Activities of NXL104 combinations with ceftazidime and aztreonam against carbapenemase-Producing Enterobacteriaceae

Safety and pharmacokinetics of single and multiple ascending doses of avibactam alone and in combination with ceftazidime in healthy male volunteers: results of two randomized, placebo-controlled studies

BACKGROUND AND OBJECTIVE

Avibactam is a novel non-β-lactam β-lactamase inhibitor effective against Ambler class A, C and some class D β-lactamases that is currently in clinical development in combination with ceftazidime for the treatment of serious Gram-negative infections. It restores the in vitro activity of a range of β-lactams, including ceftazidime, against extended-spectrum β-lactamase-producing pathogens. Two phase I studies assessed the safety and pharmacokinetics of avibactam in healthy subjects when administered alone or with ceftazidime.

METHODS

The first study (NXL104-1001) was a placebo-controlled, single-ascending dose study assessing avibactam 50, 100, 250, 500, 1000, 1500 or 2000 mg given as a 30-min intravenous infusion. After a 7-day washout, subjects in the 250 and 500 mg dosing groups received a second avibactam dose with concomitant ceftazidime 1000 or 2000 mg, respectively. The second study (NXL104-1002) was performed in two parts. Part 1 assessed multiple-ascending doses of avibactam. Subjects were randomized to receive avibactam 500, 750 or 1000 mg every 8 h (q8 h) over 5 days, or ceftazidime-avibactam 2000-500 mg q8 h over 10 days. Part 2 assessed bioavailability of avibactam after a single oral dose (500 mg) relative to a single 30-min intravenous infusion (500 mg).

RESULTS

No serious or severe adverse events were reported in either study. Avibactam exposure generally increased proportionally to dose and there was no trend for accumulation after multiple doses. Almost all avibactam was excreted largely unchanged in the urine within the first 6 h. Concomitant ceftazidime did not affect avibactam's safety and pharmacokinetic profile. Avibactam exposure after oral dosing was very low at 6.2 % of that observed after intravenous infusion.

CONCLUSION

Avibactam was generally well tolerated across all dosing regimens, when given alone or with ceftazidime. Avibactam exposure was dose related in both studies, and avibactam pharmacokinetics were linear and not affected by ceftazidime.

Targeting Antibiotic Resistance

Finding strategies against the development of antibiotic resistance is a major global challenge for the life sciences community and for public health. The past decades have seen a dramatic worldwide increase in human-pathogenic bacteria that are resistant to one or multiple antibiotics. More and more infections caused by resistant microorganisms fail to respond to conventional treatment, and in some cases, even last-resort antibiotics have lost their power. In addition, industry pipelines for the development of novel antibiotics have run dry over the past decades. A recent world health day by the World Health Organization titled "Combat drug resistance: no action today means no cure tomorrow" triggered an increase in research activity, and several promising strategies have been developed to restore treatment options against infections by resistant bacterial pathogens.

The road to avibactam: the first clinically useful non-β-lactam working somewhat like a β-lactam

Avibactam, which is the first non-β-lactam β-lactamase inhibitor to be introduced for clinical use, is a broad-spectrum serine β-lactamase inhibitor with activity against class A, class C, and, some, class D β-lactamases. We provide an overview of efforts, which extend to the period soon after the discovery of the penicillins, to develop clinically useful non-β-lactam compounds as antibacterials, and, subsequently, penicillin-binding protein and β-lactamase inhibitors. Like the β-lactam inhibitors, avibactam works via a mechanism involving covalent modification of a catalytically important nucleophilic serine residue. However, unlike the β-lactam inhibitors, avibactam reacts reversibly with its β-lactamase targets. We discuss chemical factors that may account for the apparently special nature of β-lactams and related compounds as antibacterials and β-lactamase inhibitors, including with respect to resistance. Avenues for future research including non-β-lactam antibacterials acting similarly to β-lactams are discussed.

Activity of Ceftazidime-Avibactam against Extended-Spectrum- and AmpC β-Lactamase-Producing Enterobacteriaceae Collected in the INFORM Global Surveillance Study from 2012 to 2014

The in vitro activity of ceftazidime-avibactam was evaluated against 34,062 isolates of Enterobacteriaceae from patients with intra-abdominal, urinary tract, skin and soft-tissue, lower respiratory tract, and blood infections collected in the INFORM (International Network For Optimal Resistance Monitoring) global surveillance study (176 medical center laboratories in 39 countries) in 2012 to 2014. Overall, 99.5% of Enterobacteriaceae isolates were susceptible to ceftazidime-avibactam using FDA approved breakpoints (susceptible MIC of ≤8 μg/ml; resistant MIC of ≥16 μg/ml). For individual species of the Enterobacteriaceae, the ceftazidime-avibactam MIC inhibiting ≥90% of isolates (MIC90) ranged from 0.06 μg/ml for Proteus species to 1 μg/ml for Enterobacter spp. and Klebsiella pneumoniae Carbapenem-susceptible isolates of Escherichia coli, K. pneumoniae, Klebsiella oxytoca, and Proteus mirabilis with a confirmed extended-spectrum β-lactamase (ESBL) phenotype, or a ceftazidime MIC of ≥16 μg/ml if the ESBL phenotype was not confirmed by clavulanic acid inhibition, were characterized further to identify the presence of specific ESBL- and plasmid-mediated AmpC β-lactamase genes using a microarray-based assay and additional PCR assays. Ceftazidime-avibactam demonstrated potent activity against molecularly confirmed ESBL-producing (n = 5,354; MIC90, 0.5 μg/ml; 99.9% susceptible), plasmid-mediated AmpC-producing (n = 246; MIC90, 0.5 μg/ml; 100% susceptible), and ESBL- and AmpC-producing (n = 152; MIC90, 1 μg/ml; 100% susceptible) isolates of E. coli, K. pneumoniae, K. oxytoca, and P. mirabilis We conclude that ceftazidime-avibactam demonstrates potent in vitro activity against globally collected clinical isolates of Enterobacteriaceae, including isolates producing ESBLs and AmpC β-lactamases.

In Vitro and In Vivo Activities of OP0595, a New Diazabicyclooctane, against CTX-M-15-Positive Escherichia coli and KPC-Positive Klebsiella pneumoniae

Gram-negative bacteria are evolving to produce β-lactamases of increasing diversity that challenge antimicrobial chemotherapy. OP0595 is a new diazabicyclooctane serine β-lactamase inhibitor which acts also as an antibiotic and as a β-lactamase-independent β-lactam "enhancer" against Enterobacteriaceae Here we determined the optimal concentration of OP0595 in combination with piperacillin, cefepime, and meropenem, in addition to the antibacterial activity of OP0595 alone and in combination with cefepime, in in vitro time-kill studies and an in vivo infection model against five strains of CTX-M-15-positive Escherichia coli and five strains of KPC-positive Klebsiella pneumoniae An OP0595 concentration of 4 μg/ml was found to be sufficient for an effective combination with all three β-lactam agents. In both in vitro time-kill studies and an in vivo model of infection, cefepime-OP0595 showed stronger efficacy than cefepime alone against all β-lactamase-positive strains tested, whereas OP0595 alone showed weaker or no efficacy. Taken together, these data indicate that combinational use of OP0595 and a β-lactam agent is important to exert the antimicrobial functions of OP0595.

