Prophylactic effect of FK463, a novel antifungal lipopeptide, against Pneumocystis carinii infection in mice

Performance of a Real Time PCR for Pneumocystis jirovecii Identification in Induced Sputum of AIDS Patients: Differentiation between Pneumonia and Colonization

Pneumocystis jirovecii pneumonia (PcP) remains an important cause of morbimortality worldwide and a diagnostic challenge. Conventional methods have low accuracy, hardly discriminating colonization from infection, while some new high-cost or broncho-alveolar lavage-based methods have limited usefulness in developing countries. Quantitative PCR (qPCR) tests may overcome these limitations due to their high accuracy, possibility of automation, and decreasing cost. We evaluated an in-house qPCR targeting the fungus mtSSU gene using induced sputum. Sensitivity of the assay (ten target gene copies/assay) was determined using recombinant plasmids. We prospectively studied 86 AIDS patients with subacute respiratory symptoms in whom PcP was suspected. qPCR results were determined as quantification cycles (Cq) and compared with a qualitative PCR performed in the same IS, serum 1,3-β-D-Glucan assay, and a clinical/laboratory/radiology index for PcP. The qPCR clustered the patients in three groups: 32 with Cq ≤ 31 (qPCR+), 45 with Cq ≥ 33 (qPCR-), and nine with Cq between 31-33 (intermediary), which, combined with the other three analyses, enabled us to classify the groups as having PcP, not P. jirovecii-infected, and P. jirovecii-colonized, respectively. This molecular assay may contribute to improve PcP management, avoiding unnecessary treatments, and our knowledge of the natural history of this infection.

Anidulafungin as an alternative treatment for Pneumocystis jirovecii pneumonia in patients who cannot tolerate trimethoprim/sulfamethoxazole

Evidence supporting the use of an echinocandin alone as an alternative agent for the treatment of Pneumocystis jirovecii pneumonia (PCP) is limited and controversial. This retrospective cohort study was conducted at National Taiwan University Hospital from 1 July 2015 to 31 December 2017. Using multivariable Cox regression analyses, the outcomes of patients receiving trimethoprim/sulfamethoxazole (TMP-SMZ) or anidulafungin single therapy as an alternative treatment for PCP were investigated. A total of 207 patients with PCP were screened and 170 patients were included in the final analysis, among whom 134 (78.8%) received TMP-SMZ and 36 (21.2%) received anidulafungin as alternative anti-PCP treatment. Overall 60-day mortality was 34.1% (58/170), and 60-day mortality did not differ significantly between the anidulafungin group (38.9%; 14/36) and the TMP-SMZ group (32.8%; 44/134) (P = 0.554). Age ≥60 years [hazard ratio (HR) = 1.840, 95% confidence interval (CI) 1.039-3.259; P = 0.036] and HIV infection (HR = 0.102, 95% CI 0.013-0.771; P = 0.027) independently predicted 60-day mortality. Patients with lower SpO₂/FiO₂ ratio (HR = 0.994, 95% CI 0.990-0.998; P = 0.005) showed a higher 60-day mortality. In the Kaplan-Meier survival analysis, anidulafungin as alternative anti-PCP treatment was not correlated with higher mortality (P = 0.605). Using TMP-SMZ or anidulafungin as alternative anti-PCP treatment had similar 60-day mortality. These findings suggest that anidulafungin therapy may be an effective and alternative treatment for PCP in patients who cannot tolerate TMP-SMZ.

Role of FKS Gene in the Susceptibility of Pathogenic Fungi to Echinocandins

Echinocandins are antifungal agents that specifically inhibit the biosynthesis of 1,3-β-D-glucan, a major structural component of fungal cell walls. Echinocandins are recommended as first-line or alternative/salvage therapy for candidiasis and aspergillosis in antifungal guidelines of various countries. Resistance to echinocandins has been reported in recent years. The mechanism of echinocandin resistance involves amino acid substitutions in hot spot regions of the FKS gene product, the catalytic subunit of 1,3-β-D-glucan synthase. This resistance mechanism contributes to not only acquired resistance in Candida spp., but also inherent resistance in some pathogenic fungi. An understanding of the echinocandin resistance mechanism is important to develop both effective diagnosis and treatment options for echinocandin-resistant fungal diseases.

