Correlation between antifungal susceptibilities of Coccidioides immitis in vitro and antifungal treatment with caspofungin in a mouse model

Coccidioidomycosis: A Contemporary Review

Coccidioidomycosis, colloquially known as Valley Fever, is an invasive dimorphic fungal infection caused by Coccidioides immitis and C. posadasii. The fungi are found in the arid desert soils of the southwestern US, as well as in parts of Mexico and Central and South America. Acquisition is typically via inhalation of arthroconidia which become airborne after both natural (e.g., earthquakes, dust storms, and fires) and human-related events (e.g., military maneuvers, recreational activities, agriculture, and construction). The incidence of infection in increasing likely a result of both climatic and populational changes. Further, the recognized geographic distribution of Coccidioides spp. is expanding, as cases are being diagnosed in new areas (e.g., eastern Washington, Oregon, and Utah). Most coccidioidal infections are asymptomatic (60%); however, approximately one-third develop a pulmonary illness which is a leading cause of community-acquired pneumonia in highly endemic areas. Uncommonly (0.5–2% of cases), the infection disseminates to extrapulmonary locations (e.g., skin, bones/joints, and the central nervous system), and is most commonly seen among persons with cellular immunodeficiencies (e.g., transplant recipients, HIV, and pregnancy) and non-Caucasian races (especially African Americans and Filipinos). The diagnosis of coccidioidomycosis requires astute clinical suspicion and laboratory findings, including positive serology, cultures, and/or histopathology results. Treatment is warranted among persons with pneumonia who have risk factors for complicated disease and among those with extrapulmonary disease. Novel antifungals with improved fungicidal activity and rapidity of action with fewer side effects and drug interactions are needed. Preventive strategies (e.g., education regarding the disease, dust avoidance, mask wearing, including among select groups, antifungal prophylaxis, and surveillance laboratory testing) are advised for residents and travelers to endemic areas. Currently, no preventive vaccine is available. Coccidioidomycosis has been recognized for over a century, and an expanding wealth of knowledge has been gained regarding this emerging infectious disease which will be reviewed here.

Antifungal drugs: An updated review of central nervous system pharmacokinetics

Invasive fungal infections (IFIs) in the central nervous system (CNS) are particularly hard to treat and are associated with high morbidity and mortality rates. Four chemical classes of systemic antifungal agents are used for the treatment of IFIs (eg meningitis), including polyenes, triazoles, pyrimidine analogues and echinocandins. This review will address all of these classes and discuss their penetration and accumulation in the CNS. Treatment of fungal meningitis is based on the antifungal that shows good penetration and accumulation in the CNS. Pharmacokinetic data concerning the entry of antifungal agents into the intracranial compartments are faulty. This review will provide an overview of the ability of systemic antifungals to penetrate the CNS, based on previously published drug physicochemical properties and pharmacokinetic data, for evaluation of the most promising antifungal drugs for the treatment of fungal CNS infections. The studies selected and discussed in this review are from 1990 to 2019.

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.

Large-Scale Evaluation of In Vitro Amphotericin B, Triazole, and Echinocandin Activity against Coccidioides Species from U.S. Institutions

Large-scale testing of Coccidioides isolates has not been performed, and the frequency of clinical isolates with elevated amphotericin B or triazole MICs has not been evaluated. Coccidioides isolates (n = 581) underwent antifungal susceptibility testing. Elevated MIC values were observed for fluconazole (≥16 μg/ml, 37.3% of isolates; ≥32 μg/ml, 7.9% of isolates), itraconazole (≥2 μg/ml, 1.0% of isolates), posaconazole (≥1 μg/ml, 1.0% of isolates), and voriconazole (≥2 μg/ml, 1.2% of isolates). However, mold-active triazoles exhibited low MICs for the majority of isolates tested. Additional correlation with patient outcomes to determine the relevance of elevated MICs in Coccidioides isolates is needed.

Treatment considerations in pulmonary coccidioidomycosis

INTRODUCTION

Coccidioidomycosis is an endemic fungal infection caused by the soil-dwelling fungi, Coccidioides species. Coccidioidal infections may be asymptomatic in up to two-thirds of infected persons. Pulmonary coccidioidomycosis is the most common form of symptomatic infection. Fluconazole is the antifungal agent typically used to treat pulmonary coccidioidomycosis. Other azoles and amphotericin B products may be prescribed to treat nuanced aspects of coccidioidomycosis.

AREAS COVERED

This review discusses current literature regarding medical treatment options, including the various triazoles and amphotericin B products. In addition, we discuss uncomplicated and complicated pulmonary infections and their sequelae and the approach to managing coccidioidomycosis in certain populations of patients, such as pregnant women, transplant recipients, individuals infected with human immunodeficiency virus, and recipients of tumor necrosis factor-α inhibitors. Expert commentary: Symptomatic coccidioidomycosis can present physicians with a number of challenges, including the lack of sensitivity and specificity of diagnostic tests and lack of a standard treatment approach for all patients with the infection. Ongoing and future clinical trials will determine the optimal diagnostic, therapeutic, and prophylactic approaches, particularly for patients with comorbid conditions.

