Comparative in vitro pharmacodynamics of caspofungin, micafungin, and anidulafungin against germinated and nongerminated Aspergillus conidia

Usage of Antifungal Agents in Pediatric Patients Versus Adults: Knowledge and Gaps

Invasive fungal infections (IFIs) present significant challenges in managing hospitalized and immunocompromised pediatric patients, contributing to high morbidity and mortality. Despite advancements in diagnostics and treatment, outcomes remain suboptimal due to unique clinical epidemiology, lack of pediatric-specific trials, and varied pharmacokinetics. The emergence of new antifungal classes and agents has expanded our options for preventing and treating IFIs in children, enhancing the safety and effectiveness of antifungal therapy. The oral formulations of ibrexafungerp, fosmanogepix and olorofim along with the extended dosing intervals of rezafungin show promising features for effective antifungal treatment in pediatrics. Despite the promising potential of novel antifungal drugs, their performance in heavily immunosuppressed patients remains unstudied. Until then, dedicated antifungal stewardship programs for high-risk patients are essential to optimize therapeutic outcomes, improve patient care, and limit the emergence of resistance.

Various Biomimetics, Including Peptides as Antifungals

Biomimetics, which are similar to natural compounds that play an important role in the metabolism, manifestation of functional activity and reproduction of various fungi, have a pronounced attraction in the current search for new effective antifungals. Actual trends in the development of this area of research indicate that unnatural amino acids can be used as such biomimetics, including those containing halogen atoms; compounds similar to nitrogenous bases embedded in the nucleic acids synthesized by fungi; peptides imitating fungal analogs; molecules similar to natural substrates of numerous fungal enzymes and quorum-sensing signaling molecules of fungi and yeast, etc. Most parts of this review are devoted to the analysis of semi-synthetic and synthetic antifungal peptides and their targets of action. This review is aimed at combining and systematizing the current scientific information accumulating in this area of research, developing various antifungals with an assessment of the effectiveness of the created biomimetics and the possibility of combining them with other antimicrobial substances to reduce cell resistance and improve antifungal effects.

Genomic and Molecular Identification of Genes Contributing to the Caspofungin Paradoxical Effect in Aspergillus fumigatus

Aspergillus fumigatus is a deadly opportunistic fungal pathogen responsible for ~100,000 annual deaths. Azoles are the first line antifungal agent used against A. fumigatus, but azole resistance has rapidly evolved making treatment challenging. Caspofungin is an important second-line therapy against invasive pulmonary aspergillosis, a severe A. fumigatus infection. Caspofungin functions by inhibiting β-1,3-glucan synthesis, a primary and essential component of the fungal cell wall. A phenomenon termed the caspofungin paradoxical effect (CPE) has been observed in several fungal species where at higher concentrations of caspofungin, chitin replaces β-1,3-glucan, morphology returns to normal, and growth rate increases. CPE appears to occur in vivo, and it is therefore clinically important to better understand the genetic contributors to CPE. We applied genomewide association (GWA) analysis and molecular genetics to identify and validate candidate genes involved in CPE. We quantified CPE across 67 clinical isolates and conducted three independent GWA analyses to identify genetic variants associated with CPE. We identified 48 single nucleotide polymorphisms (SNPs) associated with CPE. We used a CRISPR/Cas9 approach to generate gene deletion mutants for seven genes harboring candidate SNPs. Two null mutants, ΔAfu3g13230 and ΔAfu4g07080 (dscP), resulted in reduced basal growth rate and a loss of CPE. We further characterized the dscP phosphatase-null mutant and observed a significant reduction in conidia production and extremely high sensitivity to caspofungin at both low and high concentrations. Collectively, our work reveals the contribution of Afu3g13230 and dscP in CPE and sheds new light on the complex genetic interactions governing this phenotype. IMPORTANCE This is one of the first studies to apply genomewide association (GWA) analysis to identify genes involved in an Aspergillus fumigatus phenotype. A. fumigatus is an opportunistic fungal pathogen that causes hundreds of thousands of infections and ~100,000 deaths each year, and antifungal resistance has rapidly evolved in this species. A phenomenon called the caspofungin paradoxical effect (CPE) occurs in some isolates, where high concentrations of the drug lead to increased growth rate. There is clinical relevance in understanding the genetic basis of this phenotype, since caspofungin concentrations could lead to unintended adverse clinical outcomes in certain cases. Using GWA analysis, we identified several interesting candidate polymorphisms and genes and then generated gene deletion mutants to determine whether these genes were important for CPE. Two of these mutant strains (ΔAfu3g13230 and ΔAfu4g07080/ΔdscP) displayed a loss of the CPE. This study sheds light on the genes involved in clinically important phenotype CPE.

Evaluation of a primary antifungal prophylaxis protocol for preventing invasive mold infections after allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Invasive mold infections contribute to morbidity and mortality in patients undergoing allogeneic hematopoietic stem cell transplantation. The optimal strategy for primary antifungal prophylaxis in this patient population remains uncertain.

METHODS

Medical records of patients who underwent allogeneic hematopoietic stem cell transplantation between 1 January 2013 and 31 December 2017 were retrospectively reviewed. Adult patients were included if they received micafungin followed by fluconazole, with the option to escalate to voriconazole, for antifungal prophylaxis. The primary outcome was the incidence rate of proven or probable invasive mold infection. Secondary outcomes were time to invasive mold infection diagnosis, invasive mold infection-related mortality, and risk factors associated with invasive mold infection.

RESULTS

Two hundred patients were included in the study, a majority of whom underwent matched unrelated (46%) or matched related (33%) donor transplants. The incidence rate of proven or probable invasive mold infection was 18.4 cases per 100 patient-years, with a one-year cumulative incidence of 14%. Median time to proven or probable invasive mold infection was 94 days post-transplant (IQR 26-178), with invasive mold infection-related mortality occurring in 18 (64%) of 28 patients diagnosed with invasive mold infection. Comparison of invasive mold infection-free survival by potential risk factors failed to show any significant differences.