In Vitro Susceptibility to Ceftazidime-Avibactam of Carbapenem-Nonsusceptible Enterobacteriaceae Isolates Collected during the INFORM Global Surveillance Study (2012 to 2014)

The activity of ceftazidime-avibactam was assessed against 961 isolates of meropenem-nonsusceptible Enterobacteriaceae Most meropenem-nonsusceptible metallo-β-lactamase (MBL)-negative isolates (97.7%) were susceptible to ceftazidime-avibactam. Isolates that carried KPC or OXA-48-like β-lactamases, both alone and in combination with extended-spectrum β-lactamases (ESBLs) and/or AmpC β-lactamases, were 98.7% and 98.5% susceptible to ceftazidime-avibactam, respectively. Meropenem-nonsusceptible, carbapenemase-negative isolates demonstrated 94.7% susceptibility to ceftazidime-avibactam. Ceftazidime-avibactam activity was compromised only in isolates for which carbapenem resistance was mediated through metallo-β-lactamases.

Determination of avibactam and ceftazidime in human plasma samples by LC-MS

AIM

Avibactam, a novel non-β-lactam β-lactamase inhibitor co-administrated with the β-lactam antibiotic ceftazidime, is in clinical development. The need to evaluate its PK and PD requires accurate and reliable bioanalytical methods.

METHODS

We describe LC-MS/MS methods for the determination of avibactam and ceftazidime in human plasma. Avibactam was extracted using weak anionic exchange solid-phase extraction and analyzed on an amide column. Ceftazidime was extracted using protein precipitation and analyzed on a C18 column. Calibration curves were established over 10-10,000 ng/ml (avibactam) and 43.8-87,000 ng/ml (ceftazidime).

RESULTS & CONCLUSION

Method validation, cross-validation between three laboratories and incurred sample re-analysis demonstrated method robustness. The methods were successfully applied to multiple clinical studies.

Treatment options for infections caused by carbapenem-resistant Enterobacteriaceae: can we apply "precision medicine" to antimicrobial chemotherapy?

INTRODUCTION

For the past three decades, carbapenems played a central role in our antibiotic armamentarium, trusted to effectively treat infections caused by drug-resistant bacteria. The utility of this class of antibiotics has been compromised by the emergence of resistance especially among Enterobacteriaceae.

AREAS COVERED

We review the current mainstays of pharmacotherapy against infections caused by carbapenem-resistant Enterobacteriaceae (CRE) including tigecycline, aminoglycosides, and rediscovered 'old' antibiotics such as fosfomycin and polymyxins, and discuss their efficacy and potential toxicity. We also summarize the contemporary clinical experience treating CRE infections with antibiotic combination therapy. Finally, we discuss ceftazidime/avibactam and imipenem/relebactam, containing a new generation of beta-lactamase inhibitors, which may offer alternatives to treat CRE infections. We critically evaluate the published literature, identify relevant clinical trials and review documents submitted to the United States Food and Drug Administration.

EXPERT OPINION

Defining the molecular mechanisms of resistance and applying insights about pharmacodynamic and pharmacokinetic properties of antibiotics, in order to maximize the impact of old and new therapeutic approaches should be the new paradigm in treating infections caused by CRE. A concerted effort is needed to carry out high-quality clinical trials that: i) establish the superiority of combination therapy vs. monotherapy; ii) confirm the role of novel beta-lactam/beta-lactamase inhibitor combinations as therapy against KPC- and OXA-48 producing Enterobacteriaceae; and, iii) evaluate new antibiotics active against CRE as they are introduced into the clinic.

Healthcare-associated infections, infection control and the potential of new antibiotics in development in the USA

ABSTRACT  Healthcare-associated infections (HAIs) caused by drug-resistant Gram-negative pathogens are a significant burden on the US healthcare system. This problem has been further compounded by the recent decline in the development of new antibiotics targeting Gram-negative organisms. US healthcare agencies have been working to limit the occurrence of HAIs by several means, including surveillance systems, prevention practices, antimicrobial stewardship policies and financial incentives. Furthermore, efforts have been made to resume the development of antibiotics in the USA, with the US FDA and US government both implementing acts to boost the number of antibiotics in the clinical pipeline. This review discusses the policies instigated by the US government, including healthcare agencies and the FDA, and describes new antibiotics in development against HAIs.

Multidrug-Resistant Gram-Negative Bacterial Infections in the Hospital Setting: Overview, Implications for Clinical Practice, and Emerging Treatment Options

The increasing prevalence of infections due to multidrug-resistant (MDR) gram-negative bacteria constitutes a serious threat to global public health due to the limited treatment options available and the historically slow pace of development of new antimicrobial agents. Infections due to MDR strains are associated with increased morbidity and mortality and prolonged hospitalization, which translates to a significant burden on healthcare systems. In particular, MDR strains of Enterobacteriaceae (especially Klebsiella pneumoniae and Escherichia coli), Pseudomonas aeruginosa, and Acinetobacter baumannii have emerged as particularly serious concerns. In the United States, MDR strains of these organisms have been reported from hospitals throughout the country and are not limited to a small subset of hospitals. Factors that have contributed to the persistence and spread of MDR gram-negative bacteria include the following: overuse of existing antimicrobial agents, which has led to the development of adaptive resistance mechanisms by bacteria; a lack of good antimicrobial stewardship such that use of multiple broad-spectrum agents has helped perpetuate the cycle of increasing resistance; and a lack of good infection control practices. The rising prevalence of infections due to MDR gram-negative bacteria presents a significant dilemma in selecting empiric antimicrobial therapy in seriously ill hospitalized patients. A prudent initial strategy is to initiate treatment with a broad-spectrum regimen pending the availability of microbiological results allowing for targeted or narrowing of therapy. Empiric therapy with newer agents that exhibit good activity against MDR gram-negative bacterial strains such as tigecycline, ceftolozane-tazobactam, ceftazidime-avibactam, and others in the development pipeline offer promising alternatives to existing agents.

The β-Lactams Strike Back: Ceftazidime-Avibactam

Gram-negative resistance has reached a crucial point, with emergence of pathogens resistant to most or all available antibiotics. Ceftazidime-avibactam is a newly approved agent combining ceftazidime and a novel β-lactamase inhibitor with activity against multidrug-resistant gram-negative bacteria. Avibactam has increased potency and expanded spectrum of inhibition of class A and C β-lactamases relative to available β-lactamase inhibitors, including extended-spectrum β-lactamases, AmpC, and Klebsiella pneumoniae carbapenemase (KPC) enzymes. Avibactam expands ceftazidime's spectrum of activity to include many ceftazidime- and carbapenem-resistant Enterobacteriaceae and Pseudomonas aeruginosa. Early clinical data indicate that ceftazidime-avibactam is effective and well tolerated in patients with complicated urinary tract infections (cUTIs) and complicated intraabdominal infections (cIAI). In a phase II trial of patients with cUTIs, ceftazidime-avibactam produced similar rates of clinical and microbiologic success compared with imipenem-cilastatin (70.5% and 71.4% microbiologic success rates, respectively). Likewise, patients receiving ceftazidime-avibactam plus metronidazole in a phase II study of patients with cIAI had similar response rates to those receiving meropenem (91.2% and 93.4% clinical success rates, respectively). Based on available in vitro, in vivo, and phase II trial data, as well as preliminary phase III trial results in ceftazidime-resistant, gram-negative cUTI and cIAI, ceftazidime-avibactam received U.S. Food and Drug Administration approval for treatment of cUTI, including pyelonephritis, and cIAI, in combination with metronidazole, in adult patients with limited or no alternative treatment options. The approved dosage, ceftazidime 2 g-avibactam 0.5 g administered as a 2-hour infusion every 8 hours, was selected based on pharmacodynamic analysis and available clinical data. This dosage is under further investigation in patients with cUTI, cIAI, and nosocomial or ventilator-associated pneumonia. The current body of evidence suggests that ceftazidime-avibactam is a promising addition to our therapeutic armamentarium with potential to answer an urgent unmet medical need. Further data in highly resistant gram-negative infections, particularly those caused by KPC-producing Enterobacteriaceae, are needed. As it is introduced into clinical use, careful stewardship and rational use are essential to preserve ceftazidime-avibactam's potential utility.

