Single or 2-Dose Micafungin Regimen for Treatment of Invasive Candidiasis: Therapia Sterilisans Magna!

The distinctive pharmacokinetic profile of rezafungin, a long-acting echinocandin developed in the era of modern pharmacometrics

Echinocandin drugs are the current first-line therapy for fungal infections caused by Candida spp. Most patients require once-daily intravenous (IV) administration in a hospital or outpatient setting for treatment, which may negatively impact their quality of life and stress healthcare resources. Similar to other echinocandins, the novel FDA-, EMA-, and Medical and Healthcare Products Regulatory Agency-approved echinocandin, rezafungin (CD101), exhibited strong antifungal activity against several fungal pathogens and a low drug-drug interaction liability, which are important for medically complex patients. A pharmacometric-based approach has been adopted throughout the development of rezafungin, which contrasts with older echinocandins where dosing regimens were largely derived empirically, and only recently based on pharmacometric guidance. This state-of-the-art approach used model-based simulations incorporating pre-clinical and clinical data as it became available to optimize the dosing regimen for rezafungin. The enhanced stability of the molecular structure and the safety profile of rezafungin allow for the administration of once-weekly IV doses, compared to the daily dosing requirement for other echinocandin drugs, with this distinctive pharmacokinetic profile of rezafungin resulting in a front-loaded dosing regimen with high exposures early in therapy for enhanced fungal killing. The long shelf-life of rezafungin makes this echinocandin more flexible in terms of storage and manufacturing. Demonstrated across clinical development, rezafungin may provide patients with next-generation first-line antifungal treatment for the treatment of candidaemia and invasive candidiasis.

Echinocandin persistence directly impacts the evolution of resistance and survival of the pathogenic fungus Candida glabrata

Recent epidemiological studies documented an alarming increase in the prevalence of echinocandin-resistant (ECR) Candida glabrata blood isolates. ECR isolates are known to arise from a minor subpopulation of a clonal population, termed echinocandin persisters. Although it is believed that isolates with a higher echinocandin persistence (ECP) are more likely to develop ECR, the implication of ECP needs to be better understood. Moreover, replacing laborious and time-consuming traditional approaches to determine ECP levels with rapid, convenient, and reliable tools is imperative to advance our understanding of this emerging concept in clinical practice. Herein, using extensive ex vivo and in vivo systemic infection models, we showed that high ECP isolates are less effectively cleared by micafungin treatment and exclusively give rise to ECR colonies. Additionally, we developed a flow cytometry-based tool that takes advantage of a SYTOX-based assay for the stratification of ECP levels. Once challenged with various collections of echinocandin-susceptible blood isolates, our assay reliably differentiated ECP levels in vitro and predicted ECP levels in real time under ex vivo and in vivo conditions when compared to traditional methods relying on colony-forming unit counting. Given the high and low ECP predictive values of 92.3% and 82.3%, respectively, our assay showed a high agreement with traditional approach. Collectively, our study supports the concept of ECP level determination in clinical settings and provides a robust tool scalable for high-throughput settings. Application of this tool facilitates the interrogation of mutant and drug libraries to further our understanding of persister biology and designing anti-persister therapeutics.

IMPORTANCE

Candida glabrata is a prevalent fungal pathogen able to replicate inside macrophages and rapidly develop resistance against frontline antifungal echinocandins. Multiple studies have shown that echinocandin resistance is fueled by the survival of a small subpopulation of susceptible cells surviving lethal concentrations of echinocandins. Importantly, bacterial pathogens that exhibit high antibiotic persistence also impose a high burden and generate more antibiotic-resistant colonies. Nonetheless, the implications of echinocandin persistence (ECP) among the clinical isolates of C. glabrata have not been defined. Additionally, ECP level determination relies on a laborious and time-consuming method, which is prone to high variation. By exploiting in vivo systemic infection and ex vivo models, we showed that C. glabrata isolates with a higher ECP are associated with a higher burden and more likely develop echinocandin resistance upon micafungin treatment. Additionally, we developed an assay that reliably determines ECP levels in real time. Therefore, our study identified C. glabrata isolates displaying high ECP levels as important entities and provided a reliable and convenient tool for measuring echinocandin persistence, which is extendable to other fungal and bacterial pathogens.

