Brilacidin, a host defense peptide mimetic, potentiates ibrexafungerp antifungal activity against the human pathogenic fungus Aspergillus fumigatus

Aspergillus fumigatus is the primary etiological agent of aspergillosis. Here, we show that the host defense peptide mimetic, brilacidin (BRI) can potentiate ibrexafungerp (IBX) against clinical isolates of A. fumigatus. CAS-resistant strains with mutations in fks1 that encodes the 1,3-β-D-glucan synthase are not IBX-resistant and BRI+IBX can inhibit their growth. The combination of BRI+IBX plays a fungicidal role, increases the fungal cell permeability and decreases the fungal survival in the presence of A549 epithelial cells.

Targeting Fks1 proteins for novel antifungal drug discovery

Fungal infections are a major threat to human health. The limited availability of antifungal drugs, the emergence of drug resistance, and a growing susceptible population highlight the critical need for novel antifungal agents. The enzymes involved in fungal cell wall synthesis offer potential targets for antifungal drug development. Recent studies have enhanced our focus on the enzyme Fks1, which synthesizes β-1,3-glucan, a critical component of the cell wall. These studies provide a deeper understanding of Fks1's function in cell wall biosynthesis, pathogenicity, structural biology, evolutionary conservation across fungi, and interaction with current antifungal drugs. Here, we discuss the role of Fks1 in the survival and adaptation of fungi, guided by insights from evolutionary and structural analyses. Furthermore, we delve into the dynamics of Fks1 modulation with novel antifungal strategies and assess its potential as an antifungal drug target.

In vitro activity of ibrexafungerp against clinically relevant echinocandin-resistant Candida strains

Invasive candidiasis is a major hospital-acquired infection. Usually, echinocandins are considered first-line treatment. However, resistant phenotypes have emerged. Ibrexafungerp (IBX) is a new antifungal substance with potent anti-Candida activity. We challenged IBX with a library of 192 pheno-/genotypically echinocandin-resistant Candida isolates, focusing on the substance susceptibility, its activity on certain FKS hotspot (HS) mutated strains, and applying WTULs (wild-type upper limits). Therefore, a 9-year-old strain and patient data collection provided by the German National Reference Center for Invasive Fungal Infections were analyzed. Species identification was confirmed through ITS-sequencing. Molecular susceptibility testing was performed by sequencing HS of the FKS gene. Anidulafungin (AND) and IBX EUCAST-broth-microdilution was conducted. The four most common echinocandin-resistance mediating mutations were found in Candida glabrata [112/192 isolates; F659-(43×) and S663-(48×)] and Candida albicans [63/192 isolates; F641-(15×) and S645-(39×)]. Mutations at the HS-start sequence were associated with higher IBX MIC-values (F659 and F641 (MIC 50/90 mg/L: >4/>4 and 2/4 mg/L) in comparison to AND (F659 and F641 (MIC 50/90: 1/4 and 0.25/1 mg/L). MIC-values in HS-center mutations were almost equal [MIC50/90 in S663: 2/4 (AND and IBX); in S645: 0.5/1 (AND) and 0.25/1 (IBX) mg/L]. In total, 61 vs 78 of 192 echinocandin-resistant isolates may be classified as IBX wild type by applying WTULs, whereas the most prominent effect was seen in C. albicans [48% (30/63) vs 70% (44/63)]. IBX shows in vitro activity against echinocandin-resistant Candida and thus is an addition to the antifungal armory. However, our data suggest that this effect is more pronounced in C. albicans and strains harboring mutations, affecting the HS-center.

Safety, tolerability, and pharmacokinetics of ibrexafungerp in healthy Chinese subjects: a randomized, double-blind, placebo-controlled phase 1 trial

Ibrexafungerp (code name in China: HS-10366) is a first-in-class and orally active triterpenoid antifungal agent with broad antifungal activity against Candida spp., Aspergillus spp., and other fungal pathogens. It was approved by the U.S. Food and Drug Administration for the treatment of vulvovaginal candidiasis. The study aimed to evaluate the safety, tolerability, and pharmacokinetic (PK) characteristics of oral ibrexafungerp in healthy Chinese adults. A single-center, randomized, double-blind, placebo-controlled single ascending dose (SAD, n = 42), and multiple ascending dose (MAD, n = 28) study was conducted in healthy Chinese subjects from March to October 2022. There were three cohorts in the SAD stage (300, 600, and 1,500 mg) and two cohorts in the MAD stage [450 mg once daily (QD) for 7 days; a loading dose of 750 mg twice daily (BID) for the first 2 days followed by a maintenance dose of 750 mg QD for consecutive 5 days]. Eligible participants in each cohort were randomly assigned in a 6:1 ratio to receive either ibrexafungerp or placebo orally. The primary objectives were to evaluate the safety and tolerability. The secondary objective was to evaluate PK parameters, including Cmax, AUC, and t1/2. A total of 70 healthy Chinese subjects were enrolled in the study. The mean (SD) age was 29.0 (6.32), and 55.7% were male. All treatment-emergent adverse events (TEAEs) were mild or moderate. There were no serious adverse events, and no subjects were discontinued from the study due to TEAEs. All TEAEs were recovered or resolved. The most common TEAEs were diarrhea, abdominal pain, and nausea. In the SAD stage, Cmax, and AUC increased in an approximately dose-proportional manner in the dose range of 300-1,500 mg. The mean t1/2 was within 18.29-21.30 hours. In the MAD stage, an accumulation of exposure (Cmax and AUC) was observed following multiple doses. This phase 1 study demonstrates a favorable safety, tolerability, and PK profile of ibrexafungerp in healthy Chinese subjects.

Antifungal resistance, combinations and pipeline: oh my!

Invasive fungal infections are a strong contributor to healthcare costs, morbidity and mortality, especially amongst hospitalized patients. Historically, Candida was responsible for approximately 15% of all nosocomial bloodstream infections. In the past 10 years, the epidemiology of Candida species has altered, with increasing prevalence of resistant species. With rising fungal resistance, especially in Candida spp., the demand for novel antifungal therapies has exponentially increased over the last decade. Newer antifungal agents have become an attractive option for patients needing long-term therapy for infections or those requiring antifungal prophylaxis. Despite advances in coverage of non-Candida pathogens with newer agents, clinical scenarios involving multidrug-resistant fungal pathogens continue to arise in practice. Combination antifungal therapy can lead to a host of side-effects, some of which can be drug limiting. Additional antifungal therapies with enhanced fungal spectrum of activity and decreased rates of adverse effects are warranted. Fosmanogepix, ibrexafungerp, olorofim and rezafungin may help fill some of these gaps in the antifungal armamentarium. This article is part of the Challenges and strategies in the management of invasive fungal infections Special Issue: https://www.drugsincontext.com/special_issues/challenges-and-strategies-in-the-management-of-invasive-fungal-infections.