Bioanalytical method validation for the simultaneous determination of ceftazidime and avibactam in rat plasma

Background: Combination therapies have gained momentum in the disease management strategies of various indications. While it is challenging and more time consuming to develop a combined analytical method, the strategy of simultaneous analysis offers significant advantages in terms of efficiency and cost–effectiveness. Results: Due to a significant difference in efficacious dose for ceftazidime and avibactam, the calibration ranges validated in this paper were set to 0.05–50 μg/ml for ceftazidime and 0.005–5.0 μg/ml for avibactam. Interday results of ceftazidime were within 8% for accuracy and 9% for precision and within 9% for both accuracy and precision of avibactam. Conclusion: A sensitive and selective LC–MS/MS method was developed for the simultaneous quantification of ceftazidime and avibactam in rat plasma.

An Automated Miniaturized Method to Perform and Analyze Antimicrobial Drug Synergy Assays

In the light of emerging antibiotic resistance mechanisms found in bacteria throughout the world, discovery of drugs that potentiate the effect of currently available antibiotics remains an important aspect of pharmaceutical research in the 21st century. Well-established clinical tests exist to determine synergy in vitro, but these are only optimal for low-throughput experimentation while leaving analysis of results and interpretation of high-throughput microscale assays poorly standardized. Here, we describe a miniaturized broth microdilution checkerboard assay and data analysis method in 384-well plate format that conforms to the Clinical Laboratory and Standards Institute (CLSI) methods. This method has been automated and developed to rapidly determine the synergism of current antibiotics with various beta-lactamase inhibitors emerging from our antimicrobial research efforts. This technique increases test throughput and integrity of results, and saves test compound and labor. We facilitated the interpretation of results with an automated analysis tool allowing us to rapidly qualify inter- and intraplate robustness, determine efficacy of multiple antibiotics at the same time, and standardize the results of synergy interpretation. This procedure should enhance high-throughput antimicrobial drug discovery and supersedes former techniques.

Role of the Outer Membrane and Porins in Susceptibility of β-Lactamase-Producing Enterobacteriaceae to Ceftazidime-Avibactam

This study examined the activity of the novel antimicrobial combination ceftazidime-avibactam against Enterobacteriaceae exhibiting different outer membrane permeability profiles, specifically with or without porins and with or without expression of the main efflux pump (AcrAB-TolC). The addition of the outer membrane permeabilizer polymyxin B nonapeptide increased the antibacterial activities of avibactam alone, ceftazidime alone, and ceftazidime-avibactam against the characterized clinical isolates of Escherichia coli, Enterobacter aerogenes, and Klebsiella pneumoniae. This enhancement of activities was mainly due to increased passive penetration of compounds since inhibition of efflux by the addition of phenylalanine-arginine β-naphthylamide affected the MICs minimally. OmpF (OmpK35) or OmpC (OmpK36) pores were not the major route by which avibactam crossed the outer membranes of E. coli and K. pneumoniae. In contrast, Omp35 and Omp36 allowed diffusion of avibactam across the outer membrane of E. aerogenes, although other diffusion channels for avibactam were also present in that species. It was clear that outer membrane permeability and outer membrane pore-forming proteins play a key role in the activity of ceftazidime-avibactam. Nevertheless, the MICs of ceftazidime-avibactam (with 4 mg/liter avibactam) against the ceftazidime-resistant clinical isolates of the three species of Enterobacteriaceae studied were ≤ 8 mg/liter, regardless of outer membrane permeability changes resulting from an absence of defined porin proteins or upregulation of efflux.

Multiyear, Multinational Survey of the Incidence and Global Distribution of Metallo-β-Lactamase-Producing Enterobacteriaceae and Pseudomonas aeruginosa

Metallo-β-lactamases (MBLs) hydrolyze all classes of β-lactams except monobactams and are not inhibited by classic serine β-lactamase inhibitors. Gram-negative pathogens isolated from patient infections were collected from 202 medical centers in 40 countries as part of a global surveillance study from 2012 to 2014. Carbapenem-nonsusceptible Enterobacteriaceae and Pseudomonas aeruginosa were characterized for bla genes encoding VIM, IMP, NDM, SPM, and GIM variants using PCR and sequencing. A total of 471 MBL-positive isolates included the following species (numbers of isolates are in parentheses): P. aeruginosa (308), Klebsiella spp. (85), Enterobacter spp. (39), Proteeae (16), Citrobacter freundii (12), Escherichia coli (6), and Serratia marcescens (5) and were submitted by sites from 34 countries. Of these, 69.6% were collected in 9 countries (numbers of isolates are in parentheses): Russia (72), Greece (61), Philippines (54), Venezuela (29), and Kuwait, Nigeria, Romania, South Africa, and Thailand (20 to 25 isolates each). Thirty-two different MBL variants were detected (14 VIM, 14 IMP, and 4 NDM enzymes). Seven novel MBL variants were encountered in the study, each differing from a previously reported variant by one amino acid substitution: VIM-42 (VIM-1 [V223I]), VIM-43 (VIM-4 [A24V]), VIM-44 (VIM-2 [K257N]), VIM-45 (VIM-2 [T35I]), IMP-48 (IMP-14 [I69T]), IMP-49 (IMP-18 [V49F]), and NDM-16 (NDM-1 [R264H]). The in vitro activities of all tested antibiotics against MBL-positive Enterobacteriaceae were significantly reduced with the exception of that of aztreonam-avibactam (MIC90, 0.5 to 1 μg/ml), whereas colistin was the most effective agent against MBL-positive P. aeruginosa isolates (>97% susceptible). Although the global percentage of isolates encoding MBLs remains relatively low, their detection in 12 species, 34 countries, and all regions participating in this surveillance study is concerning.

Characterization of a Carbapenem-Hydrolyzing Enzyme, PoxB, in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is an opportunistic pathogen often associated with severe and life-threatening infections that are highly impervious to treatment. This microbe readily exhibits intrinsic and acquired resistance to varied antimicrobial drugs. Resistance to penicillin-like compounds is commonplace and provided by the chromosomal AmpC β-lactamase. A second, chromosomally encoded β-lactamase, PoxB, has previously been reported in P. aeruginosa. In the present work, the contribution of this class D enzyme was investigated using a series of clean in-frame ampC, poxB, and oprD deletions, as well as complementation by expression under the control of an inducible promoter. While poxB deletions failed to alter β-lactam sensitivities, expression of poxB in ampC-deficient backgrounds decreased susceptibility to both meropenem and doripenem but had no effect on imipenem, penicillin, and cephalosporin MICs. However, when expressed in an ampCpoxB-deficient background, that additionally lacked the outer membrane porin-encoding gene oprD, PoxB significantly increased the imipenem as well as the meropenem and doripenem MICs. Like other class D carbapenem-hydrolyzing β-lactamases, PoxB was only poorly inhibited by class A enzyme inhibitors, but a novel non-β-lactam compound, avibactam, was a slightly better inhibitor of PoxB activity. In vitro susceptibility testing with a clinical concentration of avibactam, however, failed to reduce PoxB activity against the carbapenems. In addition, poxB was found to be cotranscribed with an upstream open reading frame, poxA, which itself was shown to encode a 32-kDa protein of yet unknown function.