Micafungin Inhibits Dengue Virus Infection through the Disruption of Virus Binding, Entry, and Stability

Dengue fever is an arbovirus disease caused by infection with the dengue virus (DENV). Half of the world's population lives under the threat of dengue fever, however, researchers have yet to develop any drugs that are clinically applicable to this infection. Micafungin is a member of the echinocandins family of anti-fungal drugs, capable of blocking the synthesis of β-1,3-D-glucan in the walls of fungal cells. Previous studies have demonstrated the effectiveness of Micafungin against infections of enterovirus 71 (EV71) and chikungunya virus (CHIKV). This is the first study demonstrating the effectiveness of micafungin in inhibiting the cytopathic effects of dengue virus serotype 2 (DENV-2) in a dose-dependent manner. Time-of-addition assays verified the inhibitory effects of micafungin in pre-treated, co-treated, and full-treatment groups. Binding and entry assays also demonstrated the effectiveness of micafungin in the early stage of DENV-2 infection. The virucidal efficacy of micafungin appears to lie in its ability to destroy the virion. Molecular docking assays revealed the binding of micafungin to the envelope protein of DENV-2, thereby revealing the mechanism by which micafungin affects the early stage of DENV infection and the stability of DENV. Two other micafungin analogs, caspofungin and anidulafungin, were also shown to have the antiviral effects on DENV-2. Finally, immunofluorescence assay (IFA) and reverse-transcription quantitative polymerase chain reaction (RT-qPCR) confirmed the broad anti-DENV ability of micafungin against dengue virus serotypes 1, 3, and 4 (DENV-1, DENV-3, and DENV-4). Taken together, these results demonstrate the potential of micafungin and its analogs as candidates for the development of broad-spectrum treatments for DENV infection.

Evaluation of Ceftriaxone Plus Avibactam in an Intracellular Hollow Fiber Model of Tuberculosis: Implications for the Treatment of Disseminated and Meningeal Tuberculosis in Children

BACKGROUND

Ceftazidime-avibactam is an effective agent for the treatment of tuberculosis (TB) but requires frequent administration because of a short half-life. Due to a longer half-life, ceftriaxone could allow intermittent dosing.

METHODS

First, we identified the MIC of ceftriaxone with 15 mg/L avibactam in 30 clinical Mycobacterium tuberculosis isolates. Next, 2 ceftriaxone exposure-effect studies in the intracellular hollow fiber model of TB (HFS-TB) that mimics disseminated disease in young children, were performed. Ceftriaxone was administered once or twice daily for 28 days to explore percentage of time that the concentration persisted above MIC (%TMIC) ranging from 0 to 100%. In a third HFS-TB experiment, the "double cephalosporin" regimen of ceftazidime-ceftriaxone-avibactam was examined and analyzed using Bliss Independence.

CONCLUSION

The MIC99 of the clinical strains was 32 mg/L, in the presence of 15 mg/L avibactam. Ceftriaxone %TMIC <42 had no microbial effect in the HFS-TB, %TMIC >54% demonstrated a 4.1 log10 colony-forming units per milliliter M. tuberculosis kill, while %TMIC mediating Emax was 68%. The "double cephalosporin" combination was highly synergistic. Monte Carlo experiments of 10,000 subjects identified the optimal ceftriaxone dose as 100 mg/kg twice a day.

CONCLUSION

The combination of ceftriaxone-avibactam at 100 mg/kg could achieve Emax in >90% of children. The ceftriaxone potent activity M. tuberculosis could potentially shorten therapy in children with disseminated TB.

Extended Dosing Regimens for Fungal Prophylaxis

Invasive fungal diseases carry high morbidity and mortality in patients undergoing chemotherapy for hematological malignancies or allogeneic hematopoietic stem cell transplantation. In order to prevent these life-threatening infections, antifungal chemoprophylaxis plays an important role in daily clinical practice. Broad-spectrum antifungal triazoles are widely used but exhibit disadvantages such as relevant drug-drug interactions. Therefore, amphotericin B products or echinocandins can be an alternative in selected patient populations. As these compounds are available as intravenous formulations only, there is growing interest in extended dosing regimens. Although not approved for these agents, this strategy is a rational option, as these compounds have properties suitable for this strategy, including dose-proportional pharmacokinetics, prolonged elimination half-life, and a large therapeutic window. As the use of extended dosing regimens in antifungal prophylaxis is expanding in clinical practice, we reviewed the pharmacokinetic and pharmacodynamic rationale for this strategy, animal model data, dose escalation studies, and clinical trials supporting this concept.

Clinical Pharmacokinetics and Pharmacodynamics of Micafungin

Micafungin is a selective inhibitor of the synthesis of fungal 1,3-β-d-glucan, an essential component of the fungal cell wall. It is available as a powder for infusion only and is registered for the treatment of invasive and esophageal candidiasis in addition to prophylaxis of Candida infections in both adults and children. Average exposure after a single intravenous 100 mg dose in healthy adults is 133 mg h/L. Both exposure and maximum plasma concentration show linear dose proportional pharmacokinetics (PK) over a 0.15–8 mg/kg dose range. In healthy adults, the clearance (CL) is 10.4 mL/h/kg and volume of distribution is 0.2 L/kg; both are independent of the dose. Micafungin is metabolized by arylsulfatase, catechol-O-methyltransferase, and several cytochrome P450 (CYP) isoenzymes (3A4, 1A2, 2B6 and 2C), but no dose adjustments are necessary in patients with (severe) hepatic dysfunction. Exposure to micafungin is lower in hematology patients, and is even further lowered in critically ill patients (including burn patients) compared with healthy volunteers, which might have consequences for treatment efficacy. In children, an increased CL has been reported: 40–80 mL/h/kg in premature neonates and 20 mL/h/kg in children >4 months of age. Therefore, relatively higher doses of 4–10 mg/kg in premature neonates and 2–4 mg/kg in children with invasive candidiasis are used. However, these higher CLs may also be explained by the eightfold higher free fraction of unbound micafungin in premature neonates, meaning that an augmented dose might not be required.