Echinocandins in antifungal pharmacotherapy

Objectives

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

Key findings

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

Conclusions

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

Echinocandin antifungals: review and update

The echinocandins are a new and unique class of antifungal agents that act on the fungal cell wall by way of noncompetitive inhibition of the synthesis of 1,3-beta-glucans. All agents of this class are of parenteral formulation, with no oral preparations available. Caspofungin (Cancidas) was the first approved echinocandin, followed recently by micafungin (Mycamine) and anidulafungin (Eraxis). The precise role of the echinocandins in the antifungal armamentarium is still unfolding. Caspofungin is approved for the treatment of candidal esophagitis and candidemia, salvage therapy of Aspergillus infections and for empirical therapy of febrile neutropenia. Micafungin is likewise approved for candidal esophagitis, in addition to antifungal prophylaxis for hematopoietic stem cell transplant recipients. Anidulafungin is also approved for treatment of candidal esophagitis, as well as therapy of candidemia. There has been anecdotal use of these agents to treat less common fungal pathogens, as well as limited use as a component of combination antifungal therapy. The echinocandins are an important addition to the antifungal armamentarium in the treatment of fungal infections in both immunocompromised patients and those with normal immunity.

Colonization by Pneumocystis jirovecii and its role in disease

Although the incidence of Pneumocystis pneumonia (PCP) has decreased since the introduction of combination antiretroviral therapy, it remains an important cause of disease in both HIV-infected and non-HIV-infected immunosuppressed populations. The epidemiology of PCP has shifted over the course of the HIV epidemic both from changes in HIV and PCP treatment and prevention and from changes in critical care medicine. Although less common in non-HIV-infected immunosuppressed patients, PCP is now more frequently seen due to the increasing numbers of organ transplants and development of novel immunotherapies. New diagnostic and treatment modalities are under investigation. The immune response is critical in preventing this disease but also results in lung damage, and future work may offer potential areas for vaccine development or immunomodulatory therapy. Colonization with Pneumocystis is an area of increasing clinical and research interest and may be important in development of lung diseases such as chronic obstructive pulmonary disease. In this review, we discuss current clinical and research topics in the study of Pneumocystis and highlight areas for future research.

Comparison of echinocandin antifungals

The incidence of invasive fungal infections, especially those due to Aspergillus spp. and Candida spp., continues to increase. Despite advances in medical practice, the associated mortality from these infections continues to be substantial. The echinocandin antifungals provide clinicians with another treatment option for serious fungal infections. These agents possess a completely novel mechanism of action, are relatively well-tolerated, and have a low potential for serious drug-drug interactions. At the present time, the echinocandins are an option for the treatment of infections due Candida spp (such as esophageal candidiasis, invasive candidiasis, and candidemia). In addition, caspofungin is a viable option for the treatment of refractory aspergillosis. Although micafungin is not Food and Drug Administration-approved for this indication, recent data suggests that it may also be effective. Finally, caspofungin- or micafungin-containing combination therapy should be a consideration for the treatment of severe infections due to Aspergillus spp. Although the echinocandins share many common properties, data regarding their differences are emerging at a rapid pace. Anidulafungin exhibits a unique pharmacokinetic profile, and limited cases have shown a potential far activity in isolates with increased minimum inhibitory concentrations to caspofungin and micafungin. Caspofungin appears to have a slightly higher incidence of side effects and potential for drug-drug interactions. This, combined with some evidence of decreasing susceptibility among some strains of Candida, may lessen its future utility. However, one must take these findings in the context of substantially more data and use with caspofungin compared with the other agents. Micafungin appears to be very similar to caspofungin, with very few obvious differences between the two agents.

Echinocandin treatment of pneumocystis pneumonia in rodent models depletes cysts leaving trophic burdens that cannot transmit the infection

