In vivo pharmacodynamic target investigation for micafungin against Candida albicans and C. glabrata in a neutropenic murine candidiasis model

A Mini-Review of In Vitro Data for Candida Species, Including C. auris, Isolated during Clinical Trials of Three New Antifungals: Fosmanogepix, Ibrexafungerp, and Rezafungin

This mini-review summarizes the clinical outcomes and antifungal susceptibility results, where available, for three new antifungals, including fosmanogepix, ibrexafungerp, and rezafungin, against Candida isolates cultured from patients in clinical trials. When reported, most of the data were generated by the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method or by both the CLSI and European Committee on Antimicrobial Susceptibility Testing (EUCAST) methodologies. For fosmanogepix, we summarize the in vitro data for C. auris isolates from 9 patients and for Candida spp. cultured from 20 patients in two clinical trials. Ibrexafungerp has also been evaluated in several clinical trials. From conference proceedings, a total of 176 Candida isolates were evaluated in the FURI and CARES studies, including 18 C. auris isolates (CARES study). However, MIC data are not available for all clinical isolates. Results from the ReSTORE rezafungin phase 3 clinical study also included in vitro results against Candida spp., but no patients with C. auris infections were included. In conclusion, this mini-review summarizes insights regarding clinical outcomes and the in vitro activity of three new antifungals against Candida spp. cultured from patients in clinical trials.

Combination of Systemic and Lock-Therapies with Micafungin Eradicate Catheter-Based Biofilms and Infections Caused by Candida albicans and Candida parapsilosis in Neutropenic Rabbit Models

Vascular catheter-related infections, primarily caused by Candida albicans and Candida parapsilosis, pose significant challenges due to the formation of biofilms on catheters, leading to refractory disease and considerable morbidity. We studied the efficacy of micafungin in systemic and lock therapies to eliminate catheter-based biofilms and deep tissue infections in experimental central venous catheter (CVC)-related candidemia in neutropenic rabbits. Silastic CVCs in rabbits were inoculated with 1 × 103 CFU/mL of C. albicans or C. parapsilosis, establishing catheter-based biofilm, and subjected to various treatments. Neutropenic rabbits treated with a combination of lock therapy and systemic micafungin demonstrated the most significant reduction in fungal burden, from 5.0 × 104 to 1.8 × 102 CFU/mL of C. albicans and from 5.9 × 104 to 2.7 × 102 CFU/mL of C. parapsilosis (p ≤ 0.001), in the CVC after 24 h, with full clearance of blood cultures after 72 h from treatment initiation. The combination of lock and systemic micafungin therapy achieved eradication of C. albicans from all studied tissues (0.0 ± 0.0 log CFU/g) vs. untreated controls (liver 7.5 ± 0.22, spleen 8.3 ± 0.25, kidney 8.6 ± 0.07, cerebrum 6.3 ± 0.31, vena cava 6.6 ± 0.29, and CVC wash 2.3 ± 0.68 log CFU/g) (p ≤ 0.001). Rabbits treated with a combination of lock and systemic micafungin therapy demonstrated a ≥2 log reduction in C. parapsilosis in all treated tissues (p ≤ 0.05) except kidney. Serum (1→3)-β-D-glucan levels demonstrated significant decreases in response to treatment. The study demonstrates that combining systemic and lock therapies with micafungin effectively eradicates catheter-based biofilms and infections caused by C. albicans or C. parapsilosis, particularly in persistently neutropenic conditions, offering promising implications for managing vascular catheter-related candidemia and providing clinical benefits in cases where catheter removal is not feasible.

Therapeutic drug monitoring of antifungal therapies: do we really need it and what are the best practices?

INTRODUCTION

Despite advancements, invasive fungal infections (IFI) still carry high mortality rates, often exceeding 30%. The challenges in diagnosis, coupled with limited effective antifungal options, make managing IFIs complex. Antifungal drugs are essential for IFI management, but their efficacy can be diminished by drug-drug interactions and pharmacokinetic variability. Therapeutic Drug Monitoring (TDM), especially in the context of triazole use, has emerged as a valuable strategy to optimize antifungal therapy.

AREAS COVERED

This review provides current evidence regarding the potential benefits of TDM in IFI management. It discusses how TDM can enhance treatment response, safety, and address altered pharmacokinetics in specific patient populations.

EXPERT OPINION

TDM plays a crucial role in achieving optimal therapeutic outcomes in IFI management, particularly for certain antifungal agents. Preclinical studies consistently show a link between therapeutic drug levels and antifungal efficacy. However, clinical research in mycology faces challenges due to patient heterogeneity and the diversity of fungal infections. TDM's potential advantages in guiding Echinocandin therapy for critically ill patients warrant further investigation. Additionally, for drugs like Posaconazole, assessing whether serum levels or alternative markers like saliva offer the best measure of efficacy is an intriguing question.

Preclinical Pharmacokinetic/Pharmacodynamic Studies and Clinical Trials in the Drug Development Process of EMA-Approved Antifungal Agents: A Review

Antifungal drug development is essential as invasive fungal disease is still associated with a very high mortality rate and the emergence of resistant species in the last decade. In Europe, the European Medical Agency (EMA) approves antifungals and publishes the European Public Assessment Report (EPAR) including the information leading up to the authorisation. We looked at EMA-approved antifungals and their reports within the last 23 years. We focused primarily on the role of pharmacokinetic/pharmacodynamic indices in antifungal development and the level of information depicted in their corresponding report. Furthermore, we investigated guidelines applicable to the development process at the time and compared the content with a focus on pharmacokinetic/pharmacodynamic studies and preclinical requirements. Since 2000, six new antifungal substances have been authorised. Most were authorised for treatment of Candida infections or Aspergillus infections but also included rarer pathogens. Pharmacokinetic/pharmacodynamic indices were scarcely investigated and/or mentioned in the report. Current antifungal EMA guidelines started emphasising investigating pharmacokinetic/pharmacodynamic indices in 2010 and then again in 2016. It remains to be seen how this translates into the authorisation process for new antifungals.

Assessment of Antifungal Pharmacodynamics

Pharmacokinetic-pharmacodynamic (PK-PD) analysis is of central importance to the progress of an antifungal agent into clinical use. It is crucial to ensure that preclinical studies give the best possible prediction of the way drugs are likely to behave in a clinical setting. This review details the last 30 years of progress in terms of disease model design, efficacy outcome selection and translational modelling in antifungal PK-PD studies. The principles of how PK-PD parameters inform current clinical practice are also discussed, including a review of how these apply to existing and novel agents.

Analysis of Candida Antifungal Resistance Using Animal Infection Models

Candida frequently produces three general disease states, including mucosal candidiasis, disseminated candidiasis, and biofilm infection (which can be present with either of the other disease states). Antifungal drug resistance is intrinsic to biofilm growth and has emerged in other disease states. Mechanistic studies have uncovered the genetic pathways governing resistance to a number of antifungal agents. However, analyzing the clinical relevance of distinct mechanisms is fundamental for broadening our knowledge of antifungal drug resistance and for delineating the potential impact of targeting these pathways medically. Also, as drug-resistant strains and biofilms represent important nosocomial problems, preclinical animal models to assess the activity of novel antifungals are of great interest. Here we describe two rodent models that mimic the most common biofilm device and disseminated candidiasis states in patients. The model systems incorporate the anatomical site, immune components, and antifungal exposures relevant for the study of antifungal resistance. The models can be used to analyze mutant strains, assess the extent of drug resistance, examine biofilm formation, test new antimicrobials, and help determine drug exposures that may be linked with clinical failure.