CONCLUSIONS

In this real-life cohort of allogeneic hematopoietic stem cell transplantation recipients, the incidence of proven or probable invasive mold infection was higher than expected based on previous literature. In the absence of standard guidance on anti-mold prophylaxis in this patient population and given that unique risk factors for invasive mold infection may differ between institutions, it is essential that centers performing allogeneic hematopoietic stem cell transplantation routinely monitor their antifungal prophylaxis strategies for effectiveness.

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.

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 New Marker of Echinocandin Activity in an In Vitro Pharmacokinetic/Pharmacodynamic Model Correlates with an Animal Model of Aspergillus fumigatus Infection

The lack of a quantifiable marker for echinocandin activity hinders in vitro pharmacokinetic/pharmacodynamic (PK/PD) studies for Aspergillus spp. We developed an in vitro PK/PD model simulating the pharmacokinetics of anidulafungin and assessing its pharmacodynamics against Aspergillus fumigatus with a new, easily quantifiable, sensitive, and reproducible marker. Two clinical A. fumigatus isolates previously used in animals (AZN8196 and V52-35) with identical anidulafungin EUCAST (0.03 μg/ml) and CLSI (0.015 μg/ml) minimal effective concentrations (MEC) and one isolate (strain AFU79728) with an MEC of >16 μg/ml were tested in a two-compartment PK/PD dialysis/diffusion closed model containing a dialysis membrane (DM) tube inoculated with 10³ CFU/ml. During anidulafungin exposure, two types of fungal forms were observed inside the DM tube: floating conidia that were quantified by cultures and aberrant mycelia that were quantified by the vertical height of the mycelia attached on the DM tube. No aberrant mycelia were found for the resistant isolate or in the drug-free controls. An in vitro exposure-effect relationship was similar to that found in animals using survival as an endpoint, with a free-drug area under the concentration-time curve from 0 to 24 h (fAUC_0-24) associated with 50% of maximal activity of 2.21 (range, 1.81 to 2.71) mg · h/liter in vitro versus 2.62 (range, 1.88 to 3.65) mg · h/liter in vivo (P = 0.41). The hillslopes were also similar, with 1.96 versus 1.34 (P = 0.29). Analysis of each isolate separately showed increased antifungal susceptibility between AZN8196 and V52-35 (P < 0.001) even though they have the same CLSI and EUCAST MECs, but the strains have two 2-fold dilutions lower MICs using Etest and the XTT {2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide} method. Dose fractionation studies with all three echinocandins showed that their activities are best described by fAUC and not the maximum concentration of free drug (fC_max). The new marker correlated with in vivo outcome and can be used for in vitro PK/PD studies exploring the pharmacodynamics of echinocandins against Aspergillus spp.

Genomics-driven discovery of a novel self-resistance mechanism in the echinocandin-producing fungus Pezicula radicicola

The echinocandins are antifungal lipopeptides targeting fungi via noncompetitive inhibition of the β-1,3-d-glucan synthase FKS1 subunit. A novel echinocandin resistance mechanism involving an auxiliary copy of FKS1 in echinocandin-producing fungus Pezicula radicicola NRRL 12192 was discovered. We sequenced the genome of NRRL 12192 and predicted two FKS1-encoding genes (prfks1n and prfks1a), rather than a single FKS1 gene typical of filamentous ascomycetes. The prfks1a gene sits immediately adjacent to an echinocandin (sporiofungin) gene cluster, which was confirmed by disruption of prnrps4 and abolishment of sporiofungin production. Disruption of prfks1a dramatically increased the strain's sensitivity to exogenous echinocandins. In the absence of echinocandins, transcription levels of prfks1a relative to β-tubulin in the wild type and in Δprnrps4 stains were similar. Moreover, prfks1a is consistently transcribed at low levels and is upregulated in the presence of exogenous echinocandin, but not during growth conditions promoting endogenous production of sporiofungin. Therefore, we conclude that prfks1a is primarily responsible for protecting the fungus against extracellular echinocandin toxicity. The presence of unclustered auxiliary copies of FKS1 with high similarity to prfks1a in two other echinocandin-producing strains suggests that this previously unrecognized resistance mechanism may be common in echinocandin-producing fungi of the family Dermataceae of the class Leotiomycetes.

Echinocandin prophylaxis in patients undergoing haematopoietic cell transplantation and other treatments for haematological malignancies

Antifungal prophylaxis is the standard of care for patients undergoing intensive chemotherapy for haematological malignancy or haematopoietic cell transplantation (HCT). Prophylaxis with azoles reduces invasive fungal infections and may reduce mortality. However, breakthrough infections still occur, and the use of azoles is sometimes complicated by pharmacokinetic variability, drug interactions, adverse events and other issues. Echinocandins are highly active against Candida species, including some organisms resistant to azoles, and have some clinical activity against Aspergillus species as well. Although currently approved echinocandins require daily intravenous administration, the drugs have a favourable safety profile and more predictable pharmacokinetics than mould-active azoles. Clinical data support the efficacy and safety of echinocandins for antifungal prophylaxis in haematology and HCT patients, though data are less robust than for azoles. Notably, sparse evidence exists supporting the use of echinocandins as antifungal prophylaxis for patients with significant graft-versus-host disease (GvHD) after HCT. Two drugs that target (1,3)-β-d-glucan are in development, including an oral glucan synthase inhibitor and an echinocandin with unique pharmacokinetics permitting subcutaneous and weekly administration. Echinocandins are a reasonable alternative to azoles and other agents for antifungal prophylaxis in patients undergoing intensive chemotherapy for haematological malignancy or those receiving HCT, excluding those with significant GvHD.

