use should be limited to patients without other treatment options in the empiric and documented treatment of multidrug-resistant gram-negative organisms. Further investigation is needed in patients with carbapenemase-producing Enterobacteriaceae and multidrug-resistant P aeruginosa who have bacteremia or nosocomial or ventilator-associated pneumonia. It is imperative that ceftazidime-avibactam be used in a responsible manner so that its effectiveness can be retained.

Carbapenem resistance: overview of the problem and future perspectives

Carbapenem resistance, mainly among Gram-negative pathogens, is an ongoing public-health problem of global dimensions. This type of antimicrobial resistance, especially when mediated by transferable carbapenemase-encoding genes, is spreading rapidly causing serious outbreaks and dramatically limiting treatment options. In this article, important key points related to carbapenem resistance are reviewed and future perspectives are discussed.

Post-hemodialysis dosing of 1 vs. 2 g of ceftazidime in anuric end-stage renal disease patients on low-flux dialysis and its pharmacodynamic implications on clinical use

Ceftazidime is a cost-effective antimicrobial against Gram-negative pathogens associated with sepsis in end-stage renal disease (ESRD) hemodialysis patients with potential for wider use with the advent of ceftazidime-avibactam. Dosing ceftazidime post-hemodialysis appears attractive and convenient, but limited in vivo data on pharmacodynamic efficacy (PE) attainment, defined as >70% of the interdialytic period drug concentrations exceed susceptible pathogens minimal inhibitory concentrations (MICs) (%TMIC), warrants further assessment. We therefore evaluated PE and tolerability of 1 against 2 g regime in anuric ESRD patients on low-flux hemodialysis. Two doses of 1 or 2 g ceftazidime were administered post-hemodialysis prior to 48- and 72-hour interdialytic intervals in ESRD inpatients without active infections. Peak and trough concentrations (mg/L) were assayed using a validated liquid chromatography-tandem mass spectrometry method. Proportion of patients achieving PE for known pathogens with MICs ≤ 8 mg/L and adverse effects were assessed. Six (43%) and eight (57%) adult patients received 1 and 2 g dose, respectively. Median (25th-75th percentile), peak, 48- and 72-hour trough ceftazidime concentrations were 78 (60-98) vs. 158 (128-196), 37 (23-37) vs. 49 (39-71), and 13 (12-20) vs. 26 (21-41) mg/L, respectively, resulting in 100% TMIC for both doses. One patient on the 1-g dose experienced mild pruritus. Reliable and safe PE attainment over both 48- and 72-hour interdialytic interval was achievable with 1 g of ceftazidime dosed post-hemodialysis. The 2 g dose was equally effective and well tolerated but may not be necessary. These findings need validation in non-anuric patients, high-flux hemodialysis, and during avibactam co-administration.