Effects of dosing regimen on accumulation, retention and prophylactic efficacy of liposomal amphotericin B

Polyene Antibiotics Physical Chemistry and Their Effect on Lipid Membranes; Impacting Biological Processes and Medical Applications

This review examined a collection of studies regarding the molecular properties of some polyene antibiotic molecules as well as their properties in solution and in particular environmental conditions. We also looked into the proposed mechanism of action of polyenes, where membrane properties play a crucial role. Given the interest in polyene antibiotics as therapeutic agents, we looked into alternative ways of reducing their collateral toxicity, including semi-synthesis of derivatives and new formulations. We follow with studies on the role of membrane structure and, finally, recent developments regarding the most important clinical applications of these compounds.

Case reports of invasive mucormycosis associated neutropenic enterocolitis in leukemic children: diagnostic and treatment challenges and review of literature

Background

Bacterial enterocolitis is one of the most common neutropenic fever complications during intensive chemotherapy. Despite aggressive antibacterial treatments, this complication usually imposes high morbidity and mortality in cancer patients. Management of bacterial neutropenic enterocolitis are well known; however, management of fungal neutropenic enterocolitis may be more challenging and needs to be investigated. Prompt diagnosis and treatment may be life-saving, especially in patients at risk of mucormycosis-associated neutropenic enterocolitis.

Case presentation

We report two mucormycosis-associated neutropenic enterocolitis cases in pediatric leukemic patients receiving salvage chemotherapy for disease relapse. Both patients' clinical signs and symptoms differ from classical bacterial neutropenic enterocolitis. They were empirically treated as bacterial neutropenic enterocolitis with anti-gram-negative combination therapy. Despite broad-spectrum antimicrobial treatment, no clinical improvement was achieved, and both of them were complicated with severe abdominal pain necessitating surgical intervention. Mucormycosis is diagnosed by immunohistopathologic examination in multiple intraoperative intestinal tissue biopsies. Both patients died despite antifungal treatment with liposomal amphotericin-B and surgical intervention.

Conclusion

Mucormycosis-associated neutropenic enterocolitis is one of the most unfavorable and untreatable side effects of salvage chemotherapy in leukemic children with disease relapse. This report could be of considerable insight to the clinicians and scientists who counter the enigma of fungal infections during febrile neutropenia and help to understand better diagnosis and management.

Outpatient parenteral antifungal therapy (OPAT) for invasive fungal infections with intermittent dosing of liposomal amphotericin B

Triazole resistant A. fumigatus has been documented in many parts of the world. In the Netherlands, incidence is now above 10% and results in the need for long-term parenteral therapy with liposomal amphotericin B (LAmB). The long terminal half-life of LAmB suggests that intermittent dosing could be effective, making the application of outpatient antifungal therapy (OPAT) possible. Here, we report our experience with the use of OPAT for Invasive Fungal Infections (IFI). All adult patients treated with LAmB with a 2 or 3 times weekly administration via the outpatient departments in four academic tertiary care centers in the Netherlands and Belgium since January 2010 were included in our analysis. Patient characteristics were collected, as well as information about diagnostics, therapy dose and duration, toxicity, treatment history and outcome of the IFI. In total, 18 patients were included. The most frequently used regimen (67%) was 5 mg/kg 3 times weekly. A partial response to the daily treatment prior to discharge was confirmed by CT-scan in 17 (94%) of patients. A favorable outcome was achieved in 13 (72%) patients. Decrease in renal function occurred in 10 (56%) cases but was reversible in all and was treatment limiting in one patient only. The 100-day mortality and 1-year mortality after initiation of OPAT were 0% and 6%, respectively. In a selected population, and after confirmation of initial response to treatment, our data support the use of OPAT with LAmB for treatment of IFI in an intermittent dosing regimen.

