Navigating Antibacterial Frontiers: A Panoramic Exploration of Antibacterial Landscapes, Resistance Mechanisms, and Emerging Therapeutic Strategies

The development of effective antibacterial solutions has become paramount in maintaining global health in this era of increasing bacterial threats and rampant antibiotic resistance. Traditional antibiotics have played a significant role in combating bacterial infections throughout history. However, the emergence of novel resistant strains necessitates constant innovation in antibacterial research. We have analyzed the data on antibacterials from the CAS Content Collection, the largest human-curated collection of published scientific knowledge, which has proven valuable for quantitative analysis of global scientific knowledge. Our analysis focuses on mining the CAS Content Collection data for recent publications (since 2012). This article aims to explore the intricate landscape of antibacterial research while reviewing the advancement from traditional antibiotics to novel and emerging antibacterial strategies. By delving into the resistance mechanisms, this paper highlights the need to find alternate strategies to address the growing concern.

Emerging treatment options for skin and soft tissue infections tailoring drug selection to individual patients

PURPOSE OF REVIEW

To provide a brief overview of drugs in Phase II and III of development for the treatment of acute bacterial skin and skin structure infections (ABSSSI), offering insights into potential customized treatment options.

RECENT FINDINGS

Several drugs are currently in advanced stages of evaluation for the treatment of ABSSSI, and numerous molecules are entering in the early development phases. Notably, many of these drugs exhibit unique mechanisms of action and interesting antimicrobial spectrum.

SUMMARY

Tailoring antibiotic therapy based on patient characteristics, likely pathogens, type, site and severity of ABSSSI is crucial. Given the inherent limitations of available treatments, the development of novel agents is a pivotal avenue. Such advancements hold promise for enhancing treatment efficacy and simplifying drug selection for ABSSSI in everyday clinical practice.

Antistaphylococcal discovery pipeline; where are we now?

The serious spread of antibiotic-resistant Staphylococcal aureus strains is alarming. This is reflected by the measures governments and health-related bodies are offering to ease antibiotic drug development. Finding new active agents, preferably with novel mechanism of action, or even finding new targets for drug development are essential. In this review, we summarize the current status of novel antistaphylococcal agents undergoing clinical trials. We mainly discuss antistaphylococcal small molecules and peptides in the text with a special focus on their chemistry, while antistaphylococcal immunotherapy (antibodies) are mentioned in a summative table. This review shall serve as a summary that influences future synthetic efforts in the antistaphyloccocals development field.

Staph wars: the antibiotic pipeline strikes back

Antibiotic chemotherapy is widely regarded as one of the most significant medical advancements in history. However, the continued misuse of antibiotics has contributed to the rapid rise of antimicrobial resistance (AMR) globally. Staphylococcus aureus, a major human pathogen, has become synonymous with multidrug resistance and is a leading antimicrobial-resistant pathogen causing significant morbidity and mortality worldwide. This review focuses on (1) the targets of current anti-staphylococcal antibiotics and the specific mechanisms that confirm resistance; (2) an in-depth analysis of recently licensed antibiotics approved for the treatment of S. aureus infections; and (3) an examination of the pre-clinical pipeline of anti-staphylococcal compounds. In addition, we examine the molecular mechanism of action of novel antimicrobials and derivatives of existing classes of antibiotics, collate data on the emergence of resistance to new compounds and provide an overview of key data from clinical trials evaluating anti-staphylococcal compounds. We present several successful cases in the development of alternative forms of existing antibiotics that have activity against multidrug-resistant S. aureus. Pre-clinical antimicrobials show promise, but more focus and funding are required to develop novel classes of compounds that can curtail the spread of and sustainably control antimicrobial-resistant S. aureus infections.

Efficacy and safety of optional parenteral antimicrobial therapy for complicated skin and soft tissue infections: A systematic review and Bayesian network meta-analysis

BACKGROUND

Skin and soft tissue infections (SSTIs) carry significant economic burden, as well as morbidity and mortality, especially when caused by methicillin-resistant Staphylococcus aureus. This study aims to investigate the efficacy and safety of optional antimicrobial therapy for the treatment of complicated SSTIs (cSSTIs).

METHODS

We searched PubMed, Medline (Via Ovid SP), Embase (Via Ovid SP), and the Cochrane Central Register of Controlled Trials from their inception to March 22, 2021 for randomized controlled trials (RCTs) that studied the use of optional antimicrobial therapy for cSSTIs. Citations' screening, study selection, data extraction, and risk of bias assessment were independently performed by 2 authors. The primary outcomes were clinical and microbiological treatment success, and adverse events (AEs) were also assessed.

RESULTS

A total of 48 trials covering 24,381 patients assessing 20 types of antimicrobial treatment modalities were included. Overall, omadacycline was associated with the highest beneficial effect on clinical and microbiological treatment success and with the largest rank probability based on surface under the cumulative ranking curve values, avarofloxacin was closely followed. Both had, however, omadacycline was related to moderately safety profiles. Lefamulin ranked as the best option was associated with the lowest risk of severe AEs. Subgroup analysis showed similar results. The quality of primary outcomes was moderate to low.