Population Pharmacokinetic Model and Optimal Sampling Strategies for Micafungin in Critically Ill Patients Diagnosed with Invasive Candidiasis

Candida bloodstream infections are associated with high attributable mortality, where early initiation of adequate antifungal therapy is important to increase survival in critically ill patients. The exposure variability of micafungin, a first-line agent used for the treatment of invasive candidiasis, in critically ill patients is significant, potentially resulting in underexposure in a substantial portion of these patients. The objective of this study was to develop a population pharmacokinetic model including appropriate sampling strategies for assessing micafungin drug exposure in critically ill patients to support adequate area under the concentration-time curve (AUC) determination. A two-compartment pharmacokinetic model was developed using data from intensive care unit (ICU) patients (n = 19), with the following parameters: total body clearance (CL), volume of distribution of the central compartment (V1), inter-compartmental clearance (CL12), and volume of distribution of the peripheral compartment (V2). The final model was evaluated with bootstrap analysis and the goodness-of-fit plots for the population and individual predicted micafungin plasma concentrations. Optimal sampling strategies (with sampling every hour, 24 h per day) were developed with 1- and 2-point sampling schemes. Final model parameters (±SD) were: CL = 1.03 (0.37) (L/h/1.85 m²), V1 = 0.17 (0.07) (L/kg LBMc), CL12 = 1.80 (4.07) (L/h/1.85 m²), and V2 = 0.12 (0.06) (L/kg LBMc). Sampling strategies with acceptable accuracy and precision were developed to determine the micafungin AUC. The developed model with optimal sampling procedures provides the opportunity to achieve quick optimization of the micafungin exposure from a single blood sample using Bayesian software and may be helpful in guiding early dose decision-making.

Inositol Phosphoryl Transferase, Ipt1, Is a Critical Determinant of Azole Resistance and Virulence Phenotypes in Candida glabrata

In this study, we have specifically blocked a key step of sphingolipid (SL) biosynthesis in Candida glabrata by disruption of the orthologs of ScIpt1 and ScSkn1. Based on their close homology with S. cerevisiae counterparts, the proteins are predicted to catalyze the addition of a phosphorylinositol group onto mannosyl inositolphosphoryl ceramide (MIPC) to form mannosyl diinositolphosphoryl ceramide (M(IP)2C), which accounts for the majority of complex SL structures in S. cerevisiae membranes. High throughput lipidome analysis confirmed the accumulation of MIPC structures in ΔCgipt1 and ΔCgskn1 cells, albeit to lesser extent in the latter. Noticeably, ΔCgipt1 cells showed an increased susceptibility to azoles; however, ΔCgskn1 cells showed no significant changes in the drug susceptibility profiles. Interestingly, the azole susceptible phenotype of ΔCgipt1 cells seems to be independent of the ergosterol content. ΔCgipt1 cells displayed altered lipid homeostasis, increased membrane fluidity as well as high diffusion of radiolabeled fluconazole (3H-FLC), which could together influence the azole susceptibility of C. glabrata. Furthermore, in vivo experiments also confirmed compromised virulence of the ΔCgipt1 strain. Contrarily, specific functions of CgSkn1 remain unclear.

Therapeutic Drug Monitoring of the Echinocandin Antifungal Agents: Is There a Role in Clinical Practice? A Position Statement of the Anti-Infective Drugs Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

PURPOSE

Reduced exposure to echinocandins has been reported in specific patient populations, such as critically ill patients; however, fixed dosing strategies are still used. The present review examines the accumulated evidence supporting echinocandin therapeutic drug monitoring (TDM) and summarizes available assays and sampling strategies.

METHODS

A literature search was conducted using PubMed in December 2020, with search terms such as echinocandins, anidulafungin, caspofungin, micafungin, or rezafungin with pharmacology, pharmacokinetics (PKs), pharmacodynamics (PDs), drug-drug interactions, TDM, resistance, drug susceptibility testing, toxicity, adverse drug reactions, bioanalysis, chromatography, and mass spectrometry. Data on PD/PD (PK/PD) outcome markers, drug resistance, PK variability, drug-drug interactions, assays, and TDM sampling strategies were summarized.

RESULTS

Echinocandins demonstrate drug exposure-efficacy relationships, and maximum concentration/minimal inhibitory concentration ratio (Cmax/MIC) and area under the concentration-time curve/MIC ratio (AUC/MIC) are proposed PK/PD markers for clinical response. The relationship between drug exposure and toxicity remains poorly clarified. TDM could be valuable in patients at risk of low drug exposure, such as those with critical illness and/or obesity. TDM of echinocandins may also be useful in patients with moderate liver impairment, drug-drug interactions, hypoalbuminemia, and those undergoing extracorporeal membrane oxygenation, as these conditions are associated with altered exposure to caspofungin and/or micafungin. Assays are available to measure anidulafungin, micafungin, and caspofungin concentrations. A limited-sampling strategy for anidulafungin has been reported.

CONCLUSIONS

Echinocandin TDM should be considered in patients at known risk of suboptimal drug exposure. However, for implementing TDM, clinical validation of PK/PD targets is needed.

Precision Therapy for Invasive Fungal Diseases

Invasive fungal infections (IFI) are a common infection-related cause of death in immunocompromised patients. Approximately 10 million people are at risk of developing invasive aspergillosis annually. Detailed study of the pharmacokinetics (PK) and pharmacodynamics (PD) of antifungal drugs has resulted in a better understanding of optimal regimens for populations, drug exposure targets for therapeutic drug monitoring, and establishing in vitro susceptibility breakpoints. Importantly, however, each is an example of a “one size fits all strategy”, where complex systems are reduced to a singularity that ensures antifungal therapy is administered safely and effectively at the level of a population. Clearly, such a notion serves most patients adequately but is completely counter to the covenant at the centre of the clinician–patient relationship, where each patient should know whether they are well-positioned to maximally benefit from an antifungal drug. This review discusses the current therapy of fungal infections and areas of future research to maximise the effectiveness of antifungal therapy at an individual level.

Species Distribution of Candidemia and Their Susceptibility in a Single Japanese University Hospital: Prior Micafungin Use Affects the Appearance of Candida parapsilosis and Elevation of Micafungin MICs in Non-parapsilosis Candida Species

Introduction: Micafungin is a recommended echinocandin antifungal agent for candidemia treatment and prophylaxis. However, overuse of echinocandin antifungals may cause resistance. There is currently no information available regarding the low susceptibility associated with using micafungin. This study investigated the effect of micafungin use on changes in the detected Candida species and low susceptibility. Methods: We conducted a retrospective survey and included records of Candida spp. detected in blood cultures from January 2010 to December 2018 in our hospital. Survey items included clinical outcomes at 30 days after positive cultures, patient characteristics, and drug prescription status. Patient background information included gender, previous hospitalization, stay in the intensive care unit, comorbidities, and history of surgery (within 90 days before candidemia onset) and drug exposure. Species detected and their minimum inhibitory concentrations (MICs) and amount of antifungal prescriptions by department were investigated. Risk factors for detecting C. parapsilosis and for low susceptibility to micafungin were evaluated using multivariate analysis. Results: A total of 153 Candida clinical blood isolates were collected and C. albicans was the most prevalent species, followed by C. parapsilosis and C. glabrata. In the analysis by department, antifungal use and non-albicans Candida species were most frequently detected in the hematology department. Multivariate analysis showed that prior micafungin use increased the risk of C. parapsilosis (odds ratio (OR) 4.22; 95% confidence interval (CI) 1.39–12.79; p = 0.011). MIC₉₀ of micafungin on C. glabrata and C. parapsilosis was 1.0 μg/mL. Prior micafungin use was clarified as a risk factor resulting in MIC > 0.06 μg/mL for micafungin in non-parapsilosis Candida species (OR 13.2; 95% CI 3.23–54.2; p < 0.01). Conclusion: Prior micafungin use increased the risk of C. parapsilosis and the MIC > 0.06 μg/mL of micafungin in non-parapsilosis Candida species. Since there are only a few antifungal options, further antifungal stewardship considering azole antifungal agents use is required.

