Use of pharmacokinetic/pharmacodynamic approaches for dose optimization: a case study of plazomicin.

With limited treatment options available for multidrug-resistant bacteria, dose optimization is critical for achieving effective drug concentrations at the site of infection. Yet, selecting an appropriate dose and appropriate time to administer the dose with dosing frequency requires extensive understanding of the interplay between drug pharmacokinetics/pharmacodynamics (PK/PD), the host immune system, and bacterial-resistant mechanisms. Model-informed dose optimization (MIDO) uses PK/PD models (e.g. population PK, mechanism-based models, etc.) that incorporate preclinical and clinical data to simulate/predict performance of treatment regimens in appropriate patient populations and/or infection types that may not be well-represented in clinical trials. Here, we highlight the stages of a MIDO approach for designing optimized regimens by reviewing current clinical, preclinical, and PK/PD modeling data available for plazomicin. Plazomicin is an aminoglycoside approved in 2018 for the treatment of complicated urinary tract infections in adults. Applying knowledge gained by PK/PD modeling can guide therapeutic drug monitoring to ensure that drug exposure is appropriate for clinical efficacy while limiting drug-related toxicity.

Activity of plazomicin against carbapenem-intermediate or -resistant Escherichia coli isolates from the United States and international sites in relation to clonal background, resistance genes, co-resistance, and region.

BACKGROUND: Emerging carbapenem resistance in Escherichia coli, including sequence type 131 (ST131), threatens therapeutic efficacy. Plazomicin (PLZ), a semisynthetic aminoglycoside approved by the FDA in 2018, overcomes the most common aminoglycoside resistance mechanisms and maintains activity against many carbapenem-intermediate or -resistant (CIR) E. coli strains. OBJECTIVES: To assess plazomicin susceptibility among CIR E. coli in relation to region and multiple bacterial characteristics. METHODS: We determined broth microdilution MICs for plazomicin and 11 comparators against 343 CIR clinical E. coli isolates, then compared susceptibility results by bacterial characteristics and region. The collection comprised 203 US isolates (2002-17) and 141 isolates from 17 countries in Europe, Latin America, and the Asia-West Pacific region (2003-17). Isolates were characterized for phylogenetic group, resistance-associated sequence types (STs) and subsets thereof, and relevant ß-lactamase-encoding genes. RESULTS: Plazomicin exhibited the highest percentage susceptible (89%) after tigecycline (99%). The percentage susceptible to plazomicin varied significantly by phylogroup (63%, group B1; versus >93%, others) and ST131 subclone (92%, H30Rx; versus 87%-89%, H30R1 and non-H30), but not ST. It also varied by resistance genotype [higher with Klebsiella pneumoniae carbapenemase (KPC), lower with metallo-ß-lactamases], global region [highest for Latin America (94%), lowest for Asia-West Pacific (69%)], and US region (80%, South, versus 96%-100%, others). Although reduced susceptibility to comparators often predicted reduced susceptibility to plazomicin, even among comparator-intermediate or -resistant isolates the plazomicin-susceptible fraction was ≥77%, except for amikacin (53%). CONCLUSIONS: The likely utility of plazomicin against CIR E. coli is high overall, but varies with region and multiple bacterial characteristics.

Structural basis for plazomicin antibiotic action and resistance.

The approval of plazomicin broadened the clinical library of aminoglycosides available for use against emerging bacterial pathogens. Contrarily to other aminoglycosides, resistance to plazomicin is limited; still, instances of resistance have been reported in clinical settings. Here, we present structural insights into the mechanism of plazomicin action and the mechanisms of clinical resistance. The structural data reveal that plazomicin exclusively binds to the 16S ribosomal A site, where it likely interferes with the fidelity of mRNA translation. The unique extensions to the core aminoglycoside scaffold incorporated into the structure of plazomicin do not interfere with ribosome binding, which is analogously seen in the binding of this antibiotic to the AAC(2')-Ia resistance enzyme. The data provides a structural rationale for resistance conferred by drug acetylation and ribosome methylation, i.e., the two mechanisms of resistance observed clinically. Finally, the crystal structures of plazomicin in complex with both its target and the clinically relevant resistance factor provide a roadmap for next-generation drug development that aims to ameliorate the impact of antibiotic resistance.

