Systemic antifungal agents

Invasive fungal infection is the infectious complication with highest associated mortality. Until the 90's amphotericin B was the only drug available to treat these infections. Its spectrum of antifungal activity is excellent, but its use is associated with toxicity in many cases. The development of amphotericin B lipid formulations has resulted in a significant decrease in most of the side effects associated with this drug. Triazoles are safe and effective for treating most invasive fungal infections. Fluconazole is an excellent drug for the prevention and treatment of Candida and Cryptococcus infections, itraconazole has good activity against Candida and Aspergillus, and voriconazole has shown to be better than amphotericin B for invasive aspergillosis. Caspofungin belongs to a new group of antifungal agents, the echinocandins, which are very safe and present excellent activity against Candida and Aspergillus.     

New antifungal agents

Two new antifungal agents, voriconazole and caspofungin, are now available for treatment of systemic fungal infections. Voriconazole is an extended-spectrum triazole that is fungicidal for filamentous fungi, including Aspergillus, Scedosporium, Fusarium, Paecilomyces, and is active against all species of Candida. It has become first-line therapy for invasive aspergillosis. Voriconazole is given either by the oral or the intravenous route. Clinicians must be aware of drug-drug interactions and side effects, including visual disturbances and photosensitivity rash that can occur when voriconazole is used. Caspofungin is the first drug available from a new class of antifungal agents, echinocandins, that act to inhibit fungal cell wall synthesis. Caspofungin is fungicidal for all species of Candida and more slowly kills Aspergillus species. Caspofungin, available only for intravenous administration, has minimal side effects and very few drug interactions. The echinocandins will find most use for Candida infections and as second-line therapy for Aspergillus infections.     

New antifungal agents

Treatment of fungal infections is an area of increasing concern. This is because of the complexity of underlying illness in affected patients as well as the limited number of antifungal agents available for use. Current strategies focus on prevention of these infections in patients at high risk; however, this has the potential to lead to the emergence of clinically resistant pathogens and superinfections in these patient populations. Future efforts need to focus on earlier diagnosis and more targeted prophylaxis strategies to limit unnecessary use of these potentially toxic pharmaceuticals. Of equal importance is the development of new therapeutic options that provide viable alternatives for practitioners as well as optimal administration of currently available agents. Recent work in this area has yielded a handful of new agents that provide the first step in improving efficacy in these severely immunosuppressed patients, but outcomes still remain suboptimal for many patients suffering from severe fungal infections and/or serious underlying diseases. Clinical antifungal drug resistance must be controlled by improving a series of antifungal therapeutic strategies.     

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侵袭性真菌感染(IFI)最多发生于免疫受损或免疫功能低下的患者中,抗真菌治疗的效果直接关系到此类患者的基础疾病的疗效和长期存活,应重视抗真菌药物的规范应用。文章阐述了规范性应用抗真菌药物的概念,提倡依据不同危险因素的患者群推测可能的致病真菌,以诊断分层为基础,综合药物特性、区域性特点和价格效能比,足量、足疗程地使用抗真菌药物,并依据指南疗效评估标准评价治疗效果并调整用药。     

New antifungal agents and bronchopulmonary mycoses

The frequency of respiratory mycosal infections has increased over recent Years. Diagnosis has been improved by recent epidemiological data and advances in radiological and mycological diagnostic methods. Two new antifungal agents have recently received marketing approval: voriconazole and caspofungine. Voriconazole belongs to the echinocandin family of antifungals. Sites of action of antifungals have become more diversified: amphotericins act on ergosterol directly, azolated agents act on the synthesis of ergosterol, flucytosine affects synthesis of nucleic acids, and echinocandins alter the fungal wall. Synergetic or additive combinations, such as amphotericin-caspofungine, or voriconazole-caspofungine, can be proposed for advanced disease. Thus both first intention and secondary treatments, particularly for systemic candidiasis and aspergillosis, have been modified. These new protocols take into consideration the severity of the mycosal infection, co-morbidity, and drug combinations as well as cost.     

Using oral antifungal agents for severe fungal infections

The azole antifungal drugs fluconazole and itraconazole have changed our approach to the treatment of serious fungal infections. Increased use of these drugs has generated information of value for clinical practice.     

In vitro resistance of Candida species to antifungal agents

The purpose of this study was to determine the in vitro susceptibility to 6 antifungal agents of 143 strains of Candida species isolated from 545 patients with suspicion of fungal infection. Test ATB Fungus (bioMérieux) was used. Among all Candida isolates 91.6% were susceptible to tested polyenes and 32.9% to all azoles. Less susceptible to polyenes isolates were noted in low percentage (0.7 to 4.2%) and to azoles more frequently (32.9 to 41.2%). Candida isolates resistant to antifungal agents tested were dependent from the kind of clinical samples and species of fungi. Monitoring of the susceptibility to antifungal agents by ATB commercial test seems to be useful tool for therapeutic purposes.     

New antifungal agents under development in children and neonates

PURPOSE OF REVIEW: This review focuses on only the newest antifungal agents recently approved or still under development and the available data in pediatric and neonatal patients. The larger body of data in adult patients is used for comparative purposes only in an attempt to understand pediatric implications. RECENT FINDINGS: Pharmacokinetic data suggest differences in dosing for many newer agents in children versus adult patients, but each agent has not been fully evaluated. Voriconazole displays non-linear pharmacokinetics in adults but has linear pharmacokinetics in children, necessitating a higher dose in smaller patients and potential treatment failures using the approved adult dosing schedule. Caspofungin likewise requires higher doses relative to adult patients, and dosing in children is best accomplished on a body surface area scheme and not a body weight dosing platform. Preliminary data suggest posaconazole, an investigational triazole, in children may lead to similar levels as in adults, but very limited efficacy data are available at any dose. Micafungin dosing has been explored in neonatal patients and there is a clear trend toward lower levels obtained in the very smallest infants, highlighting the importance of the neonatal period as a separate entity to even the pediatric age group. SUMMARY: Initial data suggest dosing differences in children with some antifungals, and other newer agents have not been fully tested for the correct dosing. The underlying concern of efficacy in children compared with adult patients has never been answered as there are no randomized, phase III antifungal clinical trials from which pediatric-specific data were obtained.     