Comparative Pharmacodynamics of Echinocandins against Aspergillus fumigatus Using an In Vitro Pharmacokinetic/Pharmacodynamic Model That Correlates with Clinical Response to Caspofungin Therapy: Is There a Place for Dose Optimization?

Echinocandins have been used as primary therapy of invasive aspergillosis (IA), with suboptimal results at standard dosing. Here, we explored the efficacy of dose escalation in a validated in vitro pharmacokinetic/pharmacodynamic (PK/PD) model. Six echinocandin wild-type (WT) and three non-WT A. fumigatus isolates were tested in an in vitro PK/PD model simulating anidulafungin, caspofungin, and micafungin exposures with a free drug maximum concentration (fCmax) of 0.01 to 16 mg/liter and a half-life (t1/2) of 8 to 22 h. The relationship between the area under the dosing interval time-free drug concentration curve (fAUC0-24)/minimum effective concentration (MEC) and % aberrant mycelium formation was analyzed. PK/PD indices associated with 50 to 99.99% maximal activity (EI50 to EI99.99) were correlated with the clinical outcome of a 50-mg/day standard dose of caspofungin. The probability of target attainment (PTA) was calculated for different dosing regimens of each echinocandin via Monte Carlo analysis. A sigmoidal PK/PD relationship was found for WT isolates with EI99 values of 766, 8.8, and 115 fAUC0-24/CLSI MEC for anidulafungin, caspofungin, and micafungin, respectively. No aberrant mycelia were observed for non-WT isolates, irrespective of their MEC and drug exposure. The EI99, EI99.9, and EI99.99 values corresponded to 2-, 3-, and 4-log10 formation of aberrant mycelia and correlated with survival, favorable, and complete response rates to caspofungin primary therapy in patients with IA. A very low PTA (<13%) was found for the standard doses of all echinocandins, whereas a PTA of ≥90% was found with 100 and 150 mg/day of caspofungin and 1,400 mg/day micafungin against WT isolates. For anidulafungin, the PTA for 1,500 mg/day was 10%. Among the three echinocandins, only caspofungin at 2 or 3 times the licensed dosing was associated with a high PTA. Caspofungin dose escalation might deserve clinical validation.

Model-Informed Drug Development for Anti-Infectives: State of the Art and Future

Model-informed drug development (MIDD) has a long and rich history in infectious diseases. This review describes foundational principles of translational anti-infective pharmacology, including choice of appropriate measures of exposure and pharmacodynamic (PD) measures, patient subpopulations, and drug-drug interactions. Examples are presented for state-of-the-art, empiric, mechanistic, interdisciplinary, and real-world evidence MIDD applications in the development of antibacterials (review of minimum inhibitory concentration-based models, mechanism-based pharmacokinetic/PD (PK/PD) models, PK/PD models of resistance, and immune response), antifungals, antivirals, drugs for the treatment of global health infectious diseases, and medical countermeasures. The degree of adoption of MIDD practices across the infectious diseases field is also summarized. The future application of MIDD in infectious diseases will progress along two planes; "depth" and "breadth" of MIDD methods. "MIDD depth" refers to deeper incorporation of the specific pathogen biology and intrinsic and acquired-resistance mechanisms; host factors, such as immunologic response and infection site, to enable deeper interrogation of pharmacological impact on pathogen clearance; clinical outcome and emergence of resistance from a pathogen; and patient and population perspective. In particular, improved early assessment of the emergence of resistance potential will become a greater focus in MIDD, as this is poorly mitigated by current development approaches. "MIDD breadth" refers to greater adoption of model-centered approaches to anti-infective development. Specifically, this means how various MIDD approaches and translational tools can be integrated or connected in a systematic way that supports decision making by key stakeholders (sponsors, regulators, and payers) across the entire development pathway.

Optimization of Micafungin Dosage for Chinese Patients with Sepsis in the Intensive Care Unit Based on a Population Pharmacokinetic-Pharmacodynamic Analysis

PURPOSE

This study aimed to identify parameters that influence micafungin pharmacokinetics in Chinese patients with sepsis in the intensive care unit and optimize micafungin dosage by determining the probability of reaching pharmacodynamic targets.

METHODS

Blood samples were collected from 32 Chinese patients with sepsis who were treated with micafungin. The samples were analyzed and used to build a population pharmacokinetic model. Monte Carlo simulations were performed to estimate the probability of achieving adequate plasma levels of micafungin against Candida species.

RESULTS

Alanine aminotransferase and sequential organ failure assessment score were found to significantly influence the clearance and peripheral distribution volume of micafungin, respectively. Monte Carlo simulations based on area under the plasma concentration-time curve over 24 h showed that patients must be administered at least 200 and 250 mg micafungin daily to reach minimum inhibitory concentration breakpoints of 0.032 and 0.064 mg/L for Candida glabrata and Candida tropicalis, respectively. Additionally, a probability of target attainment of ≥ 90% could not be achieved for Candida krusei or Candida parapsilosis with a 300 mg daily dose.

CONCLUSIONS

The recommended daily dose of micafungin (100 mg) may produce low clinical success ratios in non-Candida albicans infections; therefore, higher doses should be administered to improve clinical outcomes.

Role and Interpretation of Antifungal Susceptibility Testing for the Management of Invasive Fungal Infections

Invasive fungal infections (IFIs) are associated with high mortality rates and timely appropriate antifungal therapy is essential for good outcomes. Emerging antifungal resistance among Candida and Aspergillus spp., the major causes of IFI, is concerning and has led to the increasing incorporation of in vitro antifungal susceptibility testing (AST) to guide clinical decisions. However, the interpretation of AST results and their contribution to management of IFIs remains a matter of debate. Specifically, the utility of AST is limited by the delay in obtaining results and the lack of pharmacodynamic correlation between minimal inhibitory concentration (MIC) values and clinical outcome, particularly for molds. Clinical breakpoints for Candida spp. have been substantially revised over time and appear to be reliable for the detection of azole and echinocandin resistance and for outcome prediction, especially for non-neutropenic patients with candidemia. However, data are lacking for neutropenic patients with invasive candidiasis and some non-albicans Candida spp. (notably emerging Candida auris). For Aspergillus spp., AST is not routinely performed, but may be indicated according to the epidemiological context in the setting of emerging azole resistance among A. fumigatus. For non-Aspergillus molds (e.g., Mucorales, Fusarium or Scedosporium spp.), AST is not routinely recommended as interpretive criteria are lacking and many confounders, mainly host factors, seem to play a predominant role in responses to antifungal therapy. This review provides an overview of the pre-clinical and clinical pharmacodynamic data, which constitute the rationale for the use and interpretation of AST testing of yeasts and molds in clinical practice.

Population pharmacokinetics of micafungin over repeated doses in critically ill patients: a need for a loading dose?

OBJECTIVES

To study the population pharmacokinetics of micafungin in critically ill patients, evaluate and optimize dosage regimens.

