Treatment Of Systemic Fungal Infections Research Articles

Evaluation of the efficacy and toxicity of amphotericin B incorporated in lipid nano-sphere (LNS ®)

To develop a low-dose therapeutic system for amphotericin B (AmB), the efficacy and toxicity of lipid nano-sphere (LNS ®) incorporating AmB (LNS-AmB) were evaluated and compared with those of Fungizone ®, the conventional dosage form of AmB with sodium deoxycholate. LNS-AmB and Fungizone showed nearly equal activity against fungal cells both in vitro and in vivo. In contrast to Fungizone, however, LNS-AmB did not cause significant hemolysis. In addition, the vomiting toxicity of Fungizone was largely avoided by the use of LNS-AmB in dogs, in spite of the higher plasma AmB concentrations achieved by LNS-AmB. Therefore, LNS-AmB may be selective for fungal cells over mammalian cells. In a study of its toxicity and toxicokinetics in a regimen of daily 2-h intravenous infusions for 14 consecutive days, LNS-AmB showed less toxicity to the kidney than did Fungizone in spite of the higher plasma AmB concentrations achieved. LNS-AmB, therefore, allows the treatment of systemic fungal infections at low doses without the severe nephrotoxicity of Fungizone. Size-exclusion chromatography provided evidence that, when LNS-AmB was administered to rats, AmB was retained in the LNS particles in the blood circulation, but that when Fungizone was administered, AmB was transferred to high-density lipoproteins (HDL). AmB retained in LNS particles seemed to be less toxic to the kidney than was AmB associated with HDL. Consequently, LNS-AmB has the potential to become a low-dose therapeutic system for AmB, minimizing most of the severe side effects of AmB by decreasing the total dose required.

A systematic review of the antifungal effectiveness and tolerability of amphotericin B formulations

Objective: A systematic review was performed to compare the effectiveness and tolerability of lipid-based amphotericin B (AmB) formulations and conventional AmB in the treatment of systemic fungal infections. Methods: The literature and unpublished studies were searched using MEDLINE, EMBASE, Biological Abstracts, AIDSLINE, CANCERLIT, CRD database, Cochrane Controlled Trials Register, and other databases. Search terms included: amphotericin, liposom ∗, lipid ∗, colloid ∗, antifungal agents , and mycoses. Studies were selected according to predetermined criteria. The outcome measures reviewed were efficacy, mortality, renal toxicity, and infusion-related reactions. Meta-analyses and number-needed-to-treat (NNT) analyses were performed. Results: Seven studies (8 publications) met the entry criteria. Meta-analysis showed that lipid-based formulations significantly reduced all-cause mortality risk by an estimated 28% compared with conventional AmB (odds ratio [OR], 0.72; 95% CI, 0.54 to 0.97). There was no significant difference in efficacy between the lipid-based formulations and conventional AmB (OR, 1.21; 95% CI, 0.98 to 1.49). AmB lipid complex (ABLC) and liposomal AmB (L-AmB) significantly reduced the risk of doubling serum creatinine by an estimated 58% (OR, 0.42; 95% CI, 0.33 to 0.54). There was no significant reduction in risk of infusion-related reactions with lipid-based formulations, although this was difficult to interpret given the lack of consistent control of confounding factors. Comparing the lipid-based formulations with conventional AmB, the overall NNT to prevent 1 death was 31. The NNT to prevent a doubling of serum creatinine for both ABLC and L-AmB compared with conventional AmB was 6. Conclusions: This study demonstrates advantages with lipid-based formulations over conventional AmB in terms of reduced risk of mortality and renal toxicity. Future trials in patients with proven fungal infection should control for factors such as premedication, infusion rates, fluid preloading, sodium/potassium supplementation, and concomitant medication.

