The echinocandin micafungin: a review of the pharmacology, spectrum of activity, clinical efficacy and safety

Micafungin injection for the treatment of invasive candidiasis in pediatric patients under 4 months of age

INTRODUCTION

Neonates and young infants with invasive candidiasis are particularly at increased risk of dissemination including hematogenous Candida meningoencephalitis. The echinocandins including micafungin have emerged as a preferred agent in most cases of candidemia and invasive candidiasis but data in pediatric patients under 4 months of age are limited.

AREAS COVERED

In this report, we review the micafungin use in infants younger than 4 months of age. Animal studies as well as clinical data that support its use in neonatal candidiasis are reviewed. In addition, the status of FDA approval and the rationale of micafungin dosing recommendations in infants <4 months are discussed.

EXPERT OPINION

A dose of 4 mg/kg was approved for treatment of candidemia, Candida peritonitis and abscesses excluding meningoencephalitis or ocular involvement in patients younger than 4 months of age. However, because of the risk of central nervous system dissemination as well as the difficulty in establishing this diagnosis, this dose is inadequate to treat ill infants with candidemia. More studies are needed to establish the safety and efficacy of micafungin daily dose of at least 10 mg/kg in infants younger than 4 months of age when hematogenous Candida meningoencephalitis or ocular involvement cannot be excluded.

1,3-Thiazine, 1,2,3,4-Dithiadiazole, and Thiohydrazide Derivatives Affect Lipid Bilayer Properties and Ion-Permeable Pores Induced by Antifungals

Over the past decade, thiazines, thiadiazoles, and thiohydrazides have attracted increasing attention due to their sedative, antimicrobial, antiviral, antifungal, and antitumor activities. The clinical efficacy of such drugs, as well as the possibility of developing resistance to antimicrobials, will depend on addressing a number of fundamental problems, including the role of membrane lipids during their interaction with plasma membranes. The effects of the eight 1,3- thiazine-, 1,2,3,4- dithiadiazole-, and thiohydrazide-related compounds on the physical properties of model lipid membranes and the effects on reconstituted ion channels induced by the polyene macrolide antimycotic nystatin and antifungal cyclic lipopeptides syringomycin E and fengycin were observed. We found that among the tested agents, the fluorine-containing compound N′-(3,5-difluorophenyl)-benzenecarbothiohydrazide (C6) was the most effective at increasing the electric barrier for anion permeation into the hydrophobic region of the membrane and reducing the conductance of anion-permeable syringomycin pores. A decrease in the membrane boundary potential with C6 adsorption also facilitated the immersion of positively charged syringomycin molecules into the lipid bilayer and increases the pore-forming ability of the lipopeptide. Using differential scanning microcalorimetry, we showed that C6 led to disordering of membrane lipids, possibly by potentiating positive curvature stress. Therefore, we used C6 as an agonist of antifungals forming the pores that are sensitive to membrane curvature stress and lipid packing, i.e., nystatin and fengycin. The dramatic increase in transmembrane current induced by syringomycin E, nystatin, and fengycin upon C6 treatment suggests its potential in combination therapy for treating invasive fungal infections.

Review on Current Status of Echinocandins Use

Fungal infections are rising all over the world every year. There are only five medical compound classes for treatment: triazoles, echinocandins, polyenes, flucytosine and allylamine. Currently, echinocandins are the most important compounds, because of their wide activity spectrum and much lower sides effects that may occur during therapy with other drugs. Echinocandins are secondary metabolites of fungi, which can inhibit the biosynthesis of β-(1,3)-D-glucan. These compounds have fungicidal and fungistatic activity depending on different genera of fungi, against which they are used. Echinocandin resistance is rare—the major cause of resistance is mutations in the gene encoding the β-(1,3)-D-glucan synthase enzyme. In this review of the literature we have summarized the characteristics of echinocandins, the mechanism of their antifungal activity with pharmacokinetics and pharmacodynamics, and the resistance issue.

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.