New trends in antifungal treatment: What is coming up?

New antifungal agents are needed to overcome limitations of available ones such as poor pharmacokinetic traits, toxicity, drug-drug interactions, limited clinical efficacy, and emerging antifungal resistance. New antifungal drugs belong to well-known families (azoles, polyenes, or beta-d-glucan synthase inhibitors) or to drug families showing completely new mechanisms of action. Some drugs have a head start in terms of potential to reach the clinical setting and are here reviewed.

Treatment of Vulvovaginal Candidiasis-An Overview of Guidelines and the Latest Treatment Methods

Vulvovaginal candidiasis (VVC) is a common condition associated with discomfort in affected women. Due to the presence of different forms of the disease, diverse treatment regimens are developed; the newest ones include oteseconazole and ibrexafungerp. Here, we focus on the most up-to-date recommendations regarding VVC treatment, as well as novel treatment options. Topical and oral azoles are the drugs of choice in uncomplicated mycosis. The efficacy of probiotics and substances such as TOL-463 and chlorhexidine is indicated as satisfactory; however, there are no relevant guidelines. Although the majority of researchers agree that the treatment of non-albicans VVC should be long-lasting, the recommendations are inconsistent. Another clinical problem is the treatment of VVC with azole intolerance or resistance, for which literature proposes the use of several drugs including oteseconazole, ibrexafungerp, and voriconazole. The treatment schedules for recurrent VVC include mainly fluconazole; however, alternative options such as immunotherapeutic vaccine (NDV-3A) or designed antimicrobial peptides (dAMPs) were also described. We also focused on VVC affecting pregnant women, which is a substantial challenge in clinical practice, also due to the heterogeneous relevant guidelines. Thus far, few precise recommendations are available in the literature. Future studies should focus on atypical VVC forms to elucidate the inconsistent findings.

Yeasts from blood cultures in the wake of the COVID-19 pandemic in a tertiary care hospital: Shift in species epidemiology, steady low antifungal resistance and full in vitro ibrexafungerp activity

Several institutions reported a rise not only in fungemia incidence but also in the number of cases caused by Candida auris or fluconazole-resistant C. parapsilosis during the COVID-19 pandemic. Since the pandemic broke out in early 2020, we studied its impact on fungemia incidence, species epidemiology, potential patient-to-patient transmission, and antifungal resistance in 166 incident yeast isolates collected from January 2020 to December 2022. Isolates were molecularly identified, and their antifungal susceptibilities to amphotericin B, azoles, micafungin, anidulafungin, and ibrexafungerp were studied following the European Committee on Antimicrobial Susceptibility Testing (EUCAST) method, and genotyped. The fungemia incidence (episodes per 1000 admissions) tended to decrease over time (2020 = 1.60, 2021 = 1.36, 2022 = 1.16); P > .05). Species distribution was C. albicans (50.6%, n = 84), C. parapsilosis (18.7%, n = 31), C. glabrata (12.0%, n = 20), C. tropicalis (11.4%, n = 19), C. krusei (3.0%, n = 5), other Candida spp. (1.2%, n = 2), and non-Candida yeasts (3.0%, n = 5). The highest and lowest proportions of C. albicans and C. parapsilosis were detected in 2020. The proportion of isolates between 2020 and 2022 decreased in C. albicans (60.3% vs. 36.7%) and increased in C. parapsilosis (10.3% vs. 28.6%; P < .05) and C. tropicalis (8.8% vs. 16.3%; P > .05). Only three C. albicans intra-ward clusters involving two patients each were detected, and the percentages of patients involved in intra-ward clusters reached 9.8% and 8.0% in 2020 and 2021, respectively, suggesting that clonal spreading was not uncontrolled. Fluconazole resistance (5%) exhibited a decreasing trend (P > .05) over time (2020 = 7.6%; 2021 = 4.2%; and 2022 = 2.1%). Ibrexafungerp showed high in vitro activity.

Novel Antifungals and Aspergillus Section Terrei with Potpourri Susceptibility Profiles to Conventional Antifungals

The epidemiology of invasive fungal infections (IFIs) is currently changing, driven by aggressive immunosuppressive therapy, leading to an expanded spectrum of patients at risk of IFIs. Aspergillosis is a leading cause of IFIs, which usually affects immunocompromised patients. There are a limited number of antifungal medications available for treating IFIs, and their effectiveness is often hindered by rising resistance rates and practical limitations. Consequently, new antifungals, especially those with novel mechanisms of action, are increasingly required. This study assessed the activity of four novel antifungal agents with different mechanisms of activity, namely, manogepix, rezafungin, ibrexafungerp, and olorofim, against 100 isolates of Aspergillus section Terrei, containing amphotericin-B (AmB)-wildtype/non-wildtype and azole-susceptible/-resistant strains, according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) method. In general, all tested agents showed potent and consistent activity against the tested isolates, exhibiting geometric mean (GM) and minimum effective concentration (MEC)/minimum inhibitory concentration (MIC) ranges, respectively, as follows: manogepix (0.048 mg/L, 0.032-0.5 mg/L), rezafungin (0.020 mg/L, 0.016-0.5 mg/L), ibrexafungerp (0.071 mg/L, 0.032-2 mg/L), and olorofim (0.008 mg/L, 0.008-0.032 mg/L). In terms of MIC90/MEC90, olorofim had the lowest values (0.008 mg/L), followed by rezafungin (0.032 mg/L), manogepix (0.125 mg/L), and ibrexafungerp (0.25 mg/L). All the antifungals tested demonstrated promising in vitro activity against Aspergillus section Terrei, including A. terreus as well as azole-resistant and AmB-non-wildtype cryptic species.

The antifungal pipeline for invasive fungal diseases: what does the future hold?

INTRODUCTION

Over the last two decades, we have experienced pressing needs for new additions to the antifungal armamentarium given the emergence of resistant fungi, the growth of at-risk patient populations for invasive fungal diseases (IFD), the high morbidity and mortality associated with IFD. Areas covered: The current review will discuss the five promising antifungal agents for IFD (i.e. fosmanogepix, ibrexafungerp, olorofim, rezafungin and opelconazole), now in the late-phase clinical studies, and likely to be available for clinical use in the near future. For each agent, we describe its mechanism of action, pharmacokinetic and pharmacodynamic properties, spectrum of activity as well as the safety and efficacy data, including findings from on-going clinical trials. The potential roles of these novel antifungals in clinical practice and the key considerations for clinical use will also be discussed.

