Effect of Cefepime/Enmetazobactam vs Piperacillin/Tazobactam on Clinical Cure and Microbiological Eradication in Patients With Complicated Urinary Tract Infection or Acute Pyelonephritis: A Randomized Clinical Trial.

Importance: Cefepime/enmetazobactam is a novel ß-lactam/ß-lactamase inhibitor combination and a potential empirical therapy for resistant gram-negative infections. Objective: To evaluate whether cefepime/enmetazobactam was noninferior to piperacillin/tazobactam for the primary outcome of treatment efficacy in patients with complicated urinary tract infections (UTIs) or acute pyelonephritis. Design, Setting, and Participants: A phase 3, randomized, double-blind, active-controlled, multicenter, noninferiority clinical trial conducted at 90 sites in Europe, North and Central America, South America, and South Africa. Recruitment occurred between September 24, 2018, and November 2, 2019. Final follow-up occurred November 26, 2019. Participants were adult patients aged 18 years or older with a clinical diagnosis of complicated UTI or acute pyelonephritis caused by gram-negative urinary pathogens. Interventions: Eligible patients were randomized to receive either cefepime, 2 g/enmetazobactam, 0.5 g (n = 520), or piperacillin, 4 g/tazobactam, 0.5 g (n = 521), by 2-hour infusion every 8 hours for 7 days (up to 14 days in patients with a positive blood culture at baseline). Main Outcomes and Measures: The primary outcome was the proportion of patients in the primary analysis set (patients who received any amount of study drug with a baseline gram-negative pathogen not resistant to either treatment and ≥105 colony-forming units [CFU]/mL in urine culture or the same pathogen present in concurrent blood and urine cultures) who achieved overall treatment success (defined as clinical cure combined with microbiological eradication [<103 CFU/mL in urine] of infection). Two-sided 95% CIs were computed using the stratified Newcombe method. The prespecified noninferiority margin was -10%. If noninferiority was established, a superiority comparison was also prespecified. Results: Among 1041 patients randomized (mean age, 54.7 years; 573 women [55.0%]), 1034 (99.3%) received study drug and 995 (95.6%) completed the trial. Among the primary analysis set, the primary outcome occurred in 79.1% (273/345) of patients receiving cefepime/enmetazobactam compared with 58.9% (196/333) receiving piperacillin/tazobactam (between-group difference, 21.2% [95% CI, 14.3% to 27.9%]). Treatment-emergent adverse events occurred in 50.0% (258/516) of patients treated with cefepime/enmetazobactam and 44.0% (228/518) with piperacillin/tazobactam; most were mild to moderate in severity (89.9% vs 88.6%, respectively). A total of 1.7% (9/516) of participants who received cefepime/enmetazobactam and 0.8% (4/518) of those who received piperacillin/tazobactam did not complete the assigned therapy due to adverse events. Conclusions and Relevance: Among patients with complicated UTI or acute pyelonephritis caused by gram-negative pathogens, cefepime/enmetazobactam, compared with piperacillin/tazobactam, met criteria for noninferiority as well as superiority with respect to the primary outcome of clinical cure and microbiological eradication. Further research is needed to determine the potential role for cefepime/enmetazobactam in the treatment of complicated UTI and pyelonephritis. Trial Registration: ClinicalTrials.gov Identifier: NCT03687255.

Sigmoid Emax Modeling To Define the Fixed Concentration of Enmetazobactam for MIC Testing in Combination with Cefepime.

The use of carbapenem antibiotics to treat infections caused by Enterobacterales expressing increasingly aggressive extended-spectrum ß-lactamases (ESBLs) has contributed to the emergence of carbapenem resistance. Enmetazobactam is a novel ESBL inhibitor being developed in combination with cefepime as a carbapenem-sparing option for infections caused by ESBL-producing Enterobacterales. Cefepime-enmetazobactam checkerboard MIC profiles were obtained for a challenge panel of cefepime-resistant ESBL-producing clinical isolates of Klebsiella pneumoniae. Sigmoid maximum effect (Emax) modeling described cefepime MICs as a function of enmetazobactam concentration with no bias. A concentration of 8 µg/ml enmetazobactam proved sufficient to restore >95% of cefepime antibacterial activity in vitro against >95% of isolates tested. These results support a fixed concentration of 8 µg/ml of enmetazobactam for MIC testing.

Pharmacokinetics-Pharmacodynamics of Enmetazobactam Combined with Cefepime in a Neutropenic Murine Thigh Infection Model.