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.     

Small-molecule inhibitors for the Prp8 intein as antifungal agents

Self-splicing proteins, called inteins, are present in many human pathogens, including the emerging fungal threats Cryptococcus neoformans (Cne) and Cryptococcus gattii (Cga), the causative agents of cryptococcosis. Inhibition of protein splicing in Cryptococcus sp. interferes with activity of the only intein-containing protein, Prp8, an essential intron splicing factor. Here, we screened a small-molecule library to find addititonal, potent inhibitors of the Cne Prp8 intein using a split-GFP splicing assay. This revealed the compound 6G-318S, with IC₅₀ values in the low micromolar range in the split-GFP assay and in a complementary split-luciferase system. A fluoride derivative of the compound 6G-318S displayed improved cytotoxicity in human lung carcinoma cells, although there was a slight reduction in the inhibition of splicing. 6G-318S and its derivative inhibited splicing of the Cne Prp8 intein in vivo in Escherichia coli and in C. neoformans. Moreover, the compounds repressed growth of WT C. neoformans and C. gattii. In contrast, the inhibitors were less potent at inhibiting growth of the inteinless Candida albicans. Drug resistance was observed when the Prp8 intein was overexpressed in C. neoformans, indicating specificity of this molecule toward the target. No off-target activity was observed, such as inhibition of serine/cysteine proteases. The inhibitors bound covalently to the Prp8 intein and binding was reduced when the active-site residue Cys1 was mutated. 6G-318S showed a synergistic effect with amphotericin B and additive to indifferent effects with a few other clinically used antimycotics. Overall, the identification of these small-molecule intein-splicing inhibitors opens up prospects for a new class of antifungals.

Many microbial pathogens contain self-splicing elements called inteins, which are internal proteins that self-excise from their intein-hosting proteins and catalyze ligation of the flanking sequences (exteins) with a natural peptide bond (1–4). Overall, more than 1,700 inteins have been identified (5). Among intein-containing deadly human pathogens is Mycobacterium tuberculosis, which has inteins in three critical genes, involved in replication (dnaB), iron-sulfur cluster assembly (sufB), and recombination (recA). M. tuberculosis infections cause 2 million annual tuberculosis-related deaths worldwide (6). Pathogenic fungi, such as Crypotococcus neoformans (Cne), Crypotococcus gattii (Cga), and Aspergillus fumigatus also encode inteins, in the pre-mRNA processing factor 8 (Prp8) gene (7, 8). Globally, over 300 million people are affected by invasive fungal infections, with estimated deaths of over 1 million people every year (9–12). Moreover, the emergence of severely drug-resistant strains of M. tuberculosis and pathogenic fungi, plus the deadly synergistic association with HIV/AIDS, represent significant public health challenges (13–18).Since inteins consistently interrupt highly conserved sites of intein-hosting proteins, splicing inhibition can cause a disruption of functions that are essential for the pathogen’s survival. Inteins are therefore attractive targets for drug development (7, 8, 19–21). Additionally, inteins do not occur in multicellular organisms including humans nor in unicellular organisms including bacteria normally associated with the human gut flora, making intein-inhibiting drugs highly selective for intein-containing pathogens, such as M. tuberculosis, C. neoformans, C. gattii, and A. fumigatus.Previously we found that cisplatin, a Food and Drug Administration (FDA)-approved chemotherapeutic drug, inhibited fungal Prp8 intein splicing in vitro and reduced fungal burden in vivo (8). The action of cisplatin is by the platinum ion being coordinated by the catalytic Cys1 of the inetin, thereby inhibiting the first step of splicing and subsequent branched intermediate formation and extein ligation. However, the high cytotoxicity of cisplatin and its derivatives (22–24) may limit their use in immunocompromised patients. In the present study, we performed a pilot screening of a small-molecule library and found a compound and its derivative that impede fungal Prp8 intein splicing in a dose-dependent manner. In addition, these molecules inhibited the Prp8 intein-containing fungi C. neoformans and C. gattii, but not the yeast Candida albicans, a major human pathogen that does not encode a Prp8 intein. Furthermore, C. neoformans treated with the small molecules led to accumulation of unspliced Prp8 precursor. The potency of these inhibitors is better than or comparable to the current frontline antifungal drugs. Mechanistic studies indicated that the small molecules inhibited Prp8 intein splicing by covalently binding to the Prp8 intein active-site residue Cys1, the nucleophile that initiates the protein splicing reaction.     

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.     

侵袭性真菌感染中抗真菌药物的合理使用

侵袭性真菌感染(IFI)患者病情危重,治疗较为复杂,合理使用抗真菌药物是取得理想抗真菌疗效的关键。临床医生在选择抗真菌药物时应该全面考虑患者的自身情况和(可能)感染的病原菌类型,选择抗真菌活性高、疗效确切、安全性高、耐受良好的抗真菌药物治疗。棘白菌素类是新型抗真菌药物,作用机制独特,广谱覆盖常见念珠菌和曲霉菌,治疗侵袭性念珠菌病和肺曲霉病疗效确切,药物安全性高于多烯类和三唑类,被更多的临床医生选择用于各种IFI患者的治疗。