EXPERT OPINION

There are unmet needs of these novel agents that should be addressed in the future studies. These include defining their indications and benefits, how to best target them appropriately, surveillance and stewardship of their use.

New Antifungals for Vulvovaginal Candidiasis: What Is Their Role?

New antifungals, ibrexafungerp and oteseconazole, are now available for treatment of vulvovaginal candidiasis. Both have novel antimicrobial and pharmacokinetic properties and advantages over fluconazole, although comparative trials have involved only placebo. In the absence of allergy, intolerance, and resistance, it is unclear whether these antifungals will replace fluconazole.

Novel Therapeutic Approaches to Invasive Candidiasis: Considerations for the Clinician

Invasive candidiasis (IC), due to the yeast pathogen Candida, is still a major cause of in-hospital morbidity and mortality. The limited number of antifungal drug classes and the emergence of multi-resistant Candida species, such as Candida auris and some Candida glabrata isolates, is concerning. However, recent advances in antifungal drug development provide promising perspectives for the therapeutic approach of IC. Notably, three novel antifungal agents, currently in Phase II/III clinical trials, are expected to have an important place for the treatment of IC in the future. Rezafungin is a novel echinocandin with prolonged half-life. Ibrexafungerp and fosmanogepix are two first-in-class antifungal drugs with broad spectrum activity against Candida spp., including C. auris and echinocandin-resistant species. These novel antifungal agents also represent interesting alternative options because of their acceptable oral bioavailability (ibrexafungerp and fosmanogepix) or their large interdose interval (once weekly intravenous administration for rezafungin) for prolonged and/or outpatient treatment of complicated IC. This review discusses the potential place of these novel antifungal drugs for the treatment of IC considering their pharmacologic properties and their preclinical and clinical data.

Ibrexafungerp for the Treatment of Vulvovaginal Candidiasis: Design, Development and Place in Therapy

Vulvovaginal candidiasis (VVC) is experienced by an estimated 75% of women at least once in their lifetime and is recurrent, defined as three or more infections per year (RVVC) in 5-9%. Candida albicans is the most common causative agent, but up to 19% of infections may be related to non-albicans species. Available treatment options for VVC have consisted of oral and topical azoles (except for topical nystatin, a polyene). Oral polyenes are not absorbed and therefore not effective for VVC. Fluconazole is the only oral medication FDA approved for VVC. None of these treatments are FDA approved for RVVC. Ibrexafungerp, a triterpenoid fungicidal agent, was FDA approved in 2021, becoming the first oral non-azole agent for VVC. Ibrexafungerp reaches concentrations up to 9-fold higher in vaginal tissues versus plasma. In Phase 2 clinical trials, ibrexafungerp had a clinical cure rate comparable to fluconazole at day 10, but significantly better at day 25. In Phase 3 clinical trials, ibrexafungerp had both a higher clinical and mycologic cure rate versus placebo at both days 10 and 25. In December 2022, Ibrexafungerp received FDA approval for once monthly dosing to decrease the incidence of RVVC. This approval was based on data from the CANDLE STUDY, which showed 65.4% resolution of symptoms and culture negative success through week 24, compared to 53.1% of placebo. Ibrexafungerp provides an alternative oral option for treatment of acute, severe VVC. It is the only FDA approved antifungal for RVVC. Currently, the population likely to benefit from this drug are those with azole allergy, non-albicans or azole resistant albicans species, or other azole contraindications such as drug interactions (like statins or tricyclics). Side effects are mostly gastrointestinal and mild in nature. Ibrexafungerp, like fluconazole, should be used with caution in women who are or may become pregnant.

Oral Ibrexafungerp for Vulvovaginal Candidiasis Treatment: An Analysis of VANISH 303 and VANISH 306

Background: Ibrexafungerp is a novel antifungal treatment for acute vulvovaginal candidiasis (VVC). Using pooled data from two phase three studies (VANISH 303 and 306) in the treatment of acute VVC, this analysis sought to determine the effectiveness of ibrexafungerp in various patient subgroups that may impact outcomes. Materials and Methods: Data from VANISH 303 (NCT03734991) and VANISH 306 (NCT03987620) evaluating ibrexafungerp 300 mg twice daily (BID) for 1 day versus placebo, were pooled and analyzed to determine clinical cure rate, clinical improvement, and mycological cure at the test-of-cure visit (day 11 ± 3) and symptom resolution at the follow-up visit (day 25 ± 4) in the overall population. Patient subgroups analyzed included race, body mass index (BMI), baseline vulvovaginal signs and symptoms (VSS) score, and Candida species. Results: At the test-of-cure visit, patients receiving ibrexafungerp, compared with those who received placebo, had significantly higher rates of clinical cure (56.9% [214/376 patients] vs. 35.7% [65/182 patients]), clinical improvement (68.4% [257/376 patients] vs. 45.1% [82/182 patients]), and mycological cure (54.0% [203/376 patients] vs. 24.2% [44/182 patients]; all p < 0.0001). At the follow-up visit, patients receiving ibrexafungerp had sustained responses with higher symptom resolution rates (66.8% [251/376 patients]) versus placebo (48.4% [88/182 patients]; p < 0.0001). Race, BMI, baseline VSS score (including VSS severity score 13-18), and Candida species infection did not adversely affect clinical cure rates. Safety analysis results were consistent with the individual studies. Conclusions: Ibrexafungerp provides a safe and well-tolerated first-in-class fungicidal, 1-day oral treatment for patients with acute VVC, the first new therapy in >20 years. Clinical Trial Registration Number: NCT03734991.

Ibrexafungerp in the Treatment of Vulvovaginal Candidiasis

OBJECTIVE

To review the pharmacology, efficacy, and safety of ibrexafungerp in the management of vulvovaginal candidiasis (VVC).

DATA SOURCES

Literature was sought using PubMed (1966-February 2022) and EMBASE (1973-February 2022), and clinicaltrials.gov. Search terms included ibrexafungerp, SCY-078, and VVC.

STUDY SELECTION AND DATA EXTRACTION

All studies including humans and published in English with data assessing the efficacy and safety of ibrexafungerp for the treatment of VVC were evaluated.