Third-generation cephalosporin (3GC)-resistant Enterobacteriaceae are classified as critical priority pathogens, with extended-spectrum ß-lactamases (ESBLs) as principal resistance determinants. Enmetazobactam (formerly AAI101) is a novel ESBL inhibitor developed in combination with cefepime for empirical treatment of serious Gram-negative infections in settings where ESBLs are prevalent. Cefepime-enmetazobactam has been investigated in a phase 3 trial in patients with complicated urinary tract infections or acute pyelonephritis. This study examined pharmacokinetic-pharmacodynamic (PK-PD) relationships of enmetazobactam, in combination with cefepime, for ESBL-producing isolates of Klebsiella pneumoniae in 26-h murine neutropenic thigh infection models. Enmetazobactam dose fractionation identified the time above a free threshold concentration (fT > CT ) as the PK-PD index predictive of efficacy. Nine ESBL-producing isolates of K. pneumoniae, resistant to cefepime and piperacillin-tazobactam, were included in enmetazobactam dose-ranging studies. The isolates encoded CTX-M-type, SHV-12, DHA-1, and OXA-48 ß-lactamases and covered a cefepime-enmetazobactam MIC range from 0.06 to 2 µg/ml. Enmetazobactam restored the efficacy of cefepime against all isolates tested. Sigmoid curve fitting across the combined set of isolates identified enmetazobactam PK-PD targets for stasis and for a 1-log10 bioburden reduction of 8% and 44% fT > 2 µg/ml, respectively, with a concomitant cefepime PK-PD target of 40 to 60% fT > cefepime-enmetazobactam MIC. These findings support clinical dose selection and breakpoint setting for cefepime-enmetazobactam.

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

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

Development of Broth Microdilution MIC and Disk Diffusion Antimicrobial Susceptibility Test Quality Control Ranges for the Combination of Cefepime and the Novel ß-Lactamase Inhibitor Enmetazobactam.

Third-generation cephalosporin resistance among Enterobacteriaceae, mediated by the spread of extended-spectrum ß-lactamases (ESBLs), is a very serious medical concern with limited therapeutic options. Enmetazobactam (formerly AAI101) is a novel penicillanic sulfone ß-lactamase inhibitor active against a wide range of ESBLs. The combination of enmetazobactam and cefepime has entered phase 3 development in patients with complicated urinary tract infections. Using the Clinical and Laboratory Standards Institute (CLSI) M23 tier 2 study design, broth microdilution MIC and disk diffusion quality control (QC) ranges were determined for cefepime-enmetazobactam. Enmetazobactam was tested at a fixed concentration of 8 µg/ml in the MIC assay, and a cefepime-enmetazobactam disk mass of 30/20 µg was used in the disk diffusion assay. Escherichia coli ATCC 25922, E. coli ATCC 35218, E. coli NCTC 13353, Klebsiella pneumoniae ATCC 700603, and Pseudomonas aeruginosa ATCC 27853 were chosen as reference strains. The CTX-M-15-producing E. coli NCTC 13353 isolate is recommended for routine testing to control for inhibition of ESBL activity by enmetazobactam. Broth microdilution MIC QC ranges spanned 3 to 4 doubling dilutions and contained 99.6% to 100.0% of obtained MIC values for the five reference strains. Disk diffusion yielded inhibition zone diameter QC ranges that spanned 7 mm and encompassed 97.1% to 100.0% of the obtained values. Quality control ranges were approved by the CLSI in 2017 (broth microdilution MIC) and 2019 (disk diffusion). The established QC ranges will ensure that appropriate assay performance criteria are attained using CLSI reference methodology when determining the susceptibility of clinical isolates to cefepime-enmetazobactam.

Evaluation of Oritavancin Dosing Strategies against Vancomycin-Resistant Enterococcus faecium Isolates with or without Reduced Susceptibility to Daptomycin in an In Vitro Pharmacokinetic/Pharmacodynamic Model.

The clinical development of nonsusceptibility to the lipopeptide antibiotic daptomycin remains a serious concern during therapy for infections caused by vancomycin-resistant Enterococcus faecium (VREfm). The long-acting lipoglycopeptide oritavancin exhibits potent in vitro activity against VREfm, although its safety and efficacy for treating clinical VREfm infections have not been established. In this study, novel dosing regimens of daptomycin and oritavancin were assessed against both VREfm and daptomycin-nonsusceptible VREfm isolates in an in vitro pharmacokinetic/pharmacodynamic model.

Comparative Pharmacodynamics of Single-Dose Oritavancin and Daily High-Dose Daptomycin Regimens against Vancomycin-Resistant Enterococcus faecium Isolates in an In Vitro Pharmacokinetic/Pharmacodynamic Model of Infection.