Antifungal therapeutics for dimorphic fungal pathogens

Dimorphic fungi cause several endemic mycoses which range from subclinical respiratory infections to life-threatening systemic disease. Pathogenic-phase cells of Histoplasma, Blastomyces, Paracoccidioides and Coccidioides escape elimination by the innate immune response with control ultimately requiring activation of cell-mediated immunity. Clinical management of disease relies primarily on antifungal compounds; however, dimorphic fungal pathogens create a number of challenges for antifungal drug therapy. In addition to the drug toxicity issues known for current antifungals, barriers to efficient drug treatment of dimorphic fungal infections include natural resistance to the echinocandins, residence of fungal cells within immune cells, the requirement for systemic delivery of drugs, prolonged treatment times, potential for latent infections, and lack of optimized standardized methodology for in vitro testing of drug susceptibilities. This review will highlight recent advances, current therapeutic options, and new compounds on the horizon for treating infections by dimorphic fungal pathogens.

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.

The potential of antimicrobial peptides as biocides

Antimicrobial peptides constitute a diverse class of naturally occurring antimicrobial molecules which have activity against a wide range of pathogenic microorganisms. Antimicrobial peptides are exciting leads in the development of novel biocidal agents at a time when classical antibiotics are under intense pressure from emerging resistance, and the global industry in antibiotic research and development stagnates. This review will examine the potential of antimicrobial peptides, both natural and synthetic, as novel biocidal agents in the battle against multi-drug resistant pathogen infections.

Treatment of chronic pulmonary blastomycosis with caspofungin

Current practice guidelines recommend that pulmonary blastomycosis be treated with antifungal agents such as amphotericin B and itraconazole. Echinocandins are not recommended because of poor in vitro activity against Blastomyces dermatitidis and lack of supporting clinical data. We report a case of chronic pulmonary blastomycosis treated successfully with caspofungin.

Peptide antibiotics: an alternative and effective antimicrobial strategy to circumvent fungal infections

Mycosis, caused by both filamentous fungi and pathogenic yeasts is a major concern nowadays especially in the immunocompromised patient population. The emergence of pathogenic fungi resistant to current therapies in the last few decades has intensified the search for new antifungals like cationic peptides, which are the key components of innate defense mechanism. The review provides an inventory of different peptides from a diverse array of organisms from bacteria to mammals with proven antifungal activity, their therapeutic options and also about those which are in various stages of preclinical development. Literature, on the total and semi-synthetic variants of the parent peptides that exhibit an improved antifungal activity is also reviewed.

Fungicidal versus Fungistatic: what's in a word?

BACKGROUND

Historically clinicians have preferred to use 'cidal' antifungal agents, particularly in critically ill patients. However, data to support the belief that the preferential use of a 'cidal' agent results in better patient outcomes has been lacking.

OBJECTIVE

This review examined the in vitro definitions of fungicidal and fungistatic as well as their strengths and limitations.

METHODS

A Medline search was performed in order to identify literature that examined the in vitro or in vivo impact of fungicidal and fungistatic activity. The study examined three common invasive fungal infections, namely cryptococcal meningitis, candidemia and invasive aspergillosis, where sufficient comparisons of fungicidal and fungistatic agents have been performed to allow for the evaluation of the clinical importance of these in vitro findings.

RESULTS AND CONCLUSION

A clear clinical benefit of fungicidal agents over those with fungistatic activity remains elusive. Patients with cryptococcal meningitis clearly benefit from early fungicidal therapy but require long-term suppression. The data in invasive Candida sp. infections are tantalizing and suggest that fungicidal therapy may be important. However, the data for invasive aspergillosis do not support the hypothesis that fungicidal activity improves outcomes.

Efficacy of caspofungin and posaconazole in a murine model of disseminated Exophiala infection

Disseminated phaeohyphomycosis is an uncommon infection affecting immunocompetent and immunocompromised individuals in which response to older antifungal agents has been variable. We compared the effect of six days of therapy with caspofungin, posaconazole, and amphotericin B in parallel studies of survival and fungal burden in an immunocompromised mouse model of Exophiala infection. Mice immunocompromised with cyclophosphamide were treated for 6 days starting one day after initiation of infection. Treatment regimens included amphotericin B, caspofungin, and posaconazole. In the survival studies, experimental animals were observed for 14 days. In the fungal burden tests the experimental animals were sacrificed 7 days after infection and brain and kidney burden determined. Treatment with any agent decreased mortality (P < 0.05), with 40%, 30%, and 80% observed survival of the animals treated with amphotericin B, caspofungin, and posaconazole, respectively. Amphotericin B and posaconazole treatment resulted in a decrease in fungal burden compared to untreated controls (P < 0.05). No reduction in fungal burden was noted in the caspofungin group. All three antifungals evaluated improved survival of immunocompromised mice in this otherwise fatal disseminated phaeohyphomycosis. Amphotericin B and posaconazole reduced fungal burden. Posaconazole and caspofungin appear to have potential for use in treatment of this rare infection.