Fungi in the genus Pneumocystis cause pneumonia (PCP) in hosts with debilitated immune systems and are emerging as co-morbidity factors associated with chronic diseases such as COPD. Limited therapeutic choices and poor understanding of the life cycle are a result of the inability of these fungi to grow outside the mammalian lung. Within the alveolar lumen, Pneumocystis spp., appear to have a bi-phasic life cycle consisting of an asexual phase characterized by binary fission of trophic forms and a sexual cycle resulting in formation of cysts, but the life cycle stage that transmits the infection is not known. The cysts, but not the trophic forms, express β -1,3-D-glucan synthetase and contain abundant β -1,3-D-glucan. Here we show that therapeutic and prophylactic treatment of PCP with echinocandins, compounds which inhibit the synthesis of β -1,3-D-glucan, depleted cysts in rodent models of PCP, while sparing the trophic forms which remained in significant numbers. Survival was enhanced in the echincandin treated mice, likely due to the decreased β -1,3-D-glucan content in the lungs of treated mice and rats which coincided with reductions of cyst numbers, and dramatic remodeling of organism morphology. Strong evidence for the cyst as the agent of transmission was provided by the failure of anidulafungin-treated mice to transmit the infection. We show for the first time that withdrawal of anidulafungin treatment with continued immunosuppression permitted the repopulation of cyst forms. Treatment of PCP with an echinocandin alone will not likely result in eradication of infection and cessation of echinocandin treatment while the patient remains immunosuppressed could result in relapse. Importantly, the echinocandins provide novel and powerful chemical tools to probe the still poorly understood bi-phasic life cycle of this genus of fungal pathogens.

A Clinical Review of Echinocandins in Pediatric Patients

OBJECTIVE

To identify and evaluate available data on pediatric echinocandin use.

DATA SOURCES

A PubMed search, limited to English-language articles, was conducted (1990-August 2009) using the search terms echinocandin, pediatric, child, pharmacokinetics, caspofungin, micafungin, and anidulafungin. Additional articles were retrieved from citations of selected references.

STUDY SELECTION AND DATA EXTRACTION

Relevant information on the pharmacology, pharmacokinetics, efficacy, and safety of echinocandins in children was selected. Clinical trials, retrospective reviews, and case series were identified and evaluated. Data from these sources were included in this review.

DATA SYNTHESIS

Caspofungin is the only echinocandin approved by the Food and Drug Administration for use in children. Pediatric pharmacokinetics has been evaluated with all 3 echinocandins but is limited with anidulafungin. Micafungin is the most well-studied agent in prospective clinical trials for antifungal prophylaxis in stem cell transplantation and treatment of invasive fungal infections. Caspofungin has been studied prospectively for febrile neutropenia and treatment of invasive fungal infections, but most published data are from retrospective reviews or case reports. One case report of anidulafungin for neonatal candidiasis has been published. The role of echinocandins in the management of invasive pediatric fungal infections has expanded. Micafungin and caspofungin are recommended as primary or alternative treatment of candidemia and esophageal or invasive candidiasis, and as salvage therapy for invasive aspergillosis. Micafungin is recommended for neutropenic prophylaxis in stem cell transplantation, while caspofungin may be used in febrile neutropenia as an alternative to azoles. Dosing has been well established for caspofungin only in children 3 months of age and above. Anidulafungin should be avoided in children until more pharmacokinetic and clinical data become available.

CONCLUSIONS

Further comparative trials are needed to more clearly define the role of echinocandins, either as monotherapy or in combination for difficult-to-treat infections, in the pediatric population.

[Anidulafungin: a new therapeutic approach in antifungal therapy. Pharmacology of anidulafungin]

Anidulafungin is a new echinocandin antifungal agent which inhibits beta-1,3-D-glucan synthase and disrupts fungal cell-wall synthesis. It has marked antifungal activity against Candida spp. and Aspergillus spp., including amphotericin B and triazole resistant strains. Due to the limited oral availability, anidulafungin in clinical use is available for parenteral administration only. Elimination of anidulafungin takes place via slow non-enzymatic degradation to inactive metabolites. Less than 10% and 1% of the initially administered drug is excreted unchanged into feces and urine, respectively. It does not require dosage adjustment in subjects with hepatic or renal impairment established. Anidulafungin is generally well tolerated. Adverse events appear not to be dose or infusion related. The most common treatment related adverse events are phlebitis, headache, nausea, vomiting and pyrexia. The lack of interactions with tacrolimus, cyclosporine and corticosteroids and its limited toxicity profile places anidulafungin as an attractive new option for the treatment of invasive fungal infections especially in transplant patients.