METHODS

An HPLC-fluorescence bioassay for micafungin was developed, fully validated and applied to a pharmacokinetic study conducted in 14 ICU patients. Dense blood sampling was performed from days 1 to 7. A population pharmacokinetic model accounting for interindividual (IIV) and interoccasion variability (IOV) of the PK parameters was developed. Simulations were performed to estimate the probability of target attainment (PTA) for several dosing regimens.

KEY FINDINGS

A two-compartment pharmacokinetic model best described the data, with population clearance CL = 1.31 L/h and central volume V1 = 14.2 L. The relatively high IOV observed (45% for CL, 27% for V1) sets limits for the dose individualization in this population. The low PTA on the first day of treatment suggests the need of a loading dose. PTA and CFR estimates show that the current micafungin dosage may be insufficient for the treatment of borderline susceptible Candida strains.

CONCLUSIONS

A loading dose of up to 300 mg of micafungin is needed for the treatment of invasive candidiasis in ICU patients while a maintenance dose of up to 200 mg can be considered in empirical antifungal treatment.

From bench to bedside: Perspectives on the utility of pharmacokinetics/pharmacodynamics in predicting the efficacy of antifungals in invasive candidiasis

The aim of this perspective is to give an overlook on the utility of pharmacokinetics/pharmacodynamics (PK/PD) in predicting the efficacy of antifungals in invasive candidiasis. Overall, from the available literature it appears that bridging data of PK/PD of antifungals from the laboratory to the clinic for the treatment of invasive candidiasis are feasible only partially. Fluconazole is the only antifungal agent having the pharmacodynamic threshold of efficacy identified in experimental animal models convincingly validated in the clinical setting of invasive candidiasis as well. Conversely, for voriconazole and posaconazole data on this topic are very limited. For the echinocandins, robust PK/PD identified in the laboratory represented the rationale for defining differential clinical breakpoints of echinocandins against different species of Candida by the regulatory agencies. However, translation of the findings in the clinical setting provided conflicting results. Data on PK/PD of amphotericin B and flucytosine in models of invasive candidiasis are quite limited, and clinical studies assessing the role of drug exposure on efficacy are currently lacking. The expectation is that prospective studies could test more and more frequently the validity of experimental PK/PD data of antifungals in the clinical setting of invasive candidiasis. The findings could represent a step forward in addressing adequate antifungal stewardship programmes.

Assessment of micafungin loading dosage regimens against Candida spp. in ICU patients by Monte Carlo simulations

OBJECTIVE

To assess the efficacy of loading dose on micafungin by simulating different dosage regimens.

METHODS

A published study of micafungin in ICU patients was employed to simulate nine different dosage regimens which were sorted out three groups in terms of three maintenance doses. Using pharmacokinetic parameters and pharmacodynamic data, 5000-subject Monte Carlo simulations were conducted to simulate concentration-time profiles of micafungin, calculate probabilities of target attainment (PTAs), and cumulative fractions of response (CFRs) in terms of AUC/MIC targets. PTAs were calculated using AUC/MIC cut-offs: 285 (Candida parapsilosis), 3000 (all Candida spp.), and 5000 (non-parapsilosis Candida spp.). PTA or CFR > 90% was considered optimal for a dosage regimen.

RESULTS

The concentration-time profiles of micafungin-simulated dosage regimens were obtained. PTA values were over 90% while applying the loading dose in each group of regimens: for Candida albicans and Candida glabrata (AUC/MIC = 5000), all regimens with loading dose provided PTAs of ≥ 90% for MIC ≤ 0.008 mg/L. The PTAs (AUC/MIC = 3000) were over 90% for MIC ≤ 0.008 mg/L in any regimen. However, for MIC inferior to 0.016 mg/L, only loading dosage regimens provided PTAs exceeding 90%. For C. parapsilosis (AUC/MIC = 285), the maximum MIC of achieving a PTA ≥ 90% was 0.25 mg/L both in the regimens of B (150 mg maintenance dose) and C (200 mg maintenance dose) with loading dose. In addition, CFR of any regimen with loading dose was ≥ 90% against C. albicans and C. glabrata. None of the dosage regimens achieved an expected CFR against C. parapsilosis.

CONCLUSIONS

The dosage regimen of micafungin which had a loading dose of 1.5 times was more suitable for ICU patients infected by Candida spp.

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.

Extended-Interval Dosing of Rezafungin against Azole-Resistant Aspergillus fumigatus

We evaluated extended-interval dosing of the investigational echinocandin rezafungin (1, 4, and 16 mg/kg on days 1, 4, and 7 postinoculation) for the treatment of disseminated invasive aspergillosis caused by azole-resistant Aspergillus fumigatus Survival was significantly improved in mice treated with each dose of rezafungin and supratherapeutic posaconazole (20 mg/kg twice daily). Kidney fungal burden, as measured by quantitative real-time PCR, was also significantly reduced in mice treated with rezafungin although variability was observed.

Evaluation of Candida peritonitis with underlying peritoneal fibrosis and efficacy of micafungin in murine models of intra-abdominal candidiasis

Candida peritonitis is a crucial disease, however the optimal antifungal therapy regimen has not been clearly defined. Peritoneal fibrosis (PF) can be caused by abdominal surgery, intra-abdominal infection, and malignant diseases, and is also widely recognized as a crucial complication of long-term peritoneal dialysis. However, the influence of PF on Candida peritonitis prognosis remains unknown. Here, we evaluated the severity of Candida peritonitis within the context of PF and the efficacy of micafungin using mice. A PF mouse model was generated by intraperitoneally administering chlorhexidine gluconate. Candida peritonitis, induced by intraperitoneal inoculation of Candida albicans, was treated with a 7-day consecutive subcutaneous administration of micafungin. Candida infection caused a higher mortality rate in the PF mice compared with the control mice on day 7. Proliferative Candida invasion into the peritoneum and intra-abdominal organs was confirmed pathologically only in the PF mice. However, all mice in both groups treated with micafungin survived until day 20. Micafungin treatment tends to suppress inflammatory cytokines in the plasma 12 h after infection in both groups. Our results suggest that PF enhances early mortality in Candida peritonitis. Prompt initiation and sufficient doses of micafungin had good efficacy for Candida peritonitis, irrespective of the underlying PF.

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.

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.

Invasive Candidiasis in Infants and Children: Recent Advances in Epidemiology, Diagnosis, and Treatment

This paper reviews recent advances in three selected areas of pediatric invasive candidiasis: epidemiology, diagnosis, and treatment. Although the epidemiological trends of pediatric invasive candidiasis illustrate a declining incidence, this infection still carries a heavy burden of mortality and morbidity that warrants a high index of clinical suspicion, the need for rapid diagnostic systems, and the early initiation of antifungal therapy. The development of non-culture-based technologies, such as the T2Candida system and (1→3)-β-d-glucan detection assay, offers the potential for early laboratory detection of candidemia and CNS candidiasis, respectively. Among the complications of disseminated candidiasis in infants and children, hematogenous disseminated Candida meningoencephalitis (HCME) is an important cause of neurological morbidity. Detection of (1→3)-β-d-glucan in cerebrospinal fluid serves as an early diagnostic indicator and an important biomarker of therapeutic response. The recently reported pharmacokinetic data of liposomal amphotericin B in children demonstrate dose–exposure relationships similar to those in adults. The recently completed randomized clinical trial of micafungin versus deoxycholate amphotericin B in the treatment of neonatal candidemia provides further safety data for an echinocandin in this clinical setting.