Taxonomic and diagnostic markers for identification of Coccidioides immitis and Coccidioides posadasii

The ribosomal Internal Transcribed Spacer (ITS) regions of the two recognized species of Coccidioides were studied using a reference set of strains that had been previously identified with species defining microsatellite polymorphisms. Unambiguous identification of the two species proved to be possible by amplifying and sequencing the ITS region. PCR-reactions are sensitive to amplification conditions requiring their careful optimization. Stable amplification and sequencing was achieved with primers ITS3 and 4, enabling species diagnosis. Alternatively, Restriction Fragment Length Polymorphism (RFLP) of the entire ITS region using an annealing temperature of 52 degrees C with the restriction enzymes BsrI and XcmI can also distinguish the species. Three strains typifying the species, Glenospora meteuropaea, G. metamericana and Geotrichum louisianoideum, were analyzed and found to be conspecific with C. posadasii. Although these species have nomenclatural priority over C. posadasii, the latter will be proposed for conservation as it has been included in the US select agent list. In addition, Coccidioides immitis is neotypified in this report. Results of antifungal susceptibility testing did not reveal differences between the two species.

Antifungal susceptibility profiles of Coccidioides immitis and Coccidioides posadasii from endemic and non-endemic areas

Coccidioidomycosis is a systemic fungal infection endemic in Southwestern United States, Mexico, Central and South America. The causal agents are Coccidioides immitis and C. posadasii. A large number of cases of coccidioidomycosis in New York State residents were identified. We compared susceptibility profiles of these isolates and of C. immitis isolates from California using mycelial phase inoculum and CLSI (NCCLS) M38-A broth microdilution protocol. Minimum fungicidal concentrations (MFC) were also determined. Results indicated that geometric mean MICs of amphotericin B (AMB, 0.06 microg/ml), fluconazole (FLC, 8.0 microg/ml), itraconazole (ITC, 0.07 microg/ml), ketoconazole (KTC, 0.04 microg/ml), voriconazole (VRC, 0.04 microg/ml), posaconazole (PSC, 0.17 microg/ml) and caspofungin (CSP, 0.15 microg/ml) were in susceptible range as per breakpoints published for pathogenic Candida species. However, geometric MFC for FLC was relatively higher (52.4 microg/ml). Also, no significant difference in MIC and MFC values was evident for C. immitis and C. posadasii isolates. In conclusion, current methods for antifungal susceptibility testing yield reproducible profiles for Coccidioides species, which appear to be highly susceptible to most antifungal agents.

Experimental animal models of coccidioidomycosis

Experimental models of coccidioidomycosis performed using various laboratory animals have been, and remain, a critical component of elucidation and understanding of the pathogenesis and host resistance to infection with Coccidioides spp., as well as to development of more efficacious antifungal therapies. The general availability of genetically defined strains, immunological reagents, ease of handling, and costs all contribute to the use of mice as the primary laboratory animal species for models of this disease. Five types of murine models are studied and include primary pulmonary disease, intraperitoneal with dissemination, intravenous infection emulating systemic disease, and intracranial or intrathecal infection emulating meningeal disease. Each of these models has been used to examine various aspects of host resistance, pathogenesis, or antifungal therapy. Other rodent species, such as rat, have been used much less frequently. A rabbit model of meningeal disease, established by intracisternal infection, has proven to model human meningitis well. This model is useful in studies of host response, as well as in therapy studies. A variety of other animal species including dogs, primates, and guinea pigs have been used to study host response and vaccine efficacy. However, cost and increased needs of animal care and husbandry are limitations that influence the use of the larger animal species.

Diagnosis of Coccidioidomycosis by Culture: Safety Considerations, Traditional Methods, and Susceptibility Testing

The recovery of Coccidioides spp. by culture and confirmation utilizing the AccuProbe nucleic acid hybridization method by GenProbe remain the definitive diagnostic method. Biosafety considerations from specimen collection through culture confirmation in the mycology laboratory are critical, as acquisition of coccidioidomycosis by laboratory workers is well documented. The designation of Coccidioides spp. as select agents of potential bioterrorism has mandated strict regulation of their transport and inventory. The genus appears generally susceptible, in vitro, although no defined breakpoints exist. Susceptibility testing may assist in documenting treatment failures.

Coccidioidomycosis

The difficulties in managing this potentially horrific disease, with its myriad manifestations, are immense, because host factors dramatically impact outcome. Coccidioidomycosis should warrant great respect among clinicians, because, even with dramatic improvements in therapies, outcomes remain poor. Although there have been outstanding successes with these new therapies, tragic losses after years of immense patient suffering still occur. Coccidioidomycosis is a geographically restricted fungus but is one that inflicts tremendous suffering on affected patients. In addition, because of travel and the influx of susceptible hosts, dramatic increases in patients at risk for infection are seen throughout the southwest United States. The extended-spectrum azoles, such as posaconazole and voriconazole, may prove to be more efficacious in the treatment of coccidioidomycosis than prior agents, including amphotericin B, fluconazole, and itraconazole. Additional resources are needed to conduct randomised, controlled clinical trials for the treatment of this disease.

Combination therapy of disseminated coccidioidomycosis with caspofungin and fluconazole

BACKGROUND

The current recommended therapy for diffuse coccidioidal pneumonia involves initial treatment with amphotericin B deoxycholate or high-dose fluconazole, followed by an azole after clinical improvement. Amphotericin B is more frequently used as initial therapy if the patient's deterioration is rapid.