Micafungin sodium, the second of the echinocandin class of antifungals: theory and practice

Micafungin is a new drug in the echinocandin class and is currently being investigated in Phase III clinical trials. Like other echinocandins, it inhibits 1,3-beta-D-glucan synthesis, thus achieving fungicidal activity against virtually all Candida spp., including those resistant to fluconazole, and fungistatic activity against Aspergillus spp. Micafungin sodium is available for intravenous administration only. It has a favorable safety and drug-drug interaction profile. Micafungin has been approved by the US FDA for treatment of esophageal candidiasis and for antifungal prophylaxis during the pre-engraftment phase in patients undergoing hematopoietic stem cell transplantation. Considering the competitive pricing as well as the good tolerability and efficacy, at present micafungin seems to be another choice for both of these indications. Current research has proven micafungin sodium to add a rational and effective option to the antifungal armamentarium, especially in esophageal candidiasis refractory to fluconazole treatment, in those intolerant to triazoles or in patients needing concomitant therapy interacting with triazoles. In addition to the current indications, recent uncontrolled clinical trials have demonstrated a marked success in the treatment of candidemia and invasive candidiasis. Results from in vitro studies, animal models, small clinical trials, as well as the obvious comparison with the more established caspofungin, hint at possible future indications such as invasive aspergillosis and empirical antifungal therapy. However, preclinical data on micafungin is inconsistent and published well-designed clinical studies are scarce. More controlled and sufficiently scaled trials are imperative in order to establish micafungin as a reliable and safe option in clinical practice.

The use of caspofungin in HIV-infected individuals

Fungal infections are a significant cause of HIV-related morbidity and mortality, particularly in the developing world, but also in countries with access to highly active antiretroviral therapy. New agents are essential to improve present efficacy rates, particularly in cases of drug resistance. Caspofungin is a new antifungal from the echinocandin class and is licensed for the treatment of candidal infections and as a second-line therapy for invasive aspergillosis. In this paper, the pharmacology, interaction and susceptibility data for this agent are reviewed and studies supporting the use of this agent in HIV-infected individuals are examined. Finally, evidence for the use of caspofungin for the treatment of Pneumocystis jiroveci pneumonia, an unlicensed indication, including a case series from our own unit is explored.

Progression of Pneumocystis jiroveci Pneumonia in Patients Receiving Echinocandin Therapy

Echinocandins are a novel class of antifungal drugs that target beta (1, 3)-D-glucan synthesis. Animal studies have shown that these agents have activity against Pneumocystis jiroveci infection; however, clinical data are lacking. We reviewed all cases of proven P. jiroveci pneumonia (PCP) in non-human immunodeficiency virus-infected patients at our hospital over a 5 year period (2001-2005). Two patients received conventional PCP treatment and concomitant use of echinocandins for presumed invasive aspergillus. In both cases, PCP progressed, and the patient died. The use of echinocandins in the prevention or treatment of PCP cannot be recommended without evidence to support their effectiveness.

The echinocandins: comparison of their pharmacokinetics, pharmacodynamics and clinical applications

Caspofungin, micafungin and anidulafungin are three drugs of the echinocandin class of antifungals available for intravenous treatment of invasive candidiasis and aspergillosis. They exhibit high in vitro and in vivo activities against Candida spp. and Aspergillus spp. In various clinical studies investigating candidemia and invasive candidiasis, Candida esophagitis, and fever in neutropenia, the clinical efficacy of the echinocandin tested was similar to that of established antifungals. Antifungal activity against strains no longer susceptible to conventional antifungal agents, such as fluconazole and amphotericin B suggests that echinocandins can be used as salvage therapy in life-threatening fungal infections. There is no cross-resistance to other antifungals. Excellent safety and tolerability of treatment with caspofungin has been documented over a total of 4.3 million patient days. Echinocandins are poor substrates of the cytochrome P450 enzyme family and can be safely co-administered with most drugs without the need for dosage adaptation. No dose reduction is required in renal impairment. A reduction in the daily maintenance dose has been recommended for caspofungin, but not for micafungin and anidulafungin in patients presenting with mild to moderate hepatic failure.