Beyond tissue concentrations: antifungal penetration at the site of infection

Despite advances in antifungal therapy, invasive fungal infections remain a significant cause of morbidity and mortality worldwide. One important factor contributing to the relative ineffectiveness of existing antifungal drugs is insufficient drug exposure at the site of infection. Despite the importance of this aspect of antifungal therapy, we generally lack a full appreciation of how antifungal drugs distribute, penetrate, and interact with their target organisms in different tissue subcompartments. A better understanding of drug distribution will be critical to guide appropriate use of currently available antifungal drugs, as well as to aid development of new agents. Herein we briefly review current perspectives of antifungal drug exposure at the site of infection and describe a new technique, matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging, which has the potential to greatly expand our understanding of drug penetration.

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.

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.

Pharmacokinetics of micafungin in subjects with severe hepatic dysfunction

Micafungin is an echinocandin with potent activity against a broad range of fungal species, including Candida species. The pharmacokinetic and safety profiles of micafungin have been evaluated in individuals with mild-to-moderate hepatic dysfunction, but not in individuals with severe hepatic dysfunction. Therefore, the present study assessed the pharmacokinetics and safety of a single 100 mg dose of micafungin in healthy subjects (n = 8) and subjects with severe hepatic dysfunction (n = 8). Mean maximum plasma concentration of micafungin and mean area under the plasma micafungin concentration-time curve extrapolated to infinity were lower in subjects with severe hepatic dysfunction (7.3 ± 2.4 µg/mL and 100.1 ± 34.5 h·μg/mL, respectively) than in subjects with normal hepatic function (10.3 ± 2.5 µg/mL and 142.4 ± 28.9 h·μg/mL, respectively). Mean clearance was higher in subjects with severe hepatic dysfunction (1,098 ± 347 mL/h) than in subjects with normal hepatic function (728 ± 149 mL/h). Concentrations of albumin in subjects with severe hepatic dysfunction were lower. Assessments of micafungin plasma protein binding suggested that the higher clearance in subjects with severe hepatic dysfunction may be due to higher unbound concentrations. However, the magnitude of the differences was not considered clinically meaningful and is comparable with exposures reported elsewhere for a 100-mg dose in patients treated for invasive candidiasis. Thus, dose adjustment in subjects with severe hepatic dysfunction is not warranted. Micafungin was well tolerated in all subjects throughout the study.

Trends in the utilization of, spending on, and prices for outpatient antifungal agents in US Medicaid programs: 1991-2009

BACKGROUND

The incidence of invasive fungal infections (IFIs) has increased substantially in the recent past. Advances in medical technology, including broad-spectrum antibiotics, may increase the risk for fungal infections. Moreover, immunocompromised patients with cancer, HIV/AIDS, and/or transplants are susceptible to IFIs. Meanwhile, superficial fungal infections (SFIs) are common and can be difficult to cure.

OBJECTIVE

To provide a historical perspective on a dynamic market with expensive medications, this study describes trends in the utilization of, spending on, and average per-prescription spending on outpatient antifungal medications individually, in classes (for IFIs or SFIs), and overall, by the US Medicaid programs from 1991 to 2009.

METHODS

The publicly available Medicaid State Drug Utilization Data, maintained by the Centers for Medicare & Medicaid Services, were used. Annual prescription counts and reimbursement amounts were calculated for each of the antifungals reimbursed by Medicaid. Average per-prescription spending as a proxy for drug price was calculated by dividing reimbursement by the number of prescriptions.

RESULTS

Overall utilization for Medicaid beneficiaries remained steady, with 4.56 million prescriptions in 1991 and 4.51 million in 2009. Expenditures rose from $93.87 million to $143.76 million (in current-year US$) over the same time period. The drop in the utilization of first-generation azoles over the last 5 years of the study period can be explained in part by the movement of dual-eligibles from Medicaid to Medicare Part D and in part to a rise in fungal infections better treated with second-generation azoles or echinocandins. Whereas the average per-prescription price for generic (oral) fluconazole was $8 in 2009, the price per prescription of branded (intravenous) voriconazole was $2178.