CONCLUSIONS

The use of omadacycline was associated with higher rates of clinical and microbiological treatment success for the treatment of cSSTIs, with a relative low risk of AEs. Due to the limitations of the included RCTs, high-quality and well-designed RCTs are needed to further confirm the results.

Efficacy and Safety of Iclaprim for the Treatment of Skin Structures and Soft Tissue Infections: A Methodological Framework

Background: Skin and soft tissue infections (SSTIs) are among the most common infections worldwide. They manifest in a variety of forms, such as erysipelas, cellulitis, and necrotizing fasciitis. Antibiotics are the significant method for clinical treatment of SSTIs. This study reported a methodology framework to determine the efficacy and safety of iclaprim in treatment of SSTIs.

Methods: We will search the PubMed, EMbase, CNKI, WanFang Data, VIP, and ClinicalTrials.gov from their inception to June 2022 for randomized controlled trials and cohort studies on iclaprim with SSTIs. Two authors will independently screen the eligible studies, assess the quality of the included papers, and extract the required information. Randomized controlled trials will be assessed using the Cochrane risk-of-bias tool. The Newcastle–Ottawa Scale will be used to evaluate observational studies. The quality of the evidence will be evaluated using the Grading of Recommendations Assessment Development and Evaluation system. RevMan 5.3 will be used for the data synthesis and quantitative analysis.

Results and Discussions: This study will provide the clinicians with more high-quality evidence to choose iclaprim for patients with SSTIs.

Ethics and Dissemination: This systematic review and meta-analysis will be based on published data, so ethical approval is not necessary. The results of this meta-analysis will be published in a peer-reviewed journal.

The impact of antibiotics on clinical response over time in uncomplicated cellulitis: a systematic review and meta-analysis

PURPOSE

Antibiotic treatment of uncomplicated cellulitis is highly variable with respect to agent, dose, and route of administration. As there is uncertainty about optimal/appropriate time to reassess, we aimed to assess time to clinical response.

METHODS

We conducted a systematic review of randomized controlled trials reporting clinical response of uncomplicated cellulitis to antibiotic treatment over multiple timepoints. PubMed, Embase, CENTRAL, WHO ICTRP, and clinicaltrials.gov were searched from inception to June 2021 without language restrictions. The primary outcome was time to clinical response. Other outcomes were components of clinical response (pain, severity score, redness, edema measured at ≥ 2 timepoints) and the proportion of patients with treatment failure. We performed a pooled estimate of the average time to clinical response together with 95% confidence intervals using a random effects model.

RESULTS

We included 32 randomized controlled trials (n = 13,576 participants). The mean time to clinical response was 1.68 days (95%CI 1.48-1.88; I² = 76%). The response to treatment for specific components was as follows: ~ 50% reduction of pain and severity score by day 5, a ~ 33% reduction in area of redness by day 2-3, and a 30-50% reduction of proportion of patients with edema by day 2-4. Treatment failure was variably defined with an overall failure rate of 12% (95%CI 9-16%).

CONCLUSION

The best available data suggest the optimal time to clinical reassessment is between 2 and 4 days, but this must be interpreted with caution due to considerable heterogeneity and small number of included studies.

New drugs for methicillin-resistant Staphylococcus aureus skin and soft tissue infections

PURPOSE OF REVIEW

Staphylococcus aureus is a pathogen incriminated in skin and soft tissue infections (SSTIs), with methicillin-resistant S. aureus (MRSA) becoming the predominant cause and representing a significant burden to the healthcare system. The last updated Infectious Diseases Society of America (IDSA) guidelines concerning MRSA infections and SSTIs management were published in 2011 and 2014, respectively. The UK updated guidelines for MRSA infection treatment were published in 2021. Older treatment options may be associated with toxicity and require frequent dosing. There is a paucity of recent reviews on the armamentarium of new agents for MRSA SSTIs treatment.

RECENT FINDINGS

Since 2005, several new antibiotics received a fast-track approval by the Food and Drug Administration (FDA) for SSTI treatment. These drugs include delafloxacin, omadacycline, tedizolid, ceftaroline, dalbavancin, oritavancin and telavancin. In this manuscript, we will review the data that led to these new drugs approval and discuss their advantages and disadvantages in MRSA SSTIs management.

SUMMARY

MRSA is a major cause of SSTIs. Several novel therapies covering MRSA were FDA-approved for SSTIs. However, the current IDSA guidelines for MRSA infection and SSTIs as well as the recently published UK guidelines on MRSA treatment only consider these drugs as alternative choices or do not mention them at all.

Antivitamins: A Silver Lining in the Era of Antimicrobial Resistance

Antivitamins are compounds that negate the biological effects of vitamins. They have been successfully exploited for the development of various classes of drugs. In the early 19th century, the antifolate prontosil was developed for the treatment of puerperal fever. Since then, numerous other antifolates have been used to treat a wide range of infections. Antifolates, such as methotrexate, are potent anticancer agents and antivitamin K, such as warfarin, are used as anticoagulants. Despite several years of research, most antivitamin-based drugs are limited to vitamin K and B9, and the development of antagonists for other vitamins is still in the nascent stage. In the era of antimicrobial resistance, antivitamins can be considered as a promising alternative to develop newer antimicrobials and are worth exploring further. This review discusses key antivitamins at different stages of development which have potential utility as antibiotic drug candidates. The summary of studies of antivitamins in clinical development is also narrated.