Influence of type of cancer and hematopoietic stem cell transplantation on clinical presentation of Pneumocystis jiroveci pneumonia in cancer patients

Pneumocystis jiroveci pneumonia is a common infection in patients with AIDS but an infrequent cause of pneumonia in cancer patients. Little is known about the impact of cancer type and hematopoietic stem cell transplantation on the presentation and outcome of P. jiroveci pneumonia in cancer patients. A retrospective cohort study of all patients with cancer and P. jiroveci pneumonia cared for at The M.D. Anderson Cancer Center during 1990-2003 was conducted. Eighty episodes of P. jiroveci pneumonia in 79 patients were identified. In most (67%) episodes, patients had a hematologic malignancy. In 23 (29%) episodes, patients had undergone hematopoietic stem cell transplantation. Twenty-seven percent of patients with histopathologically confirmed P. jiroveci pneumonia had nodular infiltrates on the radiographic study. Pleural effusion and pneumothorax were more common in patients with hematopoietic stem cell transplantation than in those with solid tumors. Clinical suspicion of P. jiroveci pneumonia was less common in patients with nodular infiltrates than in those without such a radiographic finding (7 vs. 39%; p=0.002). Twenty-six of 76 (34%) patients with data available died of P. jiroveci pneumonia. Predictors of death by univariate analysis included older age, tachypnea, high APACHE II score, use of mechanical ventilation or vasopressors, lower arterial pH level, absence of interstitial component, pneumothorax, and comorbid conditions (all p<0.05). Multivariate analysis identified the use of mechanical ventilation as an independent predictor of death. Death attributable to P. jiroveci pneumonia appeared to be higher in patients with hematopoietic stem cell transplantation. The clinical presentation of P. jiroveci pneumonia in cancer patients may be affected by the category of cancer and the history of hematopoietic stem cell transplantation. P. jiroveci pneumonia remains a rare yet severe infection in cancer patients.

Micafungin: a new echinocandin

Micafungin, a potent inhibitor of 1,3-beta-D-glucan synthase, has become the second available agent in the echinocandins class that is approved for use in clinical practice. This agent shares with caspofungin an identical spectrum of in vitro activity against Candida albicans, non-albicans species of Candida, and Aspergillus species, as well as several but not all pathogenic molds. If anything, its in vitro activity appears to be superior to that of caspofungin, although the clinical relevance of this observation is unclear. The clinical role of micafungin appears to be similar to that of caspofungin, although clinical data are still lacking at this stage, with initial approval only for treatment of esophageal candidiasis and prophylaxis in subjects with neutropenia. Pharmacokinetic and pharmacodynamic studies and reports of adverse effects and safety have reported similar but not identical results to those of other agents in the echinocandin class. Factors such as acquisition costs and the potential for resistance development may be more relevant to its widespread use than in vitro and in vivo data comparisons with caspofungin.

Efficacy of micafungin alone or in combination against experimental pulmonary aspergillosis

Mortality from invasive pulmonary aspergillosis approaches 80% with few useful therapeutic options available. In these studies, we examined the efficacy of micafungin (MICA) alone or in combination with other antifungals in a model of pulmonary aspergillosis in immunosuppressed DBA/2 mice infected intranasally with conidia of Aspergillus fumigatus 10AF. In the initial study, groups of mice were given saline, or 1, 3 or 10 mg kg(-1) of MICA b.i.d., s.c. All saline controls, and 90% of untreated mice succumbed to infection. The efficacy of MICA was difficult to assess because of an apparent toxicity at 10 mg kg(-1). MICA given at 1 mg/kg significantly prolonged survival over the saline controls (P = 0.008). MICA at 3 or 10 mg kg(-1) versus the saline controls approached significance. No treatment regimen differed in efficacy. The efficacy of combination therapy was assessed, with mice given either no treatment, MICA at 1 mg/kg/dose, 0.8 mg kg(-1) of intravenous amphotericin B (AMB), 100 mg kg(-1) of oral itraconazole (ICZ), or 100 mg/kg/dose of twice-daily subcutaneous nikkomycin Z (NIK). AMB alone and MICA + AMB or MICA +NIK significantly prolonged survival (P < 0.05 - 0.02) over that of the controls. ICZ alone, ICZ+MICA and NIK alone did not significantly prolong survival. MICA alone at 1 mg/kg approached significance in prolonging survival. The combination of MICA and ICZ appeared to be potentially antagonistic. Although AMB+MICA was efficacious, no synergistic activity was noted for any of the regimens. Overall, these results indicate that MICA has moderate activity against pulmonary aspergillosis and might be useful in combination with conventional AMB.