CONCLUSIONS

Overall spending by Medicaid on outpatient antifungal medications increased more slowly than did the growth of the Medicaid programs from 1991 to 2009. However, the utilization of antifungal agents for IFIs increased almost 10-fold over this period, far outpacing the rise in the number of Medicaid beneficiaries.

Differential in vivo activities of anidulafungin, caspofungin, and micafungin against Candida glabrata isolates with and without FKS resistance mutations

We recently observed that the micafungin MICs for some Candida glabrata fks hot spot mutant isolates are less elevated than those for the other echinocandins, suggesting that the efficacy of micafungin may be differentially dependent on such mutations. Three clinical C. glabrata isolates with or without (S3) fks hot spot mutations R83 (Fks2p-S663F) and RR24 (Fks1p-S629P) and low, medium, and high echinocandin MICs, respectively, were evaluated to assess the in vivo efficacy in an immunocompetent mouse model using three doses of each echinocandin. Drug concentrations were determined in plasma and kidneys by high-performance liquid chromatography (HPLC). A pharmacokinetic-pharmacodynamic mathematical model was used to define the area under the concentration-time curve (AUC) that produced half- and near-maximal activity. Micafungin was equally efficacious against the S3 and R83 isolates. The estimates for the AUCs of each echinocandin that induced half-maximal effect (E(50)s) were 194.2 and 53.99 mg · h/liter, respectively. In contrast, the maximum effect (E(max)) for caspofungin was higher against S3 than R83, but the estimates for E(50) were similar (187.1 and 203.5 mg · h/liter, respectively). Anidulafungin failed to induce a ≥1-log reduction for any of the isolates (AUC range, 139 to 557 mg · h/liter). None of the echinocandins were efficacious in mice challenged with the RR24 isolate despite lower virulence (reduced maximal growth, prolonged lag phase, and lower kidney burden). The AUC associated with half-maximal effect was higher than the average human exposure for all drug-dose-bug combinations except micafungin and the R83 isolate. In conclusion, differences in micafungin MICs are associated with differential antifungal activities in the animal model. This study may have implications for clinical practice and echinocandin breakpoint determination, and further studies are warranted.

Current perspectives on echinocandin class drugs

It has been nearly a decade since caspofungin was approved for clinical use as the first echinocandin class antifungal agent, followed by micafungin and anidulafungin. The echinocandin drugs target the fungal cell wall by inhibiting the synthesis of β-1,3-D-glucan, a critical cell wall component of many pathogenic fungi. They are fungicidal for Candida spp. and fungistatic for moulds, such as Aspergillus fumigatus, where they induce abnormal morphology and growth properties. The echinocandins have a limited antifungal spectrum but are highly active against most Candida spp., including azole-resistant strains and biofilms. As they target glucan synthase, an enzyme absent in mammalian cells, the echinocandins have a favorable safety profile. They show potent MIC and epidemiological cutoff values against susceptible Candida and Aspergillus isolates, and the frequency of resistance is low. When clinical breakthrough occurs, it is associated with high MIC values and mutations in Fks subunits of glucan synthase, which can reduce the sensitivity of the enzyme to the drug by several thousand-fold. Such strains were not adequately captured by an early clinical breakpoint for susceptibility prompting a revised lower value, which addresses the FKS resistance mechanism and new pharmacokinetic/pharmacodynamic studies. Elevated MIC values unlinked to therapeutic failure can occur and result from adaptive cell behavior, which is FKS-independent and involves the molecular chaperone Hsp90 and the calcineurin pathway. Mutations in FKS1 and/or FKS2 alter the kinetic properties of glucan synthase, which reduces the relative fitness of mutant strains causing them to be less pathogenic. The echinocandin drugs also modify the cell wall architecture exposing buried glucans, which in turn induce a variety of important host immune responses. Finally, the future for glucan synthase inhibitors looks bright with the development of new orally active compounds.