Interactions of OP0595, a Novel Triple-Action Diazabicyclooctane, with β-Lactams against OP0595-Resistant Enterobacteriaceae Mutants

OP0595 is a novel diazabicyclooctane which, like avibactam, inhibits class A and C β-lactamases. In addition, unlike avibactam, it has antibacterial activity, with MICs of 0.5 to 4 μg/ml for most members of the family Enterobacteriaceae, owing to inhibition of PBP2; moreover, it acts synergistically with PBP3-active β-lactams independently of β-lactamase inhibition, via an "enhancer effect." Enterobacteriaceae mutants stably resistant to 16 μg/ml OP0595 were selected on agar at frequencies of approximately 10(-7). Unsurprisingly, OP0595 continued to potentiate substrate β-lactams against mutants derived from Enterobacteriaceae with OP0595-inhibited class A and C β-lactamases. Weaker potentiation of partners, especially aztreonam, cefepime, and piperacillin--less so meropenem--remained frequent for OP0595-resistant Enterobacteriaceae mutants lacking β-lactamases or with OP0595-resistant metallo-β-lactamases (MBLs), indicating that the enhancer effect is substantially retained even when antibiotic activity is lost.

Activity of temocillin, mecillinam, ceftazidime, and ceftazidime/avibactam against carbapenem-non-susceptible Enterobacteriaceae without carbapenemase production

Treatment options for multidrug-resistant Gram-negative infections are scarce and therefore alternatives with a narrow spectrum or new agents are sought. Antimicrobial susceptibility to temocillin, mecillinam, ceftazidime, and ceftazidime/avibactam was determined using Etest and disk diffusion according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) methodology. A total of 77 carbapenem-nonsusceptible Enterobacteriaceae were studied, including Klebsiella pneumoniae (26%), Escherichia coli (26%), Enterobacter cloacae (26%), and Enterobacter aerogenes (22%). Several phenotypic tests, PCRs followed by sequencing and a microbiological bioassay excluded carbapenemase production in all isolates. Antimicrobial susceptibility rates were low for temocillin (15.6%, minimum inhibitory concentration [MIC] range 2 to >1,024 μg/ml), moderate for mecillinam (59.7%, MIC range 0.25 to >256 μg/ml), and excellent for ceftazidime/avibactam (100%, zone diameter range 19 to 32 mm, median 25 mm). 5.2% of the isolates were susceptible to ceftazidime alone (zone diameter range 6 to 32 mm). In this study, mecillinam exhibited moderate and ceftazidime/avibactam excellent in vitro antimicrobial activity against carbapenem-nonsusceptible Enterobacteriaceae without carbapenemase production. Ceftazidime/avibactam was able to restore previously reduced susceptibility to ceftazidime in all isolates, thus potentiating its activity. Temocillin only exhibited low in vitro antimicrobial activity against the isolates. Further evaluation of mecillinam and ceftazidime/avibactam with regard to the potential clinical utility against infections caused by these pathogens has to be performed.

Randomized pharmacokinetic and drug-drug interaction studies of ceftazidime, avibactam, and metronidazole in healthy subjects

We assessed pharmacokinetic and safety profiles of ceftazidime-avibactam administered ± metronidazole, and whether drug-drug interactions exist between ceftazidime and avibactam, or ceftazidime-avibactam and metronidazole. The first study (NCT01430910) involved two cohorts of healthy subjects. Cohort 1 received ceftazidime-avibactam (2000-500 mg) as a single infusion or as multiple intravenous infusions over 11 days to evaluate ceftazidime-avibactam pharmacokinetics. Cohort 2 received ceftazidime, avibactam, or ceftazidime-avibactam over 4 days to assess drug-drug interaction between ceftazidime and avibactam. The second study (NCT01534247) assessed interaction between ceftazidime-avibactam and metronidazole in subjects receiving ceftazidime-avibactam (2000-500 mg), metronidazole (500 mg), or metronidazole followed by ceftazidime-avibactam over 4 days. In all studies, subjects received a single-dose on the first and final days, and multiple-doses every 8 h on intervening days. Concentration-time profiles for ceftazidime and avibactam administered as single- or multiple-doses separately or together with/without metronidazole were similar. There was no evidence of time-dependent pharmacokinetics or accumulation. In both interaction studies, 90% confidence intervals for geometric least squares mean ratios of area under the curve and maximum plasma concentrations for each drug were within the predefined interval (80-125%) indicating no drug-drug interaction between ceftazidime and avibactam, or ceftazidime-avibactam and metronidazole. There were no safety concerns. In conclusion, pharmacokinetic parameters and safety of ceftazidime, avibactam, and metronidazole were similar after single and multiple doses with no observed drug-drug interaction between ceftazidime and avibactam, or ceftazidime-avibactam and metronidazole.

Ceftazidime-avibactam for the treatment of complicated urinary tract infections and complicated intra-abdominal infections

Treatment of complicated urinary tract infections and complicated intra-abdominal infections is increasingly difficult due to the rising prevalence of multidrug-resistant Gram-negative bacteria. Ceftazidime-avibactam is a combination of the established third-generation cephalosporin ceftazidime with avibactam, a novel non-β-lactam β-lactamase inhibitor, which restores the activity of ceftazidime against many β-lactamase-producing Gram-negative bacteria, including extended-spectrum β-lactamases and Klebsiella pneumoniae carbapenemases. Clinical and nonclinical studies supporting the safety and efficacy of ceftazidime-avibactam include microbiological surveillance studies of clinically relevant pathogens, in vivo animal models of infection, pharmacokinetic/pharmacodynamic target attainment analyses, Phase I clinical pharmacology studies, and Phase II/III studies in the treatment of complicated intra-abdominal infections and complicated urinary tract infections, including patients with ceftazidime-nonsusceptible Gram-negative infections.

In Vitro Activities of Ceftazidime-Avibactam, Aztreonam-Avibactam, and a Panel of Older and Contemporary Antimicrobial Agents against Carbapenemase-Producing Gram-Negative Bacilli

Among 177 carbapenemase-producing Gram-negative bacilli (108 KPC, 32 NDM, 11 IMP, 8 OXA-48, 4 OXA-181, 2 OXA-232, 5 IMI, 4 VIM, and 3 SME producers), aztreonam-avibactam was active against all isolates except two NDM producers with elevated MICs of 8/4 and 16/4 mg/liter; ceftazidime-avibactam was active against all KPC-, IMI-, SME-, and most OXA-48 group-producing isolates (93%) but not metallo-β-lactamase producers. Among older and contemporary antimicrobials, the most active were colistin, tigecycline, and fosfomycin, with overall susceptibilities of 88%, 79%, and 78%, respectively.

Antibiotic adjuvants: diverse strategies for controlling drug-resistant pathogens

The growing number of bacterial pathogens that are resistant to numerous antibiotics is a cause for concern around the globe. There have been no new broad-spectrum antibiotics developed in the last 40 years, and the drugs we have currently are quickly becoming ineffective. In this article, we explore a range of therapeutic strategies that could be employed in conjunction with antibiotics and may help to prolong the life span of these life-saving drugs. Discussed topics include antiresistance drugs, which are administered to potentiate the effects of current antimicrobials in bacteria where they are no longer (or never were) effective; antivirulence drugs, which are directed against bacterial virulence factors; host-directed therapies, which modulate the host's immune system to facilitate infection clearance; and alternative treatments, which include such therapies as oral rehydration for diarrhea, phage therapy, and probiotics. All of these avenues show promise for the treatment of bacterial infections and should be further investigated to explore their full potential in the face of a postantibiotic era.