Implications of the EUCAST Trailing Phenomenon in Candida tropicalis for the In Vivo Susceptibility in Invertebrate and Murine Models

Candida tropicalis isolates often display reduced but persistent growth (trailing) over a broad fluconazole concentration range during EUCAST susceptibility testing. Whereas weak trailing (<25% of the positive growth control) is common and found not to impair fluconazole efficacy, we investigated if more pronounced trailing impacted treatment efficacy. Fluconazole efficacy against two weakly (≤25% growth), two moderately (26% to 50% growth), and one heavily (>70% growth) trailing resistant isolate and one resistant (100% growth) isolate were investigated in vitro and in vivo (in a Galleria mellonella survival model and two nonlethal murine models). CDR1 expression levels and ERG11 sequences were characterized. The survival in fluconazole-treated G. mellonella was inversely correlated with the degree of trailing (71% to 9% survival in treatment groups). In mice, resistant and heavily trailing isolates responded poorly to fluconazole treatment. CDR1 expression was significantly higher in trailing and resistant isolates than in wild-type isolates (1.4-fold to 10-fold higher). All isolates exhibited ERG11 wild-type alleles. Heavily trailing isolates were less responsive to fluconazole in all in vivo models, indicating an impact on fluconazole efficacy. CDR1 upregulation may have contributed to the observed differences. Moderately trailing isolates responded less well to fluconazole in larvae only. This confirms clinical data suggesting fluconazole is effective against infections with such isolates in less severely ill patients and supports the current 50% growth endpoint for susceptibility testing. However, it is still unclear if the gradual loss of efficacy observed for moderately trailing isolates in the larva model may be a reason for concern in selected vulnerable patient populations.

Significantly Improved Pharmacokinetics Enhances In Vivo Efficacy of APX001 against Echinocandin- and Multidrug-Resistant Candida Isolates in a Mouse Model of Invasive Candidiasis

APX001 is a first-in-class, intravenous and orally available, broad-spectrum antifungal agent in clinical development for the treatment of life-threatening invasive fungal infections. The half-life of APX001A, the active moiety of APX001, is significantly shorter in mice than in humans (1.4 to 2.75 h in mice versus 2 to 2.5 days in humans), making the exploration of efficacy in mouse models difficult.

APX001 is a first-in-class, intravenous and orally available, broad-spectrum antifungal agent in clinical development for the treatment of life-threatening invasive fungal infections. The half-life of APX001A, the active moiety of APX001, is significantly shorter in mice than in humans (1.4 to 2.75 h in mice versus 2 to 2.5 days in humans), making the exploration of efficacy in mouse models difficult. After pretreatment with 1-aminobenzotriazole (ABT), a nonspecific cytochrome P450 inhibitor, greatly increased plasma APX001A exposure was observed in mice of different strains and of both genders. As a consequence, 26 mg/kg APX001 plus ABT sterilized kidneys in mice infected with Candida albicans, while APX001 alone at the same dose resulted in a modest burden reduction of only 0.2 log₁₀ CFU/g, relative to the vehicle control. In the presence of ABT, 2 days of once-daily dosing with APX001 at 26 mg/kg also demonstrated significant in vivo efficacy in the treatment of Candida glabrata infections in mice. Potent kidney burden reduction was achieved in mice infected with susceptible, echinocandin-resistant, or multidrug-resistant strains. In contrast, the standard of care (micafungin) was ineffective in treating infections caused by the resistant C. glabrata isolates.

Simple and robust LC–MS/MS analysis method for therapeutic drug monitoring of micafungin

Aim: To develop a simple and robust LC–MS/MS method to quantify concentrations of micafungin in human plasma for pharmacokinetic studies and therapeutic drug monitoring. Methods: Sample preparation involved protein precipitation with acetonitrile:methanol (83:17% v/v) and [13C6]-micafungin as internal standard. A rapid and selective method for micafungin was validated across a range of 0.200–10.0 mg/l. Results: The calculated accuracy for the eight-point calibration ranged from 0.7 to 5.3%. Within-run precision ranged from 0.8 to 5.9%, between-run precision ranged from 0.7 to 3.1%, and overall precision ranged from 1.3 to 6.6%. Conclusion: A simple and robust LC–MS/MS method for analyzing micafungin in human plasma has been validated and was utilized for quantification of micafungin.

Clinical and Microbiological Characteristics of Candida guilliermondii and Candida fermentati

A total of 46 clinical isolates of Candida guilliermondii and Candida famata were reidentified genetically, resulting in 27 C. guilliermondii and 12 Candida fermentati strains. The majority of C. guilliermondii strains, but not C. fermentati strains, were isolated from blood cultures. C. fermentati was more sensitive to antifungals, hydrogen peroxide, and killing by murine macrophages than was C. guilliermondii The C. guilliermondii isolates were echinocandin susceptible in vitro but resistant to micafungin in a murine model of invasive candidiasis.

In Vivo Pharmacokinetics and Pharmacodynamics of APX001 against Candida spp. in a Neutropenic Disseminated Candidiasis Mouse Model

APX001 is the prodrug of APX001A, which is a first-in-class small molecule with a unique mechanism of action that inhibits the fungal enzyme Gwt1 in the glycosylphosphatidylinositol (GPI) biosynthesis pathway. The goal of the present study was to determine which pharmacokinetic/pharmacodynamic (PK/PD) index and magnitude best correlated with efficacy in the murine disseminated candidiasis model for Candida albicans (n = 5), C. glabrata (n = 5), and C. auris (n = 4). MIC values ranged from 0.002 to 0.03 mg/liter for C. albicans, from 0.008 to 0.06 mg/liter for C. glabrata, and from 0.004 to 0.03 mg/liter for C. auris Plasma APX001A pharmacokinetic measurements were performed in mice after oral administration of 4, 16, 64, and 256 mg/kg of body weight APX001. Single-dose pharmacokinetic studies exhibited maximum plasma concentration (C_max) values of 0.46 to 15.6 mg/liter, area under the concentration-time curve (AUC) from time zero to infinity (AUC_0-inf) values of 0.87 to 70.0 mg · h/liter, and half-lives of 1.40 to 2.75 h. A neutropenic murine disseminated candidiasis model was utilized for all treatment studies, and drug dosing was by the oral route. Dose fractionation was performed against C. albicans K1, with total doses ranging from 4 to 1,024 mg/kg/day of APX001 fractionated into regimens of dosing every 3, 6, 8, and 12 h for a 24-h treatment duration. Nonlinear regression analysis was used to determine which PK/PD index best correlated with efficacy on the basis of the reduction in the number of CFU/kidney at 24 h. The 24-h free-drug AUC/MIC ratio (fAUC_0-24/MIC) was the PK/PD index that best correlated with efficacy (coefficient of determination [R²] = 0.88). Treatment studies with the remaining strains utilized regimens of 1 to 256 mg/kg of APX001 administered every 6 h for a 24-h duration with C. albicans and a 96-h study duration with C. glabrata and C. auris The dose required to achieve 50% of the maximum effect (ED₅₀) and stasis fAUC/MIC targets were as follows: for C. albicans, 3.67 ± 3.19 and 20.60 ± 6.50, respectively; for C. glabrata, 0.38 ± 0.21 and 1.31 ± 0.27, respectively; and for C. auris, 7.14 ± 4.54 and 14.67 ± 8.30, respectively. The present studies demonstrated in vitro and in vivo APX001A and APX001 potency, respectively, against C. albicans, C. glabrata, and C. auris. These results have potential relevance for clinical dose selection and evaluation of susceptibility breakpoints. The identification of a lower AUC/MIC ratio target for C. glabrata suggests that species-specific susceptibility breakpoints should be explored.