Micafungin: pharmacology, experimental therapeutics and clinical applications

Invasive fungal infections are important causes of morbidity and mortality in hospitalised patients. Current therapy with amphotericin B and antifungal triazoles has overlapping targets and is limited by toxicity and resistance. Echinocandins are a new class of antifungal drugs, which inhibit the synthesis of 1,3-beta-D-glucan. This homopolysaccharide is an important component of the cell wall of many pathogenic fungi, providing osmotic stability and functioning in cell growth and cell division. Micafungin, which is a member of the echinocandin class, exhibits in vitro fungicidal or fungistatic activity against a variety of fungal pathogens which include Candida and Aspergillus species but not Cryptococcus, Fusarium or Zygomycetes. Micafungin demonstrates linear pharmacokinetics, which are not altered by drugs metabolised through the P450 enzyme system. The preclinical and clinical data strongly support the development of micafungin for treatment of proven or suspected mucosal and invasive Candida infections in immunocompetent and immunocompromised patients. This paper reviews the preclinical and clinical pharmacology of micafungin and its potential role for treatment of fungal invasive infections in patients.

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.

Prevention of infection due to Pneumocystis spp. in human immunodeficiency virus-negative immunocompromised patients

Pneumocystis infection in humans was originally described in 1942. The organism was initially thought to be a protozoan, but more recent data suggest that it is more closely related to the fungi. Patients with cellular immune deficiencies are at risk for the development of symptomatic Pneumocystis infection. Populations at risk also include patients with hematologic and nonhematologic malignancies, hematopoietic stem cell transplant recipients, solid-organ recipients, and patients receiving immunosuppressive therapies for connective tissue disorders and vasculitides. Trimethoprim-sulfamethoxazole is the agent of choice for prophylaxis against Pneumocystis unless a clear contraindication is identified. Other options include pentamidine, dapsone, dapsone-pyrimethamine, and atovaquone. The risk for PCP varies based on individual immune defects, regional differences, and immunosuppressive regimens. Prophylactic strategies must be linked to an ongoing assessment of the patient's risk for disease.

Micafungin

OBJECTIVE

To review the pharmacology, mycology, chemistry, in vitro susceptibility, pharmacokinetics, clinical efficacy, safety, tolerability, dosage, and administration of micafungin, an echinocandin antifungal agent.

DATA SOURCES

A MEDLINE search, restricted to English language, was conducted from 1978 to November 2003. Supplementary sources included program abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy and the Infectious Diseases Society of America from 1996 to 2003 and information available through the manufacturer's Web site.

STUDY SELECTION AND DATA EXTRACTION

In vitro and preclinical studies, as well as Phase II and III clinical trials, were evaluated to summarize the clinical efficacy and safety of micafungin. All published and unpublished trials and abstracts citing micafungin were selected.

DATA SYNTHESIS

Micafungin has shown in vitro activity against many yeasts and a variety of molds. Micafungin can be administered only parenterally. Efficacy has been illustrated in open noncomparative studies of esophageal candidiasis in HIV-infected patients and in comparative trials as antifungal prophylaxis in patients undergoing hematopoietic stem-cell transplantation. Adverse events appear mild and limited; the most commonly reported adverse events include hyperbilirubinemia, nausea, and diarrhea.

CONCLUSIONS

Micafungin has activity against Aspergillus spp. and a variety of Candida spp., including azole-resistant strains. Micafungin demonstrates efficacy in the treatment of esophageal candidiasis in HIV-infected patients and appears superior to fluconazole as antifungal prophylaxis in patients undergoing hematopoietic stem-cell transplantation. Based on case reports and in vitro efficacy, micafungin may prove to be a clinically useful agent in the treatment of other fungal diseases; however, these indications await the results of clinical trials.