Recent Insights into the Paradoxical Effect of Echinocandins

Echinocandin antifungals represent one of the most important drug classes for the treatment of invasive fungal infections. The mode of action of the echinocandins relies on inhibition of the β-1,3-glucan synthase, an enzyme essentially required for the synthesis of the major fungal cell wall carbohydrate β-1,3-glucan. Depending on the species, echinocandins may exert fungicidal or fungistatic activity. Apparently independent of this differential activity, a surprising in vitro phenomenon called the “paradoxical effect” can be observed. The paradoxical effect is characterized by the ability of certain fungal isolates to reconstitute growth in the presence of higher echinocandin concentrations, while being fully susceptible at lower concentrations. The nature of the paradoxical effect is not fully understood and has been the focus of multiple studies in the last two decades. Here we concisely review the current literature and propose an updated model for the paradoxical effect, taking into account recent advances in the field.

In vitro antifungal susceptibility of clinical and environmental isolates of Aspergillus fumigatus and Aspergillus flavus in Brazil

The in vitro susceptibility of 105 clinical and environmental strains of Aspergillus fumigatus and Aspergillus flavus to antifungal drugs, such as amphotericin B, azoles, and echinocandins was evaluated by the broth microdilution method proposed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Following the EUCAST-proposed breakpoints, 20% and 25% of the clinical and environmental isolates of A. fumigatus, respectively, were found to be resistant to itraconazole (Minimal Inhibitory Concentration, MIC > 2.0 mg/L). Voriconazole showed good activity against A. fumigatus and A. flavus strains, except for one clinical strain of A. fumigatus whose MIC was 4.0 mg/L. Posaconazole (≤0.25 mg/L) also showed appreciable activity against both species of Aspergillus, except for six A. fumigatus strains with relatively higher MICs (0.5 mg/L). The MICs for Amphotericin B ranged from 0.06 to 1.0 mg/L for A. fumigatus, but were much higher (0.5–8.0 mg/L) for A. flavus. Among the echinocandins, caspofungin showed a geometric mean of 0.078 and 0.113 against the clinical and environmental strains of A. flavus, respectively, but had elevated minimal effective concentrations (MECs) for seven of the A. fumigatus strains. Anidulafungin and micafungin exhibited considerable activity against both A. fumigatus and A. flavus isolates, except for one environmental isolate of A. fumigatus that showed an MEC of 1 mg/L to micafungin. Our study proposes that a detailed investigation of the antifungal susceptibility of the genus Aspergillus from different regions of Brazil is necessary for establishing a response profile against the different classes of antifungal agents used in the treatment of aspergillosis.

Filter Adsorption of Anidulafungin to a Polysulfone-Based Hemofilter During CVVHD In Vitro

Candidemia is frequent in critically ill patients, especially in combination with an acute kidney injury (AKI). Echinocandins generally are recommended for therapy of such infections. Recent studies found no need for dosage adjustment in patients with end-stage renal disease receiving hemodialysis, or patients with AKI receiving continuous venovenous hemofiltration. The aim of this in vitro study was to examine the adsorption of anidulafungin to the surface of the hemofilter during continuous venovenous hemodialysis (CVVHD) and its effect on anidulafungin concentrations. The concentration of anidulafungin in the dialyzed fluid, and the dialysate during CVVHD in vitro was examined using three different dialyzed fluids (saline; saline with 40 g/L human albumin; and a mixture of human erythrocytes and fresh frozen plasma). After the end of dialysis, the hemofilter was opened and portions of the filter capillaries were also analyzed to determine the amount of anidulafungin adsorbed. When dialyzing saline, about 99% of the anidulafungin used adsorbed to the hemofilter capillaries; in the experiments with saline with 40 g/L albumin, about 60% adsorbed to the hemofilter's surface, and when blood was dialyzed, 35% was found adsorbed after analyzing the filter capillaries. Anidulafungin was not detectable in the dialysate of any of the experiments, consequently the dialysis clearance was 0 mL/min. In conclusion, during CVVHD in vitro we found remarkable adsorption of anidulafungin to the hemofilter's surface, yet the effect on the tissue concentration needs further examination.

Comparative Evaluation of Sensititre YeastOne and CLSI M38-A2 Reference Method for Antifungal Susceptibility Testing of Aspergillus spp. against Echinocandins

Sensititre YeastOne (YO) panels were assessed for in vitro susceptibility testing of echinocandins against 39 isolates of Aspergillus fumigatus, A. flavus, and A. terreus, including two echinocandin-resistant A. fumigatus strains, using different inocula (103, 104, and 105 CFU/ml), incubation times (16 to 48 h), and endpoints (first blue or purple well) and compared to CLSI M38-A2. The best agreement was found with an inoculum of 104 CFU/ml, incubation times of 20 h for A. flavus and of 30 h for A. fumigatus and A. terreus, and reading the first purple well. The reproducibility within ±1 2-fold dilutions was 100% for all three echinocandins. YO color endpoints were 2 to 3 2-fold dilutions lower than CLSI minimum effective concentrations (MECs) of caspofungin and 1 to 2 2-fold dilutions higher than CLSI MECs of micafungin. For anidulafungin, off-scale YO color endpoints were observed. Nevertheless, A. fumigatus echinocandin-resistant isolates were detected after 24 h of incubation.

Caspofungin Increases Fungal Chitin and Eosinophil and γδ T Cell-Dependent Pathology in Invasive Aspergillosis

The polysaccharide-rich fungal cell wall provides pathogen-specific targets for antifungal therapy and distinct molecular patterns that stimulate protective or detrimental host immunity. The echinocandin antifungal caspofungin inhibits synthesis of cell wall β-1,3-glucan and is used for prophylactic therapy in immune-suppressed individuals. However, breakthrough infections with fungal pathogen Aspergillus fumigatus are associated with caspofungin prophylaxis. In this study, we report in vitro and in vivo increases in fungal surface chitin in A. fumigatus induced by caspofungin that was associated with airway eosinophil recruitment in neutropenic mice with invasive pulmonary aspergillosis (IA). More importantly, caspofungin treatment of mice with IA resulted in a pattern of increased fungal burden and severity of disease that was reversed in eosinophil-deficient mice. Additionally, the eosinophil granule proteins major basic protein and eosinophil peroxidase were more frequently detected in the bronchoalveolar lavage fluid of lung transplant patients diagnosed with IA that received caspofungin therapy when compared with azole-treated patients. Eosinophil recruitment and inhibition of fungal clearance in caspofungin-treated mice with IA required RAG1 expression and γδ T cells. These results identify an eosinophil-mediated mechanism for paradoxical caspofungin activity and support the future investigation of the potential of eosinophil or fungal chitin-targeted inhibition in the treatment of IA.