CASE PRESENTATION

A 31-year-old Korean male with coccidioidomycosis presented to the hospital with miliary infiltrates on chest X-ray (CXR) and skin rash on the face and trunk. Initially, the patient did not respond to amphotericin B deoxycholate therapy. However, following caspofungin and fluconazole combination therapy, the patient showed favourable radiological, serological, and clinical response.

CONCLUSION

This appears to be the first case of diffuse coccidioidal pneumonia with skin involvement in an immunocompetent patient who was treated successfully with caspofungin and fluconazole. Combination therapy with caspofungin and fluconazole may, therefore, be an alternative treatment for diffuse coccidioidal pneumonia that does not respond to amphotericin B deoxycholate therapy.

In vitro Activities of Caspofungin, Amphotericin B and Azoles Against Coccidioides posadasii Strains from Northeast, Brazil

Coccidioidomycosis is a systemic infection caused by the soil-dwelling dimorphic fungi Coccidioides spp. The disease is endemic in semiarid Northeast Brazil, where it is caused by C. posadasii. The aim of this study was to perform antifungal susceptibility tests of clinical and environmental strains of C. posadasii from Northeast Brazil. The in vitro activities of caspofungin, amphotericin B and azoles against clinical and environment isolates of C. posadasii were determined in accordance with the NCLLS M-38P macrodilution method. The antifungal susceptibility analysis showed that all the strains of C. posadasii (n = 10) were sensitive to caspofungin (16 microg/ml < or = MIC < or = 32 microg/ml), amphotericin B (0.0625 mug/ml < or = MIC < or = 0.125 microg/ml), ketoconazole (0.039 microg/ml < or = MIC < or = 0.156 microg/ml), itraconazole (0.125 microg/ml < or = MIC < or = 0.5 microg/ml), fluconazole (3.125 microg/ml < or = MIC < or = 6.25 microg/ml), and voriconazole (0.125 microg/ml). This study is the first description of in vitro antifungal susceptibility pattern of Brazilian strains of C. posadasii.

Management of intracranial fungal infections in patients with haematological malignancies

The incidence of, and mortality associated with, invasive fungal infections remains far higher than hoped. As a consequence of the overall increase in the incidence of such infections over time, the incidence of central nervous system (CNS) fungal infections is also increasing and, despite improvements in diagnostic techniques and the introduction of novel antifungal agents, therapy for CNS infections is still associated with discouragingly poor results. In patients with haematological malignancies, opportunistic infections with Candida or Aspergillus remain the most common infections affecting the CNS; however, opportunistic infections with less well-known fungi are becoming more common and must be considered in the differential diagnosis. New techniques for the early diagnosis of invasive fungal infections are emerging. Pharmacologic options for treating invasive fungal infections have also improved during the past few years, with new drugs becoming available that have broader antifungal spectra and better safety profiles. Other novel treatment approaches, such as combination therapy, are also being explored. Early investigations have produced encouraging results; however, large, prospective studies involving many patients are necessary to validate the widespread use of these approaches. This review analyses the existing guidelines for treatment of CNS fungal infections and the literature available on the use of new drugs to generate sets of recommendations for treatment of these life-threatening infections in patients with haematological malignancies.

Actividad in vitro de las equinocandinas ¿Cómo debe evaluarse?

Echinocandins are a novel class of antifungal drugs. They have good activity against Candida spp and Aspergillus spp. Their low selective toxicity allows their administration at high doses with few secondary side effects. We have reviewed the available data on the endpoints for these drugs in their in vitro susceptibility testing on yeasts and moulds. The microdilution broth method is the most commonly used technique and MIC-1 (80% of growth inhibition) seems to be the most reliable endpoint when yeasts are tested. This endpoint also seems to be the most appropriate for the different drugs when they are combined with echinocandins using the checkerboard method for testing yeasts. By contrast, in the case of moulds, the minimum effective concentration (MEC) correlates better with the in vivo activity than the MIC when echinocandins are tested, and when these drugs are combined with other antifungals, MIC-2 (50% of growth inhibition) seems the most appropriate endpoint. Criteria based on drug pharmacodynamics is the most useful to define the echinocandin endpoints that best correlate with their in vivo efficacy.

Coccidioides posadasii contains a single 1,3-beta-glucan synthase gene that appears to be essential for growth

1,3-beta-Glucan synthase is responsible for the synthesis of beta-glucan, an essential cell wall structural component in most fungi. We sought to determine whether Coccidioides posadasii possesses genes homologous to known fungal FKS genes that encode the catalytic subunit of 1,3-beta-glucan synthase. A single gene, designated FKS1, was identified, and examination of its predicted protein product showed a high degree of conservation with Fks proteins from other filamentous fungi. FKS1 is expressed at similar levels in mycelia and early spherulating cultures, and expression decreases as the spherules mature. We used Agrobacterium-mediated transformation to create strains that harbor DeltaFKS1::hygB, a null allele of FKS1, and hypothesize that Fks1p function is essential, due to our inability to purify this allele away from a complementing wild-type FKS1 allele in a heterokaryotic strain. The heterokaryon appears normal with respect to growth rate and arthroconidium production; however, microscopic examination of strains with DeltaFKS1::hygB alleles revealed abnormal swelling of hyphal elements.