DATA SYNTHESIS

A phase 2 dose-finding study found ibrexafungerp had similar efficacy to fluconazole in the clinical cure of VVC (51.9% vs 58.3%, respectively). Two phase 3 clinical trials demonstrated ibrexafungerp had statistical superiority over placebo for clinical cure in moderate to severe VVC (P < 0.001 and P = 0.023, respectively). The most frequently reported adverse reactions in the clinical trials were gastrointestinal-related symptoms. To date, data comparing efficacy of ibrexafungerp and topical imidazoles in the treatment of VVC are nonexistent.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Topical imidazoles and oral fluconazole are effective for the treatment of uncomplicated VVC. Due to increased resistance, limited fluconazole coverage for non-Candida albicans species, and potential for significant drug interactions associated with fluconazole use, alternative treatments for VVC are needed. Ibrexafungerp is a new oral triterpenoid antifungal agent indicated for the treatment of VVC. Additional clinical trials are needed to evaluate long-term safety data as well as efficacy and safety in specialty populations.

CONCLUSION

Ibrexafungerp, a recently approved triterpenoid antifungal agent, is an effective and well-tolerated option for the treatment of VVC.

Ibrexafungerp: A new triterpenoid antifungal

DISCLAIMER

In an effort to expedite the publication of articles, AJHP is posting manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.

PURPOSE

The pharmacology, microbiology, pharmacokinetics, pharmacodynamics, efficacy, safety, and role of ibrexafungerp in the treatment of fungal infections are reviewed.

SUMMARY

Ibrexafungerp is the first triterpenoid antifungal. Similarly to echinocandins, it inhibits the synthesis of 1,3-β-d-glucan. However, it binds to a different site on the enzyme than echinocandins, resulting in limited cross-resistance. Ibrexafungerp exerts concentration-dependent fungicidal activity against Candida species and retains in vitro activity against most fluconazole-resistant strains. It is also active against Aspergillus species. Ibrexafungerp has been shown to be safe and effective in the treatment of vulvovaginal candidiasis caused by Candida albicans in phase 2 and phase 3 clinical trials. It is approved for vulvovaginal candidiasis in adult and postmenarchal pediatric females and is given as two 150-mg tablets orally, administered 12 hours apart. Ibrexafungerp is contraindicated in pregnancy. The most commonly reported adverse reactions were diarrhea, nausea, abdominal pain, dizziness, and vomiting. Ibrexafungerp should be avoided with strong or moderate CYP3A inducers, and the dose should be reduced with strong CYP3A inhibitors. Ibrexafungerp may be useful for patients who are not able to receive fluconazole or prefer oral therapy for the treatment of vulvovaginal candidiasis. However, it is more expensive than the 150-mg tablet of generic fluconazole, which is the current standard of care for vulvovaginal candidiasis. Clinical trials are ongoing for recurrent and complicated vulvovaginal candidiasis as well as invasive candidiasis and pulmonary aspergillosis.

CONCLUSION

Ibrexafungerp is an alternative to fluconazole for the treatment of vulvovaginal candidiasis in nonpregnant females. It has the potential to be useful for recurrent and complicated vulvovaginal candidiasis as well as certain invasive fungal infections.

Investigational Antifungal Agents for Invasive Mycoses: A Clinical Perspective

Treatment of invasive fungal infections (IFIs) remains challenging, because of the limitations of the current antifungal agents (ie, mode of administration, toxicity, and drug-drug interactions) and the emergence of resistant fungal pathogens. Therefore, there is an urgent need to expand our antifungal armamentarium. Several compounds are reaching the stage of phase II or III clinical assessment. These include new drugs within the existing antifungal classes or displaying similar mechanism of activity with improved pharmacologic properties (rezafungin and ibrexafungerp) or first-in-class drugs with novel mechanisms of action (olorofim and fosmanogepix). Although critical information regarding the performance of these agents in heavily immunosuppressed patients is pending, they may provide useful additions to current therapies in some clinical scenarios, including IFIs caused by azole-resistant Aspergillus or multiresistant fungal pathogens (eg, Candida auris, Lomentospora prolificans). However, their limited activity against Mucorales and some other opportunistic molds (eg, some Fusarium spp.) persists as a major unmet need.

Invasive candidiasis: Investigational drugs in the clinical development pipeline and mechanisms of action

INTRODUCTION

The epidemiology of invasive Candida infections is evolving. Infections caused by non-albicans Candida spp. are increasing; however, the antifungal pipeline is more promising than ever and is enriched with repurposed drugs and agents that have new mechanisms of action. Despite progress, unmet needs in the treatment of invasive candidiasis remain and there are still too few antifungals that can be administered orally or that have CNS penetration.

AREAS COVERED

The authors shed light on those antifungal agents active against Candida that are in late-stage clinical development. Mechanisms of action and key pharmacokinetic and pharmacodynamic properties are discussed. Insights are offered on the potential future roles of the investigational agents MAT-2203, oteseconazole, ATI-2307, VL-2397, NP-339, and the repurposed drug miltefosine.

EXPERT OPINION

Ibrexafungerp and fosmanogepix have novel mechanisms of action and will provide effective options for the treatment of Candida infections (including those caused by multiresistant Candida spp). Rezafungin, an echinocandin with an extended half-life allowing for once weekly administration, will be particularly valuable for outpatient treatment and prophylaxis. Despite this, there is an urgent need to garner clinical data on investigational drugs, especially in the current rise of azole-resistant and multi-drug resistant Candida spp.

Efficacy and safety of oral ibrexafungerp for the treatment of acute vulvovaginal candidiasis: a global phase 3, randomised, placebo-controlled superiority study (VANISH 306)

Objective

To evaluate the efficacy and safety of ibrexafungerp versus placebo for acute vulvovaginal candidiasis (VVC) treatment.

Design

Global phase 3, randomised, placebo‐controlled superiority study.

Setting

Study sites in the USA (n = 19) and Bulgaria (n = 18).

Population

Female patients aged ≥12 years with acute VVC and a vulvovaginal signs and symptoms (VSS) score ≥4 at baseline.

Methods

Patients were randomly assigned 2:1 to ibrexafungerp (300 mg twice for 1 day) or placebo.

Main outcome measures

The primary endpoint was the percentage of patients with a clinical cure (VSS = 0) at the test‐of‐cure visit (day 11 ± 3). Secondary endpoints included percentages of patients with mycological eradication, clinical cure and mycological eradication (overall success), clinical improvement (VSS ≤1) at test‐of‐cure visit, and complete resolution of symptoms at follow‐up visit (day 25 ± 4).