Inhibition of Klebsiella β-Lactamases (SHV-1 and KPC-2) by Avibactam: A Structural Study

β-Lactamase inhibition is an important clinical strategy in overcoming β-lactamase-mediated resistance to β-lactam antibiotics in Gram negative bacteria. A new β-lactamase inhibitor, avibactam, is entering the clinical arena and promising to be a major step forward in our antibiotic armamentarium. Avibactam has remarkable broad-spectrum activity in being able to inhibit classes A, C, and some class D β-lactamases. We present here structural investigations into class A β-lactamase inhibition by avibactam as we report the crystal structures of SHV-1, the chromosomal penicillinase of Klebsiella pneumoniae, and KPC-2, an acquired carbapenemase found in the same pathogen, complexed with avibactam. The 1.80 Å KPC-2 and 1.42 Å resolution SHV-1 β-lactamase avibactam complex structures reveal avibactam covalently bonded to the catalytic S70 residue. Analysis of the interactions and chair-shaped conformation of avibactam bound to the active sites of KPC-2 and SHV-1 provides structural insights into recently laboratory-generated amino acid substitutions that result in resistance to avibactam in KPC-2 and SHV-1. Furthermore, we observed several important differences in the interactions with amino acid residues, in particular that avibactam forms hydrogen bonds to S130 in KPC-2 but not in SHV-1, that can possibly explain some of the different kinetic constants of inhibition. Our observations provide a possible reason for the ability of KPC-2 β-lactamase to slowly desulfate avibactam with a potential role for the stereochemistry around the N1 atom of avibactam and/or the presence of an active site water molecule that could aid in avibactam desulfation, an unexpected consequence of novel inhibition chemistry.

Impact of the New Delhi metallo-beta-lactamase on beta-lactam antibiotics

Since the first New Delhi metallo-beta-lactamase (NDM) report in 2009, NDM has spread globally causing various types of infections. NDM-positive organisms produce in vitro resistance phenotypes to carbapenems and many other antimicrobials. It is thus surprising that the literature examining clinical experiences with NDM does not report corresponding poor clinical outcomes. There are many instances where good clinical outcomes are described, despite a mismatch between administered antimicrobials and resistant in vitro susceptibilities. Available in vitro data for either monotherapy or combination therapy does not provide an explanation for these observations. However, animal studies do begin to shed more light on this phenomenon. They imply that the in vivo expression of NDM may not confer clinical resistance to all cephalosporin and carbapenem antibiotics as predicted by in vitro testing but other resistance mechanisms need to be present to generate a resistant phenotype. As such, previously abandoned therapies, particularly carbapenems and beta-lactamase inhibitor combinations, may retain utility against infections caused by NDM producers.

Empiric therapy for hospital-acquired, Gram-negative complicated intra-abdominal infection and complicated urinary tract infections: a systematic literature review of current and emerging treatment options

BACKGROUND

Empiric therapy for healthcare-associated infections remains challenging, especially with the continued development of Gram-negative organisms producing extended-spectrum β-lactamases (ESBLs) and the threat of multi-drug-resistant organisms. Current treatment options for resistant Gram-negative infections include carbapenems, tigecycline, piperacillin-tazobactam, cefepime, ceftazidime, and two recently approved therapies, ceftolozane-tazobactam and ceftazidime-avibactam.

METHODS

This systematic literature review surveys the published clinical trial evidence available since 2000 in support of both current and emerging treatment options in the settings of complicated intra-abdominal infection (cIAI) and complicated urinary tract infection (cUTI). When available, clinical cure rates for patients with infections from ESBL-producing strains are provided, as is information about efficacy against Pseudomonas aeruginosa.

RESULTS

Clinical trial evidence to guide selection of empiric antibiotic therapy in patients with complicated, hospital-acquired, Gram-negative IAIs and UTIs is limited. Though most of the clinical trials explored in this overview enrolled patients with complicated infections, often patients with severe infections and multiple comorbidities were excluded.

CONCLUSIONS

Practitioners in the clinical setting who are treating patients with complicated, hospital-acquired, Gram-negative IAIs and UTIs need to consider the possibility of polymicrobial infections, antibiotic-resistant organisms, and/or severely ill patients with multiple comorbidities. There is a severe shortage of evidence-based research to guide the selection of empiric antibiotic therapy for many patients in this setting. New therapies recently approved or in late-stage development promise to expand the number of options available for empiric therapy of these hospital-acquired, Gram-negative infections.

Focus on ceftazidime-avibactam for optimizing outcomes in complicated intra-abdominal and urinary tract infections

INTRODUCTION

Complicated intra-abdominal infections and urinary tract infections are frequently associated with Gram-negative bacteria and treatment can be hampered by the involvement of resistant organisms. A common resistance mechanism is β-lactamase production which confers resistance to β-lactam antibiotics.

AREAS COVERED

This article summarizes β-lactamases found among Gram-negative bacteria as well as providing an overview of complicated intra-abdominal infections and urinary tract infections and the impact inappropriate antibiotic therapy and antibiotic resistance has in their treatment. The author reviews the activity of ceftazidime-avibactam , including animal model data and microbiological data from Phase II clinical trials. This article also highlights Phase III clinical trials of ceftazidime-avibactam that are ongoing or completed and briefly discusses other β-lactamase inhibitor combinations currently in development.

EXPERT OPINION

The increasing problem and complexity of β-lactamase resistance has been met by resurgence in the development of β-lactamase inhibitor combinations. These show promise in the treatment of resistant infections. One β-lactamase inhibitor in advanced development with a broad spectrum of activity is avibactam, covering class A, class C and some class D enzymes. Importantly, the activity of avibactam also includes carbapenemases such as the KPC and OXA-48. The combination of avibactam with the cephalosporin ceftazidime is attractive, given the spectrum of antimicrobial activity and the low toxicity of the cephalosporin class.

In vitro activity of aztreonam-avibactam against a global collection of Gram-negative pathogens from 2012 and 2013

The combination of aztreonam plus avibactam is being developed for use in infections caused by metallo-β-lactamase-producing Enterobacteriaceae strains that also produce serine β-lactamases. The in vitro activities of aztreonam-avibactam and comparator antimicrobials were determined against year 2012 and 2013 clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii using the broth microdilution methodology recommended by the Clinical and Laboratory Standards Institute (CLSI). A total of 28,501 unique clinical isolates were obtained from patients in 190 medical centers within 39 countries. MIC90 values of aztreonam and aztreonam-avibactam against all collected isolates of Enterobacteriaceae (n = 23,516) were 64 and 0.12 μg/ml, respectively, with 76.2% of the isolates inhibited by ≤4 μg/ml of aztreonam (the CLSI breakpoint) and 99.9% of the isolates inhibited by ≤4 μg/ml of aztreonam-avibactam using a fixed concentration of 4 μg/ml of avibactam. The MIC90 was 32 μg/ml for both aztreonam and aztreonam-avibactam against P. aeruginosa (n = 3,766). Aztreonam alone or in combination with avibactam had no in vitro activity against isolates of A. baumannii. PCR and sequencing were used to characterize 5,076 isolates for β-lactamase genes. Aztreonam was not active against most Enterobacteriaceae isolates producing class A or class C enzymes alone or in combination with class B metallo-β-lactamases. In contrast, >99% of Enterobacteriaceae isolates producing all observed Ambler classes of β-lactamase enzymes were inhibited by ≤4 μg/ml aztreonam in combination with avibactam, including isolates that produced IMP-, VIM-, and NDM-type metallo-β-lactamases in combination with multiple serine β-lactamases.

Phase 1 study assessing the steady-state concentration of ceftazidime and avibactam in plasma and epithelial lining fluid following two dosing regimens

OBJECTIVES

The aim of this Phase 1, open-label study (NCT01395420) was to measure and compare concentrations of ceftazidime and avibactam in bronchial epithelial lining fluid (ELF) and plasma, following administration of two different dosing regimens in healthy subjects.