[Differential pharmacokinetic characteristics of micafungin. Experience in special populations]

Currently, three echinocandins are available for the treatment of fungal infections. Micafungin is the latest drug to be incorporated into this group of antifungal agents. Although the mechanism of action of micafungin is similar to that of other echinocandins, this molecule has certain pharmacokinetic characteristics that distinguish it from other drugs in this group. Nowadays, there is wide information on the pharmacokinetic behavior of micafungin, mainly from patients included in clinical trials. However, there is far less knowledge of the pharmacokinetics of this echinocandin in special populations. The aim of the current review was to analyze the available information on the pharmacokinetics of micafungin in pediatric patients, the elderly, patients with renal insufficiency or liver failure, and transplant recipient.

Higher clearance of micafungin in neonates compared with adults: role of age-dependent micafungin serum binding

Micafungin, a new echinocandin antifungal agent, has been used widely for the treatment of various fungal infections in human populations. Micafungin is predominantly cleared by biliary excretion and it binds extensively to plasma proteins. Micafungin body weight-adjusted clearance is higher in neonates than in adults, but the mechanisms underlying this difference are not understood. Previous work had revealed the roles of sinusoidal uptake (Na(+) -taurocholate co-transporting peptide, NTCP; organic anion transporting polypeptide, OATP) as well as canalicular efflux (bile salt export pump, BSEP; breast cancer resistance protein, BCRP) transporters in micafungin hepatobiliary elimination. In the present study, the relative protein expression of hepatic transporters was compared between liver homogenates from neonates and adults. Also, the extent of micafungin binding to serum from neonates and adults was measured in vitro. The results indicate that relative expression levels of NTCP, OATP1B1/3, BSEP, BCRP and MRP3 were similar in neonates and in adults. However, the micafungin fraction unbound (f(u) ) in neonatal serum was about 8-fold higher than in the adult serum (0.033±0.012 versus 0.004±0.001, respectively). While there was no evidence for different intrinsic hepatobiliary clearance of micafungin between neonates and adults, our data suggest that age-dependent serum protein binding of micafungin is responsible for its higher clearance in neonates compared with adults.

Screening for antifungal peptides and their modes of action in Aspergillus nidulans

Many short cationic peptides have been identified as potent antimicrobial agents, but their modes of action are not well understood. Peptide synthesis on cellulose membranes has resulted in the generation of peptide libraries, while high-throughput assays have been developed to test their antibacterial activities. In this paper a microtiter plate-based screening method for fungi has been developed and used to test nine antibacterial peptides against the model fungus Aspergillus nidulans. Microscopical studies using sublethal peptide concentrations caused defects in polarized growth, including increased branch formation and depolarized hyphae. We characterized the mode of action for one of our target peptides, Sub5 (12 amino acids), which has already been shown to possess pharmacological potential as an antibacterial agent and is able to interact with ATP and ATP-dependent enzymes. The MIC for A. nidulans is 2 μg/ml, which is in the same range as the MICs reported for bacteria. Fluorescein isothiocyanate (FITC)-labeled Sub5 targeted the cytoplasmic membrane, particularly hyphal tips, and entered the cytoplasm after prolonged exposure, independent of endocytosis. Interestingly, Sub5 peptide treatment disturbed sterol-rich membrane domains, important for tip growth, at hyphal tips. A very similar peptide, FITC-P7, also accumulated on the cell membrane but did not have antibacterial or antifungal activity, suggesting that the cytoplasmic membrane is a first target for the Sub5 peptide; however, the antifungal activity seems to be correlated with the ability to enter the cytoplasm, where the peptides might act on other targets.