Results

At the test‐of‐cure visit, patients receiving ibrexafungerp had significantly higher rates of clinical cure (63.3% [119/188] versus 44.0% [37/84]; P = 0.007), mycological eradication (58.5% [110/188] versus 29.8% [25/84]; P < 0.001), overall success (46.1% [82/188] versus 28.4% [23/84]; P = 0.022) and clinical improvement (72.3% [136/188] versus 54.8% [46/84]; P = 0.01) versus those receiving placebo. Symptom resolution was sustained and further increased with ibrexafungerp (73.9%) versus placebo (52.4%) at follow‐up (P = 0.001). Ibrexafungerp was generally well tolerated. Adverse events were primarily gastrointestinal and were mild to moderate in severity.

Conclusions

Ibrexafungerp demonstrated statistical superiority over placebo for the primary and secondary endpoints. Ibrexafungerp is a promising novel, well‐tolerated and effective oral 1‐day treatment for acute VVC.

Tweetable abstract

Ibrexafungerp is statistically superior to placebo for the treatment of vulvovaginal candidiasis.

Ibrexafungerp is statistically superior to placebo for the treatment of vulvovaginal candidiasis.

Linked article This article is commented on by KSJ Olah, p. 421–422 in this issue. To view this mini commentary visit https://doi.org/10.1111/1471-0528.17000.

Phase 2 randomized study of oral ibrexafungerp vs fluconazole in vulvovaginal candidiasis

Background

Vulvovaginal candidiasis affects approximately 75% of women in their lifetime. Approved treatment options are limited to oral or topical azoles. Ibrexafungerp, a novel, first-in-class oral triterpenoid glucan synthase inhibitor, has demonstrated broad fungicidal Candida activity and a favorable tolerability profile. The primary objective of this dose-finding study was to identify the optimal dose of oral ibrexafungerp in patients with acute vulvovaginal candidiasis.

Methods

Patients with vulvovaginal signs and symptoms score ≥7 were randomized equally to 6 treatments groups: 5 treatment doses of oral ibrexafungerp or oral fluconazole 150 mg. The primary endpoint was the percentage of patients with a clinical cure (complete resolution of vulvovaginal signs and symptoms) at the test-of-cure visit (day 10).

Results

Overall, 186 patients were randomized into the 6 treatment groups. Results, using the modified intent-to-treat population (baseline positive culture), are reported for ibrexafungerp 300 mg twice daily (BID) for 1 day (n = 27), which was the dose selected for phase 3 studies, and fluconazole 150 mg for 1 day (n = 24). At day 10, the clinical cure rates for ibrexafungerp and fluconazole were 51.9% and 58.3%, respectively; at day 25, patients with no signs or symptoms were 70.4% and 50.0%, respectively. During the study ibrexafungerp patients required less antifungal rescue medications compared with fluconazole (3.7% vs 29.2%, respectively). Ibrexafungerp was well tolerated, with the most common treatment-related adverse events being mild gastrointestinal events.

Conclusions

Ibrexafungerp is a well-tolerated novel antifungal with comparable efficacy to fluconazole in the treatment of acute vulvovaginal candidiasis.

Clinical Trials Registration

NCT03253094

Ibrexafungerp versus placebo for vulvovaginal candidiasis treatment: a phase 3, randomized, controlled superiority trial (VANISH 303)

Background

Current treatment of vulvovaginal candidiasis (VVC) is largely limited to azole therapy. Ibrexafungerp is a first-in-class triterpenoid antifungal with broad-spectrum anti-Candida fungicidal activity. The objective of this study was to evaluate the efficacy and safety of ibrexafungerp compared with placebo in patients with acute VVC.

Methods

Patients were randomly assigned 2:1 to receive ibrexafungerp (300 mg twice for 1 day) or placebo. The primary endpoint was the percentage of patients with a clinical cure (complete resolution of vulvovaginal signs and symptoms [VSS] = 0) at test-of-cure (day 11 ± 3). Secondary endpoints included the percentage of patients with mycological eradication, overall success (clinical cure and mycological eradication), clinical improvement (VSS ≤ 1) at test-of-cure, and symptom resolution at follow-up (day 25 ± 4).

Results

Patients receiving ibrexafungerp had significantly higher rates of clinical cure (50.5% [95/188] vs 28.6% [28/98]; P = .001), mycological eradication (49.5% [93/188] vs 19.4% [19/98]; P < .001), and overall success (36.0% [64/178] vs 12.6% [12/95]; P < .001) compared with placebo. Symptom resolution was sustained and further increased with ibrexafungerp compared with placebo (59.6% [112/188] vs 44.9% [44/98]; P = .009) at follow-up. Post hoc analysis showed similar rates of clinical cure and clinical improvement at test-of-cure for Black patients (54.8% [40/73] and 63.4% [47/73], respectively) and patients with a body mass index >35 (54.5% [24/44] and 68.2% [30/44], respectively) compared with overall rates. Ibrexafungerp was well tolerated. Adverse events were primarily gastrointestinal and mild in severity.

Conclusions

Ibrexafungerp provides a promising safe and efficacious oral treatment that mechanistically differs from current azole treatment options for acute VVC.

In Vitro pH Activity of Ibrexafungerp against Fluconazole-Susceptible and -Resistant Candida Isolates from Women with Vulvovaginal Candidiasis

The vaginal environment with candidiasis has a pH of 3.8 to 4.5 and this has a negative effect on the activity of antifungals. Ibrexafungerp was evaluated against 187 Candida isolates, including fluconazole-sensitive and -resistant Candida albicans, Candida glabrata, Candida krusei, Candida parapsilosis, and Candida tropicalis with the media adjusted to pH 7.0 and pH 4.5. Ibrexafungerp MIC values were not adversely affected when tested at pH 4.5. Ibrexafungerp exhibited significant activity against all isolates at pH 4.5.

Recent advances and future perspectives in the pharmacological treatment of Candida auris infections

INTRODUCTION

Candida auris is responsible for hospital outbreaks worldwide. Some C. auris isolates may show concomitant resistance to azoles, echinocandins, and polyenes, thereby possibly leaving clinicians with few therapeutic options.

AREAS COVERED

Antifungal agents both in early and in late phases of clinical development showing anti-C. auris activity.