Structural and phylogenetic analyses of resistance to next-generation aminoglycosides conferred by AAC(2') enzymes.

Plazomicin is currently the only next-generation aminoglycoside approved for clinical use that has the potential of evading the effects of widespread enzymatic resistance factors. However, plazomicin is still susceptible to the action of the resistance enzyme AAC(2')-Ia from Providencia stuartii. As the clinical use of plazomicin begins to increase, the spread of resistance factors will undoubtedly accelerate, rendering this aminoglycoside increasingly obsolete. Understanding resistance to plazomicin is an important step to ensure this aminoglycoside remains a viable treatment option for the foreseeable future. Here, we present three crystal structures of AAC(2')-Ia from P. stuartii, two in complex with acetylated aminoglycosides tobramycin and netilmicin, and one in complex with a non-substrate aminoglycoside, amikacin. Together, with our previously reported AAC(2')-Ia-acetylated plazomicin complex, these structures outline AAC(2')-Ia's specificity for a wide range of aminoglycosides. Additionally, our survey of AAC(2')-I homologues highlights the conservation of residues predicted to be involved in aminoglycoside binding, and identifies the presence of plasmid-encoded enzymes in environmental strains that confer resistance to the latest next-generation aminoglycoside. These results forecast the likely spread of plazomicin resistance and highlight the urgency for advancements in next-generation aminoglycoside design.

New Antibiotics for Multidrug-Resistant Bacterial Strains: Latest Research Developments and Future Perspectives.

The present work aims to examine the worrying problem of antibiotic resistance and the emergence of multidrug-resistant bacterial strains, which have now become really common in hospitals and risk hindering the global control of infectious diseases. After a careful examination of these phenomena and multiple mechanisms that make certain bacteria resistant to specific antibiotics that were originally effective in the treatment of infections caused by the same pathogens, possible strategies to stem antibiotic resistance are analyzed. This paper, therefore, focuses on the most promising new chemical compounds in the current pipeline active against multidrug-resistant organisms that are innovative compared to traditional antibiotics: Firstly, the main antibacterial agents in clinical development (Phase III) from 2017 to 2020 are listed (with special attention on the treatment of infections caused by the pathogens Neisseria gonorrhoeae, including multidrug-resistant isolates, and Clostridium difficile), and then the paper moves on to the new agents of pharmacological interest that have been approved during the same period. They include tetracycline derivatives (eravacycline), fourth generation fluoroquinolones (delafloxacin), new combinations between one ß-lactam and one ß-lactamase inhibitor (meropenem and vaborbactam), siderophore cephalosporins (cefiderocol), new aminoglycosides (plazomicin), and agents in development for treating drug-resistant TB (pretomanid). It concludes with the advantages that can result from the use of these compounds, also mentioning other approaches, still poorly developed, for combating antibiotic resistance: Nanoparticles delivery systems for antibiotics.

Advances in novel antibiotics to treat multidrug-resistant gram-negative bacterial infections.

Antimicrobial resistance is a growing threat to public health and an increasingly common problem for acute care physicians to confront. Several novel antibiotics have been approved in the past decade to combat these infections; however, physicians may be unfamiliar with how to appropriately utilize them. The purpose of this review is to evaluate novel antibiotics active against resistant gram-negative bacteria and highlight clinical information regarding their use in the acute care setting. This review focuses on novel antibiotics useful in the treatment of infections caused by resistant gram-negative organisms that may be seen in the acute care setting. These novel antibiotics include ceftolozane/tazobactam, ceftazidime/avibactam, meropenem/vaborbactam, imipenem/cilistatin/relebactam, cefiderocol, plazomicin, eravacycline, and omadacycline. Acute care physicians should be familiar with these novel antibiotics so they can utilize them appropriately.

In vitro activity of plazomicin against quinolone-resistant gram-negative bacteria isolated from catheter-associated urinary tract infections.