Translation of Pharmacodynamic Biomarkers of Antibiotic Efficacy in Specific Populations to Optimize Doses

Antibiotic efficacy determination in clinical trials often relies on non-inferiority designs because they afford smaller study sample sizes. These efficacy studies tend to exclude patients within specific populations or include too few patients to discern potential differences in their clinical outcomes. As a result, dosing guidance in patients with abnormal liver and kidney function, age across the lifespan, and other specific populations relies on drug exposure-matching. The underlying assumption for exposure-matching is that the disease course and the response to the antibiotic are similar in patients with and without the specific condition. While this may not be the case, clinical efficacy studies are underpowered to ensure this is true. The current paper provides an integrative review of the current approach to dose selection in specific populations. We review existing clinical trial endpoints that could be measured on a more continuous rather than a discrete scale to better inform exposure-response relationships. The inclusion of newer systemic biomarkers of efficacy can help overcome the current limitations. We use a modeling and simulation exercise to illustrate how an efficacy biomarker can inform dose selection better. Studies that inform response-matching rather than exposure-matching only are needed to improve dose selection in specific populations.

Potential role of new-generation antibiotics in acute bacterial skin and skin structure infections

PURPOSE OF REVIEW

To summarize the available results of primary analyses from high-quality randomized studies of either recently approved or possible future agents for the treatment of acute bacterial skin and skin structure infections (ABSSSI).

RECENT FINDINGS

In the last 2 decades, several novel agents have been approved for the treatment of ABSSSI, that are also active against methicillin-resistant Staphylococcus aureus (MRSA). In addition to already available agents, further molecules are in clinical development that could become available for treating ABSSSI in the forthcoming future.

SUMMARY

The current and future availability of several new-generation antibiotics will allow to modulate therapeutic choices not only on efficacy but also on other relevant factors such as the combination of the drug safety profile and the comorbidities of any given patient, the expected adherence to outpatient therapy, and the possibilities of early discharge or avoiding hospitalization by means of oral formulations, early switch from intravenous to oral therapy, or single-dose administration of long-acting intravenous agents. With the advent of new-generation antibiotics, all these factors are becoming increasingly essential for tailoring treatment to individual patients in line with the principles of personalized medicine, and for optimizing the use of healthcare resources.

Treatment of methicillin-resistant Staphylococcus aureus (MRSA): updated guidelines from the UK

These evidence-based guidelines are an updated version of those issued in 2008. They have been produced following a review of the published literature (2007-18) pertaining to the treatment of infections caused by MRSA. The guidelines update, where appropriate, previous recommendations, taking into account changes in the UK epidemiology of MRSA, ongoing national surveillance data and the efficacy of novel anti-staphylococcal agents licensed for use in the UK. Emerging therapies that have not been licensed for use in the UK at the time of the review have also been assessed.

Staphylococcal Skin and Soft Tissue Infections

Staphylococcus aureus is the most common bacteria causing purulent skin and soft tissue infections. Many disease-causing S aureus strains are methicillin resistant; thus, empiric therapy should be given to cover methicillin-resistant S aureus. Bacterial wound cultures are important for characterizing local susceptibility patterns. Definitive antibiotic therapy is warranted, although there are no compelling data demonstrating superiority of any one antibiotic over another. Antibiotic choice is predicated by the infection severity, local susceptibility patterns, and drug-related safety, tolerability, and cost. Response to therapy is expected within the first days; 5 to 7 days of therapy is typically adequate to achieve cure.

Iclaprim reduces the incidence and severity of Staphylococcus aureus-induced septic arthritis in a murine model

Staphylococcus aureus is the most common non-gonococcal aetiology of septic arthritis. The efficacy of iclaprim against S. aureus LS-1, a clinical strain identified from a patient with septic arthritis, was studied in MF1 mice to evaluate the activity of iclaprim, which is in clinical development, in preventing joint infections. Iclaprim (2.5–80 mg kg⁻¹) administered as a single dose via the tail vein reduced the incidence of S. aureus septic arthritis and mortality in an experimental murine model of septic arthritis.

Afabicin, a First-in-Class Antistaphylococcal Antibiotic, in the Treatment of Acute Bacterial Skin and Skin Structure Infections: Clinical Noninferiority to Vancomycin/Linezolid

Afabicin (formerly Debio 1450, AFN-1720) is a prodrug of afabicin desphosphono, an enoyl-acyl carrier protein reductase (FabI) inhibitor, and is a first-in-class antibiotic with a novel mode of action to specifically target fatty acid synthesis in Staphylococcus spp. The efficacy, safety, and tolerability of afabicin were compared with those of vancomycin/linezolid in the treatment of acute bacterial skin and skin structure infections (ABSSSI) due to staphylococci in this multicenter, parallel-group, double-blind, and double-dummy phase 2 study.