EXPERT OPINION

The research on antifungal agents active against C. auris has made important steps forward in recent years: (i) the development of drugs with novel mechanisms of action, such as ibrexafungerp and fosmanogepix, could provide a valid option against C. auris strains resistant to one or more older antifungals, including pan-resistant strains; (ii) rezafungin could allow once weekly administration of an active drug in the case of echinocandin-susceptible isolates, providing an effective outpatient treatment, while at the same time relieving selective pressure on novel classes; (iii) the development of oral formulations could allow step-down therapy and/or early discharge, or even to avoid hospitalization in mild or noninvasive diseases; (iv) according to available data, these novel agents show a good safety profile and a low potential for drug-drug interactions.

Ibrexafungerp Demonstrates In Vitro Activity against Fluconazole-Resistant Candida auris and In Vivo Efficacy with Delayed Initiation of Therapy in an Experimental Model of Invasive Candidiasis

Candida auris is an emerging pathogen that has rapidly spread to many countries on multiple continents. Invasive infections caused by this species are associated with significant mortality, and treatment options are limited due to antifungal resistance. Ibrexafungerp is the first-in-class member of the triterpenoids, which inhibit the production of (1,3)-β-d-glucan and can be administered orally. We evaluated the in vitro activity and in vivo efficacy of ibrexafungerp against C. auris Antifungal susceptibility was tested by broth microdilution against 54 C. auris isolates. Neutropenic mice were intravenously infected with a clinical isolate, and a 7-day treatment course was begun 24 h postinoculation with vehicle control, ibrexafungerp (20, 30, and 40 mg/kg orally twice daily), fluconazole (20 mg/kg orally once daily), or caspofungin (10 mg/kg intraperitoneally once daily). Fungal burden was assessed by colony counts in the kidneys on day 8 and on day 21 or as mice became moribund in the survival arm. Ibrexafungerp demonstrated consistent activity, with MICs ranging between 0.25 and 2 μg/ml against all isolates. Marked improvements in survival were observed in mice treated with the higher doses of ibrexafungerp and caspofungin. Similarly, reductions in kidney fungal burden were also observed in these groups. No improvements in survival or reductions in fungal burden were observed with fluconazole, consistent with the in vitro resistance of the isolate used to establish infection to this azole. These results demonstrate that ibrexafungerp is effective in vivo against C. auris even when the start of therapy is delayed.

In Vitro Activity of Ibrexafungerp against a Collection of Clinical Isolates of Aspergillus, Including Cryptic Species and Cyp51A Mutants, Using EUCAST and CLSI Methodologies

Ibrexafungerp is a new orally-available 1,3-β-D-glucan synthesis inhibitor in clinical development. Its in vitro activity and that of amphotericin B, voriconazole, and micafungin were evaluated against a collection of 168 clinical isolates of Aspergillus spp., including azole-susceptible and azole-resistant (Cyp51A mutants) Aspergillus fumigatus sensu stricto (s.s.) and cryptic species of Aspergillus belonging to six species complexes showing different patterns of antifungal resistance, using EUCAST and CLSI antifungal susceptibility testing reference methods. Ibrexafungerp displayed low geometric means of minimal effective concentrations (MECs) against A. fumigatus s.s. strains, both azole susceptible (0.040 mg/L by EUCAST and CLSI versus 1.231 mg/L and 0.660 mg/L for voriconazole, respectively) and azole resistant (0.092 mg/L and 0.056 mg/L, EUCAST and CLSI, while those for voriconazole were 2.144 mg/L and 2.000 mg/L). Ibrexafungerp was active against most of the cryptic species of Aspergillus tested, yielding MEC values only comparable to those of micafungin. Nevertheless, this new compound exhibited a moderate activity against A. ustus complex species, MECs ≥ 0.5 mg/L against Aspergillus insuetus and Aspergillus keveii strains, and was inactive against the Aspergillus alliaceus isolates tested (MEC₉₀s ≥ 16 mg/L). All in all, ibrexafungerp shows encouraging in vitro results against cryptic species of Aspergillus and azole-susceptible and azole resistant strains of A. fumigatus, some of which are difficult to treat using the available therapeutic options.

Ibrexafungerp, a Novel Oral Triterpenoid Antifungal in Development: Overview of Antifungal Activity Against Candida glabrata

Systemic infections caused by Candida species are an important cause of morbidity and mortality among immunocompromised and non-immunocompromised patients. In particular, Candida glabrata is an emerging species within the Candida family that causes infections ranging from superficial to life-threatening systemic disease. Echinocandins and azoles are typically the first-line therapies used to treat infections caused by C. glabrata, however, there is an increasing prevalence of resistance to these antifungal agents in patients. Thus, a need exists for novel therapies that demonstrate high efficacy against C. glabrata. Ibrexafungerp is a first-in-class glucan synthase inhibitor with oral availability developed to address this increasing antifungal resistance. Ibrexafungerp demonstrates broad in vitro activity against wild-type, azole-resistant, and echinocandin-resistant C. glabrata species. Furthermore, ibrexafungerp has shown efficacy in low pH environments, which suggests its potential effectiveness in treating vulvovaginal candidiasis. Additional preclinical and clinical studies are needed to further examine the mechanism(s) of ibrexafungerp, including acting as a promising new agent for treating C. glabrata infections.

An evaluation of ibrexafungerp for the treatment of invasive candidiasis: the evidence to date

INTRODUCTION

Invasive fungal infections, especially candidemia and invasive candidiasis, cause significant morbidity and mortality. The epidemiology of candida infections have changed dramatically due to an increase in risk factors associated with the development of infection and the emergence of resistant isolates such as C. glabrata and C. auris. This has prompted the search for novel and effective antifungals.

AREAS COVERED

The results of in vitro studies evaluating the activity of ibrexafungerp against Candida species are reviewed and the pharmacokinetic/pharmacodynamic properties are highlighted. Available results and safety data from limited clinical studies are discussed.

EXPERT OPINION

Ibrexafungerp demonstrates potent in vitro activity against susceptible and resistant Candida species, including echinocandin-resistant C. glabrata and multidrug-resistant C. auris. It also offers the flexibility of a parenteral and an oral preparation, minimal adverse effects, and low drug-drug interactions. In Phase 2/3 clinical trials, ibrexafungerp appears to have excellent clinical activity in patients with candidemia, invasive candidiasis, and mucosal candidiasis. Although there are several ongoing clinical trials, ibrexafungerp appears to be a promising agent and an important addition to the antifungal armamentarium necessary to treat emerging and resistant pathogens, including several of the Candida species.