PATIENTS AND METHODS

Healthy volunteers received 2000 mg of ceftazidime + 500 mg of avibactam (n = 22) or 3000 mg of ceftazidime + 1000 mg of avibactam (n = 21), administered intravenously every 8 h for 3 days (total of nine doses). Bronchoscopy with bronchoalveolar lavage was performed once per subject, 2, 4, 6 or 8 h after the last infusion. Pharmacokinetic parameters were estimated from individual plasma concentrations and the composite ELF concentration-time profile. Safety was assessed.

RESULTS

Forty-three subjects received treatment (2000 mg of ceftazidime + 500 mg of avibactam, n = 22; 3000 mg of ceftazidime + 1000 mg of avibactam, n = 21). Plasma and ELF concentrations increased dose-proportionally for both drugs, with 1.5- and 2-fold increases in AUCτ, for respective components. Ceftazidime Cmax and AUCτ in ELF were ∼ 23%-26% and 31%-32% of plasma exposure. Avibactam Cmax and AUCτ in ELF were ∼ 28%-35% and 32%-35% of plasma exposure. ELF and plasma elimination were similar for both drugs. No serious adverse events were observed.

CONCLUSIONS

Both ceftazidime and avibactam penetrated dose-proportionally into ELF, with ELF exposure to both drugs ∼ 30% of plasma exposure.

OP0595, a new diazabicyclooctane: mode of action as a serine β-lactamase inhibitor, antibiotic and β-lactam 'enhancer'

OBJECTIVES

The production of a growing diversity of β-lactamases by Gram-negative bacteria challenges antimicrobial chemotherapy. OP0595, discovered separately by each of Meiji Seika Pharma and Fedora Pharmaceuticals, is a new diazabicyclooctane serine β-lactamase inhibitor that also acts as an antibiotic and as a β-lactamase-independent β-lactam 'enhancer'.

METHODS

Inhibitory activity against serine β-lactamases and affinity for PBPs were determined using nitrocefin and Bocillin FL, respectively. MICs alone and in combination with β-lactam agents were measured according to CLSI recommendations. Morphological changes in Escherichia coli were examined by phase-contrast microscopy.

RESULTS

IC50s of OP0595 for class A and C β-lactamases were <1000 nM, with covalent binding demonstrated to the active-site serine of CTX-M-44 and AmpC enzymes. OP0595 also had direct antibiotic activity against many Enterobacteriaceae, associated with inhibition of PBP2 and conversion of the bacteria into spherical forms. Synergy between OP0595 and β-lactam agents was seen against strains producing class A and C β-lactamases vulnerable to inhibition. Lastly, OP0595 lowered the MICs of PBP3-targeted partner β-lactam agents for a non-β-lactamase-producing E. coli mutant that was resistant to OP0595 itself, indicating β-lactamase-independent 'enhancer'-based synergy.

CONCLUSIONS

OP0595 acts in three ways: (i) as an inhibitor of class A and C β-lactamases, covalently binding at their active sites; (ii) as an antibacterial, by inhibiting PBP2 of several Enterobacteriaceae; and (iii) as an 'enhancer' of β-lactam agents that bind to other PBPs besides PBP2 for several Enterobacteriaceae. OP0595 has considerable potential to overcome resistance when it is combined with various β-lactam agents.

Validation of Sensititre Dry-Form Broth Microdilution Panels for Susceptibility Testing of Ceftazidime-Avibactam, a Broad-Spectrum-β-Lactamase Inhibitor Combination

Ceftazidime-avibactam is a broad-spectrum-β-lactamase inhibitor combination in late-stage clinical development for the treatment of serious infections. In preparation for clinical microbiology laboratory use, a validation experiment was initiated to evaluate a commercial broth microdilution product (Sensititre dried MIC susceptibility system) compared to reference panels using 525 recent clinical isolates. Among 11 pathogen groups, all had Sensititre MIC/reference MIC ratios predominantly at 1 (47.5% to 97.5%), and automated and manual endpoint results did not differ. Enterobacteriaceae MIC comparisons showed a modest skewing of Sensititre MIC results toward an elevated MIC (33.9%), but the essential agreement was 98.9% with 100.0% reproducibility. In conclusion, Sensititre panels produced accurate ceftazidime-avibactam MIC results, allowing quality MIC guidance for therapy following regulatory approvals.

Activities of ceftazidime, ceftaroline, and aztreonam alone and combined with avibactam against isogenic Escherichia coli strains expressing selected single β-lactamases

Avibactam is a novel β-lactamase inhibitor that restores the activity of otherwise hydrolyzed β-lactams against Gram-negative bacteria expressing different classes of serine β-lactamases. In the last decade, β-lactam-avibactam combinations were tested against a variety of clinical isolates expressing multiple commonly encountered β-lactamases. Here, we analyzed isogenic Escherichia coli strains expressing selected single β-lactamase genes that were not previously tested or were not characterized in an isogenic background. The activities of ceftazidime, ceftaroline, and aztreonam alone and in combination with 4 mg/L of avibactam, as well as comparator agents, were assessed against a unique collection of isogenic strains of E. coli carrying selected extended-spectrum, inhibitor-resistant, and/or carbapenem-hydrolyzing bla genes. When combined with avibactam, ceftazidime, ceftaroline, or aztreonam MICs were reduced for 91.4%, 80.0%, and 80.0% of isolates, respectively. The data presented add to our understanding of the microbiologic spectrum of these β-lactams with avibactam and serve as a reference for further studies.

Phase I study assessing the safety, tolerability, and pharmacokinetics of avibactam and ceftazidime-avibactam in healthy Japanese volunteers

Avibactam is a novel non-β-lactam β-lactamase inhibitor that has been shown to restore the in vitro activity of ceftazidime against pathogens producing Ambler class A, C, and some class D β-lactamases. This study aimed to evaluate the safety, tolerability, and pharmacokinetics of single and multiple doses of avibactam alone or with ceftazidime in healthy Japanese subjects. In this Phase I, double-blind study (NCT01291602), 16 healthy Japanese males, mean age 28.8 years, were randomized in a 2:2:1 ratio to receive avibactam 500 mg (n = 6), ceftazidime 2000 mg plus avibactam 500 mg (n = 7), or placebo (n = 3), each administered as a 100 ml intravenous infusion over 2 h, once on Day 1, every 8 h on Days 3-6, and once on Day 7. There were no deaths or serious adverse events. Nine treatment-emergent adverse events were reported in three subjects in the avibactam group - including one elevation in transaminase levels, and three vital signs events (tachycardia, palpitations, and orthostatic hypotension) - and one in the ceftazidime-avibactam group. All events were considered mild. After single or multiple dosing, plasma concentrations of avibactam and ceftazidime declined in a multi-exponential manner. No plasma concentration accumulation was observed, and the majority of avibactam was excreted unchanged in urine within 24 h. No clinically relevant changes in intestinal bacterial flora were observed. In conclusion, avibactam alone and ceftazidime-avibactam were generally well tolerated in healthy male Japanese subjects, and avibactam pharmacokinetics were comparable whether administered alone or in combination with ceftazidime.

Effect of age and sex on the pharmacokinetics and safety of avibactam in healthy volunteers

PURPOSE

Avibactam is a novel non-β-lactam β-lactamase inhibitor currently being assessed in combination with ceftazidime, ceftaroline fosamil, and aztreonam. The objectives of this study were to investigate the pharmacokinetics, safety, and tolerability of avibactam in healthy young (aged 18-45 years) and elderly (aged ≥65 years) volunteers of both sexes.