Quinolone resistance among uropathogens is an increasing concern. Plazomicin is a new aminoglycoside that shows promising results against resistant bacteria. However, no study has yet tested its effect specifically on quinolone-resistant organisms. This study aimed to evaluate the in vitro activity of plazomicin and comparator drugs against quinolone-resistant Gram-negative isolates of catheter-associated urinary tract infections (CAUTI). Plazomicin demonstrated high inhibiting activity against Enterobacteriaceae isolates (95.9% at MIC≤ 2 mg/L), with MIC50/90 was 1/2 mg/L. High MICs values were detected against non-Enterobacteriaceae isolates (MIC50/90, 4/32 mg/L). Plazomicin had susceptibility rate of 97.2% against Enterobacteriaceae isolates carrying aminoglycosides modifying enzymes (AME) genes, while other aminoglycosides, amikacin and gentamicin showed reduced activity (32.4% and 25.4%, respectively). In conclusion, plazomicin showed potent in vitro activity against quinolone-resistant Enterobacteriaceae causing CAUTI, regardless of the AME pattern.

Comparative activity of plazomicin against extended-spectrum cephalosporin-resistant Escherichia coli clinical isolates (2012-2017) in relation to phylogenetic background, sequence type 131 subclones, blaCTX-M genotype, and resistance to comparator agents.

Extended-spectrum cephalosporin-resistant Escherichia coli (ESCREC) are a growing threat. Leading ESCREC lineages include sequence type ST131, especially its (blaCTX-M-15-associated) H30Rx subclone and (blaCTX-M-27-associated) C1-M27 subset within the H30R1 subclone. The comparative activity against such strains of alternative antimicrobial agents, including the recently developed aminoglycoside plazomicin, is undefined, so was investigated here. We assessed plazomicin and 11 comparators for activity against 216 well-characterized ESCREC isolates (Minnesota, 2012-2017) and then compared broth microdilution MICs with phylogenetic and clonal background, beta-lactamase genotype (blaCTX-M; group 1 and 9 variants), and co-resistance. Percent susceptible was > 99% for plazomicin, meropenem, imipenem, and tigecycline; 96-98% for amikacin and ertapenem; and ≤ 75% for the remaining comparators. For most comparators, MICs varied significantly in relation to multiple bacterial characteristics, in agent-specific patterns. By contrast, for plazomicin, the only bacterial characteristic significantly associated with MICs was ST131 subclone: plazomicin MICs were lowest among O16 ST131 isolates and highest among ST131-H30R1 C1-M27 subclone isolates. Additionally, plazomicin MICs varied significantly in relation to resistance vs. susceptibility to comparator agents only for amikacin and levofloxacin. For most study agents, antimicrobial activity against ESCREC varied extensively in relation to multiple bacterial characteristics, including clonal background, whereas for plazomicin, it varied only by ST131 subclone (C1-M27 isolates least susceptible, O16 isolates most susceptible). These findings support plazomicin as a reliable alternative for treating ESCREC infections and urge continued attention to the C1-M27 ST131 subclone.

Transcriptomic characterization of dying hair cells in the avian cochlea.

Sensory hair cells are prone to apoptosis caused by various drugs including aminoglycoside antibiotics. In mammals, this vulnerability results in permanent hearing loss because lost hair cells are not regenerated. Conversely, hair cells regenerate in birds, making the avian inner ear an exquisite model for studying ototoxicity and regeneration. Here, we use single-cell RNA sequencing and trajectory analysis on control and dying hair cells after aminoglycoside treatment. Interestingly, the two major subtypes of avian cochlear hair cells, tall and short hair cells, respond differently. Dying short hair cells show a noticeable transient upregulation of many more genes than tall hair cells. The most prominent gene group identified is associated with potassium ion conductances, suggesting distinct physiological differences. Moreover, the dynamic characterization of >15,000 genes expressed in tall and short avian hair cells during their apoptotic demise comprises a resource for further investigations toward mammalian hair cell protection and hair cell regeneration.

Distribution of genes encoding 16S rRNA methyltransferase in plazomicin-nonsusceptible carbapenemase-producing Enterobacterales in Brazil.