There are limited therapeutic options to treat infections caused by vancomycin-resistant Enterococcus faecium (VREfm). The lipoglycopeptide oritavancin exhibits in vitro activity against this pathogen, although its utility against infections caused by VREfm has not been clinically established. In this study, the pharmacodynamic activity of free-drug levels associated with 12 mg/kg/day of daptomycin and a single 1,200-mg dose of oritavancin were determined against three VanA VREfm isolates in an in vitro pharmacokinetic/pharmacodynamic model.

Effects of Oritavancin on Coagulation Tests in the Clinical Laboratory.

Previous studies have shown that some lipoglycopeptide and lipopeptide antimicrobial agents may cause falsely elevated values for some phospholipid-dependent coagulation tests. The effect of oritavancin, a lipoglycopeptide antibiotic, on coagulation test results was explored using pooled human plasma samples spiked with drug and in a clinical study after an infusion of a single 1,200-mg intravenous dose of oritavancin in normal healthy volunteers. Pooled plasma with oritavancin added ex vivo showed concentration-dependent prolongation of prothrombin time/international normalized ratio (PT/INR), activated partial thromboplastin time (aPTT), and dilute Russell viper venom time (DRVVT) test results. In contrast, oritavancin had no effect on the activated protein C resistance assay, chromogenic anti-factor Xa assay (anti-FXa), thrombin time, and an immunoassay for the laboratory diagnosis of heparin-induced thrombocytopenia. In participants that received a single dose of oritavancin, elevations in PT/INR result, aPTT, DRVVT, activated clotting time, and silica clotting time occurred, with the maximum times to resolution of test interference determined to be 12, 120, 72, 24, and 18 h, respectively. The anti-FXa assay was unaffected, whereas transient elevations in D dimer levels were observed in 30% of participants, with a maximum time to resolution of 72 h. Although oritavancin has no impact on the coagulation system in vivo, a single dose of oritavancin can produce falsely elevated values of some coagulation tests used to monitor hemostasis. The interference of oritavancin on affected tests is transient, and the test results revert to normal ranges within specified times after dosing.

Comparative In Vitro Activities of Oritavancin, Dalbavancin, and Vancomycin against Methicillin-Resistant Staphylococcus aureus Isolates in a Nondividing State.

Antibacterial agents that kill nondividing bacteria may be of utility in treating persistent infections. Oritavancin and dalbavancin are bactericidal lipoglycopeptides that are approved for acute bacterial skin and skin structure infections in adults caused by susceptible Gram-positive pathogens. Using time-kill methodology, we demonstrate that oritavancin exerts bactericidal activity against methicillin-resistant Staphylococcus aureus (MRSA) isolates that are maintained in a nondividing state in vitro, whereas dalbavancin and the glycopeptide vancomycin do not.

Evaluation of the activity of cefepime/enmetazobactam against Enterobacterales bacteria collected in Europe from 2019 to 2021, including third-generation cephalosporin-resistant isolates.

OBJECTIVES: This study was performed to investigate the activity of the novel ß-lactam/ß-lactamase inhibitor combination cefepime/enmetazobactam, against recently circulating Enterobacterales isolates from Europe from 2019 to 2021. METHODS: A total of 2627 isolates were collected, and antimicrobial susceptibility was determined according to the European Committee on Antimicrobial Susceptibility Testing guidelines. Isolates with phenotypic resistance to ceftriaxone and ceftazidime (but susceptible to meropenem) and isolates nonsusceptible to meropenem were screened for the presence of ß-lactamases. RESULTS: Overall, susceptibility to third-generation cephalosporins was 77%, and 97.3% were susceptible to meropenem. Cefepime/enmetazobactam susceptibility was 97.9% (72% of these isolates were Klebsiella pneumoniae from Italy), compared with 80.0% susceptibility to piperacillin/tazobactam and 99.4% to ceftazidime/avibactam. A total of 320 isolates (12.2%) were resistant to third-generation cephalosporins but susceptible to meropenem, and virtually all (96.3%) carried an extended-spectrum ß-lactamase with or without an AmpC and these were all susceptible to cefepime/enmetazobactam. Most meropenem-nonsusceptible isolates carried a KPC (68%), which were not inhibited by cefepime/enmetazobactam but were inhibited by ceftazidime/avibactam. Additionally, most meropenem-nonsusceptible isolates carrying OXA-48 (9/12 isolates) were susceptible to cefepime/enmetazobactam. CONCLUSIONS: Cefepime/enmetazobactam was highly active against Enterobacterales isolates, especially those resistant to third-generation cephalosporins. These data suggest that cefepime/enmetazobactam could be used as a carbapenem-sparing agent to replace piperacillin/tazobactam.