Pharmacodynamics of a Long-Acting Echinocandin, CD101, in a Neutropenic Invasive-Candidiasis Murine Model Using an Extended-Interval Dosing Design

Echinocandins are important in the prevention and treatment of invasive candidiasis but limited by current dosing regimens that include daily intravenous administration. The novel echinocandin CD101 has a prolonged half-life of approximately 130 h in humans, making it possible to design once-weekly dosing strategies. The present study examined the pharmacodynamic activity of CD101 using the neutropenic invasive candidiasis mouse model against select Candida albicans (n = 4), C. glabrata (n = 3), and C. parapsilosis (n = 3) strains. The CD101 MIC ranged from 0.03 to 1 mg/liter. Plasma pharmacokinetic measurements were performed using uninfected mice after intraperitoneal administration of 1, 4, 16, and 64 mg/kg. The elimination half-life was prolonged at 28 to 41 h. Neutropenic mice were infected with each strain by lateral tail vein injection, treated with a single dose of CD101, and monitored for 7 days, at which time the organism burden was enumerated from the kidneys. Dose-dependent activity was observed for each organism. The pharmacokinetic/pharmacodynamic (PK/PD) index of the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC index) correlated well with efficacy (R², 0.74 to 0.93). The median stasis 24-h free-drug AUC/MIC targets were as follows: for C. albicans, 2.92; for C. glabrata, 0.07; and for C. parapsilosis, 2.61. The PK/PD targets for 1-log₁₀ kill endpoint were 2- to 4-fold higher. Interestingly, the aforementioned PK/PD targets of CD101 were numerically lower for all three species than those of other echinocandins. In summary, CD101 is a promising, novel echinocandin with advantageous pharmacokinetic properties and potent in vivo pharmacodynamic activity.

Pharmacokinetic Properties of Micafungin in Critically Ill Patients Diagnosed with Invasive Candidiasis

The estimated attributable mortality rate for invasive candidiasis (IC) in the intensive care unit (ICU) setting varies from 30 to 40%. Physiological changes in critically ill patients may affect the distribution and elimination of micafungin, and therefore, dosing adjustments might be mandatory. The objective of this study was to determine the pharmacokinetic parameters of micafungin in critically ill patients and assess the probability of target attainment. Micafungin plasma concentrations were measured to estimate the pharmacokinetic properties of micafungin. MIC values for Candida isolates were determined to assess the probability of target attainment for patients. Data from 19 patients with suspected or proven invasive candidiasis were available for analysis. The median area under the concentration-time curve from 0 to 24 h at steady state (AUC_0-24) was 89.6 mg · h/liter (interquartile range [IQR], 75.4 to 113.6 mg · h/liter); this was significantly lower than the median micafungin AUC_0-24 values of 152.0 mg · h/liter (IQR, 136.0 to 162.0 mg · h/liter) and 134.0 mg · h/liter (IQR, 118.0 to 148.6 mg · h/liter) in healthy volunteers (P = <0.0001 and P = <0.001, respectively). All Candida isolates were susceptible to micafungin, with a median MIC of 0.016 mg/liter (IQR, 0.012 to 0.023 mg/liter). The median AUC_0-24/MIC ratio was 5,684 (IQR, 4,325 to 7,578), and 3 of the 17 evaluable patients (17.6%) diagnosed with proven invasive candidiasis did not meet the AUC/MIC ratio target of 5,000. Micafungin exposure was lower in critically ill patients than in healthy volunteers. The variability in micafungin exposure in this ICU population could be explained by the patients' body weight. Our findings suggest that healthier patients (sequential organ failure assessment [SOFA] score of <10) weighing more than 100 kg and receiving 100 mg micafungin daily are at risk for inappropriate micafungin exposure and potentially inadequate antifungal treatment. (This study has been registered at ClinicalTrials.gov under identifier NCT01716988.).

Effects of Echinocandins in Combination with Nikkomycin Z against Invasive Candida albicans Bloodstream Isolates and the fks Mutants

We evaluated the in vitro and in vivo effects of nikkomycin Z combined with an echinocandin (anidulafungin or micafungin) against two Candida albicans isolates and their lab-derived echinocandin-resistant fks mutants with FKS1 S645Y and FKS1 S645P. Synergistic effects were observed in all tested strains (fractional inhibitory concentration index, <0.5). Enhanced survival was observed in an immunocompromised murine model (log-rank test, P < 0.02). Our study demonstrated the therapeutic potential of nikkomycin Z-echinocandin combinations in managing echinocandin resistance.

Population Pharmacokinetic Model and Pharmacokinetic Target Attainment of Micafungin in Intensive Care Unit Patients

OBJECTIVE

To study the pharmacokinetics of micafungin in intensive care patients and assess pharmacokinetic (PK) target attainment for various dosing strategies.

METHODS

Micafungin PK data from 20 intensive care unit patients were available. A population-PK model was developed. Various dosing regimens were simulated: licensed regimens (I) 100 mg daily; (II) 100 mg daily with 200 mg from day 5; and adapted regimens 200 mg on day 1 followed by (III) 100 mg daily; (IV) 150 mg daily; and (V) 200 mg daily. Target attainment based on a clinical PK target for Candida as well as non-Candida parapsilosis infections was assessed for relevant minimum inhibitory concentrations [MICs] (Clinical and Laboratory Standards Institute). Parameter uncertainty was taken into account in simulations.

RESULTS

A two-compartment model best fitted the data. Clearance was 1.10 (root square error 8%) L/h and V 1 and V 2 were 17.6 (root square error 14%) and 3.63 (root square error 8%) L, respectively. Median area under the concentration-time curve over 24 h (interquartile range) on day 14 for regimens I-V were 91 (67-122), 183 (135-244), 91 (67-122), 137 (101-183) and 183 (135-244) mg h/L, respectively, for a typical patient of 70 kg. For the MIC/area under the concentration-time curve >3000 target (all Candida spp.), PK target attainment was >91% on day 14 (MIC 0.016 mg/L epidemiological cut-off) for all of the dosing regimens but decreased to (I) 44%, (II) 91%, (III) 44%, (IV) 78% and (V) 91% for MIC 0.032 mg/L. For the MIC/area under the concentration-time curve >5000 target (non-C. parapsilosis spp.), PK target attainment varied between 62 and 96% on day 14 for MIC 0.016.

CONCLUSIONS

The licensed micafungin maintenance dose results in adequate exposure based on our simulations with a clinical PK target for Candida infections but only 62% of patients reach the target for non-C. parapsilosis. In the case of pathogens with an attenuated micafungin MIC, patients may benefit from dose escalation to 200 mg daily. This encourages future study.

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.

Dose Reduction of Caspofungin in Intensive Care Unit Patients with Child Pugh B Will Result in Suboptimal Exposure

Background and Objectives

Caspofungin is an echinocandin antifungal agent used as first-line therapy for the treatment of invasive candidiasis. The maintenance dose is adapted to body weight (BW) or liver function (Child-Pugh score B or C). We aimed to study the pharmacokinetics of caspofungin and assess pharmacokinetic target attainment for various dosing strategies.

Methods

Caspofungin pharmacokinetic data from 21 intensive care unit (ICU) patients was available. A population pharmacokinetic model was developed. Various dosing regimens (loading dose/maintenance dose) were simulated: licensed regimens (I) 70/50 mg (for BW <80 kg) or 70/70 mg (for BW >80 kg); and (II) 70/35 mg (for Child-Pugh score B); and adapted regimens (III) 100/50 mg (for Child-Pugh score B); (IV) 100/70 mg; and (V) 100/100 mg. Target attainment based on a preclinical pharmacokinetic target for Candida albicans was assessed for relevant minimal inhibitory concentrations (MICs).