New agents for the treatment of systemic fungal infections – current status

Systemic antifungal chemotherapy is enjoying its most dynamic era. More antifungal agents are under development than ever before, including agents in entirely new classes. Major goals of current investigations are to identify compounds with a wide spectrum of activity, minimal toxicity and a high degree of target specificity. The antifungal drugs in development include new azoles {voriconazole, posaconazole (formerly SCH-56592), ravuconazole (formerly BMS-207147)}, lipid formulations of amphotericin B, a lipid formulation of nystatin, echinocandins {anidulafungin (formerly, LY-303366, VER-002), caspofungin (formerly MK-991), micafungin (formerly FK-463)}, antifungal peptides other than echinocandins, and sordarin derivatives. This discussion reviews the currently available antifungal agents and summarises the developmental issues that surround these new systemic antifungal drugs.

Kokzidioidomykose

Coccidioidomycosis is a systemic mycosis that is acquired by inhalation. It is endemic in desert-like areas of the southwest USA and neighboring regions, but is becoming increasingly prevalent in other regions of the world as a result of widespread travel. The clinical spectrum is broad, ranging from inapparent infections or symptoms of acute respiratory infection with spontaneous recovery to various manifestations of disseminated coccidioidomycosis. Since the majority of patients with disseminated coccidioidomycosis present with cutaneous manifestations, early diagnosis of this potentially life-threatening disease by dermatologists is important. Atypical skin changes, pulmonary infiltrates and a history of travel to areas where the disease is endemic are indicative of coccidioidomycosis. For conclusive diagnosis, identification of the fungus by histopathologic examination or culture is desirable. Serological tests can be helpful for establishing the diagnosis and monitoring the course of the disease. The treatment of choice for cutaneous coccidioidomycosis is currently oral azole antifungal agents, such as itraconazole 400 mg daily, continued for 6 months after clinical response. Since relapses are frequent after discontinuation of the treatment, close clinical, serological and radiological follow-up is required for years.

In vitro activities of new antifungal agents against Chaetomium spp. and inoculum standardization

Chaetomium is an unusual etiological agent of human infections, but the mortality rate among immunocompromised patients is considerably greater than that among nonimmunocompromised individuals. We investigated the in vitro antifungal susceptibilities to novel antifungal agents of 19 strains belonging to three species of Chaetomium which have been involved in human infections, i.e., Chaetomium globosum, C. atrobrunneum, and C. nigricolor, and one strain of the closely related species Achaetomium strumarium. A modification of the NCCLS reference microdilution method (M38-A) was used to evaluate the in vitro activities of ravuconazole, voriconazole, albaconazole, and micafungin. Micafungin was not active at all, while the geometric mean MICs and minimum effective concentrations of the three triazoles were less than 0.5 and 0.4 micro g/ml, respectively.

New and emerging antifungal agents: impact on respiratory infections

Fungal pathogens are increasingly important causes of respiratory disease, yet the number of antifungal agents available for clinical use is limited. Use of amphotericin B deoxycholate is hampered by severe toxicity. Triazole agents currently available have significant drug interactions; fluconazole has a limited spectrum of activity and itraconazole was, until recently, available only in oral formulations with limited bioavailability. The development of resistance to all three agents is increasingly being recognized and some filamentous fungi are resistant to the action of all of these agents. In the past few years, new antifungal agents and new formulations of existing agents have become available.The use of liposomal amphotericin B preparations is associated with reduced, but still substantial, rates of nephrotoxicity and infusion-related reactions. An intravenous formulation of itraconazole has been introduced, and several new triazole agents have been developed, with the view of identifying agents that have enhanced potency, broader spectra of action and improved pharmacodynamic properties. One of these, voriconazole, has completed large-scale clinical trials. In addition, caspofungin, the first of a new class of agents, the echinocandins, which inhibit cell wall glucan synthesis, was approved for use in the US in 2001 as salvage therapy for invasive aspergillosis. It is hoped that the availability of these agents will have a significant impact on the morbidity and mortality of fungal respiratory infections. However, at the present time, our ability to assess their impact is limited by the problematic nature of conducting trials for antifungal therapy.

Mucosal and Systemic Fungal Infections in Patients with AIDS

In countries where highly active antiretroviral therapy (HAART) is widely available, a decrease in the incidence of fungal infections has been observed in the last 5 years compared with countries that cannot afford this treatment. Even refractory fungal infections may be controlled when HAART is given to patients, and end-stage AIDS infections, such as aspergillosis, are now only infrequently seen. In contrast, fungal infections in certain regions, such as penicilliosis in Southeast Asia or cryptococcosis in Sub-Saharan Africa, are a growing problem. Antifungal therapy for documented infections has not changed very much during recent years; however, new drugs such as caspofungin and voriconazole may be more effective in the treatment of opportunistic fungal infections, in particular, those involving resistant organisms. Secondary antifungal prophylaxis for many opportunistic pathogens can now be temporarily or even permanently discontinued in many HIV-positive patients who have a marked improvement in immune function parameters, such as CD4(+) cell counts, after initiation of HAART. The link between effective virustatic control of HIV infection and a decreasing incidence of fungal infections has been recognised; and so, despite the availability of very effective new antifungal drugs, the cornerstone of treatment and prevention of opportunistic fungal infections in patients with HIV infection is effective antiretroviral therapy including protease inhibitors.