Plasma protein adsorption patterns on surfaces of Amphotericin B-containing fat emulsions

Nephrotoxicity of the conventional Amphotericin B formulation Fungizone ® is the most common side effect in treatment of systemic fungal infections. Lipid formulations of Amphotericin B including fat emulsions showed a reduced nephrotoxicity. In vivo distribution studies of lipid formulations have shown an accumulation of Amphotericin B in liver and spleen, while concentration in the kidneys is reduced. Blood proteins adsorbed onto particles after intravenous administration are regarded as the key factors determining their in vivo fate. Two-dimensional polyacrylamid gel electrophoresis is a powerful tool for analysis of protein adsorption patterns. This paper deals with the question if there is any correlation between proteins adsorbed on surfaces of AmB fat emulsions produced with a new production technique and the potentially organ distribution of this formulation.

Ion Channel Behavior of Amphotericin B in Sterol-Free and Cholesterol- or Ergosterol-Containing Supported Phosphatidylcholine Bilayer Model Membranes Investigated by Electrochemistry and Spectroscopy

Amphotericin B (AmB) is a popular drug frequently applied in the treatment of systemic fungal infections. In the presence of ruthenium (II) as the maker ion, the behavior of AmB to form ion channels in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes were studied by cyclic votammetry, AC impedance spectroscopy, and UV/visible absorbance spectroscopy. Different concentrations of AmB ranging from a molecularly dispersed to a highly aggregated state of the drug were investigated. In a fixed cholesterol or ergosterol content (5 mol %) in glassy carbon electrode-supported model membranes, our results showed that no matter what form of AmB, monomeric or aggregated, AmB could form ion channels in supported ergosterol-containing phosphatidylcholine bilayer model membranes. However, AmB could not form ion channels in its monomeric form in sterol-free and cholesterol-containing supported model membranes. On the one hand, when AmB is present as an aggregated state, it can form ion channels in cholesterol-containing supported model membranes; on the other hand, only when AmB is present as a relatively highly aggregated state can it form ion channels in sterol-free supported phosphatidylcholine bilayer model membranes. The results showed that the state of AmB played an important role in forming ion channels in sterol-free and cholesterol-containing supported phosphatidylcholine bilayer model membranes.

Use of high-performance liquid chromatographic and microbiological analyses for evaluating the presence or absence of active metabolites of the antifungal posaconazole in human plasma

Posaconazole (SCH 56592) is a novel broad spectrum triazole antifungal agent that is currently in phase III clinical trials for the treatment of systemic fungal infections. This study was initiated to determine if orally administered posaconazole to humans would result in the formation of active metabolite(s). Plasma samples from a multiple-rising dose study in healthy volunteers were analyzed by validated HPLC and microbiological methods. The HPLC analysis involved extraction with a mixture of organic solvent (methylene chloride–hexane) followed by separation on a C 18 column and quantification by UV absorbance at 262 nm. The microbiological assay was performed utilizing an agar diffusion method using Candida pseudotropicalis ATCC 46764 as the test organism. Potency was determined by comparing the growth inhibition zones produced by the test sample to those produced by standard concentrations prepared in plasma. Individual and mean plasma concentration–time profiles were similar for both HPLC and microbiological assays. The area under the plasma concentration–time curves of the microbiological and HPLC results were similar with a mean (RSD) ratio of 105.5% (5.3%), indicating that there was no relevant biologically active metabolite of posaconazole in human plasma.

Preface

Abstract The clinical problems caused by life-threatening, deeptissue fungal infections affect many different medical and surgical specialities where immunosuppression through disease or therapeutic advance has created a substantial sub-category of patients at risk of mycosis. Amphotericin B remains one of the first-line agents for treatment of almost all systemic mycoses, but the agent in its conventional deoxycholate formulation carries a serious penalty in terms of nephrotoxicity. Novel, lipid-associated formulations of amphotericin B have been introduced to combat the toxicity problem without loss of therapeutic efficacy. This supplement is based upon papers presented at an international symposium held in Australia on 8–9 July 2000. It focuses on AmBisome, a liposome-encapsulated formulation of amphotericin B, and draws together information on many general aspects of the diagnosis and treatment of deep tissue mycoses as well as providing a comprehensive set of reviews of all aspects of AmBisome —its pharmacology, toxicology, pharmacokinetics and clinical efficacy in a variety of mycoses and patient types. There is now considerably more clinical experience with lipid forms of amphotericin B than when the previous supplement on AmBisome was published by the Journal of Antimicrobial Chemotherapy in October 1999.1 Because the topic of the supplement is a formulation of an antifungal agent, not the agent itself, and because lipid-based formulations can vary in composition even when they are nominally prepared in the same way, we have taken the unusual step of referring to the various amphotericin B lipid formulations, and to ‘conventional’ amphotericin B-deoxycholate for injection, by their trade names. The editors would like to thank Christine Burley of the JAC Editorial Office, and Regine Buffels of Gilead Sciences for their untiring support and assistance in the preparation of this supplement. Reference 1. Speller, D. C. E. & Warnock, D. W. (Eds). (1991). Liposomal amphotericin B (AmBisome) in the treatment of systemic fungal infection. Journal of Antimicrobial Chemotherapy28, Suppl. B, 1–118.