Afabicin (formerly Debio 1450, AFN-1720) is a prodrug of afabicin desphosphono, an enoyl-acyl carrier protein reductase (FabI) inhibitor, and is a first-in-class antibiotic with a novel mode of action to specifically target fatty acid synthesis in Staphylococcus spp. The efficacy, safety, and tolerability of afabicin were compared with those of vancomycin/linezolid in the treatment of acute bacterial skin and skin structure infections (ABSSSI) due to staphylococci in this multicenter, parallel-group, double-blind, and double-dummy phase 2 study. Randomized patients (1:1:1) received either low-dose (LD) afabicin (intravenous [i.v.] 80 mg, followed by oral 120 mg, twice a day [BID]), high-dose (HD) afabicin (i.v. 160 mg, followed by oral 240 mg, BID), or vancomycin/linezolid (i.v. vancomycin 1 g or 15 mg/kg, followed by oral linezolid 600 mg, BID). The most frequent baseline pathogen was Staphylococcus aureus (97.5% of microbiological intent-to-treat [mITT] population), and 50.4% of patients had methicillin-resistant S. aureus. Clinical response rates at 48 to 72 h postrandomization in the mITT population were comparable among treatment groups (94.6%, 90.1%, and 91.1%, respectively). Both LD and HD afabicin were noninferior to vancomycin/linezolid (differences, −3.5% [95% confidence interval {CI}, −10.8%, 3.9%] and 1.0% [95% CI, −7.3%, 9.2%], respectively). Most common treatment-emergent adverse events were mild and were headache (9.1% and 16.8%) and nausea (6.4% and 8.4%) with LD and HD afabicin, respectively. Afabicin was efficacious and well tolerated in the treatment of ABSSSI due to staphylococci, and these data support further development of afabicin for the treatment of ABSSSI and potentially other types of staphylococcal infections. (This study has been registered at ClinicalTrials.gov under identifier NCT02426918.)

Emerging drugs for treating methicillin-resistant Staphylococcus aureus

Introduction: In clinical practice, methicillin-resistant Staphylococcus aureus (MRSA) represents a major threat and has been associated with high rates of inadequate antibiotic treatment and significant increases in morbidity, mortality, and overall healthcare costs. The association between the prescription of an inappropriate or delayed antibiotic and impaired clinical outcomes has been widely described. Areas covered: To address the threat of MRSA, many new therapeutic options with a peculiar activity against MRSA have been recently developed and approved. New agents are characterized by specific issues in terms of spectrum of activity, pharmacokinetics, risk of drug-drug interactions, and toxicity, with potential advantages that should be considered in everyday clinical practice. Expert opinion: The most attractive characteristic of new drugs is represented by the broad spectrum of activity against multidrug-resistant pathogens; moreover, new compounds in most cases are characterized by favorable toxicity profiles compared with old drugs currently used in clinical practice. Some of the new antimicrobials will be also available as oral formulations, with the potential for oral switch, even in infections due to resistant pathogens. In particular conditions/populations (e.g. liver failure, renal disease, pregnancy, diabetic, children, and elderly), novel antibiotics with reduced toxicity could be an important option, including after hospital discharge.

A pooled analysis of patients with wound infections in the Phase 3 REVIVE trials: randomized, double-blind studies to evaluate the safety and efficacy of iclaprim versus vancomycin for treatment of acute bacterial skin and skin structure infections

Introduction. Iclaprim is a diaminopyrimidine antibiotic for the treatment of acute bacterial skin and skin structure infections (ABSSSI) due to Gram-positive pathogens.Aim. This analysis evaluates patients with wound infections from two Phase 3 trials of ABSSSI.Methodology. Six-hundred-two patients with wound infections from two Phase 3, double-blinded, randomized, multicenter, active controlled trials (REVIVE-1/-2) were evaluated in a post hoc analysis of iclaprim 80 mg compared with vancomycin 15 mg kg^-1 administered intravenously every 12 h for 5-14 days. The primary endpoint was to determine whether iclaprim was non-inferior (10 % margin) to vancomycin in achieving a ≥20 % reduction from baseline in lesion size 48-72 h after starting study drug (early clinical response [ECR]). Safety was assessed.Results. In REVIVE-1, ECR was 83.5 % with iclaprim versus 79.7 % with vancomycin (treatment difference 3.77%, 95 % CI -4.50%, 12.04%). In REVIVE-2, ECR was 82.7 % with iclaprim versus 76.3 % with vancomycin (treatment difference 6.38%, 95 % CI -3.35%, 16.12%). In the pooled dataset, iclaprim had similar ECR rates compared with vancomycin among wound infection patients (83.2 % vs 78.2 %) with a treatment difference of 5.01 % (95 % CI -1.29%, 11.32%). The safety profile was similar in iclaprim- and vancomycin-treated patients, except for a higher incidence of diarrhea with vancomycin (n=17) compared with iclaprim (n=6) and fatigue with iclaprim (n=17) compared with vancomycin (n=8).Conclusion. Based on early clinical response, iclaprim achieved non-inferiority to vancomycin with a similar safety profile in patients with wound infections suspected or confirmed as caused by Gram-positive pathogens. Iclaprim may be a valuable treatment option for wound infections.