Development and validation of an in vivo Candida albicans biofilm denture model

The most common form of oral candidiasis, denture-associated stomatitis, involves biofilm growth on an oral prosthetic surface. Cells in this unique environment are equipped to withstand host defenses and survive antifungal therapy. Studies of the biofilm process on dentures have primarily been limited to in vitro models. We developed a rodent acrylic denture model and characterized the Candida albicans and mixed oral bacterial flora biofilm formation, architecture, and drug resistance in vivo, using time course quantitative culture experiments, confocal microscopy, scanning electron microscopy, and antifungal susceptibility assays. We also examined the utility of the model for measurement of C. albicans gene expression and tested the impact of a specific gene product (Bcr1p) on biofilm formation. Finally, we assessed the mucosal host response to the denture biofilm and found the mucosal histopathology to be consistent with that of acute human denture stomatitis, demonstrating fungal invasion and neutrophil infiltration. This current oral denture model mimics human denture stomatitis and should be useful for testing the impact of gene disruption on biofilm formation, studying the impact of anti-infectives, examining the biology of mixed Candida-oral bacterial flora biofilm infections, and characterizing the host immunologic response to this disease process.

In vitro investigation of the hepatobiliary disposition mechanisms of the antifungal agent micafungin in humans and rats

The purpose of the present study was to elucidate the transport mechanisms responsible for elimination of micafungin, a new semisynthetic echinocandin antifungal agent, which is predominantly cleared by biliary excretion in humans and rats. In vitro studies using sandwich-cultured rat and human hepatocytes were conducted. Micafungin uptake occurred primarily (∼75%) by transporter-mediated mechanisms in rat and human. Micafungin uptake into hepatocytes was inhibited by taurocholate (K(i) = 61 μM), Na(+) depletion (45-55% reduced), and 10 μM rifampin (20-25% reduced); these observations support the involvement of Na(+)-taurocholate-cotransporting polypeptide (NTCP/Ntcp) and, to a lesser extent, organic anion-transporting polypeptides in the hepatic uptake of micafungin. The in vitro biliary clearance of micafungin, as measured by the B-CLEAR technique, amounted to 14 and 19 μl/(min · mg protein) in human and rat, respectively. In vitro biliary excretion of micafungin was reduced by 80 and 75% in the presence of the bile salt export pump (BSEP) inhibitors taurocholate (100 μM) and nefazodone (25 μM), respectively. Biliary excretion of micafungin also was reduced in the presence of breast cancer resistance protein inhibitors [N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) (10 μM) and fumitremorgin C (10 μM)]. In vitro biliary excretion of micafungin was not significantly altered by coincubation with P-glycoprotein or multidrug resistance-associated protein 2 inhibitors. These results suggest that NTCP/Ntcp and BSEP/Bsep are primarily responsible for hepatobiliary disposition of micafungin in human and rat. Interference with hepatic bile acid disposition could be one mechanism underlying hepatotoxicity associated with micafungin in some patients.

Echinocandins: The Newest Class of Antifungals

Objective:

To review the mechanism of action, antifungal spectrum of activity, pharmacodynamics, pharmacokinetics, clinical efficacy, and safety of the echinocandins.

Data Sources:

A MEDLINE search (1982–May 2009) was conducted for articles published in the English language using the key words caspofungin, micafungin, anidulafungin, and echinocandins.

Study Selection and Data Extraction:

Medicinal chemistry, in vitro, and animal studies, as well as human trials were reviewed for information on the pharmacodynamics, pharmacokinetics, efficacy, and safety of each echinocandin. Clinical trials were reviewed and included to compare and contrast the available echinocandins.

Data Synthesis:

Three echinocandin antifungal agents are currently approved for use in the US: caspofungin, micafungin, and anidulafungin. The echinocandins have a unique mechanism of action, inhibiting β-(1,3)-d-glucan synthase, an enzyme that is necessary for the synthesis of an essential component of the cell wall of several fungi. The echinocandins display fungistatic activity against Aspergillus spp. and fungicidal activity against most Candida spp., including strains that are fluconazole-resistant. The echinocandins have been shown to be efficacious for the treatment of esophageal candidiasis, candidemia, and invasive candidiasis. In addition, caspofungin has demonstrated efficacy as empiric treatment of febrile neutropenia and salvage therapy for the treatment of invasive aspergillosis, and it is the only echinocandin approved for use in pediatric patients. Micafungin is the only echinocandin approved for use as prophylaxis against Candida infections in patients undergoing hematopoietic stem cell transplantation. Overall, resistance to echinocandins is still rare, and all agents are well tolerated, with similar adverse effect profiles and few drug–drug interactions.