Micafungin

Micafungin, an echinocandin antifungal agent with a novel mechanism of action, inhibits beta-(1,3)-D-glucan synthase interfering with fungal cell wall synthesis. It shows excellent antifungal activity against a broad range of Candida spp., including azole-resistant strains, and Aspergillus spp. in in vitro and animal studies. In HIV-positive patients, intravenous micafungin 50-150 mg/day dose-dependently eradicated endoscopically confirmed oesophageal candidiasis, with micafungin 100 and 150 mg/day being more effective than micafungin 50 mg/day and as effective as fluconazole 200 mg/day in a double-blind trial. In nonblind trials, micafungin (monotherapy or combination therapy) was effective against invasive aspergillosis, candidiasis and candidaemia in paediatric and adult patients with newly diagnosed or refractory infections. Micafungin 50 mg/day provided significantly better antifungal prophylaxis than fluconazole 400 mg/day in 882 haematopoietic stem cell transplant recipients in a randomised, double-blind trial. Respective overall success rates were 80% and 73.5%. Micafungin is generally well tolerated. Adverse events were not dose- or infusion-related with micafungin 12.5-900 mg/day; no histamine-like reactions occurred. Micafungin was as well tolerated as fluconazole, with numerically fewer micafungin recipients discontinuing treatment (4.2% vs 7.2%).

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.

Newer Systemic Antifungal Agents

The past few years have seen the advent of several new antifungal agents, including those of a new class and a new generation of an existing class. Caspofungin, the first available echinocandin, has greatly expanded the antifungal armamentarium by providing a cell wall-active agent with candidacidal activity as well as demonstrated clinical efficacy in the therapy of aspergillosis refractory to available therapy. In addition, in clinical trials, caspofungin had comparable efficacy to amphotericin B for candidaemia and invasive Candida infections. Caspofungin and two more recently introduced echinocandins, micafungin and anidulafungin, are available as intravenous formulations only and characterised by potent anti-candidal activity, as well as few adverse events and drug interactions. Voriconazole, the first available second-generation triazole, available in both intravenous and oral formulations, has added a new and improved therapeutic option for primary therapy of invasive aspergillosis and salvage therapy for yeasts and other moulds. In a randomised trial, voriconazole demonstrated superior efficacy and a survival benefit compared with amphotericin B followed by other licensed antifungal therapy. This and data from a noncomparative study led to voriconazole becoming a new standard of therapy for invasive aspergillosis. Voriconazole has several important safety issues, including visual adverse events, hepatic enzyme elevation and skin reactions, as well as a number of drug interactions. Posaconazole, only available orally and requiring dose administration four times daily, shows encouraging efficacy in difficult to treat infections due to zygomycetes. Ravuconazole, available in both intravenous and oral formulations, has broad-spectrum in vitro potency and in vivo efficacy against a wide range of fungal pathogens. Clinical studies are underway. Despite the advances offered with each of these drugs, the morbidity and mortality associated with invasive fungal infections remains unacceptable, especially for the most at-risk patients. For individuals with severe immunosuppression as a result of chemotherapy, graft-versus-host disease and its therapy, or transplantation, new drugs and strategies are greatly needed.

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.

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.

Eradication of invasive mucormycosis--effectiveness of the Echinocandin FK463

BACKGROUND

Invasive rhinocerebral mucormycosis is a rare and often fatal opportunistic fungal infection. It is encountered in immunocompromised hosts exemplified by those with diabetes, human immunodeficiency viruses and particularly haematologic malignancies typically after high-dose chemotherapy and stem cell transplantation. In contrast to the more usual outcome with rapid progression and death. We now describe a successful eradication attributable to the use of a newly available antifungal agent.

SETTING

Haematology department and bone marrow transplantation unit.

MATERIAL AND METHOD

Two patients are contrasted. The first with acute leukaemia developed rapidly progressive facial swelling with mucormycosis proven on biopsy. Treatment over 2 months with maximally tolerated doses of amphotericin failed to halt intracranial extension and death resulted. The second, presented with acute lymphoblastic leukaemia in August 1997, underwent successful autologous bone marrow transplantation in February 1998. Relapse followed in March 1999 and after reinduction and consolidation receive a matched unrelated volunteer allograft in September 1999. A second recurrence was documented in April 2000 and in spite of achieving remission he developed a fever that was managed empirically with intravenous amphotericin and, on discharge, oral itraconazole. Left-sided facial swelling expanded rapidly and biopsy showed extensive invasion of the maxillary sinus with mucormycosis. FK463 was added on 5 June 2000 with gradual reduction in facial pain and within 1 month all clinical signs and resolved. Serial biopsies that included histopathologic investigation and microbiologic cultures confirmed eradication of the invasive mucor. In view of the potential danger of recrudescence this treatment regimen was continued through further chemotherapy and, once again disease-free, a second matched unrelated volunteer allograft took place in August 2000. Full reassessment at the time failed to demonstration any residual fungus. Engraftment was confirmed but neutropenic sepsis resulted in severe inflammatory response syndrome with progression to multiple organ dysfunction to which he succumbed without any evidence of leukaemic or systemic mycosis.