METHODS

This was a Phase I, open-label study in which healthy volunteers aged ≥18 years were enrolled into 4 cohorts: young male, young female, elderly male, and elderly female (n = 8 in each group). Subjects were excluded if they had any condition requiring regular medication or any other relevant conditions. All subjects received a single dose of avibactam 500 mg/100 mL given intravenously over 30 minutes. Pharmacokinetic measurements included Cmax, Tmax, AUC0-∞, plasma clearance, and t½.

FINDINGS

Within the two age categories the mean age across male and female subjects was well matched. The majority of subjects in the young cohort were black (≥62.5%), whilst the majority of those in the elderly cohorts were white (≥75%). Mean avibactam plasma clearance was similar between the young male, young female, and elderly male cohorts (10.16, 10.34, and 9.82 L/h, respectively), and slightly lower in elderly women (7.98 L/h). Mean Cmax was similar in young male, young female, and elderly female subjects (33.8, 36.9, and 38.4 µg/mL) but lower in elderly male subjects (26.5 µg/mL). Point estimates comparing the ratio of Cmax in male and female subjects over all age groups suggested that Cmax values were 18% lower (90% CI, 30%-5% lower) in male subjects compared with female subjects. Mean AUC0-∞ data were similar between the young male, young female, and elderly male cohorts (49.86, 49.75, and 52.40 µg·h/mL) but higher in elderly women (66.23 µg·h/mL). Point estimates comparing the ratio of AUC0-∞ in elderly and young subjects across both sexes suggested that AUC0-∞ values were 17% higher (90% CI, 5%-31%) in elderly subjects compared with young subjects. The t½ was slightly longer for elderly subjects compared with younger subjects. The most common adverse event was administration/venipuncture site bruising (6 events); all adverse events were mild.

IMPLICATIONS

No notable differences in pharmacokinetics were observed between the male and female cohorts. The generalizability of the study is limited due to its small sample size. However, the small differences observed between the young and elderly cohorts are not sufficient to warrant dosing adjustments based on age.

Activity of ceftazidime-avibactam against fluoroquinolone-resistant Enterobacteriaceae and Pseudomonas aeruginosa

Ceftazidime-avibactam and comparator antibiotics were tested by the broth microdilution method against 200 Enterobacteriaceae and 25 Pseudomonas aeruginosa strains resistant to fluoroquinolones (including strains with the extended-spectrum β-lactamase [ESBL] phenotype and ceftazidime-resistant strains) collected from our institution. The MICs and mechanisms of resistance to fluoroquinolone were also studied. Ninety-nine percent of fluoroquinolone-resistant Enterobacteriaceae strains were inhibited at a ceftazidime-avibactam MIC of ≤4 mg/liter (using the susceptible CLSI breakpoint for ceftazidime alone as a reference). Ceftazidime-avibactam was very active against ESBL Escherichia coli (MIC90 of 0.25 mg/liter), ESBL Klebsiella pneumoniae (MIC90 of 0.5 mg/liter), ceftazidime-resistant AmpC-producing species (MIC90 of 1 mg/liter), non-ESBL E. coli (MIC90 of ≤0.125 mg/liter), non-ESBL K. pneumoniae (MIC90 of 0.25 mg/liter), and ceftazidime-nonresistant AmpC-producing species (MIC90 of ≤0.5 mg/liter). Ninety-six percent of fluoroquinolone-resistant P. aeruginosa strains were inhibited at a ceftazidime-avibactam MIC of ≤8 mg/liter (using the susceptible CLSI breakpoint for ceftazidime alone as a reference), with a MIC90 of 8 mg/liter. Additionally, fluoroquinolone-resistant mutants from each species tested were obtained in vitro from two strains, one susceptible to ceftazidime and the other a β-lactamase producer with a high MIC against ceftazidime but susceptible to ceftazidime-avibactam. Thereby, the impact of fluoroquinolone resistance on the activity of ceftazidime-avibactam could be assessed. The MIC90 values of ceftazidime-avibactam for the fluoroquinolone-resistant mutant strains of Enterobacteriaceae and P. aeruginosa were ≤4 mg/liter and ≤8 mg/liter, respectively. We conclude that the presence of fluoroquinolone resistance does not affect Enterobacteriaceae and P. aeruginosa susceptibility to ceftazidime-avibactam; that is, there is no cross-resistance.

Carbapenemase-producing Gram-negative bacteria: current epidemics, antimicrobial susceptibility and treatment options

ABSTRACT 

Carbapenemases, with versatile hydrolytic capacity against β-lactams, are now an important cause of resistance of Gram-negative bacteria. The genes encoding for the acquired carbapenemases are associated with a high potential for dissemination. In addition, infections due to Gram-negative bacteria with acquired carbapenemase production would lead to high clinical mortality rates. Of the acquired carbapenemases, Klebsiella pneumoniae carbapenemase (Ambler class A), Verona integron-encoded metallo-β-lactamase (Ambler class B), New Delhi metallo-β-lactamase (Ambler class B) and many OXA enzymes (OXA-23-like, OXA-24-like, OXA-48-like, OXA-58-like, class D) are considered to be responsible for the worldwide resistance epidemics. As compared with monotherapy with colistin or tigecycline, combination therapy has been shown to effectively lower case-fatality rates. However, development of new antibiotics is crucial in the present pandrug-resistant era.

Multidrug-resistant Gram-negative bacteria in solid organ transplant recipients with bacteremias

Bloodstream infections (BSIs) remain as life-threatening complications and are associated with significant morbidity and mortality among solid organ transplant (SOT) recipients. Multidrug-resistant (MDR) Gram-negative bacteria can cause serious bacteremias in these recipients. Reviews have aimed to investigate MDR Gram-negative bacteremias; however, they were lacking in SOT recipients in the past. To better understand the characteristics of bacteremias due to MDR Gram-negative bacteria, optimize preventive and therapeutic strategies, and improve the outcomes of SOT recipients, this review summarize the epidemiology, clinical and laboratory characteristics, and explores the mechanisms, prevention, and treatment of MDR Gram-negative bacteria.

Emerging issues in gram-negative bacterial resistance: an update for the practicing clinician

The rapid and global spread of antimicrobial-resistant organisms in recent years has been unprecedented. Although resistant gram-positive infections have been concerning to clinicians, the increasing incidence of antibiotic-resistant gram-negative infections has become the most pressing issue in bacterial resistance. Indiscriminate antimicrobial use in humans and animals coupled with increased global connectivity facilitated the transmission of gram-negative infections harboring extended-spectrum β-lactamases in the 1990s. Carbapenemase-producing Enterobacteriaceae, such as those containing Klebsiella pneumoniae carbapenemases and New Delhi metallo-β-lactamases, have been the latest scourge since the late 1990s to 2000s. Besides β-lactam resistance, these gram-negative infections are often resistant to multiple drug classes, including fluoroquinolones, which are commonly used to treat community-onset infections. In certain geographic locales, these pathogens, which have been typically associated with health care-associated infections, are disseminating into the community, posing a significant dilemma for clinicians treating community-onset infections. In this Concise Review, we summarize emerging trends in antimicrobial resistance. We also review the current knowledge on the detection, treatment, and prevention of infection with these organisms, with a focus on the carbapenemase-producing gram-negative bacilli. Finally, we discuss emerging therapies and areas that need further research and effort to stem the spread of antimicrobial resistance.

Novel antibiotics: are we still in the pre-post-antibiotic era?

Purpose

Therapeutic efficacy and safety in infections due to multidrug-resistant bacteria can be improved by the clinical development of new compounds and devising new derivatives of already useful antibiotics. Due to a striking global increase in multidrug-resistant Gram-positive but even more Gram-negative organisms, new antibiotics are urgently needed.