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.

Potential Microbiological Effects of Higher Dosing of Echinocandins

The antifungal "paradoxical effect" has been described as the reversal of growth inhibition at high doses of echinocandins, most usually caspofungin. This microbiological effect appears to be a cellular compensatory response to cell wall damage, resulting in alteration of cell wall content and structure as well as fungal morphology and growth. In vitro studies demonstrate this reproducible effect in a certain percentage of fungal isolates, but animal model and clinical studies are less consistent. The calcineurin and Hsp90 cell signaling pathways appear to play a major role in regulating these cellular and structural changes. Regardless of the clinical relevance of this paradoxical growth effect, understanding the specific actions of echinocandins is paramount to optimizing their use at either standard or higher dosing schemes, as well as developing future improvements in our antifungal arsenal.

Dose optimization of voriconazole/anidulafungin combination against Aspergillus fumigatus using an in vitro pharmacokinetic/pharmacodynamic model and response surface analysis: clinical implications for azole-resistant aspergillosis

BACKGROUND

Combination therapy of voriconazole with an echinocandin is often employed in order to increase the efficacy of voriconazole monotherapy.

METHODS

Four clinical Aspergillus fumigatus isolates with different in vitro susceptibilities to voriconazole (MIC 0.125-2 mg/L) and anidulafungin (MEC 0.008-0.016 mg/L) were tested in an in vitro pharmacokinetic/pharmacodynamic model simulating human serum concentrations of standard dosages of voriconazole and anidulafungin. Fungal growth was assessed using galactomannan production and quantitative PCR. Drug concentrations were determined with bioassays. Pharmacodynamic interactions were assessed using Bliss independence analysis (BI) and Loewe additivity-based canonical mixture response-surface non-linear regression analysis (LA). Probability of target attainment (PTA) was estimated with Monte Carlo analysis for different doses of anidulafungin (25, 50 and 100 mg) and azole resistance rates (5%-25%).

RESULTS

Synergy [BI 51% (8%-80%), LA 0.63 (0.38-0.79)] was found at low anidulafungin (fC_max/MEC <10) and voriconazole (fAUC/MIC <10) exposures, whereas antagonism [BI 12% (5%-18%, LA 1.12 (1.04-4.6)] was found at higher drug exposures. The largest increase in PTA was found with 25 mg of anidulafungin and voriconazole MIC distributions with high (>10%) resistance rates. PTAs for isolates with voriconazole MICs of 1, 2 and 4 mg/L was 78%, 12% and 0% with voriconazole monotherapy and 96%-100%, 68%-82% and 9%-20% with combination therapy, respectively. Optimal activity was associated with a voriconazole tC_min/MIC ratio of 1.5 for monotherapy and 0.75 for combination therapy.

CONCLUSIONS

The present study indicated that the combination of voriconazole with low-dose anidulafungin may increase the efficacy and reduce the cost and potential toxicity of antifungal therapy, particularly against azole-resistant A. fumigatus isolates and in patients with subtherapeutic serum levels. This hypothesis warrants further in vivo verification.

Caspofungin: Pharmacodynamics, pharmacokinetics, clinical uses and treatment outcomes

Over the past decade, echinocandins have emerged as first-line antifungal agents for many Candida infections. The echinocandins have a unique mechanism of action, inhibiting the synthesis of β-1,3-d-glucan polymers, key components of the cell wall in pathogenic fungi. Caspofungin was the first echinocandin antifungal agent to become licensed for use. The objectives of this review are to summarize the existing published data on caspofungin, under the subject headings of chemistry and mechanism of action, spectrum of activity, pharmacodynamics, pharmacokinetics, clinical studies, safety, drug interactions, dosing, and an overview of the drug's current place in therapy.

Caspofungin Treatment of Aspergillus fumigatus Results in ChsG-Dependent Upregulation of Chitin Synthesis and the Formation of Chitin-Rich Microcolonies

Treatment of Aspergillus fumigatus with echinocandins such as caspofungin inhibits the synthesis of cell wall β-1,3-glucan, which triggers a compensatory stimulation of chitin synthesis. Activation of chitin synthesis can occur in response to sub-MICs of caspofungin and to CaCl₂ and calcofluor white (CFW), agonists of the protein kinase C (PKC), and Ca²⁺-calcineurin signaling pathways. A. fumigatus mutants with the chs gene (encoding chitin synthase) deleted (ΔAfchs) were tested for their response to these agonists to determine the chitin synthase enzymes that were required for the compensatory upregulation of chitin synthesis. Only the ΔAfchsG mutant was hypersensitive to caspofungin, and all other ΔAfchs mutants tested remained capable of increasing their chitin content in response to treatment with CaCl₂ and CFW and caspofungin. The resulting increase in cell wall chitin content correlated with reduced susceptibility to caspofungin in the wild type and all ΔAfchs mutants tested, with the exception of the ΔAfchsG mutant, which remained sensitive to caspofungin. In vitro exposure to the chitin synthase inhibitor, nikkomycin Z, along with caspofungin demonstrated synergistic efficacy that was again AfChsG dependent. Dynamic imaging using microfluidic perfusion chambers demonstrated that treatment with sub-MIC caspofungin resulted initially in hyphal tip lysis. However, thickened hyphae emerged that formed aberrant microcolonies in the continued presence of caspofungin. In addition, intrahyphal hyphae were formed in response to echinocandin treatment. These in vitro data demonstrate that A. fumigatus has the potential to survive echinocandin treatment in vivo by AfChsG-dependent upregulation of chitin synthesis. Chitin-rich cells may, therefore, persist in human tissues and act as the focus for breakthrough infections.