Pharmacodynamics of a simulated single 1,200-milligram dose of oritavancin in an in vitro pharmacokinetic/pharmacodynamic model of methicillin-resistant staphylococcus aureus infection.

The safety and efficacy of a single 1,200-mg dose of the lipoglycopeptide oritavancin are currently being investigated in two global phase 3 studies of acute bacterial skin and skin structure infections. In this study, an in vitro pharmacokinetic/pharmacodynamic model was established to compare the free-drug pharmacodynamics associated with a single 1,200-mg dose of oritavancin to once-daily dosing with daptomycin at 6 mg/kg of body weight and twice-daily dosing with vancomycin at 1,000 mg against three methicillin-resistant Staphylococcus aureus (MRSA) strains over 72 h. The area under the bacterial-kill curve (AUBKC) was used to assess the antibacterial effect of each dosing regimen at 24 h (AUBKC(0-24)), 48 h (AUBKC(0-48)), and 72 h (AUBKC(0-72)). The rapid bactericidal activities of oritavancin and daptomycin contributed to lower AUBKC(0-24)s for the three MRSA strains than with vancomycin (P < 0.05, as determined by analysis of variance [ANOVA]). Oritavancin exposure also resulted in a lower AUBKC(0-48) and AUBKC(0-72) against one MRSA strain and a lower AUBKC(0-48) for another strain than did vancomycin exposure (P < 0.05). Furthermore, daptomycin exposure resulted in a lower AUBKC(0-48) and AUBKC(0-72) for one of the MRSA isolates than did vancomycin exposure (P < 0.05). Lower AUBKC(0-24)s for two of the MRSA strains (P < 0.05) were obtained with oritavancin exposure than with daptomycin. Thus, the antibacterial effect from the single-dose regimen of oritavancin is as effective as that from either once-daily dosing with daptomycin or twice-daily dosing with vancomycin against the MRSA isolates tested in an in vitro pharmacokinetic/pharmacodynamic model over 72 h. These results provide further justification to assess the single 1,200-mg dose of oritavancin for treatment of acute bacterial skin and skin structure infections.

Impact of surfactants and other body fluids on in vitro activity of a novel ß-lactamase inhibitor enmetazobactam in combination with cefepime against clinical isolates of Klebsiella pneumoniae.

Surfactants might impact treatment of lower respiratory tract infections. Moreover, other body fluids, such as urine or serum, could impact antibacterial activity as well. Therefore, the impact of surfactants, urine, and serum on the antibacterial activity of the novel ß-lactam/ß-lactamase inhibitor combination of cefepime-enmetazobactam (FPE) was determined. Ten clinical isolates of Klebsiella pneumoniae, and the quality control strains K. pneumoniae ATCC 700603 and Escherichia coli NCTC 13353, were tested. Minimal Inhibitory Concentration (MIC) determinations (all strains) and Time Kill Curves (TKC) (one clinical isolate) were determined for FPE and piperacillin-tazobactam (TZP) with and without surfactant formulations Survanta® (SUR; 1%v/v) and Curosurf® (CUR; 1 mg ml-1). Determination of daptomycin MIC against Staphylococcus aureus ATCC 29213 in the presence and absence of surfactants was used as a positive control. Additionally, the impact of growth media supplemented with pooled human urine or serum were also evaluated by MIC testing. Expectedly, media supplemented with SUR increased the daptomycin MIC against S. aureus ATCC 29213. In contrast, the surfactants had no impact on the antibacterial activity of FPE against the tested Enterobacterales isolates. TKC experiments also revealed no impact of CUR on the antibacterial activity of FPE. These results demonstrate that the antibacterial activity of FPE is unaffected in the presence of lung surfactant. Moreover, FPE was not impacted by media supplemented with urine or serum.

Strain-specific differences in the genetic control of two closely related mycobacteria.