Conclusions:

Echinocandins, the newest addition to the arsenal of antifungals, offer potential advantages over other classes of agents. Clinicians should assess their distinguishing characteristics, including route of metabolism, drug interaction profile, and approved indications for use, when determining which agent to include on a formulary.

Recent approaches to antifungal therapy for invasive mycoses

Invasive fungal infections with primary and opportunistic mycoses have become increasingly common in recent years and pose a major diagnostic and therapeutic challenge. They represent a major area of concern in today's medical fraternity. The occurrence of invasive fungal diseases, particularly in AIDS and other immunocompromised patients, is life-threatening and increases the economic burden. Apart from the previously known polyenes and imidazole-based azoles, newly discovered triazoles and echinocandins are more effective in terms of specificity, yet some immunosuppressed hosts are difficult to treat. The main reasons for this include antifungal resistance, toxicity, lack of rapid and microbe-specific diagnoses, poor penetration of drugs into sanctuary sites, and lack of oral or intravenous preparations. In addition to combination antifungal therapy, other novel antimycotic treatments such as calcineurin signaling pathway blockers and vaccines have recently emerged. This review briefly summarizes recent developments in the pharmacotherapeutic treatment of invasive fungal infections.

[Future role of micafungin in the treatment of invasive mycoses caused by filamentous fungi]

BACKGROUND

Micafungin is a echinocandin. It inhibits beta-1,3-D-glucan synthesis, thus achieving fungicidal activity against virtually all Candida spp., including those resistant to fluconazole, and fungistatic activity against Aspergillus spp., as well as several but not all pathogenic molds. Results from in vitro studies, animal models, small clinical trials, hint at possible future indications such as invasive aspergillosis and empirical viantifungal therapy, although currently there is little information published.

AIMS

To describe published data of micafungin as treatment against invasive mold infections, specially analysing its role in the inmunodepressed host and critical care setting.

METHODS

A systematic review of literature using the principal medical search engines was performed. Terms such as micafungin, aspergillosis, zygomycosis, invasive fungal infections, emerging fungal infections, antifungal treatment or therapy, antifungal prophylaxis, empiric or pre-emptive therapy were crossed. Febrile neutropenia patients were excluded.

RESULTS

Several studies in these setting were identified and were described in this review. Although there were no blinded randomized clinical trials published, treatment or prophylaxis of invasive aspergillosis and other invasive mould infections with micafungin described in open clinical studies were analyzed.

CONCLUSIONS

Micafungin could play a future important role as a primary or rescue therapy, alone or in combination, in the treatment or prophylaxis of invasive fungal infections caused by moulds. New randomized clinical trials are needed to confirm their efficacy.

Correlating echinocandin MIC and kinetic inhibition of fks1 mutant glucan synthases for Candida albicans: implications for interpretive breakpoints