BACKGROUND: The presence of 16S rRNA methyltranferases (16S-RMTases) in carbapenemase-producing Enterobacterales (CPE) is a major concern because it inactivates all clinical use of aminoglycosides, including plazomicin. The aim of this study is to investigate the prevalence of 16S-RMTases in CPE nonsusceptible to plazomicin collected in different Brazilian hospitals. METHODS: All isolates with plazomicin MIC ≥ 4 µg/mL (n = 67) were screened for the presence of 16S-RMTases by sequencing. RESULTS: 54 (80.6%) isolates encoded 16S-RMTase genes (41 rmtB1, 7 armA, 3 rmtD2, 1 rmtD1 and 2 rmtC). Among 41 samples rmtB1 positive, 40 co-harbored blaKPC-2 and 1 blaOXA-48 gene. Of the seven isolates harboring armA gene, 6 were New Delhi Metallo-beta-lactamase (NDM)-producer. rmtD was only found in isolates Klebsiella pneumoniae Carbapenemase (KPC)-producers, one in Serratia marcescens with rmtD2, not reported in Brazil. CONCLUSION: The co-existence of 16S-RMTase and CPE is worrisome because of limited treatment options and the endemic characteristic of (KPC) and NDM in Brazil.

Aminoglycoside antibiotics can inhibit or activate twister ribozyme cleavage.

Interactions between aminoglycoside antibiotics and the twister ribozyme were investigated in this study. An initial screen of 17 RNA-binding antibiotics showed that a number of aminoglycosides inhibit the ribozyme, while a subset of aminoglycosides enhances twister cleavage. Initial kinetic analysis of the twister ribozyme showed a sevenfold inhibition of ribozyme cleavage by paromomycin and a fivefold enhancement of cleavage by sisomicin. Direct binding between the twister ribozyme RNA and paromomycin or sisomicin was measured by microscale thermophoresis. Selective 2'-hydroxyl acylation analysed by primer extension shows that both paromomycin and sisomicin induce distinctive tertiary structure changes to the twister ribozyme. Published crystal structures and mechanistic analysis of the twister ribozyme have deduced a nucleobase-mediated general acid-base catalytic mechanism, in which a conserved guanine plays a key role. Here, we show that paromomycin binding induces a structural transition to the twister ribozyme such that a highly conserved guanine in the active site becomes displaced, leading to inhibition of cleavage. In contrast, sisomicin binding appears to change interactions between P3 and L2, inducing allosteric changes to the active site that enhance twister RNA cleavage. Therefore, we show that small-molecule binding can modulate twister ribozyme activity. These results suggest that aminoglycosides may be used as molecular tools to study this widely distributed ribozyme.

Dissociating antibacterial from ototoxic effects of gentamicin C-subtypes.

Gentamicin is a potent broad-spectrum aminoglycoside antibiotic whose use is hampered by ototoxic side-effects. Hospital gentamicin is a mixture of five gentamicin C-subtypes and several impurities of various ranges of nonexact concentrations. We developed a purification strategy enabling assaying of individual C-subtypes and impurities for ototoxicity and antimicrobial activity. We found that C-subtypes displayed broad and potent in vitro antimicrobial activities comparable to the hospital gentamicin mixture. In contrast, they showed different degrees of ototoxicity in cochlear explants, with gentamicin C2b being the least and gentamicin C2 the most ototoxic. Structure-activity relationships identified sites in the C4'-C6' region on ring I that reduced ototoxicity while preserving antimicrobial activity, thus identifying targets for future drug design and mechanisms for hair cell toxicity. Structure-activity relationship data suggested and electrophysiological data showed that the C-subtypes both bind and permeate the hair cell mechanotransducer channel, with the stronger the binding the less ototoxic the compound. Finally, both individual and reformulated mixtures of C-subtypes demonstrated decreased ototoxicity while maintaining antimicrobial activity, thereby serving as a proof-of-concept of drug reformulation to minimizing ototoxicity of gentamicin in patients.

Expected plazomicin susceptibility in India based on the prevailing aminoglycoside resistance mechanisms in Gram-negative organisms derived from whole-genome sequencing.