Successful eradication of chronic symptomatic Candida krusei urinary tract infection with increased dose micafungin in a liver and kidney transplant recipient: Case report and review of the literature

Treatment of symptomatic candiduria is notoriously challenging because of the limited repository of antifungals that achieve adequate urinary concentrations. Fluconazole, amphotericin B-based products, and flucytosine are established treatment options for most Candida species. Candida krusei exhibits intrinsic resistance to fluconazole and decreased susceptibility to amphotericin B and flucytosine. In transplant patients, both amphotericin B-based products and flucytosine are less desirable because of their toxicities. Other triazole antifungals are unappealing because they do not achieve adequate urinary concentrations, have multiple toxicities, and interact with transplant-related immunosuppressive medications. Echinocandins are well-tolerated but have been traditionally deferred in the treatment of symptomatic funguria because of their poor urinary concentrations but there is a small but emerging body of literature supporting their use. Here, we present a case of successful eradication of chronic symptomatic C krusei urinary tract infection with micafungin 150 milligrams daily in a liver and kidney transplant recipient, and we review the literature on treatment of symptomatic candiduria.

Overview of antifungal dosing in invasive candidiasis

In the past, most antifungal therapy dosing recommendations for invasive candidiasis followed a 'one-size fits all' approach with recommendations for lowering maintenance dosages for some antifungals in the setting of renal or hepatic impairment. A growing body of pharmacokinetic/pharmacodynamic research, however now points to a widespread 'silent epidemic' of antifungal underdosing for invasive candidiasis, especially among critically ill patients or special populations who have altered volume of distribution, protein binding and drug clearance. In this review, we explore how current adult dosing recommendations for antifungal therapy in invasive candidiasis have evolved, and special populations where new approaches to dose optimization or therapeutic drug monitoring may be needed, especially in light of increasing antifungal resistance among Candida spp.

Pharmacological Basis of CD101 Efficacy: Exposure Shape Matters

CD101 is a novel echinocandin with concentration-dependent fungicidal activity in vitro and a long half-life (∼133 h in humans, ∼70 to 80 h in mice). Given these characteristics, it is likely that the shape of the CD101 exposure (i.e., the time course of CD101 concentrations) influences efficacy. To test this hypothesis, doses which produce the same total area under the concentration-time curve (AUC) were administered to groups of neutropenic ICR mice infected with Candida albicans R303 using three different schedules. A total CD101 dose of 2 mg/kg was administered as a single intravenous (i.v.) dose or in equal divided doses of either 1 mg/kg twice weekly or 0.29 mg/kg/day over 7 days. The studies were performed using a murine disseminated candidiasis model. Animals were euthanized at 168 h following the start of treatment. Fungi grew well in the no-treatment control group and showed variable changes in fungal density in the treatment groups. When the CD101 AUC from 0 to 168 h (AUC_0–168) was administered as a single dose, a >2 log₁₀ CFU reduction from the baseline at 168 h was observed. When twice-weekly and daily regimens with similar AUC values were administered, net fungal stasis and a >1 log₁₀ CFU increase from the baseline were observed, respectively. These data support the hypothesis that the shape of the CD101 AUC influences efficacy. Thus, CD101 administered once per week demonstrated a greater degree of fungal killing than the same dose divided into twice-weekly or daily regimens.

Unraveling Drug Penetration of Echinocandin Antifungals at the Site of Infection in an Intra-abdominal Abscess Model

Intra-abdominal candidiasis (IAC) is a prominent invasive fungal infection associated with high mortality. Prompt antifungal therapy and source control are crucial for successful treatment. Echinocandin antifungal drugs are first-line agents; however, their clinical effectiveness is highly variable, with known potential for breakthrough resistance, and little is known about drug exposure at the site of infection. Using matrix-assisted desorption ionization mass spectrometry imaging technology, we investigated the spatial and quantitative distribution in tissue lesions for two echinocandin drugs, micafungin and CD101, in a clinically relevant IAC mouse model. Drug accumulation within lesions was observed with both drugs at their humanized therapeutic doses. CD101, but not micafungin, accumulated in lesions at levels above the mutant prevention concentration of the infecting strain. These findings indicate that current echinocandin drugs are limited by penetration at the site of infection and have implications for clinical outcomes and emergence of resistance in patients with IAC.