AmBisome: liposomal formulation, structure, mechanism of action and pre-clinical experience.

Amphotericin B is the treatment of choice for life-threatening systemic fungal infections such as candidosis and aspergillosis. To improve this drug's efficacy and reduce its acute and chronic toxicities, several lipid formulations of the drug have been developed, including AmBisome, a liposomal formulation of amphotericin B. The liposome is composed of high transition temperature phospholipids and cholesterol, designed to incorporate amphotericin B securely into the liposomal bilayer. AmBisome can bind to fungal cell walls, where the liposome is disrupted. The amphotericin B, after being released from the liposomes, is thought to transfer through the cell wall and bind to ergosterol in the fungal cell membrane. This mechanism of action of AmBisome results in its potent in vitro fungicidal activity while the integrity of the liposome is maintained in the presence of mammalian cells, for which it has minimal toxicity. In animal models, AmBisome is effective in treating both intracellular (leishmaniasis and histoplasmosis) and extracellular (candidosis and aspergillosis) systemic infections. Because of its low toxicity at the organ level, intravenous AmBisome can be safely delivered at markedly high doses of amphotericin B (1-30 mg/kg) for the treatment of systemic fungal infections. AmBisome has a circulating half-life of 5-24 h in animals, and in animal models appears to localize at sites of infection in the brain (cryptococcosis, aspergillosis, coccidioidomycosis), lungs (blastomycosis, paracoccidioidomycosis, aspergillosis) and kidneys (candidosis), delivering amphotericin B that remains bioavailable in tissues for several weeks following treatment.

Can we decrease amphotericin nephrotoxicity?

Amphotericin B (AmB) is considered the drug of choice for the treatment of systemic fungal infections. Nephrotoxicity is a major complication associated with its use, and appears to be related to higher cumulative doses, diuretic use, abnormal serum creatinine at baseline, and the use of concomitant nephrotoxic drugs. The two major hypotheses for the pathogenesis of AmB-related nephrotoxicity are direct effects of the drug on epithelial cell membranes and vasoconstriction. During the last few years, some randomized trials have tested different strategies to reduce AmB-induced renal toxicity. These strategies include sodium supplementation, low-dose dopamine, slower infusion rates, the administration of AmB in lipid emulsions, and in lipid formulations. The results of these trials showed that the lipid formulations of AmB significantly reduce nephrotoxicity. Unfortunately, these agents are costly, restricting their use to patients with a high risk of developing renal failure.

Amphotericin biosynthesis in Streptomyces nodosus: deductions from analysis of polyketide synthase and late genes

Background: The polyene macrolide amphotericin B is produced by Streptomyces nodosus ATCC14899. Amphotericin B is a potent antifungal antibiotic and has activity against some viruses, protozoans and prions. Treatment of systemic fungal infections with amphotericin B is complicated by its low water-solubility and side effects which include severe nephrotoxicity. Analogues with improved properties could be generated by manipulating amphotericin biosynthetic genes in S. nodosus. Results: A large polyketide synthase gene cluster was cloned from total cellular DNA of S. nodosus. Nucleotide sequence analysis of 113 193 bp of this region revealed six large polyketide synthase genes as well as genes for two cytochrome P450 enzymes, two ABC transporter proteins, and genes involved in biosynthesis and attachment of mycosamine. Phage KC515-mediated gene disruption was used to show that this region is involved in amphotericin production. Conclusions: The availability of these genes and the development of a method for gene disruption and replacement in S. nodosus should allow production of novel amphotericins. A panel of analogues could lead to identification of derivatives with increased solubility, improved biological activity and reduced toxicity.

