In vitro antibacterial activity of the ceftazidime-avibactam combination against enterobacteriaceae, including strains with well-characterized ß-lactamases.

The novel ß-lactamase inhibitor avibactam is a potent inhibitor of class A, class C, and some class D enzymes. The in vitro antibacterial activity of the ceftazidime-avibactam combination was determined for a collection of Enterobacteriaceae clinical isolates; this collection was enriched for resistant strains, including strains with characterized serine ß-lactamases. The inhibitor was added either at fixed weight ratios to ceftazidime or at fixed concentrations, with the latter type of combination consistently resulting in greater potentiation of antibacterial activity. In the presence of 4 µg/ml of avibactam, the ceftazidime MIC50 and MIC90 (0.25 and 2 µg/ml, respectively) were both below the CLSI breakpoint for ceftazidime. Further comparisons with reference antimicrobial agents were performed using this fixed inhibitor concentration. Against most ceftazidime-susceptible and -nonsusceptible isolates, the addition of avibactam resulted in a significant increase in ceftazidime activity, with MICs generally reduced 256-fold for extended-spectrum ß-lactamase (ESBL) producers, 8- to 32-fold for CTX-M producers, and >128-fold for KPC producers. Overall, MICs of a ceftazidime-avibactam combination were significantly lower than those of the comparators piperacillin-tazobactam, cefotaxime, ceftriaxone, and cefepime and similar or superior to those of imipenem.

Activities of ceftazidime and avibactam against ß-lactamase-producing Enterobacteriaceae in a hollow-fiber pharmacodynamic model.

Avibactam is a novel non-ß-lactam ß-lactamase inhibitor that is currently undergoing phase 3 clinical trials in combination with ceftazidime. Ceftazidime is hydrolyzed by a broad range of ß-lactamases, but avibactam is able to inhibit the majority of these enzymes. The studies described here attempt to provide insight into the amount of avibactam required to suppress bacterial growth in an environment where the concentrations of both agents are varying as they would when administered to humans. Following the simulation of a single intravenous dose of the drug, ceftazidime alone had no effect on any test organism, but a ceftazidime-avibactam combination resulted in rapid killing of all of the strains, with growth suppressed for the 8 h of the study. For seven of eight strains, this was achieved with a 1-g-250-mg profile, but a 2-g-500-mg profile was necessary to completely suppress a high-level-AmpC-producing isolate. When ceftazidime was infused continuously for 24 h with a single bolus dose of avibactam, rapid killing of all of the strains was again observed, with growth suppressed for 10 to >24 h. Regrowth appeared to commence once the avibactam concentration dropped below a critical concentration of approximately 0.3 µg/ml. In a third series of studies, ceftazidime was administered every 8 h for 24 h with avibactam administered at fixed concentrations for short periods during each ceftazidime dose profile. Simulating a 1-g dose of ceftazidime, an avibactam pulse of >0.25 and <0.5 µg/ml was required to suppress growth for 24 h.

In vitro and in vivo activities of HPi1, a selective antimicrobial against Helicobacter pylori.

A high-throughput screen (HTS) was performed to identify molecules specifically active against Helicobacter pylori, the causative agent of peptic ulcer and gastric carcinoma. Currently, treatment of H. pylori infection is suboptimal, with failure rates approaching 25%, despite triple therapy with two broad-spectrum antibiotics and a proton pump inhibitor or quadruple therapy with added bismuth. The HTS was performed in 384-well plates, and reduction of the metabolic indicator resazurin was used as a reporter for cell growth. Diverse molecules from commercial sources were identified as hits, and in vitro validations included measurements of MIC and time-dependent killing as well as anaerobic susceptibility testing against a panel of gut microbes. In vivo validation included testing in the mouse model of H. pylori infection. The small molecule HPi1 (3-hydrazinoquinoxaline-2-thiol) had excellent potency, with an MIC of 0.08 to 0.16 µg/ml and good selectivity for H. pylori compared to a panel of commensal bacteria. HPi1 was also effective in a mouse model of H. pylori infection, reducing colony counts to below the limit of detection after oral dosing of 25 mg/kg/day for 3 days. HPi1 is a promising lead in the search for more effective and specific H. pylori therapeutics.

Potentiation of azole antifungals by 2-adamantanamine.

Azoles are among the most successful classes of antifungals. They act by inhibiting α-14 lanosterol demethylase in the ergosterol biosynthesis pathway. Oropharyngeal candidiasis (OPC) occurs in about 90% of HIV-infected individuals, and 4 to 5% are refractory to current therapies, including azoles, due to the formation of resistant biofilms produced in the course of OPC. We reasoned that compounds affecting a different target may potentiate azoles to produce increased killing and an antibiofilm therapeutic. 2-Adamantanamine (AC17) was identified in a screen for compounds potentiating the action of miconazole against biofilms of Candida albicans. AC17, a close structural analog to the antiviral amantadine, did not affect the viability of C. albicans but caused the normally fungistatic azoles to become fungicidal. Transcriptome analysis of cells treated with AC17 revealed that the ergosterol and filamentation pathways were affected. Indeed, cells exposed to AC17 had decreased ergosterol contents and were unable to invade agar. In vivo, the combination of AC17 and fluconazole produced a significant reduction in fungal tissue burden in a guinea pig model of cutaneous candidiasis, while each treatment alone did not have a significant effect. The combination of fluconazole and AC17 also showed improved efficacy (P value of 0.018) compared to fluconazole alone when fungal lesions were evaluated. AC17 is a promising lead in the search for more effective antifungal therapeutics.

Hitting a Moving Target: A Strategic Tool for Analyzing Terrorist Threats.

The subject of terrorism risk can be confusing for both the general public and for those responsible for protecting us from attack. Relatively minor terrorist threats are often conflated with much more serious ones, in part because it is hard to quantify either intent or technical ability to carry out an attack. Plotting threats on a "potential mass casualties" versus "ease of obtainment or production" matrix creates some order out of a seemingly endless array of worldwide threats, and it highlights those threats that are in need of more urgent attention. The specific threats on this 2x2 matrix can fall into one or multiple quadrants, which can be qualitatively described as "most dangerous," "dangerous but difficult," "worrisome," and "persistent terror." By placing threats into these quadrants and illustrating movement within and between them, the matrix can help (1) visualize and parse a diverse set of threats, (2) view how threats have changed over time and judge the efficacy of current countermeasures, and (3) evaluate the merit of future actions and investments. Having a dynamic matrix that can visually map the comparative risk of terrorist threat events in toto and that can help us monitor the effectiveness of present and future resource investments can add intellectual rigor to some of the most difficult and daunting decisions pertaining to our nation's safety and security.

Diazabicyclooctanes (DBOs): a potent new class of non-ß-lactam ß-lactamase inhibitors.

The ß-lactams have been among the most successful classes of antibacterial agents for the past half century. However, a disturbing increase in resistance to ß-lactams has been noted among Gram-negative bacteria, which is attributable to ß-lactamase enzymes not within the spectrum of currently marketed ß-lactams or ß-lactam/ß-lactamase inhibitor combinations. Diazabicyclooctanes (DBOs) were first investigated as ß-lactam mimics in the mid-1990s by chemists at Hoechst Marion Roussel (now part of Sanofi-Aventis) and proved to be a rich source of ß-lactamase inhibitors (BLI). Two members of this novel series of highly potent, broad spectrum BLIs are now in clinical development and their properties are reviewed here.