Pharmacokinetics and safety of intravitreal caspofungin

Caspofungin exhibits potent antifungal activities against Candida and Aspergillus species. The elimination rate and retinal toxicity of caspofungin were determined in this study to assess its pharmacokinetics and safety in the treatment of fungal endophthalmitis. Intravitreal injections of 50 μg/0.1 ml of caspofungin were administered to rabbits. Levels of caspofungin in the vitreous and aqueous humors were determined using high-performance liquid chromatography (HPLC) at selected time intervals (10 min and 1, 2, 4, 8, 16, 24, and 48 h), and the half-lives were calculated. Eyes were intravitreally injected with caspofungin to obtain concentrations of 10 μg/ml, 50 μg/ml, 100 μg/ml, and 200 μg/ml. Electroretinograms were recorded 4 weeks after injections, and the injected eyes were examined histologically. The concentrations of intravitreal caspofungin at various time points exhibited an exponential decay with a half-life of 6.28 h. The mean vitreous concentration was 6.06 ± 1.76 μg/ml 1 h after intravitreal injection, and this declined to 0.47 ± 0.15 μg/ml at 24 h. The mean aqueous concentration showed undetectable levels at all time points. There were no statistical differences in scotopic a-wave and b-wave responses between control eyes and caspofungin-injected eyes. No focal necrosis or other abnormality in retinal histology was observed. Intravitreal caspofungin injection may be considered to be an alternative treatment for fungal endophthalmitis based on its antifungal activity, lower retinal toxicity, and lower elimination rate in the vitreous. More clinical data are needed to determine its potential role as primary therapy for fungal endophthalmitis.

Trailing or paradoxical growth of Aspergillus flavus exposed to caspofungin is independent of genotype

There are limited data on in vitro susceptibility testing of echinocandins against Aspergillus species. The objective of this study was to describe the phenotypes of Aspergillus flavus observed on exposure to caspofungin in vitro and to test whether these phenotypes were associated with A. flavus genotypes. The caspofungin MICs of 37 A. flavus clinical isolates collected from 14 patients with invasive aspergillosis were determined using Etest assays. Caspofungin MICs ranged from 0.012 to 0.064 mg l(-1); the modal MIC was 0.023 mg l(-1) and the MIC₅₀ and MIC₉₀ were 0.032 and 0.064 mg l(-1), respectively. A clear end point was noted in 24 (65 %) isolates, whereas seven (19 %) displayed a trailing effect and six (16 %) showed paradoxical growth when exposed to caspofungin. In these A. flavus isolates, the absence of a significant population structure or genetic differentiation indicated that trailing or paradoxical growth phenotypes were independent of microsatellite genotype.

Amphotericin B- and voriconazole-echinocandin combinations against Aspergillus spp.: Effect of serum on inhibitory and fungicidal interactions

Antifungal combination therapy with voriconazole or amphotericin B and an echinocandin is often employed as primary or salvage therapy for management particularly of refractory aspergillosis. The pharmacodynamic interactions of amphotericin B- and voriconazole-based combinations with the three echinocandins caspofungin, micafungin, and anidulafungin in the presence of serum were tested against 15 Aspergillus fumigatus complex, A. flavus complex, and A. terreus complex isolates to assess both their growth-inhibitory and fungicidal activities. The in vitro activity of each drug alone and in combination at a 1:1 fixed concentration ratio was tested with a broth microdilution colorimetric method, and interactions were assessed by isobolographic analysis. Synergy was found for all amphotericin B- and voriconazole-based combinations, with amphotericin B-based combinations showing strong inhibitory synergistic interactions (interaction indices of 0.20 to 0.52) and with voriconazole-based combinations demonstrating strong fungicidal synergistic interactions (interaction indices of 0.10 to 0.29) (P < 0.001). Drug- and species-specific differences were found, with caspofungin and the A. fumigatus complex exhibiting the weakest synergistic interactions. In the presence of serum, the synergistic interactions were reduced in the order (from largest to smallest decrease) micafungin > anidulafungin > caspofungin, and A. flavus complex > A. fumigatus complex > A. terreus complex, resulting in additive interactions, particularly for inhibitory activities of amphotericin B-echinocandin combinations and fungicidal activities of voriconazole-echinocandin combinations. Drug- and species-specific differences were found in the presence of serum for inhibitory activities of antifungal drugs, with the lowest interaction indices being observed for amphotericin B-caspofungin (median, 0.77) and for the A. terreus complex (median, 0.56). The present in vitro data showed that serum had a major impact on synergistic interactions of amphotericin B-echinocandin and voriconazole-echinocandin combinations, resulting in additive interactions and explaining the indifferent outcomes usually observed in vivo.

Inhibitory and fungicidal effects of antifungal drugs against Aspergillus species in the presence of serum

Given the high protein binding rates of antifungal drugs and the effect of serum proteins on Aspergillus growth, we investigated the in vitro pharmacodynamics of amphotericin B, voriconazole, and three echinocandins in the presence of human serum, assessing both inhibitory and fungicidal effects. In vitro inhibitory (IC) and fungicidal (FC) concentrations against 5 isolates of Aspergillus fumigatus, Aspergillus flavus, and Aspergillus terreus were determined with a CLSI M38-A2-based microdilution method using the XTT methodology after 48 h of incubation at 35 °C with a medium supplemented with 50% human serum. In the presence of serum, the IC and FC of amphotericin B and the IC of echinocandins were increased (1.21- to 13.44-fold), whereas voriconazole IC and FC were decreased (0.22- to 0.90-fold). The amphotericin B and voriconazole FC/IC ratios did not change significantly (0.59- to 2.33-fold) in the presence of serum, indicating that the FC increase was due to the IC increase. At echinocandin concentrations above the minimum effective concentration (MEC), fungal growth was reduced by 10 to 50% in the presence of human serum, resulting in complete inhibition of growth for some isolates. Thus, the in vitro activities of amphotericin B and echinocandins were reduced, whereas that of voriconazole was enhanced, in the presence of serum. These changes could not be predicted by the percentage of protein binding, indicating that other factors and/or secondary mechanisms may account for the observed in vitro activities of antifungal drugs against Aspergillus species in the presence of serum.