The host response to mycobacterial infection depends on host and pathogen genetic factors. Recent studies in human populations suggest a strain specific genetic control of tuberculosis. To test for mycobacterial-strain specific genetic control of susceptibility to infection under highly controlled experimental conditions, we performed a comparative genetic analysis using the A/J- and C57BL/6J-derived recombinant congenic (RC) mouse panel infected with the Russia and Pasteur strains of Mycobacterium bovis Bacille Calmette Guérin (BCG). Bacillary counts in the lung and spleen at weeks 1 and 6 post infection were used as a measure of susceptibility. By performing genome-wide linkage analyses of loci that impact on tissue-specific bacillary burden, we were able to show the importance of correcting for strain background effects in the RC panel. When linkage analysis was adjusted on strain background, we detected a single locus on chromosome 11 that impacted on pulmonary counts of BCG Russia but not Pasteur. The same locus also controlled the splenic counts of BCG Russia but not Pasteur. By contrast, a locus on chromosome 1 which was indistinguishable from Nramp1 impacted on splenic bacillary counts of both BCG Russia and Pasteur. Additionally, dependent upon BCG strain, tissue and time post infection, we detected 9 distinct loci associated with bacillary counts. Hence, the ensemble of genetic loci impacting on BCG infection revealed a highly dynamic picture of genetic control that reflected both the course of infection and the infecting strain. This high degree of adaptation of host genetics to strain-specific pathogenesis is expected to provide a suitable framework for the selection of specific host-mycobacteria combinations during co-evolution of mycobacteria with humans.

Third-generation cephalosporin resistance in clinical isolates of Enterobacterales collected between 2016-2018 from USA and Europe: genotypic analysis of ß-lactamases and comparative in vitro activity of cefepime/enmetazobactam.

OBJECTIVES: This study aimed to investigate third-generation cephalosporin (3GC) resistance determinants [extended-spectrum ß-lactamases (ESBLs), AmpC ß-lactamases and OXA-type ß-lactamases] in contemporary clinical Enterobacterales isolates and to determine the in vitro activity of ß-lactams and ß-lactam/ß-lactamase inhibitor combinations, including the investigational combination of cefepime and the novel ß-lactamase inhibitor enmetazobactam. METHODS: Antibacterial susceptibility of 7168 clinical Enterobacterales isolates obtained between 2016-2018 from North America and Europe was determined according to CLSI guidelines. Phenotypic resistance to the 3GC ceftazidime (MIC ≥ 16 µg/mL) and/or ceftriaxone (MIC ≥ 4 µg/mL) but retaining susceptibility to meropenem (MIC ≤ 1 µg/mL) was determined. ß-Lactamase genotyping was performed on clinical isolates with ceftazidime, ceftriaxone, cefepime or meropenem MIC ≥ 1 µg/mL. RESULTS: Phenotypic resistance to 3GCs occurred in 17.5% of tested isolates, whereas 2.1% of isolates were resistant to the carbapenem meropenem. Within the 3GC-resistant subgroup, 60.1% (n = 752) of isolates encoded an ESBL, 25.6% (n = 321) encoded an AmpC-type ß-lactamase and 0.9% (n = 11) encoded an OXA-type ß-lactamase. Susceptibility of the subgroup to piperacillin/tazobactam (57.5%) and ceftolozane/tazobactam (71.3%) was <90% based on breakpoints established by the CLSI. Projected susceptibility to cefepime/enmetazobactam was 99.6% when applying the cefepime susceptible, dose-dependent breakpoint of 8 µg/mL. Against ESBL-producing isolates (n = 801) confirmed by genotyping, only susceptibility to meropenem (96.0%) and cefepime/enmetazobactam (99.9%) exceeded 90%. CONCLUSION: This study describes the antibacterial activity of important therapies against contemporary 3GC-resistant clinical Enterobacterales isolates and supports the development of cefepime/enmetazobactam as a carbapenem-sparing option for ESBL-producing pathogens.

Assessment of oritavancin serum protein binding across species.

Biophysical methods to study the binding of oritavancin, a lipoglycopeptide, to serum protein are confounded by nonspecific drug adsorption to labware surfaces. We assessed oritavancin binding to serum from mouse, rat, dog, and human by a microbiological growth-based method under conditions that allow near-quantitative drug recovery. Protein binding was similar across species, ranging from 81.9% in human serum to 87.1% in dog serum. These estimates support the translation of oritavancin exposure from nonclinical studies to humans.

Oritavancin disrupts membrane integrity of Staphylococcus aureus and vancomycin-resistant enterococci to effect rapid bacterial killing.

Oritavancin is an investigational lipoglycopeptide in clinical development for the treatment of acute bacterial skin and skin structure infections. In this study, we demonstrate that oritavancin causes bacterial membrane depolarization and permeabilization leading to cell death of Gram-positive pathogens and that these effects are attributable to the 4'-chlorobiphenylmethyl group of the molecule.

Ultrastructural effects of oritavancin on methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus.

The ultrastructural effects of the lipoglycopeptide oritavancin on methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococcus (VRE) were examined by transmission electron microscopy. Oritavancin but not vancomycin induced aberrant septum formation and loss of staining of nascent septal cross walls in MRSA. Septal distortions were also observed in VRE exposed to oritavancin.