Results

A two-compartment model best fitted the data. Clearance was 0.55 L/h and the apparent volumes of distribution in the central and peripheral compartments were 8.9 and 5.0 L, respectively. The median area under the plasma concentration–time curve from time zero to 24 h on day 14 for regimens I–V were 105, 65, 93, 130, and 186 mg·h/L, respectively. Pharmacokinetic target attainment was 100 % (MIC 0.03 µg/mL) irrespective of dosing regimen but decreased to (I) 47 %, (II) 14 %, (III) 36 %, (IV) 69 %, and (V) 94 % for MIC 0.125 µg/mL.

Conclusion

The caspofungin maintenance dose should not be reduced in non-cirrhotic ICU patients based on the Child-Pugh score if this classification is driven by hypoalbuminemia as it results in significantly lower exposure. A higher maintenance dose of 70 mg in ICU patients results in target attainment of >90 % of the ICU patients with species with an MIC of up to 0.125 µg/mL.

Echinocandins in antifungal pharmacotherapy

Objectives

Echinocandins are the newest addition of the last decade to the antifungal armamentarium, which, owing to their unique mechanism of action, selectively target the fungal cells without affecting mammalian cells. Since the time of their introduction, they have come to occupy an important niche in the antifungal pharmacotherapy, due to their efficacy, safety, tolerability and favourable pharmacokinetic profiles. This review deals with the varying facets of echinocandins such as their chemistry, in-vitro and in-vivo evaluations, clinical utility and indications, pharmacokinetic and pharmacodynamic profiles, and pharmacoeconomic considerations.

Key findings

Clinical studies have demonstrated that the echinocandins – caspofungin, micafungin and anidulafungin – are equivalent, if not superior, to the mainstay antifungal therapies involving amphotericin B and fluconazole. Moreover, echinocandin regimen has been shown to be more cost-effective and economical. Hence, the echinocandins have found favour in the management of invasive systemic fungal infections.

Conclusions

The subtle differences in echinocandins with respect to their pharmacology, clinical therapy and the mechanisms of resistance are emerging at a rapid pace from the current pool of research which could potentially aid in extending their utility in the fungal infections of the eye, heart and nervous system.

Pharmacodynamic Optimization for Treatment of Invasive Candida auris Infection

Candida auris is an emerging multidrug-resistant threat. The pharmacodynamics of three antifungal classes against nine C. auris strains was explored using a murine invasive candidiasis model. The total drug median pharmacodynamic (PD) target associated with net stasis was a fluconazole AUC/MIC (the area under the concentration-time curve over 24 h in the steady state divided by the MIC) of 26, an amphotericin B C_max/MIC (maximum concentration of drug in serum divided by the MIC) of 0.9, and a micafungin AUC/MIC of 54. The micafungin PD targets for C. auris were ≥20-fold lower than those of other Candida species in this animal model. Clinically relevant micafungin exposures produced the most killing among the three classes.

Pharmacokinetics of antifungal drugs: practical implications for optimized treatment of patients

Introduction

Because of the high mortality of invasive fungal infections (IFIs), appropriate exposure to antifungals appears to be crucial for therapeutic efficacy and safety.

Materials and methods

This review summarises published pharmacokinetic data on systemically administered antifungals focusing on co-morbidities, target-site penetration, and combination antifungal therapy.

Conclusions and discussion

Amphotericin B is eliminated unchanged via urine and faeces. Flucytosine and fluconazole display low protein binding and are eliminated by the kidney. Itraconazole, voriconazole, posaconazole and isavuconazole are metabolised in the liver. Azoles are substrates and inhibitors of cytochrome P450 (CYP) isoenzymes and are therefore involved in numerous drug–drug interactions. Anidulafungin is spontaneously degraded in the plasma. Caspofungin and micafungin undergo enzymatic metabolism in the liver, which is independent of CYP. Although several drug–drug interactions occur during caspofungin and micafungin treatment, echinocandins display a lower potential for drug–drug interactions. Flucytosine and azoles penetrate into most of relevant tissues. Amphotericin B accumulates in the liver and in the spleen. Its concentrations in lung and kidney are intermediate and relatively low myocardium and brain. Tissue distribution of echinocandins is similar to that of amphotericin. Combination antifungal therapy is established for cryptococcosis but controversial in other IFIs such as invasive aspergillosis and mucormycosis.

Pharmacokinetics of Anidulafungin in Critically Ill Intensive Care Unit Patients with Suspected or Proven Invasive Fungal Infections

Echinocandins, such as anidulafungin, are the first-line treatment for candidemia or invasive candidiasis in critically ill patients. There are conflicting data on the pharmacokinetic properties of anidulafungin in intensive care unit (ICU) patients. Adult ICU patients (from 3 hospitals) receiving anidulafungin for suspected or proven fungal infections were included in the present study. Patients were considered evaluable if a pharmacokinetic curve for day 3 could be completed. Twenty-three of 36 patients (7 female and 16 male) were evaluable. The median (range) age and body weight were 66 (28 to 88) years and 76 (50 to 115) kg, respectively. Pharmacokinetic sampling on day 3 (n = 23) resulted in a median anidulafungin area under the concentration-time curve from 0 to 24 h (AUC_0-24) of 72.1 (interquartile range [IQR], 61.3 to 94.0) mg · h · liter^-1, a median daily trough concentration (C₂₄) of 2.2 (IQR, 1.9 to 2.9) mg/liter, a median maximum concentration of drug in serum (C_max) of 5.3 (IQR, 4.1 to 6.0) mg/liter, a median volume of distribution (V) of 46.0 (IQR, 32.2 to 60.2) liters, and a median clearance (CL) of 1.4 (IQR, 1.1 to 1.6) liters · h^-1 Pharmacokinetic sampling on day 7 (n = 13) resulted in a median AUC_0-24 of 82.7 (IQR, 73.0 to 129.5) mg · h · liter^-1, a median minimum concentration of drug in serum (C_min) of 2.8 (IQR, 2.2 to 4.2) mg/liter, a median C_max of 5.9 (IQR, 4.6 to 8.0) mg/liter, a median V of 39.7 (IQR, 32.2 to 54.4) liters, and a median CL of 1.2 (IQR, 0.8 to 1.4) liters · h^-1 The geometric mean ratio for the AUC_day7/AUC_day3 term was 1.13 (90% confidence interval [CI], 1.03 to 1.25). The exposure in the ICU patient population was in accordance with previous reports on anidulafungin pharmacokinetics in ICU patients but was lower than that for healthy volunteers or other patient populations. Larger cohorts of patients or pooled data analyses are necessary to retrieve relevant covariates. (This study has been registered at ClinicalTrials.gov under identifier NCT01438216.).

Antifungal pharmacodynamics: Latin America's perspective

The current increment of invasive fungal infections and the availability of new broad-spectrum antifungal agents has increased the use of these agents by non-expert practitioners, without an impact on mortality. To improve efficacy while minimizing prescription errors and to reduce the high monetary cost to the health systems, the principles of pharmacokinetics (PK) and pharmacodynamics (PD) are necessary. A systematic review of the PD of antifungals agents was performed aiming at the practicing physician without expertise in this field. The initial section of this review focuses on the general concepts of antimicrobial PD. In vitro studies, fungal susceptibility and antifungal serum concentrations are related with different doses and dosing schedules, determining the PD indices and the magnitude required to obtain a specific outcome. Herein the PD of the most used antifungal drug classes in Latin America (polyenes, azoles, and echinocandins) is discussed.