Background: Aminoglycoside resistance is a growing challenge, and it is commonly mediated by the aminoglycoside-modifying enzymes (AMEs), followed by 16S rRNA methyl transferase. Plazomicin, a novel aminoglycoside agent approved by the Food and Drug Administration for complicated urinary tract infections is proven to overcome resistance mediated by AMEs but not due to 16S rRNA methyl transferase (16SRMTases). We undertook this study to predict the efficacy of plazomicin in India based on the antimicrobial resistance profile derived from whole-genome sequencing (WGS). Methodology: A total of 386 clinical isolates of Escherichia coli, Klebsiella pneumoniae and Acinetobacter baumannii subjected to WGS were screened for aminoglycoside-resistance mechanisms such as AMEs and 16SRMTases and its association with carbapenemases. Results: AMEs was present in all E. coli, A. baumannii and in 90% of K. pneumoniae. In addition, up to 47% of E. coli and 38% of K. pneumoniae co-carried 16SRMTases with AMEs genes. However, A. baumannii showed 87% of isolates co-harbouring 16SRMTase. bla NDM, bla Oxa-48-like and bla Oxa-23-like were the most predominant carbapenemases in E. coli, K. pneumoniae and A. baumannii, respectively. Notably, 48% of NDM-producing E. coli and 35% of Oxa-48-like producing K. pneumoniae were identified to co-harbour AMEs + RMTAses, where plazomicin may not be useful. Conclusion: Overall, 53%, 62% and 14% of carbapenemase-producing E. coli, K. pneumoniae and A. baumannii harbours only AMEs, indicating the role of plazomicin use. Plazomicin can be used both for ESBLs as "carbapenem-sparing agent" and carbapenemase producers as "colistin-sparing agent." For optimal use, it is essential to know the molecular epidemiology of resistance in a given geographical region where plazomicin empirical therapy is considered.

Manufacture of pH- and HAase-responsive hydrogels with on-demand and continuous antibacterial activity for full-thickness wound healing.

A kind of "intelligent" antibacterial dressing-A-HA/HA-ADH/SS hydrogel was in situ formed quickly via dynamic covalent bonds cross-linking between aldehyde hyaluronic acid (A-HA), adipic acid dihydrazide graft hyaluronic acid (HA-ADH) and sisomicin sulfate (SS). FT-IR, SEM and rheological results displayed that the hydrogels were successfully prepared. The hydrogels had good optical transmittance, injectability, self-healing ability, cytocompatibility, antioxidant activity and hemostatic performance which were beneficial to observe the wound healing condition and provide a good healing environment for wounds. In addition, the hydrogels showed a pH- and HAase- dependent degradability, which allowed them to release more SS at infected wound and then exert on-demand and sustained antibacterial effect against S. aureus and E. coli. The results of wound healing and histological examination revealed that these hydrogels have a good therapeutic effect in the full-thickness mouse skin defect wound. Thus, the hydrogels are expected to be used as potential wound dressings to improve wound healing.

In vitro activity of plazomicin compared to other clinically relevant aminoglycosides in carbapenem-resistant Enterobacteriaceae.

We evaluated the in vitro activity of plazomicin against other aminoglycosides in 122 clinical carbapenem-resistant Enterobacteriaceae isolates using several clinical susceptibility breakpoints. Plazomicin had excellent in vitro activity with 98% overall susceptibility. Amikacin was the next most active with 86% overall susceptibility. This dropped to 55% when switching from Clinical Laboratory and Standards Institute to US Committee on Antimicrobial Susceptibility Testing breakpoints.

Comparative in vitro activity of plazomicin and older aminoglyosides against Enterobacterales isolates; prevalence of aminoglycoside modifying enzymes and 16S rRNA methyltransferases.