CONCLUSION

Echinocandin FK463 is of documented value in managing invasive candidiasis and aspergillosis. This is believed to be the first case of successful outcome with one of the angiotrophic zygomycetes.

Efficacy of micafungin alone or in combination against systemic murine aspergillosis

We tested the efficacy of micafungin (FK) alone or in combination with other antifungals against systemic murine aspergillosis. FK alone at 10 mg/kg of body weight/dose prolonged survival (P = 0.01) and reduced CFU in the brain and kidney. Combination therapy that used suboptimal FK with amphotericin B or itraconazole prolonged survival. Although no survivors were free of infection, no antagonism was seen. Nikkomycin Z with FK showed significantly greater potency (P < 0.01) than either alone.

Clinical pharmacology of antifungal compounds

Prompted by the worldwide surge in fungal infections, the past decade has witnessed a considerable expansion in antifungal drug research. New compounds have entered the clinical arena, and major progress has been made in defining paradigms of antifungal therapies. This article provides an up-to-date review on the clinical pharmacology, indications, and dosage recommendations of approved and currently investigational therapeutics for treatment of invasive fungal infections in adult and pediatric patients.

From natural products to clinically useful antifungals

In our search for natural products with a broad spectrum of antifungal activity as lead compounds for novel treatments for mycoses, we have isolated echinocandin-type lipopeptide FR901379 and lipopeptidolactone FR901469, as novel water-soluble antifungal agents that inhibit the synthesis of 1,3-beta-glucan, a key component of the fungal cell wall. Since the cell wall is a feature unique to fungi and is not present in nonfungal eukaryotic cells, inhibitors of the synthesis of fungal cell wall components such as 1,3-beta-glucan have potential for selective toxicity to fungi and not to the host. In this short review, we describe efforts directed at synthetic modification of FR901469 and FR901379 with the ultimate goal of identifying new entities with suitable profiles as development candidate compounds. The main thrust of our work to date has been replacement of the highly flexible lipophilic side chains of the natural products with a view to reducing the hemolytic potential associated with these compounds, and to enhance chemical stability and/or in vivo antifungal efficacy. As a result of these efforts, we recently discovered a novel analog, FK463 (micafungin). Micafungin is currently in phase III clinical trials worldwide as a parenteral agent for various mycoses, and a new drug application (NDA) was recently filed in Japan.

Clinical efficacy of echinocandin antifungals

The prevalence of fungal infections has increased significantly over the past few decades. Candida and Aspergillus spp. are the most common fungal pathogens due to recent changes in medical technology. Amphotericin B continues to be the treatment of choice in many severe disseminated mycosis cases, but problems with toxicity, resistance and non-availability of an absorbable oral form are important drawbacks. The azoles offer a less toxic alternative but often they are not as effective as amphotericin B and resistance is an increasing problem. The echinocandins are new active antifungal agents with a novel mechanism of action. During the past year, one agent has been released and two others are undergoing advanced stages of investigation. Although these agents are not the ideal antifungal drug, they do offer new options of therapy.

Prevention of infection caused by Pneumocystis carinii in transplant recipients

Pneumocystis carinii remains an important pathogen in patients who undergo solid-organ and hematopoietic transplantation. Infection results from reactivation of latent infection and via de novo acquisition of infection from environmental sources. The risk of infection depends on the intensity and duration of immunosuppression and underlying immune deficits. The risk is greatest after lung transplants, in individuals with invasive cytomegalovirus disease, during intensive immunosuppression for allograft rejection, and during periods of neutropenia. Prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMZ) prevents many opportunistic infections, including infection with P. carinii, Toxoplasma gondii, and community-acquired respiratory, gastrointestinal, and urinary tract pathogens. Intolerance of TMP-SMZ is common; desensitization is useful less often in transplant patients than in patients with AIDS. Alternative agents provide a narrower spectrum of protection than does TMP-SMZ and less adequate protection against Pneumocystis species. Clinically, the diagnosis of breakthrough Pneumocystis pneumonia often requires invasive procedures. Strategies for the prevention of Pneumocystis infection must be individualized on the basis of a stratification of risk for each patient.