Antimicrobial dosing in acute renal replacement

Acute kidney injury (AKI) is a common problem in hospitalized patients and is associated with significant morbidity and mortality. Two large trials showed no benefit from increased doses of renal replacement therapy (RRT) despite previous clinical data suggesting that increased clearance from RRT has beneficial effects. Since infection is the leading cause of death in AKI, my group and others hypothesized that increased RRT antibiotic clearance might create a competing morbidity. The data from my group, as well as those of other groups, show that many patients are underdosed when routine "1 size fits all" antibiotic dosing is used in patients with AKI receiving continuous RRT (CRRT). Here, concepts of drug distribution and clearance in AKI are briefly discussed and then 1 antibiotic (piperacillin) is discussed in depth to illustrate the challenges in applying the medical literature to clinical practice. The fact that published data on drug dosing in AKI and dialysis reflect the evolution of practice patterns and often do not apply to present prescribing habits is also discussed. A more general approach to drug dosing facilitates situation-specific prescribing by the nephrologist and critical care specialist.

Susceptibility screening of hyphae-forming fungi with a new, easy, and fast inoculum preparation method

In vitro susceptibility testing of clinically important fungi becomes more and more essential due to the rising number of fungal infections in patients with impaired immune system. Existing standardized microbroth dilution methods for in vitro testing of molds (CLSI, EUCAST) are not intended for routine testing. These methods are very time-consuming and dependent on sporulating of hyphomycetes. In this multicentre study, a new (independent of sporulation) inoculum preparation method (containing a mixture of vegetative cells, hyphae, and conidia) was evaluated. Minimal inhibitory concentrations (MIC) of amphotericin B, posaconazole, and voriconazole of 180 molds were determined with two different culture media (YST and RPMI 1640) according to the DIN (Deutsches Institut für Normung) microdilution assay. 24 and 48 h MIC of quality control strains, tested per each test run, prepared with the new inoculum method were in the range of DIN. YST and RPMI 1640 media showed similar MIC distributions for all molds tested. MIC readings at 48 versus 24 h yield 1 log(2) higher MIC values and more than 90 % of the MICs read at 24 and 48 h were within ± 2 log(2) dilution. MIC end point reading (log(2 MIC-RPMI 1640)-log(2 MIC-YST)) of both media demonstrated a tendency to slightly lower MICs with RPMI 1640 medium. This study reports the results of a new, time-saving, and easy-to-perform method for inoculum preparation for routine susceptibility testing that can be applied for all types of spore-/non-spore and hyphae-forming fungi.

Microcolony imaging of Aspergillus fumigatus treated with echinocandins reveals both fungistatic and fungicidal activities

Background

The echinocandins are lipopeptides that can be employed as antifungal drugs that inhibit the synthesis of 1,3-β-glucans within the fungal cell wall. Anidulafungin and caspofungin are echinocandins used in the treatment of Candida infections and have activity against other fungi including Aspergillus fumigatus. The echinocandins are generally considered fungistatic against Aspergillus species.

Methods

Culture of A. fumigatus from conidia to microcolonies on a support of porous aluminium oxide (PAO), combined with fluorescence microscopy and scanning electron microscopy, was used to investigate the effects of anidulafungin and caspofungin. The PAO was an effective matrix for conidial germination and microcolony growth. Additionally, PAO supports could be moved between agar plates containing different concentrations of echinocandins to change dosage and to investigate the recovery of fungal microcolonies from these drugs. Culture on PAO combined with microscopy and image analysis permits quantitative studies on microcolony growth with the flexibility of adding or removing antifungal agents, dyes, fixatives or osmotic stresses during growth with minimal disturbance of fungal microcolonies.

Significance

Anidulafungin and caspofungin reduced but did not halt growth at the microcony level; additionally both drugs killed individual cells, particularly at concentrations around the MIC. Intact but not lysed cells showed rapid recovery when the drugs were removed. The classification of these drugs as either fungistatic or fungicidal is simplistic. Microcolony analysis on PAO appears to be a valuable tool to investigate the action of antifungal agents.

The composition of the culture medium influences the β-1,3-glucan metabolism of Aspergillus fumigatus and the antifungal activity of inhibitors of β-1,3-glucan synthesis

In vitro testing of Aspergillus fumigatus susceptibility to echinocandins has always been a challenge. Using a simple and quick colorimetric method to analyze the activity of inhibitors of β-1,3-glucan synthesis, we found that the composition of the culture medium significantly influences glucan synthesis and consequently the antifungal properties of inhibitors of β-1,3-glucan synthesis when they are tested alone or in combination with chitin synthase inhibitors.

Caspofungin therapy in immunocompromised children and neonates

The prevalence of invasive fungal infections is increasing and the infections are becoming a major problem in immunocompromised children and neonates. Fortunately, there has been a recent surge in the development of new antifungal agents. Caspofungin, the first licensed echinocandin, is a novel class of antifungal and is approved for use in children 3 months of age or older for the treatment of invasive candidiasis, salvage therapy for invasive aspergillosis and as empirical therapy for febrile neutropenia. This article reviews the published data on the use of caspofungin in immunocompromised children and neonates with invasive fungal infections.

Anidulafungin: is it a promising option in the treatment of pediatric invasive fungal infections?