Emerging Treatment Options for Infections by Multidrug-Resistant Gram-Positive Microorganisms

Antimicrobial agents are currently the mainstay of treatment for bacterial infections worldwide. However, due to the increased use of antimicrobials in both human and animal medicine, pathogens have now evolved to possess high levels of multi-drug resistance, leading to the persistence and spread of difficult-to-treat infections. Several current antibacterial agents active against Gram-positive bacteria will be rendered useless in the face of increasing resistance rates. There are several emerging antibiotics under development, some of which have been shown to be more effective with an improved safety profile than current treatment regimens against Gram-positive bacteria. We will extensively discuss these antibiotics under clinical development (phase I-III clinical trials) to combat Gram-positive bacteria, such as Staphylococcus aureus, Enterococcus faecium and Streptococcus pneumoniae. We will delve into the mechanism of actions, microbiological spectrum, and, where available, the pharmacokinetics, safety profile, and efficacy of these drugs, aiming to provide a comprehensive review to the involved stakeholders.

Methicillin-resistant Staphylococcus aureus: an overview of basic and clinical research

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most successful modern pathogens. The same organism that lives as a commensal and is transmitted in both health-care and community settings is also a leading cause of bacteraemia, endocarditis, skin and soft tissue infections, bone and joint infections and hospital-acquired infections. Genetically diverse, the epidemiology of MRSA is primarily characterized by the serial emergence of epidemic strains. Although its incidence has recently declined in some regions, MRSA still poses a formidable clinical threat, with persistently high morbidity and mortality. Successful treatment remains challenging and requires the evaluation of both novel antimicrobials and adjunctive aspects of care, such as infectious disease consultation, echocardiography and source control. In this Review, we provide an overview of basic and clinical MRSA research and summarize the expansive body of literature on the epidemiology, transmission, genetic diversity, evolution, surveillance and treatment of MRSA.

FDA approved antibacterial drugs: 2018-2019

Bacterial resistance to existent antibiotherapy is a perpetual internationally-recognized problem. Year after year, there is a continuous need for novel antibacterial drugs and this research and development efforts recently resulted in few new drugs or combination of drugs proposed for the use into the clinic. This review focuses on the novel US FDA approved antibacterial agents in the last two years (2018-2019). Plazomicin, eravacycline, sarecycline, omadacycline, rifamycin (2018) and imipenem, cilastatin and relebactam combination, pretomanid, lefamulin, cefiderocol (2019) are new therapeutic options. Plazomicin aminoglycoside antibiotic targets Enterobacteriaceae infections, being mainly used for the complicated urinary tract infections. The fully synthetic fluorocycline eravacycline gained approval for the complicated intra-abdominal infections. The tetracycline-derived antibiotic sarecycline might be a useful strategy for the management of non-nodular moderate to severe acne, while the other tetracycline-derived antibiotic approved, omadacycline, may be used for the patients with acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia. The already-known RNA-synthesis suppressor rifamycin is now also approved for noninvasive Escherichia Coli-caused travelers' diarrhea. Two combinatorial strategies were approved for complicated urinary tract infections, complicated intra-abdominal infections (imipenem, cilastatin and relebactam) and lung tuberculosis (pretomanid in combination with bedaquiline and linezolid). Lefamulin is a semisynthetic pleuromutilin antibiotic for community-acquired bacterial pneumonia, while cefiderocol, a cephalosporin antibiotic is the last antibacterial drug approved in 2019, for the use in complicated urinary tract infections. Despite of these new developments, there is an ongoing need and urgency to develop novel antibiotic strategies and drugs to overrun the bacterial resistance to antibiotics.

Important new therapies for methicillin-resistant Staphylococcus aureus

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) infections represent a leading cause of infection-related morbidity and mortality worldwide. There has been a welcome increase in the number of agents available for the treatment of MRSA infection over the last decade and several clinical trials are currently investigating the role of new experimental strategies.Areas covered: The purpose of this manuscript is to review the efficacy and safety of recently approved anti-MRSA molecules as well as some newer agents currently under investigation with a specific focus on the potential role of these drugs in everyday clinical practice.Expert opinion: Many new drugs with an activity against MRSA have been recently approved or are in an advanced stage of development. All these compounds represent promising options to enhance our antibiotic armamentarium. However, data regarding the use of these new compounds in real-life terms are limited and their best placement in therapy and in terms of optimization of medical resources and balance of cost-effectiveness requires further investigation.

The safety of treatment options for acute bacterial skin and skin structure infections

INTRODUCTION

Acute bacterial skin and skin-structure infections (ABSSSI) may develop in both in-patients and out-patients, possibly with a severe clinical presentation. Since most phase 3 randomized clinical trials have shown non-inferiority in efficacy across different agents, considerations regarding their different safety profiles inevitably play a crucial role in the everyday choice about which of them should be employed for the treatment of ABSSSI.

AREAS COVERED

In this review, the authors discuss the safety profile of different treatment options for ABSSSI.