Itraconazole oral solution and intravenous formulations: a review of pharmacokinetics and pharmacodynamics

Itraconazole is a triazole antifungal agent with a broad spectrum of activity. It is well tolerated and highly efficacious, particularly because its main metabolite, hydroxy-itraconazole, also has considerable antifungal activity. Two new formulations of itraconazole, an oral solution and an intravenous formulation, have recently been developed, which combine lipophilic itraconazole with cyclodextrin. These formulations have improved the solubility of itraconazole, leading to enhanced absorption and bioavailability compared with the original capsule formulation, without having an impact on the tolerability profile of itraconazole. The oral solution and intravenous formulations of itraconazole produce consistent plasma concentrations and are ideal for the treatment of systemic fungal infections in a wide range of patient populations. The additional flexibility offered by the different routes of administration means that itraconazole treatment can be specifically tailored for use in all patients, including children and those requiring intensive care.

Amphotericin B colloidal dispersion: an improved antifungal therapy

Amphotericin B colloidal dispersion (ABCD) is a near 1:1 discoidal complex of amphotericin B (AMB) and sodium cholesteryl sulfate (SCS) arranged as a bilayer of SCS interspersed with AMB via noncovalent interactions. The complex is stable in blood and plasma with minimal dissociation. In vitro and in vivo studies show that ABCD is as effective and four to five times safer than conventional AMB (CAB) for fungal infection. Compared with CAB treatment, ABCD demonstrates reduced peak plasma levels, prolonged residence time, and lowered AMB levels in most tissues including kidney, the major target of toxicity for CAB. In 572 patients with systemic fungal infections secondary to severe underlying disease, ABCD doses ≤6 mg/kg/day were well tolerated, even in those who failed to tolerate or respond to CAB. Mild-to-moderate, dose-dependent, infusion-related adverse events typically seen with CAB were also observed with ABCD, with no sign of renal or hepatic toxicity. Complete or partial recovery was seen in 57.3%. Therefore, ABCD should be considered as an alternative treatment of systemic fungal infections.

Clinical experience with itraconazole in systemic fungal infections.

The broad spectrum antifungal itraconazole is an effective and well tolerated agent for the prophylaxis and treatment of systemic fungal infections. The recent development of an itraconazole oral solution and an intravenous itraconazole solution has increased the options for the use of this drug and increased the oral bioavailability in a variety of at-risk patients. Reliable absorption of the itraconazole oral solution has been demonstrated in patients with HIV infection, neutropenic patients with haematological malignancy, bone marrow transplant recipients and neutropenic children. In clinical trials, itraconazole oral solution (5 mg/kg/day) was more effective at preventing systemic fungal infection in patients with haematological malignancy than placebo, fluconazole suspension (100 mg/day) or oral amphotericin-B (2 g/kg/day) and was highly effective at preventing fungal infections in liver transplant recipients. There were no unexpected adverse events with the itraconazole oral solution in any of these trials. In addition, intravenous itraconazole solution is at least as effective as intravenous amphotericin-B in the empirical treatment of neutropenic patients with systemic fungal infections, and drug-related adverse events are more frequent in patients treated with amphotericin-B. A large proportion of patients with confirmed aspergillosis also respond to treatment with intravenous itraconazole followed by oral itraconazole. The new formulations of itraconazole are therefore effective agents for prophylaxis and treatment of most systemic fungal infections in patients with haematological malignancy.