Cases of invasive fungal infections are increasing globally due to an increase in the immunosuppressed population, the use of broad-spectrum antibiotics and the invasive instrumentation of patients in intensive care units. Ongoing emergence of resistance and problems with toxicity have resulted in the need for the development of new antifungal agents. Anidulafungin, the most recently developed echinocandin, is approved by the US FDA for treatment of candidemia, other forms of Candida infection and esophageal candidiasis in non-neutropenic adult patients, but it is not currently licensed for pediatric usage. The drug is projected to be distinctive owing to its unique pharmacokinetics and is already listed in adult antifungal treatment guidelines. In this article, anidulafungin will be reviewed with a focus on pediatric patients.

In vitro echinocandin susceptibility of Aspergillus isolates from patients enrolled in the Transplant-Associated Infection Surveillance Network

We determined the echinocandin minimum effective concentration (MEC) values for caspofungin, micafungin, and anidulafungin against 288 Aspergillus isolates prospectively collected from transplant patients with proven or probable invasive aspergillosis between 2001 and 2006 as part of the Transplant-Associated Infection Surveillance Network (TRANSNET). We demonstrated that the vast majority of Aspergillus isolates had MEC values at or below the epidemiological cutoff values for caspofungin, micafungin, and anidulafungin, including those from patients who had received caspofungin.

[Echinocandins in children]

Echinocandins are a new class of antifungal agents with a specific mechanism of action. These drugs inhibit the enzyme 1,3β-D-glucan synthetase which is responsible for the formation of 1,3β-D-glucan, an essential fungal cell wall component. They have a good activity against Candida species and Aspergillus. Three agents are available at the present time or under development : caspofungin, micafungin and anidulafungin. These drugs require intravenous administration. Efficacy, safety, rare drugs interactions and specificity of action are advantages for therapy of invasive fungal infections. In France, micafungin and caspofungin are approved for a pediatric use.

Polyphasic identification and susceptibility to seven antifungals of 102 Aspergillus isolates recovered from immunocompromised hosts in Greece

In this study, the first such study in Greece, we used polyphasic identification combined with antifungal susceptibility study to analyze Aspergillus clinical isolates comprising 102 common and rare members of sections Fumigati, Flavi, Terrei, Nidulantes, Nigri, Circumdati, Versicolores, and Usti. High amphotericin B MICs (>2 μg/ml) were found for 17.6% of strains. Itraconazole, posaconazole, and voriconazole MICs of >4 μg/ml were shown in 1%, 5%, and 0% of the isolates, respectively. Anidulafungin, micafungin, and caspofungin minimum effective concentrations (MECs) of ≥2 μg/ml were correspondingly recorded for 4%, 9%, and 33%, respectively, of the strains.

The evaluation of in vitro pharmacodynamic properties of amphotericin B, voriconazole and caspofungin against A. fumigatus isolates by the conventional and colorimetric time-kill assays

Aspergillus fumigatus is an opportunistic pathogen responsible for life-threatening infections in immuncompromised patients. Data about the in vitro pharmacodynamics of antifungals against A. fumigatus are limited. In the present study, we investigated the fungicidal activities, at concentrations of 1, 4 and 16 times the minimum inhibitory concentration (MIC), of caspofungin (CAS), amphotericin B (AMB) and voriconazole (VORI) against eight A. fumigatus isolates through the use of time kill and 2,3-Bis [2-methoxy-4-nitro-5-(sulfenylamino) carbonyl-2H-tetrazolium-hydroxide] (XTT) reduction tests. By the conventional time kill test, AMB was fungicidal (≥99.9% reduction in colony forming units; CFU) for all isolates at 4-16 MICs after 48 h incubation. The fungicidal effect for VORI was determined at 4 × MIC for one isolate and at 16 × MIC for four isolates at 48 h of exposure. CAS was also fungicidal at 1 × MIC for one isolate and at 4-16 MICs for two isolates at 48 h. While the percentage of median killing of AMB was found by the time-kill method with XTT as 99% at 4 × MIC and 99.28% at 16 × MIC, that of VORI was 94.5% at 4 × MIC and 92.88% at 16 × MIC after 48 h of incubation. However, a significant increase was observed compared to initial inoculum size with CAS after 48 h. Since the XTT method measures all cellular viability in media, it may give more reliable results about pharmacodynamics of antifungal agents against Aspergillus spp. than the time kill test.

Pharmacokinetics, antifungal activity and clinical efficacy of anidulafungin in the treatment of fungal infections

IMPORTANCE OF THE FIELD

Anidulafungin is one of three available intravenous echinocandins that plays an important role in the treatment of serious fungal infections. Currently, anidulafungin is approved for the treatment of esophageal candidiasis, candidemia and other invasive Candida infections including intra-abdominal abscesses and peritonitis.

AREAS COVERED IN THIS REVIEW

This paper covers a comprehensive review of anidulafungin.

WHAT THE READER WILL GAIN

The reader will be provided the most recent data available regarding the pharmacology, pharmacokinetics, in vitro activity and clinical utility of anidulafungin for the treatment of serious fungal infections.

TAKE HOME MESSAGE

Echinocandin antifungals, such as anidulafungin, are now considered first line for the treatment of candidemia and invasive candidiasis, particularly in critically ill patients or those who have previously received azole therapy. Anidulafungin has potent in vitro activity against Candida and Aspergillus species, predictable pharmacokinetics that does not require dosage adjustment, few drug interactions and is well tolerated. Because of these favorable characteristics, anidulafungin is an important addition to our antifungal armamentarium.