Comparative in vitro activity of plazomicin and 4 older aminoglycosides was evaluated with broth microdilution in 714 blood isolates from 14 hospitals in Turkey. Isolates included Escherichia coli (n=320), Klebsiella spp. (n=294), Enterobacter spp. (n=69), Serratia marcescens (n=20), and Citrobacter spp. (n=11). Isolates resistant to older aminoglycosides (n=240) were screened for aminoglycoside modifying enzyme genes: aac(6')-Ib, aac(3)-Ia, aac(3)-IIa, ant(2″)-Ia. Isolates with high MICs for plazomicin (n=41) were screened for 16S rRNA methyltransferase genes (armA, rmtA, rmtB, rmtC, rmtD, rmtE, rmtF, rmtG, rmtH, npmA) and 2 carbapenemase genes (blaOXA-48, blaNDM-1). Overall, resistance to plazomicin, amikacin, netilmicin, gentamicin, and tobramycin was 7.7%, 7.4%, 31.5%, 32.9%, and 34.7%, respectively. aac(6')-Ib and aac(3)-IIa were the most common AME genes. Co-occurrence of blaNDM-1 with armA and rmtC and blaOXA-48 with armA was striking. Enterobacter cloacae carrying rmtC+blaNDM-1, S. marcescens with armA+blaOXA-48, and rmtF+ blaOXA-48 in K. pneumoniae were reported for the first time.

Plazomicin: an intravenous aminoglycoside antibacterial for the treatment of complicated urinary tract infections.

INTRODUCTION: Antimicrobial resistance continues to be a major public health concern due to the emergence and spread of multi-drug resistant (MDR) organisms, including extended spectrum ß-lactamase (ESBL) and carbapenemase producing Enterobacterales. Plazomicin is a novel aminoglycoside that demonstrates activity against MDR gram-negatives, including those producing ESBLs and most carbapenemases, and retains activity against aminoglycoside modifying enzymes as a result of structural modifications. The information discussed is meant to assist in identifying plazomicin's place in therapy and to expand the clinician's armamentarium. AREAS COVERED: Herein, we review the pharmacology, microbiology, clinical efficacy, and safety of plazomicin. To gather relevant information, a literature search was performed using PubMed, Ovid, and Google Scholar electronic databases. Search terms used include plazomicin, ACHN-490, extended spectrum ß-lactamase, ESBL, CRE, aminoglycoside modifying enzymes, and AME. Additional information was obtained from FDA review documents and research abstracts presented at international conferences. EXPERT OPINION: Plazomicin is a promising carbapenem or ß-lactam/ß-lactamase inhibitor-sparing alternative for the treatment of complicated urinary tract infections caused by MDR Enterobacterales. Although robust data for bloodstream infections and bacterial pneumonias are lacking, plazomicin may be considered in individual clinical scenarios if combination therapy is warranted provided supportive microbiological data and therapeutic drug monitoring are available.

ARGONAUT II Study of the In Vitro Activity of Plazomicin against Carbapenemase-Producing Klebsiella pneumoniae.

Plazomicin was tested against 697 recently acquired carbapenem-resistant Klebsiella pneumoniae isolates from the Great Lakes region of the United States. Plazomicin MIC50 and MIC90 values were 0.25 and 1 mg/liter, respectively; 680 isolates (97.6%) were susceptible (MICs of ≤2 mg/liter), 9 (1.3%) intermediate (MICs of 4 mg/liter), and 8 (1.1%) resistant (MICs of >32 mg/liter). Resistance was associated with rmtF-, rmtB-, or armA-encoded 16S rRNA methyltransferases in all except 1 isolate.

Activity of Plazomicin Tested against Enterobacterales Isolates Collected from U.S. Hospitals in 2016-2017: Effect of Different Breakpoint Criteria on Susceptibility Rates among Aminoglycosides.

Plazomicin was active against 97.0% of 8,783 Enterobacterales isolates collected in the United States (2016 and 2017), and only 6 isolates carried 16S rRNA methyltransferases conferring resistance to virtually all aminoglycosides. Plazomicin (89.2% to 95.9% susceptible) displayed greater activity than amikacin (72.5% to 78.6%), gentamicin (30.4% to 45.9%), and tobramycin (7.8% to 22.4%) against carbapenem-resistant and extensively drug-resistant isolates. The discrepancies among the susceptibility rates for these agents was greater when applying breakpoints generated using the same stringent contemporary methods applied to determine plazomicin breakpoints.