Treatment of Systemic Fungal Infections in Older Patients

Systemic fungal infections are an increasing problem in older adults. For several of the endemic mycoses, this increase is the result of increased travel and leisure activities in areas endemic for these fungi. Immunosuppressive agents, care in an intensive care unit, and invasive devices all contribute to infection with opportunistic fungi. Treatment of systemic fungal infections is usually with an azole or amphotericin B. The preferred regimen depends on the specific fungal infection, the site and the severity of the infection, the state of immunosuppression of the patient and the possible toxicities of each drug for a specific patient. In older adults, drug-drug interactions between the azoles and drugs commonly prescribed for older persons may lead to serious toxicity, and absorption of itraconazole can be problematic. Amphotericin B is associated with significant nephrotoxicity, especially in older adults with pre-existing renal disease, and infusion-related adverse effects. Newer lipid formulations of amphotericin B can obviate some of these toxicities, but their role in the treatment of systemic fungal infections in older adults has not yet been clarified.

Pharmacology of itraconazole.

Itraconazole is a triazole antifungal agent that has a broad spectrum of activity and is well tolerated. Itraconazole is highly efficacious, particularly because its main metabolite, hydroxy-itraconazole, also has considerable antifungal activity. The original capsule formulation of itraconazole may lead to variability in absorption and the plasma concentration. For the treatment of superficial fungal infections, this is not problematical because itraconazole accumulates at the infection site, making consistently high plasma concentrations unnecessary -- a characteristic that has been exploited in the development of a pulse regimen. Because consistent plasma concentrations are critical for the more serious systemic fungal infections, variable absorption of itraconazole from the capsules limits their application. Moreover, underlying disease processes and medical interventions can reduce absorption from the capsules in some patients with systemic fungal infections. To widen the beneficial application of itraconazole to include such patients, an oral solution and an intravenous formulation were developed. These formulations combine lipophilic itraconazole with hydroxypropyl-beta-cyclodextrin, a ring of substituted glucose molecules, which improves the solubility of itraconazole. The enhanced absorption and bioavailability of itraconazole from these new formulations make them ideal for the treatment of systemic fungal infections in a wide range of patient populations. The additional flexibility offered by the different routes of administration also means that itraconazole can be used in patients at high risk, such as children or those requiring intensive care, for whom the capsule formulation may be impractical.

Immunotherapy in patients with systemic mycoses: a promising adjunct.

Evidence from several in vitro and animal model studies suggests a modulatory role of haemopoietic, T(H)1 and T(H)2 cytokines in host defence against fungi, and highlights their potential utility as adjunctive therapy for management of systemic mycoses (SM). However, there are limited clinical data to support the use of cytokines in prevention and treatment of SM. Thus, at present no adjunctive treatment is justified for routine use in all patients. Potential application of these immunomodulatory agents include the use of granulocyte-macrophage colony-stimulating factor or macrophage colony-stimulating factor in the management of mycoses in neutropenic patients with myelogenous leukaemia or bone marrow transplantation. Interferon-gamma may have a useful role against aspergillosis in patients with chronic granulomatous disease. Granulocyte colony-stimulating factor-elicited white blood cell transfusions may be life saving to patients with refractory SM. Better understanding of synergy between cytokines and specific antifungals may provide powerful tools for managing these serious infections.

Search for New Lead Compounds from Higher Plants

Higher plants represent a rich source of new molecules with pharmacological properties, which are lead compounds for the development of new drugs. During the last decades, the renewed interest in investigating natural products has led to the advent of several important drugs, such as the anticancer substances vinblastine, vincristine and taxol, or the antimalarial agent artemisinin. Success in natural products reasearch is conditioned by a careful plant selection, based on various criteria such as chemotaxonomic data, information from traditional medicine, field observations or even random collection. One main strategy in the isolation of new leads consists of the so-called bioactivity-guided isolation, in which pharmacological or biological assays are used to target the isolation of bioactive compounds. One major drawback of this strategy is the frequent isolation of known metabolites. Therefore, hyphenated techniques (LC-UV/DAD, LC-MS, LC-NMR) have been developed, in order to detect as early as possible potential original structures. These compounds can then be tested in various bioassays. Using a combination of hyphenated techniques and bioactivity-guided isolation procedures, a series of new diterpenoic antifungal quinones have been isolated from the African tree, Bobgunnia madagascariensis (Leguminosae) and recently patented for their strong activity and for their potential use in the treatment of systemic mycoses.

Management of fungal infections in neutropenic patients: more doubts than certainties?