Intravenous Antibiotic and Antifungal Agent Pharmacokinetic-Pharmacodynamic Dosing in Adults with Severe Burn Injury

PURPOSE

Despite advances in the care of patients with severe burn injury, infection-related morbidity and mortality remain high and can potentially be reduced with antimicrobial dosing optimized for the infecting pathogen. However, anti-infective dose selection is difficult because of the highly abnormal physiologic features of burn patients, which can greatly affect the pharmacokinetic (PK) disposition of these agents. We review published PK data from burn patients and offer evidence-based dosing recommendations for antimicrobial agents in burn-injured patients.

METHODS

Because most infections occur at least 48 hours after initial burn injury and anti-infective therapy often lasts ≥10 days, we reviewed published data informing PK-pharmacodynamic (PD) dosing of anti-infectives administered during the second, hypermetabolic stage of burn injury, in those with >20% total body surface area burns, and in those with normal or augmented renal clearance (estimated creatinine clearance ≥130 mL/min). Analyses were performed using 10,000-patient Monte Carlo simulations, which uses PK variability observed in burn patients and MIC data to determine the probability of reaching predefined PK-PD targets. The probability of target attainment, defined as the likelihood that an anti-infective dosing regimen would achieve a specific PK-PD target at the single highest susceptible MIC, and the cumulative fraction of response, defined as the population probability of target attainment given a specific dose and a distribution of MICs, were calculated for each recommended anti-infective dosing regimen.

FINDINGS

Evidence-based doses were derived for burn-injured patients for 15 antibiotics and 2 antifungal agents. Published data were unavailable or insufficient for several agents important to the care of burn patients, including newer antifungal and antipseudomonal agents. Furthermore, available data suggest that antimicrobial PK properties in burned patients is highly variable. We recommend that, where possible, therapeutic drug monitoring be performed to optimize PK-PD parameter achievement in individual patients.

IMPLICATIONS

Given the high variability in PK disposition observed in burn patients, doses recommended in the package insert may not achieve PK-PD parameters associated with optimal infectious outcomes. Our study is limited by the necessity for fixed assumptions in depicting this highly variable patient population. New rapid-turnaround analytical technology is needed to expand the menu of antimicrobial agents for which therapeutic drug monitoring is available to guide dose modification within a clinically actionable time frame.

Safety and Efficacy of Intermittent Intravenous Administration of High-Dose Micafungin

BACKGROUND

The use of mold-active azoles for antifungal prophylaxis after allogeneic stem cell transplantation (SCT) is hindered by adverse events and drug-drug interactions. Higher doses of echinocandins administered intermittently may be an alternative in this setting.

METHODS

This was a single-center, observational 5-year study to characterize the safety and efficacy of intermittent administration of high-dose intravenous micafungin (≥5 doses of ≥300 mg micafungin 2-3 times weekly) in patients with acute leukemia and allogeneic SCT recipients.

RESULTS

A total of 104 patients (84 allogeneic SCT recipients and 20 patients with leukemia) received intermittent high-dose intravenous micafungin, 83 (79.8%) as prophylaxis. Large variability in the micafungin dosing regimen was observed; 78 (75%) patients received >75% of their course as 300 mg micafungin 3 times weekly. Liver function tests decreased from baseline to end of treatment (EOT; P < .001). Patients with normal baseline liver function (n = 55 [52%]) maintained similar enzyme levels throughout the study. For patients with abnormal baseline liver function (n = 49 [47%]), liver function tests significantly improved from baseline to EOT (P ≤ .005). Duration and/or micafungin dosing algorithms were not associated with liver toxicity at EOT. There were no significant changes in renal function, and infusion-related reactions or deaths were not observed. Five of 83 (6.0%) patients in the prophylaxis group developed a breakthrough fungal infection.

CONCLUSIONS

In this largest cohort of patients to date, intermittent administration of high-dose micafungin was well tolerated, without any associated liver or renal function abnormalities, and may be considered an alternative antifungal prophylactic strategy. Prospective studies are needed to further validate these findings.

Echinocandins: The Expanding Antifungal Armamentarium

The echinocandins are large lipopeptide molecules that, since their discovery approximately 41 years ago, have emerged as important additions to the expanding armamentarium against invasive fungal diseases. Echinocandins exert in vitro and in vivo fungicidal action against most Candida species and fungistatic action against Aspergillus species. However, the population of patients at risk for developing invasive fungal infections continues to increase. New therapeutic strategies using echinocandins are needed to improve clinical outcomes in patients with invasive fungal disease.

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

The time the earth takes to rotate its axis (the day) has dictated how often pharmaceutical compounds are dosed. The scientific link between the 2 events is materia medica arcana. As an example, in the treatment of invasive candidiasis, antifungal therapy with intravenous micafungin is dosed daily. A literature review revealed population pharmacokinetic analyses, in vivo pharmacokinetics/pharmacodynamics studies, and maximum-tolerated-dose studies of micafungin that examined optimal micafungin dosing strategies. The half-life of micafungin in patient blood was 14 hours in several studies, but was even longer in different organs, so that the concentration will persist above minimum inhibitory concentrations of Candida species for several days. Studies in mice and rabbits with persistent neutropenia and disseminated candidiasis, otherwise fatal, demonstrated that a single large dose of micafungin could clear disseminated candidiasis, even though the micafungin half-life in such animals is shorter than in humans. Human pharmacokinetics/pharmacodynamics studies confirmed this link between micafungin efficacy and the ratio of the area under the concentration-time curve, and the optimal exposures initially identified in neutropenic animals. Maximum tolerated dose studies have demonstrated safety of 900 mg administered daily for several weeks, whereas case reports demonstrate efficacy and safety of single 1400-mg doses. Thus, a single dose of micafungin, or 2 such doses within a few days of each other, is not only logical, but might even lead to faster clearance of Candida.

Pharmacodynamics for antifungal drug development: an approach for acceleration, risk minimization and demonstration of causality

The treatment of invasive fungal diseases constitutes a significant unmet medical need. There are relatively few antifungal agents in clinical development and a paucity of novel targets. Morbidity and mortality remain high and clinical outcomes are compromised by submaximal efficacy, emergence of drug resistance and drug-related toxicity. Thus, new antifungal agents are urgently required. A deep understanding of exposure-response relationships underpins the development of safe and effective clinical regimens of any therapeutic agent. Pharmacokinetics (PK) and pharmacodynamics (PD) is increasingly recognized as a vital tool in the development of new antimicrobial agents and maximizes the probability that the right dose will be studied the first time. There is currently no information or agreement as to what constitutes an adequate PK/PD package for the development of a new antifungal agent. This review provides a summary of the achievements of antifungal PK/PD for the treatment of invasive candidiasis, invasive aspergillosis and cryptococcal meningoencephalitis, and outlines the necessary components of a PK/PD package for a new antifungal agent. Such information is critical for the accelerated and efficient development of new agents and enables improved clinical outcomes to be secured.

[Echinocandins: Applied pharmacology]

The echinocandins share pharmacodynamic properties, although there are some interesting differences in their pharmacokinetic behaviour in the clinical practice. They are not absorbed by the oral route. They have a somewhat special distribution in the organism, as some of them can reach high intracellular concentrations while, with some others, the concentration is reduced. They are highly bound to plasma proteins, thus it is recommended to administer a loading dose for anidulafungin and caspofungin, although this procedure is not yet clear with micafungin. Echinocandins are excreted via a non-microsomal metabolism, so the urinary concentration is very low. Some carrier proteins that take part in the biliary clearance process are probably involved in the interactions described with caspofungin and micafungin. These two drugs must be used with caution in patients with severely impaired hepatic function, while all of them can be used without special precautions when there is renal impairment or the patient requires renal replacement therapy.