A Second-Generation Fungerp Analog, SCY-247, Shows Potent In Vivo Activity in a Murine Model of Hematogenously Disseminated Candida albicans

Echinocandins are a first-line therapy for Candida infections through their ability to inhibit the synthesis of polymer β-(1,3)-d-glucan. However, there has been an emergence of multidrug-resistant fungal species necessitating the development of novel antifungal agents to combat invasive fungal infections. SCY-247, a second-generation glucan synthase inhibitor of the triterpenoid class (fungerps), is currently being developed as a potential therapy option. We determined the pharmacokinetics (PKs) of SCY-247 following oral (gavage) administration in mice and evaluated the efficacy of SCY-247 in a murine model of hematogenously disseminated candidiasis caused by Candida albicans Plasma concentrations of SCY-247 were measurable through the last collected time point in all dose groups. Mean concentrations of SCY-247 increased with dose levels, with concentrations of SCY-247 higher after multiple doses than after a single dose. Treatment with SCY-247 resulted in decreased fungal burden and improvement in survival rates against C. albicans disseminated infection. Treatment with 10 mg/kg of body weight of SCY-247 showed a significant reduction in CFU compared with the untreated control (3-log decrease on average) (P = 0.008). Similarly, 40 mg/kg SCY-247 demonstrated a statistically significant reduction in kidney CFU compared with untreated mice (average log CFU ± SD of 2.38 ± 2.58 versus 6.26 ± 0.51; P = 0.001). Mice treated with SCY-247 at 40 mg/kg exhibited a 100% survival rate at the end of the study, contrasted with 62.5% (5 of 8) survival rate in untreated mice. The results of this investigation indicate that SCY-247 is a promising novel anti-fungal agent with activity against Candida infections.

Efficacy of Ibrexafungerp (SCY-078) against Candida auris in an In Vivo Guinea Pig Cutaneous Infection Model

Candida auris has been shown to have a high risk of skin colonization in hospitalized patients, possibly contributing to nosocomial spread. In a guinea pig skin model, animals were evaluated for clinical appearance, tissue fungal burden, histology, and pharmacokinetics. Oral dosing with 10 mg/kg ibrexafungerp (IBX) reduced the severity of lesions and significantly reduced the C. auris fungal burden in infected animals compared with untreated controls. This indicates promise for use of IBX in controlling skin infection and colonization of hospitalized patients.

Ibrexafungerp: A Novel Oral Triterpenoid Antifungal in Development for the Treatment of Candida auris Infections

Candida auris is an emerging multidrug-resistant fungal pathogen reported worldwide. Infections due to C. auris are usually nosocomial and associated with high rates of fluconazole resistance and mortality. Echinocandins are utilized as the first-line treatment. However, echinocandins are only available intravenously and are associated with increasingly higher rates of resistance by C. auris. Thus, a need exists for novel treatments that demonstrate potent activity against C. auris. Ibrexafungerp is a first-in-class triterpenoid antifungal agent. Similar to echinocandins, ibrexafungerp inhibits (1→3)-β-D-glucan synthase, a key component of the fungal cell wall, resulting in fungicidal activity against Candida spp. Ibrexafungerp demonstrates broad in vitro activity against various Candida spp. including C. auris and C. auris isolates with fks mutations. Minimum inhibitory concentration (MIC₅₀ and MIC₉₀) values in >400 C. auris isolates were 0.5 μg/mL and 1.0 μg/mL, respectively. Clinical results were reported for two patients with invasive candidiasis or candidemia due to C. auris treated during the CARES (Candidiasis Caused by Candida Auris) trial, an ongoing open-label study. These patients experienced a complete response after treatment with ibrexafungerp. Thus, ibrexafungerp represents a promising new antifungal agent for treating C. auris infections.

Oral Ibrexafungerp: an investigational agent for the treatment of vulvovaginal candidiasis

INTRODUCTION

Vulvovaginal candidiasis (VVC) is a common fungal infection caused by predominantly Candida albicans, and is diagnosed in up to 40% of women with vaginal complaints in the primary care setting. Approximately 75% of women experience at least one episode during their reproductive years.

AREAS COVERED

Ibrexafungerp is an orally active, semi-synthetic triterpenoid glucan synthase inhibitor under development for treatment and prevention of VVC. We present the chemistry, mechanism of action, pharmacology, microbiology, and results from clinical studies with ibrexafungerp in women with VVC.

EXPERT OPINION

Ibrexafungerp addresses several unmet needs with existing antifungal drugs as a first in a new class of antifungal agents with a novel mechanism of action demonstrating no antifungal cross resistance with azoles, and fungicidal activity against Candida spp., including fluconazole-resistant species. Some of the key attributes of ibrexafungerp related to VVC include oral one-day dosing, high tissue penetration, enhanced activity at low pH seen in the vagina, low risk for clinically significant drug-drug interactions, and a low risk of adverse events. If approved, ibrexafungerp will be the first new antifungal agent available for the treatment of VVC in more than 20 years and the only oral, non-azole antifungal approved for women suffering from VVC.

Penetration of Ibrexafungerp (Formerly SCY-078) at the Site of Infection in an Intra-abdominal Candidiasis Mouse Model

Ibrexafungerp (IBX), formerly SCY-078, is a novel, oral and intravenous, semisynthetic triterpenoid glucan synthase inhibitor in clinical development for treating multiple fungal infections, including invasive candidiasis. Intra-abdominal candidiasis (IAC) is one of the most common types of invasive candidiasis associated with high mortality largely due to poor drug exposure in infected lesions. To better understand the potential of IBX to treat such infections, we investigated its penetration at the site of infection. Using matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) and laser capture microdissection (LCM)-directed high-pressure liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), we investigated tissue distribution and lesion-specific drug exposure of IBX in a clinically relevant IAC mouse model. After a single-dose treatment, IBX quickly distributed into tissues and efficiently accumulated within lesions. Drug concentrations of IBX within the liver abscesses were almost 100-fold higher than the serum concentration. In addition, drug penetration after repeated treatment of IBX was compared with micafungin. IBX exhibited robust and long-lasting lesion penetration after repeated treatment. These data indicate that IBX penetrates into intra-abdominal abscesses highly efficiently and holds promise as a potential therapeutic option for IAC patients.