Methods

This paper provides a review of novel antibiotic compounds which are already in clinical development, mainly in phase III clinical trials.

Conclusion

Each of these new trials increases the possibility of new antibiotics receiving approval.

In vitro activity of ceftazidime, ceftaroline and aztreonam alone and in combination with avibactam against European Gram-negative and Gram-positive clinical isolates

Recent clinical isolates of key Gram-negative and Gram-positive bacteria were collected in 2012 from hospitalised patients in medical centres in four European countries (France, Germany, Italy and Spain) and were tested using standard broth microdilution methodology to assess the impact of 4 mg/L avibactam on the in vitro activities of ceftazidime, ceftaroline and aztreonam. Against Enterobacteriaceae, addition of avibactam significantly enhanced the level of activity of these antimicrobials. MIC(90) values (minimum inhibitory concentration that inhibits 90% of the isolates) of ceftazidime, ceftaroline and aztreonam for Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii and Morganella morganii were reduced up to 128-fold or greater when combined with avibactam. A two-fold reduction in the MIC(90) of ceftazidime to 8 mg/L was noted in Pseudomonas aeruginosa isolates when combined with avibactam, whereas little effect of avibactam was noted on the MIC values of the test compounds when tested against Acinetobacter baumannii isolates. Avibactam had little effect on the excellent activity of ceftazidime, ceftaroline and aztreonam against Haemophilus influenzae. It had no impact on the in vitro activity of ceftazidime and ceftaroline against staphylococci and streptococci. This study demonstrates that addition of avibactam enhances the activities of ceftazidime, ceftaroline and aztreonam against Enterobacteriaceae and P. aeruginosa but not against A. baumannii.

Development of novel antibacterial drugs to combat multiple resistant organisms

BACKGROUND

Infections due to multidrug-resistant (MDR) bacteria are increasing both in hospitals and in the community and are characterized by high mortality rates. New molecules are in development to face the need of active compounds toward resistant gram-positive and gram-negative pathogens. In particular, the Infectious Diseases Society of America (IDSA) has supported the initiative to develop ten new antibacterials within 2020. Principal targets are the so-called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, and Enterobacteriaceae).

PURPOSE

To review the characteristics and the status of development of new antimicrobials including new cephalosporins, carbapenems, beta-lactamase inhibitors, aminoglycosides, quinolones, oxazolidones, glycopeptides, and tetracyclines.

CONCLUSIONS

While numerous new compounds target resistant gram-positive pathogens and have been approved for clinical use, very few new molecules are active against MDR gram-negative pathogens, especially carbapenemase producers. New glycopeptides and oxazolidinones are highly efficient against methicillin-resistant S. aureus (MRSA), and new cephalosporins and carbapenems also display activity toward MDR gram-positive bacteria. Although new cephalosporins and carbapenems have acquired activity against MRSA, they offer few advantages against difficult-to-treat gram-negatives. Among agents that are potentially active against MDR gram-negatives are ceftozolane/tazobactam, new carbapenems, the combination of avibactam with ceftazidime, and plazomicin. Since a relevant number of promising antibiotics is currently in development, regulatory approvals over the next 5 years are crucial to face the growing threat of multidrug resistance.

Characterization of Escherichia coli NDM isolates with decreased susceptibility to aztreonam/avibactam: role of a novel insertion in PBP3

OBJECTIVES

The spread of NDM-1 amongst Enterobacteriaceae has highlighted a significant threat to the clinical management of serious infections. The combination of aztreonam and avibactam, a non-β-lactam β-lactamase inhibitor, may provide a much-needed therapeutic alternative. This combination was potent against most NDM-containing Enterobacteriaceae, although activity was diminished against many Escherichia coli isolates. These E. coli isolates were characterized to elucidate the mechanism of decreased susceptibility to aztreonam/avibactam.

METHODS

MIC determinations were performed using broth microdilution, and whole-genome sequencing was performed to enable sequence-based analyses.

RESULTS

The decreased susceptibility was not due to avibactam being unable to inhibit the serine β-lactamases found in the E. coli isolates. Rather, it was manifested by a four-amino-acid insertion in PBP3. This same insertion was also found in non-NDM-containing E. coli that had reduced susceptibility to aztreonam/avibactam. Construction of an isogenic mutant confirmed that this insertion resulted in decreased susceptibility to aztreonam and several cephalosporins, but had no impact on carbapenem potency. Structural analysis suggests that this insertion will impact the accessibility of the β-lactam drugs to the transpeptidase pocket of PBP3.

CONCLUSIONS

The acquisition of β-lactamases is the predominant mechanism of β-lactam resistance in Enterobacteriaceae. We have demonstrated that small PBP3 changes will affect the susceptibility to a broad range of β-lactams. These changes were identified in multiple MLST lineages of E. coli, and were enriched in NDM-containing isolates. However, they were not present in other key species of Enterobacteriaceae despite significant conservation among the PBP3 proteins.

In vitro susceptibility of characterized β-lactamase-producing strains tested with avibactam combinations

Avibactam, a broad-spectrum β-lactamase inhibitor, was tested with ceftazidime, ceftaroline, or aztreonam against 57 well-characterized Gram-negative strains producing β-lactamases from all molecular classes. Most strains were nonsusceptible to the β-lactams alone. Against AmpC-, extended-spectrum β-lactamase (ESBL)-, and KPC-producing Enterobacteriaceae or Pseudomonas aeruginosa, avibactam lowered ceftazidime, ceftaroline, or aztreonam MICs up to 2,048-fold, to ≤4 μg/ml. Aztreonam-avibactam MICs against a VIM-1 metallo-β-lactamase-producing Enterobacter cloacae and a VIM-1/KPC-3-producing Escherichia coli isolate were 0.12 and 8 μg/ml, respectively.

In vitro activity of ceftazidime-avibactam combination in in vitro checkerboard assays

To evaluate the in vitro effects of the combination of ceftazidime and avibactam on the MICs of both compounds, checkerboard assays were performed for 81 clinical strains, including 55 Enterobacteriaceae strains (32 Klebsiella pneumoniae, 19 Escherichia coli, 1 Citrobacter freundii, and 3 Enterobacter cloacae) and 26 strains of Pseudomonas aeruginosa, all with known resistance mechanisms such as extended-spectrum β-lactamases (ESBLs) and carbapenemases, phenotypically or molecularly determined. Phenotypically ceftazidime-resistant strains (n=69) were analyzed in more detail. For the Enterobacteriaceae strains, a concentration-dependent effect of avibactam was found for most strains with a maximum effect of avibactam at a concentration of 4 mg/liter, which decreased all ceftazidime MICs to ≤4 mg/liter. Avibactam alone also showed antibacterial activity (the MIC50 and MIC90 being 8 and 16 mg/liter, respectively). For the ceftazidime-resistant P. aeruginosa strains, considerable inhibition of β-lactamases by avibactam was acquired at a concentration of 4 mg/liter, which decreased all ceftazidime MICs except one to ≤8 mg/liter (the CLSI and EUCAST susceptible breakpoint). Increasing the concentration of avibactam further decreased the MICs, resulting in a maximum effect for most strains at 8 to 16 mg/liter. In summary, for most strains, the tested addition of avibactam of 4 mg/liter restored the antibacterial activity of ceftazidime to a level comparable to that of wild-type strains, indicating full inhibition, and strains became susceptible according to the EUCAST and CLSI criteria. Based on these in vitro data, avibactam is a promising inhibitor of different β-lactamases, including ESBLs and carbapenemases.