Pharmacodynamics of ceftazidime plus the serine beta-lactamase inhibitor AM-112 against Escherichia coli containing TEM-1 and CTX-M-1 beta-lactamases

The pharmacodynamics of avibactam in combination with ceftaroline or ceftazidime against β-lactamase-producing Enterobacteriaceae studied in an in vitro model of infection

Objectives

Pharmacodynamics of β-lactamase inhibitors are an area of intense interest as new β-lactam/β-lactamase inhibitor combinations enter clinical development and clinical practice. Avibactam, a non-β-lactam β-lactamase inhibitor, has been combined with ceftaroline or ceftazidime but these two combinations have not been directly compared.

Methods

Using an in vitro pharmacokinetic model we simulated human drug concentration-time courses associated with ceftaroline 600 mg every 8 h and ceftazidime 2000 mg every 8 h. Avibactam was given by continuous infusion at a range of concentrations up to 10 mg/L and antibacterial effect assessed against a CTX-M-producing Escherichia coli , AmpC-hyperproducing Enterobacter cloacae and KPC-producing Klebsiella pneumoniae. Simulations were performed over 72 h.

Results

Avibactam, at a concentration of 1-2 mg/L, produced maximum bacterial clearance over 72 h for the E. coli and E. cloacae strains with both ceftaroline and ceftazidime. Avibactam (4 mg/L) was required for maximum reduction in bacterial load with the KPC-producing K. pneumoniae. A series of dose fractionation experiments were performed with avibactam against each of the three strains and AUC, C max or T  >   avibactam concentration of 1, 2 or 4 mg/L related to antibacterial effect as measured by change in bacterial count at 24 h. AUC or C max were best related to 24 h antibacterial effect for avibactam though there was no consistent pattern favouring one over the other.

Conclusions

As AUC is a much easier and more reliable pharmacokinetic measure than C max , it would be useful to explore how AUC-based indices for avibactam exposures could be used for translating the results of the present study into patients' therapy.

Combating multidrug-resistant Gram-negative bacterial infections

INTRODUCTION

Multidrug-resistant (MDR) bacterial infections, especially those caused by Gram-negative pathogens, have emerged as one of the world's greatest health threats. The development of novel antibiotics to treat MDR Gram-negative bacteria has, however, stagnated over the last half century.

AREAS COVERED

This review provides an overview of recent R&D activities in the search for novel antibiotics against MDR Gram-negatives. It provides emphasis in three key areas. First, the article looks at new analogs of existing antibiotic molecules such as β-lactams, tetracyclines, and aminoglycoside as well as agents against novel bacterial targets such as aminoacyl-tRNA synthetase and peptide deformylase. Second, it also examines alternative strategies to conventional approaches including cationic antimicrobial peptides, siderophores, efflux pump inhibitors, therapeutic antibodies, and renewed interest in abandoned treatments or those with limited indications. Third, the authors aim to provide an update on the current clinical development status for each drug candidate.

EXPERT OPINION

The traditional analog approach is insufficient to meet the formidable challenge brought forth by MDR superbugs. With the disappointing results of the genomics approach for delivering novel targets and drug candidates, alternative strategies to permeate the bacterial cell membrane, enhance influx, disrupt efflux, and target specific pathogens via therapeutic antibodies are attractive and promising. Coupled with incentivized business models, governmental policies, and a clarified regulatory pathway, it is hoped that the antibiotic pipeline will be filled with an effective armamentarium to safeguard global health.

Current challenges in antimicrobial chemotherapy: focus on ß-lactamase inhibition

The use of the three classical beta-lactamase inhibitors (clavulanic acid, tazobactam and sulbactam) in combination with beta-lactam antibacterials is currently the most successful strategy to combat beta-lactamase-mediated resistance. However, these inhibitors are efficient in inactivating only class A beta-lactamases and the efficiency of the inhibitor/antibacterial combination can be compromised by several mechanisms, such as the production of naturally resistant class B or class D enzymes, the hyperproduction of AmpC or even the production of evolved inhibitor-resistant class A enzymes. Thus, there is an urgent need for the development of novel inhibitors. For serine active enzymes (classes A, C and D), derivatives of the beta-lactam ring such as 6-beta-halogenopenicillanates, beta-lactam sulfones, penems and oxapenems, monobactams or trinems seem to be potential starting points to design efficient molecules (such as AM-112 and LK-157). Moreover, a promising non-beta-lactam molecule, NXL-104, is now under clinical development. In contrast, an ideal inhibitor of metallo-beta-lactamases (class B) remains to be found, despite the huge number of potential molecules already described (biphenyl tetrazoles, cysteinyl peptides, mercaptocarboxylates, succinic acid derivatives, etc.). The search for such an inhibitor is complicated by the absence of a covalent intermediate in their catalytic mechanisms and the fact that beta-lactam derivatives often behave as substrates rather than as inhibitors. Currently, the most promising broad-spectrum inhibitors of class B enzymes are molecules presenting chelating groups (thiols, carboxylates, etc.) combined with an aromatic group. This review describes all the types of molecules already tested as potential beta-lactamase inhibitors and thus constitutes an update of the current status in beta-lactamase inhibitor discovery.