EXPERT OPINION

The spread of methicillin-resistant Staphylococcus aureus (MRSA) in the last decades has inevitably influenced the therapeutic approach to ABSSSI. Adequate knowledge of the peculiar toxicity profile of each drug active against MRSA is essential for guiding, monitoring and managing adverse events, in turn reducing any unfavorable impact of toxicity on patients' outcomes. In the next five years, potential toxicity will play a critical role in establishing the best available therapy for each specific patient, together with consideration regarding the possibility of avoiding hospitalization or allowing a switch from intravenous to oral therapy and early discharge.

Perspectives on synthetic pharmacotherapy for the treatment of nosocomial pneumonia

Introduction: Nosocomial pneumonia is the second most common infection in hospital settings, resulting in substantial increases in morbidity, mortality, and length of hospital stay. The rapid increase in resistance of nosocomial pathogens to many antibiotics and the high dissemination of resistance genes highlight the need for innovative approaches to combat difficult-to-treat nosocomial respiratory infections. Areas covered: This review summarizes the synthetic antimicrobials that are currently in development for the treatment of nosocomial pneumonia, focusing on antibiotics in the final phases of clinical development and on the strategies employed by novel synthetic antimicrobial peptides. Expert opinion: Several novel synthetic antimicrobials are currently in the pipeline, and it appears that new antimicrobial peptides or mimetics will soon be made available, expanding the opportunities to treat nosocomial pneumonia. However, the approval process for use in the treatment of nosocomial pneumonia is arduous. Given that significant investments by pharmaceutical companies have ended in failure to obtain the approval of regulatory agencies, novel platforms for antimicrobial discovery are needed. The identification of new and fully synthetic chemical structures with activity against nosocomial pathogens needs to be followed by preclinical studies in large animals and by pharmacokinetic and pharmacodynamic studies in specific critically ill populations to assess lung penetration.

A Pooled Analysis of the Safety and Efficacy of Iclaprim Versus Vancomycin for the Treatment of Acute Bacterial Skin and Skin Structure Infections in Patients With Intravenous Drug Use: Phase 3 REVIVE Studies

PURPOSE

This analysis evaluates the efficacy and safety of iclaprim versus vancomycin for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) in patients who were intravenous drug users (IVDUs).

METHODS

A total of 621 patients who were IVDUs from 2 parallel Phase III, double-blind, randomized (1:1), active-controlled, multinational, multicenter trials (REVIVE-1 and REVIVE-2) were analyzed separately and pooled. This post hoc analysis summarizes the efficacy and safety profile of iclaprim 80 mg fixed dose compared with vancomycin 15 mg/kg administered intravenously during 2 h every 12 h for 5-14 days among this population. The primary end point of these studies was to determine whether iclaprim was noninferior (10% margin) to vancomycin in achieving a ≥20% reduction in lesion size at 48-72 h after initiation of treatment with the study drug (early clinical response) in the intent-to-treat population. The safety profile was assessed based on adverse events and laboratory parameters.

FINDINGS

Iclaprim had higher early clinical response rates (85.8%; 95% CI, 81.5%-89.4%) compared with vancomycin (79.8%; 95% CI, 74.8%-84.2%) among patients with ABSSSIs who were IVDUs, with a treatment difference of +6.00% (95% CI, 0.06-12.0). The safety profile was similar in the iclaprim and vancomycin arms, with 3.7% and 5.0%, respectively, of patients discontinuing study therapy because of adverse events and 1.9% and 3.4%, respectively, of patients developing serious adverse events.

IMPLICATIONS

Iclaprim had a higher early clinical response rate and favorable safety profile compared with vancomycin for the treatment of ABSSSIs in patients who were IVDUs. Iclaprim may be a valuable treatment option for ABSSSIs in this patient population.

In Vitro Activity of Iclaprim against Isolates in Two Phase 3 Clinical Trials (REVIVE-1 and -2) for Acute Bacterial Skin and Skin Structure Infections

Iclaprim, a selective bacterial dihydrofolate reductase inhibitor, and other antibiotics were tested against Gram-positive isolates from two phase 3 studies of acute bacterial skin and skin structure infections (ABSSSIs) (REVIVE-1 and -2). Seven hundred ninety baseline isolates, including Staphylococcus aureus, β-hemolytic streptococci, and Streptococcus anginosus group, underwent antibacterial susceptibility testing. Iclaprim had an MIC₉₀ of 0.12 μg/ml for S. aureus (0.12 μg/ml for methicillin susceptible, 0.25 μg/ml for methicillin resistant), 0.25 μg/ml for β-hemolytic streptococci, and 0.008 μg/ml for S. anginosus group. Iclaprim demonstrated potent activity against these Gram-positive ABSSSI isolates.

The effects of iclaprim on exotoxin production in methicillin-resistant and vancomycin-intermediate Staphylococcus aureus

PURPOSE

Extracellular protein toxins contribute to the pathogenesis of Staphylococcus aureus infections. The present study compared the effects of iclaprim and trimethoprim - two folic acid synthesis inhibitors - with nafcillin and vancomycin on production of Panton-Valentine leukocidin (PVL), alpha haemolysin (AH) and toxic-shock syndrome toxin I (TSST-1) in methicillin-resistant and vancomycin-intermediate S. aureus (MRSA and VISA, respectively).