glabrata and with the Activities of Six Comparator Agents

Ibrexafungerp (SCY-078) is a novel first-in-class antifungal agent targeting glucan synthase. Candida auris is an emerging multidrug-resistant species that has caused outbreaks on five continents. We investigated the in vitro activity of ibrexafungerp against C. auris by applying EUCAST E.Def 7.3.1 methodology. C. albicans and C. glabrata, as well as anidulafungin, micafungin, amphotericin B, fluconazole, voriconazole, and isavuconazole, were included as comparators. Three C. auris reference strains (CBS12372, CBS12373, and CBS10913) and 122 C. auris, 16 C. albicans, and 16 C. glabrata isolates were evaluated. C. albicans ATCC 64548, C. parapsilosis ATCC 22019, and C. krusei ATCC 6258 served as quality control strains. Echinocandin-resistant isolates were fks sequenced. MIC ranges and modal MIC and MIC₅₀ values were determined. Wild-type upper limits (the upper MIC value where the wild-type distribution ends) were determined according to EUCAST principles for setting ECOFFs. Nine repetitions of three QC strains and MICs for C. albicans and C. glabrata yielded narrow MIC ranges with modal MICs in agreement with established EUCAST modal MICs, confirming a robust test performance. The ibrexafungerp MICs against C. auris isolates displayed a Gaussian distribution with a modal MIC (range) of 0.5 mg/liter (0.06 to 2 mg/liter), suggesting uniform susceptibility. Of 122 isolates, 8 were echinocandin resistant and harbored the S639F Fks1 alteration. All but one were fluconazole resistant, and the MIC distributions for voriconazole and isavuconazole were multimodal confirming variable susceptibility. Ibrexafungerp demonstrated promising activity against C. auris, including isolates resistant to echinocandins and/or other agents. The MICs were similar to those reported for the Clinical and Laboratory Standards Institute method, suggesting that a common clinical breakpoint may be appropriate.

Fungal Cell Wall: Emerging Antifungals and Drug Resistance

The cell wall is an essential component in fungal homeostasis. The lack of a covering wall in human cells makes this component an attractive target for antifungal development. The host environment and antifungal stress can lead to cell wall modifications related to drug resistance. Antifungals targeting the cell wall including the new β-D-glucan synthase inhibitor ibrexafungerp and glycosyl-phosphatidyl Inositol (GPI) anchor pathway inhibitor fosmanogepix are promising weapons against antifungal resistance. The fosmanogepix shows strong in vitro activity against the multidrug-resistant species Candida auris, Fusarium solani, and Lomentospora prolificans. The alternative carbon sources in the infection site change the cell wall β-D-glucan and chitin composition, leading to echinocandin and amphotericin resistance. Candida populations that survive echinocandin exposure develop tolerance and show high chitin content in the cell wall, while fungal species such as Aspergillus flavus with a higher β-D-glucan content may show amphotericin resistance. Therefore understanding fungal cell dynamics has become important not only for host-fungal interactions, but also treatment of fungal infections. This review summarizes recent findings regarding antifungal therapy and development of resistance related to the fungal cell wall of the most relevant human pathogenic species.

In Vitro Activity of Ibrexafungerp, a Novel Glucan Synthase Inhibitor against Candida glabrata Isolates with FKS Mutations

Ibrexafungerp is a first-in-class glucan synthase inhibitor. In vitro activity was determined for 89 Candida glabrata isolates with molecularly identified FKS1 or FKS2 mutations conferring resistance to the echinocandins. All isolates were resistant to at least one echinocandin (i.e., anidulafungin, caspofungin, or micafungin) by broth microdilution. Results for ibrexafungerp were compared with those for each echinocandin. Ibrexafungerp had good activity against all echinocandin-resistant C. glabrata isolates.

Echinocandins for the Treatment of Invasive Aspergillosis: from Laboratory to Bedside

Echinocandins (caspofungin, micafungin, anidulafungin), targeting β-1,3-glucan synthesis of the cell wall, represent one of the three currently available antifungal drug classes for the treatment of invasive fungal infections. Despite their limited antifungal activity against Aspergillus spp., echinocandins are considered an alternative option for the treatment of invasive aspergillosis (IA). This drug class exhibits several advantages, such as excellent tolerability and its potential for synergistic interactions with some other antifungals. The objective of this review is to discuss the in vitro and clinical efficacy of echinocandins against Aspergillus spp., considering the complex interactions between the drug, the mold, and the host. The antifungal effect of echinocandins is not limited to direct inhibition of hyphal growth but also induces an immunomodulatory effect on the host's response. Moreover, Aspergillus spp. have developed important adaptive mechanisms of tolerance to survive and overcome the action of echinocandins, such as paradoxical growth at increased concentrations. This stress response can be abolished by several compounds that potentiate the activity of echinocandins, such as drugs targeting the heat shock protein 90 (Hsp90)-calcineurin axis, opening perspectives for adjuvant therapies. Finally, the present and future places of echinocandins as prophylaxis, monotherapy, or combination therapy of IA are discussed in view of the emergence of pan-azole resistance among Aspergillus fumigatus isolates, the occurrence of breakthrough IA, and the advent of new long-lasting echinocandins (rezafungin) or other β-1,3-glucan synthase inhibitors (ibrexafungerp).

A Novel 1,3-Beta-d-Glucan Inhibitor, Ibrexafungerp (Formerly SCY-078), Shows Potent Activity in the Lower pH Environment of Vulvovaginitis

Ibrexafungerp (IBX) (formerly SCY-078) is a novel glucan synthase inhibitor whose oral availability is being evaluated for efficacy against vulvovaginal candidiasis (VVC). Bioavailability and in vitro activity are important efficacy indicators, but accepted susceptibility methods do not always accurately predict activity in an acidic environment, such as the vagina. Studies were 3-fold, as follows: (i) pharmacokinetic study following oral administration in a murine model; (ii) susceptibility testing of isolates from a phase 2 VVC clinical trial by CLSI M27-A4 methodology; and (iii) susceptibility testing of Candida albicans and Candida glabrata isolates obtained from this trial group in RPMI 1640 adjusted to 3 different pH values, 7.0, 5.72, and 4.5, compared to susceptibility testing for micafungin and fluconazole. IBX readily accumulated in vaginal tissues and secretions following oral administration. Potent in vitro activity was demonstrated against Candida strains obtained at baseline and end of study visits. Moreover, the geometric mean (GM) values for IBX at pH 4.5 were dramatically lower than those at pH 7.0 and 5.72. The MIC₉₀ values of micafungin remained the same regardless of pH value, while those of fluconazole tended to increase with lower pH values. IBX is able to reach target tissues following oral administration at pharmacologically meaningful levels. IBX demonstrated potent in vitro activity, with no development of resistance, following repeated exposure over the course of the clinical trial. Importantly, activity of IBX in an acidic medium suggests a therapeutic advantage of this novel antifungal in the treatment of vaginal Candida infections.