Profiling the Aspergillus fumigatus proteome in response to caspofungin

The proteomic response of Aspergillus fumigatus to caspofungin was evaluated by gel-free isobaric tagging for relative and absolute quantitation (iTRAQ) as a means to determine potential biomarkers of drug action. A cell fractionation approach yielding 4 subcellular compartment fractions was used to enhance the resolution of proteins for proteomic analysis. Using iTRAQ, a total of 471 unique proteins were identified in soluble and cell wall/plasma membrane fractions at 24 and 48 h of growth in rich media in a wild-type drug-susceptible strain. A total of 122 proteins showed at least a 2-fold change in relative abundance following exposure to caspofungin (CSF) at just below the minimum effective concentration (0.12 μg/ml). The largest changes were seen in the mitochondrial hypoxia response domain protein (AFUA_1G12250), the level of which decreased >16-fold in the secreted fraction, and ChiA1, the level of which decreased 12.1-fold in the cell wall/plasma membrane fraction. The level of the major allergen and cytotoxin AspF1 was also shown to decrease by 12.1-fold upon the addition of drug. A subsequent iTRAQ analysis of an echinocandin-resistant strain (fks1-S678P) was used to validate proteins specific to drug action. A total of 103 proteins in the 2 fractions tested by iTRAQ were differentially expressed in the wild-type susceptible strain but not significantly changed in the resistant strain. Of these potential biomarkers, 11 had levels that changed at least 12-fold. Microarray analysis of the susceptible strain was performed to evaluate the correlation between proteomics and genomics, with a total of 117 genes found to be changing at least 2-fold. Of these, a total of 22 proteins with significant changes identified by iTRAQ also showed significant gene expression level changes by microarray. Overall, these data have the potential to identify biomarkers that assess the relative efficacy of echinocandin drug therapy.

Liposomal amphotericin B and echinocandins as monotherapy or sequential or concomitant therapy in murine disseminated and pulmonary Aspergillus fumigatus infections

Monotherapy and combination therapy were compared using optimal doses of liposomal amphotericin B, micafungin, or caspofungin in Aspergillus fumigatus pulmonary and disseminated infections. Mice were challenged intravenously (2.8 x 10(4) to 5.7 x 10(4) conidia) or intranasally (5.8 x 10(7) conidia) with A. fumigatus. Drugs (5, 10, or 15 mg/kg of body weight) were given for 3 or 6 days as single, concomitant, or sequential therapy (i.e., days 1 to 3 and then days 4 to 6). Mice were monitored for survival, and tissues were assayed for fungal burden and drug concentrations. Treatments starting 24 h postchallenge significantly prolonged survival in disseminated aspergillosis (P < 0.002), but only liposomal amphotericin B treatments or treatments beginning with liposomal amphotericin B increased survival to 100% in the pulmonary aspergillosis model. Fungi in kidneys and spleens (disseminated) and lungs (pulmonary) were significantly decreased (P < or = 0.04) by liposomal amphotericin B, liposomal amphotericin B plus echinocandin, or liposomal amphotericin B prior to echinocandin. In the disseminated infection, liposomal amphotericin B and micafungin (10 or 15 mg/kg) had similar kidney drug levels, while in the spleen, 5 and 15 mg/kg liposomal amphotericin B gave higher drug levels than micafungin (P < 0.02). In the pulmonary infection, drug levels in lungs and spleen with 5-mg/kg dosing were significantly higher with liposomal amphotericin B than with caspofungin (P < or = 0.002). In summary, treatment of A. fumigatus infections with liposomal amphotericin B plus echinocandin or liposomal amphotericin B prior to echinocandin was as effective as liposomal amphotericin B alone, and a greater decrease in the fungal burden with liposomal amphotericin B supports using liposomal amphotericin B prior to echinocandin.

Role of trehalose biosynthesis in Aspergillus fumigatus development, stress response, and virulence

Aspergillus fumigatus is a pathogenic mold which causes invasive, often fatal, pulmonary disease in immunocompromised individuals. Recently, proteins involved in the biosynthesis of trehalose have been linked with virulence in other pathogenic fungi. We found that the trehalose content increased during the developmental life cycle of A. fumigatus, throughout which putative trehalose synthase genes tpsA and tpsB were significantly expressed. The trehalose content of A. fumigatus hyphae also increased after heat shock but not in response to other stressors. This increase in trehalose directly correlated with an increase in expression of tpsB but not tpsA. However, deletion of both tpsA and tpsB was required to block trehalose accumulation during development and heat shock. The DeltatpsAB double mutant had delayed germination at 37 degrees C, suggesting a developmental defect. At 50 degrees C, the majority of DeltatpsAB spores were found to be nonviable, and those that were viable had severely delayed germination, growth, and subsequent sporulation. DeltatpsAB spores were also susceptible to oxidative stress. Surprisingly, the DeltatpsAB double mutant was hypervirulent in a murine model of invasive aspergillosis, and this increased virulence was associated with alterations in the cell wall and resistance to macrophage phagocytosis. Thus, while trehalose biosynthesis is required for a number of biological processes that both promote and inhibit virulence, in A. fumigatus the predominant effect is a reduction in pathogenicity. This finding contrasts sharply with those for other fungi, in which trehalose biosynthesis acts to enhance virulence.

Echinocandin pharmacodynamics: review and clinical implications

Echinocandins have made a significant impact in the treatment of select invasive fungal infections, most notably invasive candidiasis and aspergillosis. However, treatment outcomes for such infections are still less than optimal, prompting an examination of dosing and administration techniques in an attempt to exploit known pharmacodynamic properties and improve outcomes. Echinocandins generally exhibit concentration-dependent, fungicidal activity against Candida spp. and fungistatic activity against Aspergillus spp. However, increasing drug concentrations of echinocandins above the organism's MIC may result in a paradoxical increase in fungal growth as demonstrated in some in vitro and in vivo models (known most commonly as the 'Eagle effect'). Therefore, the potential impact of dose escalations on improving the clinical efficacy of echinocandins based on in vitro and animal models are uncertain and are still being evaluated. In addition, such strategies have to consider the potential for increased treatment-related toxicities and costs. To date, published clinical studies (both superiority and non-inferiority) demonstrating the potential for dose-related improvements in treatment outcomes have been limited to mucocutaneous and oesophageal candidiasis. Further research is needed to determine if a role exists for optimizing echinocandin pharmacodynamics in various clinical settings.