METHODOLOGY

Northern blotting and RT-PCR were used to assess gene transcription; toxin-specific bioassays were used to measure protein toxin production.

RESULTS

As shown previously, sub-inhibitory concentrations (sub-MIC) of nafcillin increased and prolonged MRSA toxin gene transcription and enhanced PVL, TSST-1 and AH production. Sub-inhibitory doses of iclaprim and trimethoprim delayed maximal AH gene (hla) transcription and suppressed AH production; both drugs delayed, but neither reduced, maximal TSST-1 production. Trimethoprim significantly increased lukF-PV expression and PVL production compared to both untreated and iclaprim-treated cultures. Higher concentrations of iclaprim and trimethoprim markedly suppressed MRSA growth, mRNA synthesis and toxin production. In VISA, iclaprim, vancomycin and nafcillin variably increased tst and hla expression, but only nafcillin increased toxin production. Despite its ability to increase hla expression, iclaprim was the most potent inhibitor of AH production.

CONCLUSIONS

We conclude that, due to its ability to suppress toxin production, iclaprim should be effective against severe staphylococcal infections caused by toxin-producing MRSA and VISA strains, especially given its ability to concentrate at sites of infection such as skin and skin structures and the lung.

Potential for Cost Saving with Iclaprim Owing to Avoidance of Vancomycin-Associated Acute Kidney Injury in Hospitalized Patients with Acute Bacterial Skin and Skin Structure Infections

BACKGROUND AND OBJECTIVE

Vancomycin is the most prescribed antibiotic for hospitalized adults with skin and skin structure infections. Vancomycin is associated with acute kidney injury. Iclaprim is an antibiotic under development for the treatment of patients with acute bacterial skin and skin structure infections and is not associated with acute kidney injury. This economic model sought to determine the potential cost saving with iclaprim owing to avoidance of vancomycin-associated acute kidney injury among hospitalized patients with acute bacterial skin and skin structure infections.

MATERIALS AND METHODS

A hospital cost-minimization model was developed to estimate the overall cost impact of replacing empiric vancomycin with iclaprim among hospitalized adult patients with skin and skin structure infections. The structural model included: vancomycin acquisition; vancomycin assay; incidence of vancomycin-associated acute kidney injury; excess hospital length of stay if acute kidney injury occurred; frequency/cost of specialty physician consults after occurrence of acute kidney injury; and probability/cost of acute dialysis as a result of acute kidney injury. Iclaprim treatment duration was 7 days and iclaprim acquisition cost was varied to determine the upper end of the daily iclaprim price that still conferred cost savings relative to vancomycin. Duration of hospitalization for iclaprim was assumed to be the same as patients with no acute kidney injury.

RESULTS

Based on the overall acute kidney injury rate (9.2%), the neutral acquisition price threshold for iclaprim vs. vancomycin was US$1373.47/regimen. Across various subpopulations where acute kidney injury risk ranged between 9.2 and 16.7%, the daily iclaprim acquisition cost that still conferred cost savings was up to US$300/day.

CONCLUSIONS

Iclaprim has the potential to reduce the economic burden of acute bacterial skin and skin structure infections in hospitalized patients at risk for vancomycin-associated acute kidney injury when iclaprim acquisition is US$300/day or less.

Iclaprim: a differentiated option for the treatment of skin and skin structure infections

INTRODUCTION

Iclaprim is a selective bacterial dihydrofolate reductase (DHFR) inhibitor. Although there are alternative options for the treatment of acute bacterial skin and skin structure infections (ABSSSI), iclaprim is differentiated from other available antibiotics. Areas covered: Iclaprim is under clinical development for ABSSSI. This review summarizes the mechanism of action, pharmacokinetics, microbiology, clinical development program, and the differentiation of iclaprim from other antibiotics. Expert commentary: Iclaprim has a different mechanism of action (DHFR inhibitor) compared to most other antibiotics, is active and rapidly bactericidal against Gram-positive pathogens including antibiotic-resistant pathogens, and suppresses bacterial exotoxins (alpha hemolysin, Panton Valentine leukocidin, and toxic shock syndrome toxin-1). Compared to trimethoprim, iclaprim has lower MIC_90s, can be given without a sulfonamide, overcomes select trimethoprim resistance, and does not cause hyperkalemia. Iclaprim is administered as a fixed dose, does not require dose adjustment in renally-impaired or obese patients, and was not associated with nephrotoxicity in the Phase 3 pivotal REVIVE studies. Iclaprim represents a novel, alternative option for the treatment of severe skin and skin structure infections due to Gram-positive bacteria, particularly in patients at risk of acute kidney injury.

Iclaprim, a dihydrofolate reductase inhibitor antibiotic in Phase III of clinical development: a review of its pharmacology, microbiology and clinical efficacy and safety

Iclaprim is under clinical development for treating acute bacterial skin and skin structure infections (ABSSSI) and nosocomial pneumonia most often due to Gram-positive bacteria, including infections due to drug-resistant bacteria. In two recent Phase III studies of patients with acute bacterial skin and skin structure infections, intravenous iclaprim 80 mg every 12 h was noninferior to dose-adjusted vancomycin. Additional studies are planned for patients with nosocomial pneumonia. Iclaprim represents an alternative for the treatment of severe skin and pulmonary infections due to Gram-positive bacteria.