Echinocandin antifungal drugs

The echinocandins are large lipopeptide molecules that are inhibitors of beta-(1,3)-glucan synthesis, an action that damages fungal cell walls. In vitro and in vivo, the echinocandins are rapidly fungicidal against most Candida spp and fungistatic against Aspergillus spp. They are not active at clinically relevant concentrations against Zygomycetes, Cryptococcus neoformans, or Fusarium spp. No drug target is present in mammalian cells. The first of the class to be licensed was caspofungin, for refractory invasive aspergillosis (about 40% response rate) and the second was micafungin. Adverse events are generally mild, including (for caspofungin) local phlebitis, fever, abnormal liver function tests, and mild haemolysis. Poor absorption after oral administration limits use to the intravenous route. Dosing is once daily and drug interactions are few. The echinocandins are widely distributed in the body, and are metabolised by the liver. Results of studies of caspofungin in candidaemia and invasive candidiasis suggest equivalent efficacy to amphotericin B, with substantially fewer toxic effects. Absence of antagonism in combination with other antifungal drugs suggests that combination antifungal therapy could become a general feature of the echinocandins, particularly for invasive aspergillosis.

Caspofungin: the first in a new class of antifungal agents

Caspofungin is the first approved agent from a new class of antifungals, the echinocandins. By targeting the fungal cell wall (as opposed to the fungal cell membrane), the echinocandins exhibit a unique mechanism of action relative to the other currently approved antifungal agents. Preclinical (in vitro and in vivo) studies have demonstrated activity for caspofungin against the most commonly encountered fungi in the hospital setting, namely Candida and Aspergillus species. Caspofungin is administered as a once-a-day, intravenous formulation. Notably, caspofungin is neither an inhibitor, inducer, nor metabolite of the cytochrome p450 system. To date, few drug-drug interactions have been seen for this echinocandin. A number of Phase II and III clinical studies in documented invasive candidiasis, esophageal candidiasis, and invasive aspergillosis have been completed and have demonstrated efficacy for caspofungin against all three diseases. In all studies, caspofungin manifested an excellent safety profile with few serious, drug-related adverse events or discontinuations due to drug-related adverse events. Isolated symptoms compatible with histamine release have been infrequently reported. In clinical studies, drug-related nephrotoxicity with caspofungin has been rare, and the incidence of liver transaminase elevations has been similar to the incidence seen with comparator agents. Results from a Phase III study as empirical therapy in patients with febrile neutropenia are anticipated in late 2003. Overall, caspofungin represents an important addition to the current antifungal armamentarium.

The echinocandin antifungals: an overview of the pharmacology, spectrum and clinical efficacy

For over four decades, the principal target of antifungal therapy has been the fungal cell membrane sterol ergosterol. Although this has proven to be a successful and relatively selective antifungal target, collateral toxicity to mammalian cells (amphotericin B) and drug interactions (azoles) have been by-products of agents that target the fungal cell membrane. In the 1970s, the echinocandins were identified during the screening of fungal fermentation products for new antibiotic agents. These agents were subsequently shown to inhibit production of beta(1,3)-glucan, a key structural component of the fungal cell wall. Subsequent chemical modification of these natural products has led to the development of safer, semi-synthetic beta(1,3)-glucan synthase inhibitors with enhanced microbiological and clinical efficacy against infections caused by Candida and Aspergillus species. In this review, the pharmacology, spectrum and clinical efficacy of the three leading beta(1,3)glucan synthase inhibitors (caspofungin, micafungin and anidulafungin), which have completed phase III clinical trials, will be discussed and a perspective for the role of these agents in the management of life-threatening mycoses will be offered.

Caspofungin in the treatment of candidosis and aspergillosis

Antifungal agents can be classified by their site of action in fungal cells, which can have important implications for both efficacy and tolerability. Currently available agents include the polyenes, nucleoside analogs, and the azoles. With the exception of 5-fluorocytosine, all agents act by interfering with the structural or functional integrity of the fungal plasma membrane. However, the non-selective nature of this therapeutic target results in concomitant cross-inhibition (or toxicity) in mammalian cells. New compounds that interfere with the fungal cell wall--a target not present in mammalian cells--therefore constitute an important focus of current clinical research. Caspofungin, the first representative of a new class of antifungals that inhibit beta-(1,3)-D-glucan synthesis, exerts potent activity against Candida and Aspergillus spp. and appears to be generally well tolerated. This paper reviews the data on caspofungin.

Caspofungin

Caspofungin, the first inhibitor of fungal beta-1,3 glucan synthesis to receive approval by the United States Food and Drug Administration, is effective for the treatment of mucosal and invasive candidiasis and invasive aspergillosis. It is also active in vitro and in animal models against a number of other filamentous and dimorphic endemic fungi and in animal models of Pneumocystis carinii infection. In vitro studies and some animal studies almost always indicate an absence of antagonism when caspofungin is combined with azole or polyene antifungal agents. Caspofungin has an excellent safety profile. Caspofungin may prove to be useful in empirical therapy for suspected invasive fungal infections. Additional clinical trial data that expand our knowledge of the usefulness of caspofungin for these and other mycoses, including its administration in combination with other antifungal agents, is anticipated. Caspofungin is an important addition to the antifungal pharmacopoeia.

