In Vitro Antibacterial Activity of Imipenem/Relebactam against Clinical Isolates in Japan

Tazobactam/ceftolozane (TAZ/CTLZ) and relebactam/imipenem (REL/IPM) susceptibility in Japan: Nationwide surveillance of respiratory bacterial pathogens in 2019/20

Tazobactam/ceftolozane (TAZ/CTLZ) and relebactam/imipenem/cilastatin (REL/IPM/CS) are expected to be effective for treating patients with antimicrobial-resistant infections, particularly gram-negative pathogens, but nationwide surveillance of these has not been investigated thoroughly in Japan. Pseudomonas aeruginosa (n = 164), Klebsiella pneumoniae (n = 141), and Haemophilus influenzae (n = 156) isolated from respiratory infected patients in Japan from June 2019 through December 2020 provided by the Japanese Surveillance Committee were used. Antimicrobial susceptibility testing for TAZ/CTLZ, REL/IPM and comparator agents against isolates were carried out by broth microdilution methods according to the Clinical and Laboratory Standards Institute standard. The MIC50/90 of TAZ/CTLZ against P. aeruginosa and K. pneumoniae were 0.5/1 μg/mL and 0.25/0.5 μg/mL, those of REL/IPM were 0.25/1 μg/mL and 0.25/0.5 μg/mL, respectively, and all isolates were susceptible to both drugs. Susceptible rates for P. aeruginosa to IPM, ceftazidime (CAZ), and levofloxacin (LVFX) were 84.1, 87.8, and 76.8 %, and those of K. pneumoniae to tazobactam/piperacillin, CAZ, and LVFX were 98.6, 98.6, and 95.0 %, respectively. The MIC50/90 of TAZ/CTLZ for H. influenzae were 0.5/2 μg/mL, comparable to those of cefepime (CFPM), 1/2 μg/mL, but susceptible rate to TAZ/CTLZ and CFPM differed at 50.6 and 100 %, respectively. This difference was estimated from the different clinical breakpoints between TAZ/CTLZ (0.5 μg/mL) and CFPM (2 μg/mL) and the epidemiological prevalence of β-lactamase negative ampicillin resistance (BLNAR), which is high in Japan but rare in the US/EU. Excellent in vitro activities for TAZ/CTLZ and REL/IPM against major causative gram-negative bacteria in RTI patients were observed.

Global Resistance of Imipenem/Relebactam against Gram-Negative Bacilli: Systematic Review and Meta-Analysis

Background

Relebactam, previously known as MK-7655, is currently being tested in combination with imipenem as a class A and class C β-lactamase inhibitor, including KPC from Klebsiella pneumoniae.

Objective

The objective of the current study was to evaluate the activity of imipenem/relebactam against gram-negative bacilli.

Methods

After applying exclusion and inclusion criteria, 72 articles with full texts that describe the prevalence of imipenem/relebactam resistance were chosen for the meta-analysis and systematic review. Articles published between January 2015 and February 2023 were surveyed. The systematic literature search was conducted in PubMed, Web of Science, Google Scholar, and Scopus.

Results

The pooled estimation of 282,621 sample isolates revealed that the prevalence rate of imipenem/relebactam resistance is roughly 14.6% (95% CI, 0.116%-0.182%).

Conclusions

The findings of this analysis show that imipenem/relebactam resistance is rare in the majority of developed countries. Given that relebactam has proven to restore the activity of imipenem against current clinical isolates, further research into imipenem/relebactam is necessary.

Klebsiella pneumoniae Susceptibility to Carbapenem/Relebactam Combinations: Influence of Inoculum Density and Carbapenem-to-Inhibitor Concentration Ratio

The inoculum effect (IE) is a well-known phenomenon with beta-lactams. At the same time, the IE has not been extensively studied with carbapenem/carbapenemase inhibitor combinations. The antibiotic-to-inhibitor concentration ratio used in susceptibility testing can influence the in vitro activity of the combination. To explore the role of these factors, imipenem/relebactam and doripenem/relebactam MICs were estimated against six Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae strains at standard inocula (SI) and high inocula (HI) by two methods: with a fixed relebactam concentration and with a fixed, pharmacokinetic-based carbapenem-to-relebactam concentration ratio. The combination MICs at HI, compared to SI, increased with most of the tested strains. However, the IE occurred with only two K. pneumoniae strains regardless of the MIC testing method. The relationship between the MICs at SI and the respective inoculum-induced MIC changes was observed when the MICs were estimated at pharmacokinetic-based carbapenem-to-relebactam concentration ratios. Thus, (1) IE was observed with both carbapenem/relebactam combinations regardless of the MIC testing method; however, IE was not observed frequently among tested K. pneumoniae strains. (2) At HI, carbapenem/relebactam combination MICs increased to levels associated with carbapenem resistance. (3) Combination MICs determined at pharmacokinetic-based carbapenem-to-inhibitor concentration ratios predict susceptibility elevations at HI in KPC-producing K. pneumoniae.