A Phase 3, Randomized, Double-Blind, Multicenter Study To Evaluate the Safety and Efficacy of Intravenous Iclaprim versus Vancomycin for Treatment of Acute Bacterial Skin and Skin Structure Infections Suspected or Confirmed To Be Due to Gram-Positive Pathogens (REVIVE-2 Study)

Iclaprim is a novel diaminopyrimidine antibiotic that may be an effective and safe treatment for serious skin infections. The safety and effectiveness of iclaprim were assessed in a global phase 3, double-blind, randomized, active-controlled trial. Six hundred thirteen adults with acute bacterial skin and skin structure infections (ABSSSIs) suspected or confirmed to be due to Gram-positive pathogens were randomized to iclaprim (80 mg) or vancomycin (15 mg/kg of body weight), both of which were administered intravenously every 12 h for 5 to 14 days. The primary endpoint was a ≥20% reduction in lesion size compared with that at the baseline at 48 to 72 h after the start of administration of study drug in the intent-to-treat population. Among patients randomized to iclaprim, 78.3% (231 of 295) met this primary endpoint, whereas 76.7% (234 of 305) of those receiving vancomycin met this primary endpoint (difference, 1.58%; 95% confidence interval, -5.10% to 8.26%). This met the prespecified 10% noninferiority margin. Iclaprim was well tolerated, with most adverse events being categorized as mild. In conclusion, iclaprim was noninferior to vancomycin in this phase 3 clinical trial for the treatment of acute bacterial skin and skin structure infections. On the basis of these results, iclaprim may be an efficacious and safe treatment for skin infections suspected or confirmed to be due to Gram-positive pathogens. (This trial has been registered at ClinicalTrials.gov under identifier NCT02607618.).

Pharmacokinetic and Pharmacodynamic Analyses To Determine the Optimal Fixed Dosing Regimen of Iclaprim for Treatment of Patients with Serious Infections Caused by Gram-Positive Pathogens

Iclaprim is a bacterial dihydrofolate reductase inhibitor that is currently being evaluated in two phase 3 trials for the treatment of patients with acute bacterial skin and skin structure infections (ABSSSI). Prior animal infection model studies suggest that the pharmacokinetic/pharmacodynamic (PK/PD) drivers for efficacy are area under the concentration-time curve from 0 to 24 h at steady state (AUC0-24ss), AUC/MIC, and time above the MIC during the dosing interval (T > MIC), while QTc prolongation was associated with the maximal concentration at steady state (Cmaxss) in a thorough QTc phase 1 study. Using PK data collected from 470 patients from the previously conducted phase 3 complicated skin and skin structure infection (cSSSI) trials, population PK modeling and Monte Carlo simulation (MCS) were used to identify a fixed iclaprim dosage regimen for the ongoing phase 3 ABSSSI studies that maximizes AUC0-24ss, AUC/MIC, and T > MIC while minimizing the probability of a Cmaxss of ≥800 ng/ml relative to the values for the previously employed cSSSI regimen of 0.8 mg/kg of body weight infused intravenously over 0.5 h every 12 h. The MCS analyses indicated that administration of 80 mg as a 2-h infusion every 12 h provides 28%, 28%, and 32% increases in AUC0-24ss, AUC/MIC, and T > MIC, respectively, compared to values for the 0.8-mg/kg cSSSI regimen, while decreasing the probability of a Cmaxss of ≥800 ng/ml, by 9%. Based on PK/PD analyses, 80 mg iclaprim administered over 2 h every 12 h was selected as the dosing scheme for subsequent phase 3 clinical trials.

An Updated Review of Iclaprim: A Potent and Rapidly Bactericidal Antibiotic for the Treatment of Skin and Skin Structure Infections and Nosocomial Pneumonia Caused by Gram-Positive Including Multidrug-Resistant Bacteria

New antibiotics are needed because of the increased morbidity and mortality associated with multidrug-resistant bacteria. Iclaprim, a bacterial dihydrofolate reductase inhibitor, not currently approved, is being studied for the treatment of skin infections and nosocomial pneumonia caused by Gram-positve bacteria, including multidrug-resistant bacteria. Iclaprim showed noninferiority at -10% to linezolid in 1 of 2 phase 3 studies for the treatment of complicated skin and skin structure infections with a weight-based dose (0.8 mg/kg) but did not show noninferiority at -10% to linezolid in a second phase 3 study. More recently, iclaprim has shown noninferiority at -10% to vancomycin in 2 phase 3 studies for the treatment of acute bacterial skin and skin structure infections with an optimized fixed dose (80 mg). A phase 3 study for the treatment of hospital-acquired bacterial and ventilator-associated bacterial pneumonia is upcoming. If, as anticipated, iclaprim becomes available for the treatment of skin and skin structure infections, it will serve as an alternative to current antibiotics for treatment of severe infections. This article will provide an update to the chemistry, preclinical, pharmacology, microbiology, clinical and regulatory status of iclaprim.