Caspofungin: first approved agent in a new class of antifungals

Caspofungin (Cancidas, Merck & Co. Inc.) is the first echinocandin antifungal agent to gain FDA-approval for use in the US. It has excellent clinical activity against Candida spp. and Aspergillus spp. but lacks significant activity against Cryptococcus neoformans. Caspofungin may have some activity against dimorphic fungi such as Histoplasma capsulatum and Coccidioides immitis, but no clinical data is available for treatment of these infections. Caspofungin has demonstrated poor activity against most filamentous fungi in vitro. Several clinical trials have demonstrated its efficacy in the treatment of oropharyngeal, oesophageal and invasive candidiasis, as well as invasive aspergillosis. As a result of caspofungin's unique mechanism of action, and the high morbidity and mortality of invasive fungal infections, there is considerable interest in using this new antifungal agent as part of a combination antifungal therapy. In vitro studies and small case series indicate that caspofungin does not appear to be antagonistic when combined with other antifungals, such as itraconazole, voriconazole or amphotericin B against Aspergillus spp. Caspofungin exerts concentration-dependent killing effects in many different in vitro and animal models of disseminated fungal infection. The usual daily dose is 50 mg/day i.v. following a 70 mg i.v. loading dose. However, higher caspofungin doses have been safely administered and up to 70 mg/day can be administered for patients who fail to respond to lower doses. Caspofungin has an excellent safety profile with reduced toxicities, compared to other licensed antifungal agents. Fever, thrombophlebitis, headache and liver enzyme elevations were the most common drug-related side effects reported in clinical trials so far. Additional data are needed to document its safety in long-term use, and with higher doses in patients with invasive fungal infections. Caspofungin is a promising agent as first-line therapy for invasive candidiasis, and as salvage therapy for invasive aspergillosis. However, more clinical data are needed to define its role as primary therapy for invasive aspergillosis, and its role in combination antifungal therapy.

Antifungal pharmacotherapy for invasive mould infections

The incidence of invasive mould infections is increasing and is associated with significant morbidity and mortality. Among the most prevalent of these infections are those caused by Aspergillus and Fusarium species. Invasive disease caused by moulds frequently presents as a pulmonary infection, but haematogenous infection can occur. Some moulds cause cutaneous disease through either direct inoculation of the skin or secondary spread to the skin after dissemination from another body site. Early diagnosis can often be difficult and, unfortunately, diagnosis occurs late in the course of illness in many cases. Treatment options have historically been limited by the need for intravenous administration (amphotericin B), significant toxicities (amphotericin B), lack of reliable in vitro activity (e.g., amphotericin B in Fusarium and Scedosporium apiospermum infections) and relative lack of clinical experience with newer agents. The recent approval of voriconazole (Vfend, Pfizer) introduces a treatment option that demonstrates both in vitro and in vivo activity against a variety of moulds. With the recent development of the new echinocandin class of antifungal agents and newer broad-spectrum azole antifungal agents with in vitro mould activity, there is a renewed emphasis on fungal treatment strategies. Antimould therapy presents challenges in adverse effect avoidance and management, drug interactions and pharmacoeconomic considerations. Furthermore, combination therapy is being explored with these various new antifungal agents. The administration of an optimal fungicidal therapy early in the course of the illness and control of the underlying disease are vital to prevent complications and mortality from these tenacious mycoses.

Evaluation of broth microdilution testing parameters and agar diffusion Etest procedure for testing susceptibilities of Aspergillus spp. to caspofungin acetate (MK-0991)

The NCCLS M38-A document does not describe guidelines for testing caspofungin acetate (MK-0991) and other echinocandins against molds. This study evaluated the susceptibilities of 200 isolates of Aspergillus fumigatus, A. flavus, A. nidulans, A. niger, and A. terreus to caspofungin (MICs and minimum effective concentrations [MECs]) by using standard RPMI 1640 (RPMI) and antibiotic medium 3 (M3), two inoculum sizes (10(3) and 10(4) CFU/ml), and two MIC determination criteria (complete [MICs-0] and prominent growth inhibition [MICs-2]) at 24 and 48 h. Etest MICs were also determined. In general, caspofungin MIC-2 and MEC pairs were comparable with both media and inocula (geometric mean ranges of MECs and MICs, respectively, with larger inoculum: 0.12 to 0.64 microg/ml and 0.12 to 0.44 microg/ml with RPMI versus 0.04 to 0.51 microg/ml and 0.03 to 0.21 microg/ml with M3); however, MEC results were less influenced by testing conditions than MICs, especially with the larger inoculum. Overall, the agreement between caspofungin Etest MICs and broth dilution values was higher with MECs obtained with M3 (>90%) and the large inoculum than under the other testing conditions. Because RPMI is a more stable and chemically defined medium than M3, the determination at 24 h of the easier visual MECs with RPMI and the inoculum recommended in the M38-A document appears to be a suitable procedure at present for in vitro testing of caspofungin against Aspergillus spp. Future in vitro correlations with in vivo outcome of both microdilution and Etest procedures may detect more-relevant testing conditions.

