Determining the in vitro susceptibility of tebipenem, an oral carbapenem, against third-generation cephalosporin-resistant Escherichia coli and Klebsiella pneumoniae isolated from bloodstream infections

Novel agents in development for the treatment of resistant Gram-negative infections

INTRODUCTION

Several novel agents are in advanced stages of clinical development, potentially expanding our treatment options against third- and fourth-generation cephalosporin-resistant and carbapenem-resistant Gram-negative bacteria (GNB), including those pathogens for which the current number of effective treatments is limited.

AREAS COVERED

This review focuses on agents that have completed or ongoing phase-3 studies. A PubMed search was conducted up to 31 May 2024.

EXPERT OPINION

Novel agents in late-stage clinical development belong to the β-lactam or β-lactam/β-lactamase inhibitor combinations class and display variable antimicrobial activity depending on the specific β-lactamases expressed by GNB, particularly carbapenemases. While many of these novel agents demonstrate in vitro activity against carbapenem-resistant GNB, their efficacy has mainly been evaluated in phase-3 randomized controlled trials (RCT) for infections caused by carbapenem-susceptible GNB. Although evidence from real-world observational studies is generally less robust than that from RCT, it could be crucial for updating clinical guidelines on treating carbapenem-resistant GNB with these new agents in the absence of dedicated RCT.

The interaction of the azetidine thiazole side chain with the active site loop (ASL) 3 drives the evolution of IMP metallo-β-lactamase against tebipenem

Imipenemase (IMP) metallo-β-lactamases (MBLs) hydrolyze almost all available β-lactams including carbapenems and are not inhibited by any commercially available β-lactamase inhibitor. Tebipenem (TP) pivoxil is the first orally available carbapenem and possesses a unique bicyclic azetidine thiazole moiety located at the R2 position. TP has potent in vitro activity against Enterobacterales producing extended-spectrum and/or AmpC β-lactamases. Thus far, the activity of TP against IMP-producing strains is understudied. To address this knowledge gap, we explored the structure activity relationships of IMP MBLs by investigating whether IMP-6, IMP-10, IMP-25, and IMP-78 [MBLs with expanded hydrolytic activity against meropenem (MEM)] would demonstrate enhanced activity against TP. Most of the Escherichia coli DH10B strains expressing IMP-1 variants displayed a ≥twofold MIC difference between TP and MEM, while those expressing VIM or NDM variants demonstrated comparable MICs. Catalytic efficiency (kcat/KM) values for the TP hydrolysis by IMP-1, IMP-6, IMP-10, IMP-25, and IMP-78 were significantly lower than those obtained for MEM. Molecular dynamic simulations reveal that V67F and S262G substitutions (found in IMP-78) reposition active site loop 3, ASL-3, to better accommodate the bicyclic azetidine thiazole side chain, allowing microbiological/catalytic activity to approach that of comparison MBLs used in this study. These findings suggest that modifying the R2 side chain of carbapenems can significantly impact hydrolytic stability. Furthermore, changes in conformational dynamics due to single amino acid substitutions should be used to inform drug design of novel carbapenems.

Antibacterial agents active against Gram Negative Bacilli in phase I, II, or III clinical trials

INTRODUCTION

Antimicrobial resistance is a major threat to modern healthcare, and it is often regarded that the antibiotic pipeline is 'dry.'

AREAS COVERED

Antimicrobial agents active against Gram negative bacilli in Phase I, II, or III clinical trials were reviewed.

EXPERT OPINION

Nearly 50 antimicrobial agents (28 small molecules and 21 non-traditional antimicrobial agents) active against Gram-negative bacilli are currently in clinical trials. These have the potential to provide substantial improvements to the antimicrobial armamentarium, although it is known that 'leakage' from the pipeline occurs due to findings of toxicity during clinical trials. Significantly, a lack of funding for large phase III clinical trials is likely to prevent trials occurring for the indications most relevant to loss of life attributed to antimicrobial resistance such as ventilator-associated pneumonia. Non-traditional antimicrobial agents face issues in clinical development such as a lack of readily available and reliable susceptibility tests, and the potential need for superiority trials rather than non-inferiority trials. Most importantly, concrete plans must be made during clinical development for access of new antimicrobial agents to areas of the world where resistance to Gram negative bacilli is most frequent.