An evidence based approach to prophylaxis and therapy of invasive fungal infections depends on the knowledge of epidemiology and of risk factors for these infections, as well as on the appreciation of merits and limitation of the available clinical trials. A progressive increase in the incidence of systemic fungal infections, most often caused by Candida and Aspergillus, in patients with cancer and neutropenia has been observed in recent years. This increase of systemic fungal infections recognizes a multifactorial origin, including host defense impairment and type of underlying disease. The various combinations of these different risk factors make the patients affected by systemic fungal infections a non-homogeneous population and, therefore, the transferability of the results of many clinical trials from one population to another is difficult. Clinical trials on prophylaxis and treatment of systemic fungal infections moreover have many limitations: they are often of small size, are frequently non-comparative, enrol population at different risk for infection, use different criteria to define success or failure of therapy. These limitations make the interpretation of the trial results difficult. As randomised clinical trials and metanalysis are considered the most valuable sources of information on new treatments, it dearly appears that the mentioned difficulties in interpreting available data from the literature may expose patients to an increased risk of receiving an inappropriate or non-optimal treatment. Better designed studies are needed to clarify the many controversial questions in antifungal prophylaxis and therapy.

New antifungal agents and preparations

In neutropenic patients amphotericin B remains the drug of choice for the treatment of systemic fungal infections. On the basis of a superior efficacy in combination with a lower toxicity, the triazoles have superseded the older azoles. Regularly, amphotericin B and a triazole are used simultaneously without any evidence from clinical trials that such a strategy is safe and efficacious. Liposomal preparation, lipid complex or colloidal dispersion of amphotericin B have been produced successfully to reduce toxicity. However, there is only one small randomised study that hints at the superiority of liposomal amphotericin B over amphotericin B deoxycholate. Promising new agents like candins, sordarins, high dose oral terbinafine, the third generation azoles, and liposomal nystatin are under development. The first phase II study on voriconazole in the treatment of pulmonary aspergillosis has produced encouraging results. The major promise of the new candins lies in the activity against Candida species, including those resistant to the azoles and polyenes, and in a mechanism of action totally different from the established antifungals. Cytokines and colony stimulating factors are theoretically very promising but there are no clinical studies that warrant routine use.

New agents for treatment of systemic fungal infections

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 SCH56592), ravuconazole [formerly BMS-207147]), lipid formulations of amphotericin B, a lipid formulation of nystatin, echinocandins (VER-002 [formerly, LY303366], caspofungin [formerly MK-991], FK463), 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.

感染症とＤＤＳ リポソームによる抗菌薬製剤設計

Amphotericin B(AmB), polyene macrolide antibiotics, has been used for the treatment of systemic fungal infections. It is necessary to administer at higher dosage to treat pulmonary aspergillosis, however, its clinical use is limited by toxic side effects. Several kinds of carrier system, such as liposomes, microsphere and polymer micelles, have been developed to resolve the problems. Liposomal formulations of AmB, which make it possible to reduce its toxicity and improve the therapeutic efficacy, have been developed and now on the market in USA and Europe. But, further improvements of the encapsulation of AmB in liposomes and therapeutic efficacy have still been required, Enhanced encapsulation of AmB in liposomes by complex formation between AmB and polyethylene glycol-lipid derivatives, DSPE-PEG, has clearly solved the problems, which have been investigated by us. Hydration by 9% sucrose solution and incorporation of DSPE-PEG are required for the high encapsulation efficacy. AmB-encapsulating PEG liposomes showed not only high encapsulation of AmB but also high retention of AmB in Liposomes in vitro and long-circulation property in vivo. We also prepared the novel AmB-encapsulating PEG-immunoliposomes carrying monoclonal antibodies at the distal ends of the PEG chains. AmB-PEG-immunoliposomes and AmB-PEG liposomes showed the higher therapeutic effects on murine model of pulmonary aspergillosis than that of commercially used liposomes. Many experiments on the encapsulation of antimicrobial agents in liposomes have been demonstrated, but there are not so much drugs-carrier system applied for therapy. Determination of the optimum functional carrier system should be important for the practical uses.