Microbial natural products as a source of antifungals

The vast number and variety of chemotherapeutic agents isolated from microbial natural products and used to treat bacterial infections have greatly contributed to the improvement of human health during the past century. However, only a limited number of antifungal agents (polyenes and azoles, plus the recently introduced caspofungin acetate) are currently available for the treatment of life-threatening fungal infections. Furthermore, the prevalence of systemic fungal infections has increased significantly during the past decade. For this reason, the development of new antifungal agents, preferably with novel mechanisms of action, is an urgent medical need. A selection of antifungal agents in early stages of development, produced by micro-organisms, is summarized in this review. The compounds are classified according to their mechanisms of action, covering inhibitors of the synthesis of cell wall components (glucan, chitin and mannoproteins), of sphingolipid synthesis (serine palmitoyltransferase, ceramide synthase, inositol phosphoceramide synthase and fatty acid elongation) and of protein synthesis (sordarins). In addition, some considerations related to the chemotaxonomy of the producing organisms and some issues relevant to antifungal drug discovery are also discussed.

Laboratory evaluation of new antifungal agents against rare and refractory mycoses

PURPOSE OF REVIEW

An increase in refractory invasive fungal infections in the setting of marrow/solid organ transplantation and other immune-compromising clinical entities has provided the impetus for the development of new, more efficacious/less toxic antifungal agents. This review (1) examines currently available laboratory methods for the in-vitro evaluation of these new agents against both yeasts and filamentous fungi; (2) provides a summary of the most attractive investigational agents currently undergoing clinical trials/development; and (3) outlines the major refractory mycoses in contemporary medicine.

RECENT FINDINGS

Fluconazole-resistant Candida spp., Trichosporon spp., zygomycetous genera, the endemic mycoses, Scedosporium, Aspergillus, and Fusarium spp., and an ever-expanding list of lesser-known hyaline and phaeoid genera inciting invasive fungal infections comprise the bulk of refractory mycoses in the immune-compromised host. In-vitro data generated from reference-based antifungal susceptibility testing methods indicate an increased armamentarium of potentially efficacious agents against most of these mycoses.

SUMMARY

The newly approved antifungal agents caspofungin and voriconazole, used either as monotherapy or in combination regimens, have a significantly improved spectrum of activity over previously available therapeutic options. Correlation of clinical outcomes with investigational agents demonstrating in-vivo/in-vitro activity will provide critical information needed for the development of clinically significant minimum inhibitory concentration interpretative breakpoints.

Comparative evaluation of disk diffusion with microdilution assay in susceptibility testing of caspofungin against Aspergillus and Fusarium isolates

We compared the disk diffusion and broth microdilution methods for susceptibility testing of caspofungin against Aspergillus (n = 78) and Fusarium (n = 22) isolates. Microdilution testing followed the NCCLS M-38P guidelines but was performed in antibiotic medium 3 supplemented to 2% glucose (AM3). Disk diffusion assays were performed on AM3 agar plates with a 2- micro g caspofungin disk. By both methods, caspofungin showed favorable activity against Aspergillus isolates and no activity against Fusarium isolates. In the disk-based format, intrazonal growth that was not influenced by the drug concentration gradient was consistently observed for all of the Aspergillus isolates tested.

Caspofungin: an echinocandin antifungal agent

BACKGROUND

The mainstays of treatment for nosocomial fungal infections have been amphotericin B and azole derivatives. Caspofungin acetate is a new echinocandin antifungal agent with a mechanism of action that targets a structural component of the fungal cell wall.

OBJECTIVE

This article describes the pharmacologic properties and potential clinical usefulness of caspofungin.

METHODS

Relevant information was identified through searches of MEDLINE (1966-September 2001). Iowa Drug Information Service (1966-September 2001), and International Pharmaceutical Abstracts (1970-September 2001), as well as meeting abstracts of the Infectious Diseases Society of America and the Interscience Conference on Antimicrobial Agents and Chemotherapy (1996-2001), using the terms caspofungin, MK-0991, pneumocandin, echinocandin, candin, and beta-(1,3)-glucan inhibitor.

RESULTS

In vitro, caspofungin exhibits antifungal activity against an array of clinically important yeasts and molds, including Candida and Aspergillus spp. The proposed susceptibility breakpoint for caspofungin against Candida spp, the most common cause of nosocomial fungal infections, is a minimum inhibitory concentration of < or =1 microg/mL. In humans, caspofungin has a volume of distribution of 9.67 L, is extensively bound to albumin (97%), has a plasma elimination half-life of 9 to 11 hours, and is metabolized to inactive metabolites in the liver. Dose adjustment based on age, sex, race, or renal function does not appear to be necessary, although patients with moderate hepatic insufficiency (Child-Pugh score 7-9) should receive a lower maintenance dose. The results of clinical trials, although somewhat preliminary, suggest that caspofungin is effective in the treatment of esophageal and oropharyngeal candidiasis and invasive aspergillosis. When combined with other antifungal agents, caspofungin produces a synergistic or additive effect against a variety of clinically important fungi. The most commonly reported adverse events with caspofungin have included fever, infusion-related reactions, headache, nausea, elevations in liver transaminase levels, and histamine-type reactions. The recommended dosage in adults is 70 mg IV on day 1 followed by 50 mg/d, with the duration of treatment depending on the severity of the patient's underlying condition and the clinical response.

CONCLUSION

Although additional studies are needed, caspofungin appears to be a promising agent for the treatment of patients with difficult-to-treat or life-threatening fungal infections.