A detailed kinetic characterization of echinocandin inhibition was performed for mutant 1,3-beta-d-glucan synthase enzymes from clinical isolates of Candida albicans with nine different FKS1 mutations resulting in high MICs. Among 14 mutant Fks1p enzymes studied, the kinetic parameters 50% inhibitory concentration and K(i) increased 50-fold to several thousandfold relative to those for the wild type. Enzymes with mutations at Ser645 (S645P, S645Y, and S645F) within hot spot 1 showed the most prominent decrease in sensitivity, while those with mutations at the N- and C-terminal ends of hot spot 1 generally retained greater sensitivity to all three drugs. Kinetic inhibitions by caspofungin, micafungin, and anidulafungin were comparable among the fks1 mutant enzymes, although absolute values did vary with specific mutations. Amino acid substitutions in Fks1p did not alter K(m) values, although some mutations decreased the V(max). Given the association of FKS1 mutations with clinical resistance, an evaluation of the kinetic parameters for the inhibition of mutant 1,3-beta-D-glucan synthase as a function of the MIC enabled an independent evaluation of the recently adopted susceptibility breakpoint for echinocandin drugs. Overall, a breakpoint MIC of >or=2 microg/ml for caspofungin captured nearly 100% of fks1 C. albicans strains when a kinetic inhibition rise threshold of <or=50-fold for the K(i) was used as a measure of susceptibility. A similar MIC breakpoint for micafungin and anidulafungin was less inclusive, and a projected MIC of >or=0.5 microg/ml was required for >95% coverage of clinical isolates. However, when MIC determinations were performed in the presence of 50% serum, all fks1 mutants showed MIC values of >or=2 microg/ml for the three echinocandin drugs. The 1,3-beta-D-glucan synthase kinetic inhibition data support the proposed susceptibility breakpoint for caspofungin in C. albicans, but a lower susceptibility breakpoint (<or=0.5 microg/ml) may be more appropriate for anidulafungin and micafungin. Overall, the data indicate that MIC testing with caspofungin may serve as a surrogate marker for resistance among the class of echinocandin drugs.

Management of Candida infections in the adult intensive care unit

The epidemiology of Candida infection in intensive care units (ICUs) and the management strategies for such infections in non-neutropenic intensive care patients are discussed in this review. Candida species are one of the leading causes of nosocomial bloodstream infections and a significant cause of morbidity in patients admitted to the ICU. Prophylactic, pre-emptive and empiric treatment strategies for Candida infections have been explored in ICU patients. Routine prophylaxis should not be administered to the whole population of ICU patients, because the concerns about the selection of azole-resistant Candida strains or the induction of resistance are justified. Treatment of fungal infections is now possible with newer antifungal agents, including newer azoles (e.g., voriconazole, posaconazole) and echinocandins (e.g., micafungin, anidulafungin). However, there is a critical need for improvement in diagnosis of invasive Candida infection in order to provide clinicians the opportunity to intervene earlier in the diseases course.

Antifungal management practices in liver transplant recipients

We sought to determine the approach to antifungal prophylaxis, and diagnostic and therapeutic practices for the management of invasive aspergillosis in liver transplant recipients. Data were collected by an electronic survey questionnaire sent to all active liver transplant programs in North America; 63% (67/106) of the sites completed the survey. Overall, 91% of the sites employed antifungal prophylaxis; 28% used universal prophylaxis and 72% targeted it toward high-risk patients. Fluconazole was the most commonly used agent for universal and targeted prophylaxis. The leading choice for mold-active agents for antifungal prophylaxis was the echinocandins. Combination therapy was used as primary therapy for invasive aspergillosis in 47%, and as salvage in 80%. Thus, a vast majority of the surveyed programs employ antifungal prophylaxis and most use targeted prophylaxis. Consideration of these practices could guide clinical trial design to optimize antifungal prophylaxis in these patients. Our findings also merit investigations to better define the role of diagnostic assays and combination therapeutic strategies for invasive aspergillosis in liver transplant recipients.

A small protein that fights fungi: AFP as a new promising antifungal agent of biotechnological value

As fungal infections are becoming more prevalent in the medical or agricultural fields, novel and more efficient antifungal agents are badly needed. Within the scope of developing new strategies for the management of fungal infections, antifungal compounds that target essential fungal cell wall components are highly preferable. Ideally, newly developed antimycotics should also combine major aspects such as sustainability, high efficacy, limited toxicity and low costs of production. A naturally derived molecule that possesses all the desired characteristics is the antifungal protein (AFP) secreted by the filamentous ascomycete Aspergillus giganteus. AFP is a small, basic and cysteine-rich peptide that exerts extremely potent antifungal activity against human- and plant-pathogenic fungi without affecting the viability of bacteria, yeast, plant and mammalian cells. This review summarises the current knowledge of the structure, mode of action and expression of AFP, and highlights similarities and differences concerning these issues between AFP and its related proteins from other Ascomycetes. Furthermore, the potential use of AFP in the combat against fungal contaminations and infections will be discussed.