[Liposomal amphotericin B: Clinical pharmacology, pharmacokinetics and pharmacodynamics]

Liposomal amphotericin B is a lipid formulation of the antifungal drug amphotericin B with some distinguishing characteristics in its pharmacological behavior that entail some clinical differences of great interest. The significant improvement in the systemic and renal tolerability is one of them. This fact is related to the great stability of the liposome, promoted by its negative charge, the presence of cholesterol and the remarkable thermo-stability of the remaining lipids that compose it. In this situation, amphotericin B seems to be released from the liposome not spontaneously but when the liposome binds to the ergosterol in the fungal cell membrane. For this reason, there is almost no free amphotericin B in plasma or tissues, although it seems that its availability is greater when there is fungal infection. As a consequence, when the pharmacokinetic behavior is studied, the concentration and availability of liposomal amphotericin B are very high, and its volume of distribution is reduced in comparison with the other formulations.

Safety and Efficacy of Intermittent High-Dose Liposomal Amphotericin B Antifungal Prophylaxis in Haemato-Oncology: An Eight-Year Single-Centre Experience and Review of the Literature

Triazoles remain first-line agents for antifungal prophylaxis in high-risk haemato-oncology patients, but their use is increasingly contraindicated due to drug–drug interactions and additive toxicities with novel treatments. In this retrospective, single-centre, observational study, we present our eight-year experience of antifungal prophylaxis using intermittent high-dose liposomal Amphotericin B (L-AmB). All adults identified through our Antifungal Stewardship Programme as receiving L-AmB prophylaxis at 7.5 mg/kg once-weekly between February 2012 and January 2020 were included. Adverse reactions, including infusion reactions, electrolyte loss, and nephrotoxicity, were recorded. ‘Breakthrough’ invasive fungal infection (IFI) occurring within four weeks of L-AmB was classified using European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group (EORTC/MSG) criteria. Moreover, 114 courses of intermittent high-dose L-AmB prophylaxis administered to 92 unique patients were analysed. Hypokalaemia was the most common grade 3–4 adverse event, with 26 (23%) courses. Grade 3 nephrotoxicity occurred in 8 (7%) and reversed in all six patients surviving to 90 days. There were two (1.8%) episodes of breakthrough IFI, one ‘probable’ and one ‘possible’. In this study, the largest evaluation of intermittent high-dose L-AmB prophylaxis conducted to date, toxicity was manageable and reversible and breakthrough IFI was rare. L-AmB prophylaxis represents a viable alternative for patients with a contraindication to triazoles.

Nucleic Acid Aptamers as a Potential Nucleus Targeted Drug Delivery System

BACKGROUND

Nucleus targeted drug delivery provides several opportunities for the treatment of fatal diseases such as cancer. However, the complex nucleocytoplasmic barriers pose significant challenges for delivering a drug directly and efficiently into the nucleus. Aptamers representing singlestranded DNA and RNA qualify as next-generation highly advanced and personalized medicinal agents that successfully inhibit the expression of certain proteins; possess extraordinary gene-expression for manoeuvring the diseased cell's fate with negligible toxicity. In addition, the precisely directed aptamers to the site of action present a tremendous potential to reach the nucleus by escaping the ensuing barriers to exhibit a better drug activity and gene expression.

OBJECTIVE

This review epigrammatically highlights the significance of targeted drug delivery and presents a comprehensive description of the principal barriers faced by the nucleus targeted drug delivery paradigm and ensuing complexities thereof. Eventually, the progress of nucleus targeting with nucleic acid aptamers and success achieved so far have also been reviewed.

METHODS

Systematic literature search was conducted of research published to date in the field of nucleic acid aptamers.

CONCLUSION

The review specifically points out the contribution of individual aptamers as the nucleustargeting agent rather than aptamers in conjugated form.

Preclinical Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, and Antifungal Activity of Liposomal Amphotericin B

The improved safety profile and antifungal efficacy of liposomal amphotericin B (LAmB) compared to conventional amphotericin B deoxycholate (DAmB) is due to several factors including, its chemical composition, rigorous manufacturing standards, and ability to target and transit through the fungal cell wall. Numerous preclinical studies have shown that LAmB administered intravenously distributes to tissues frequently infected by fungi at levels above the minimum inhibitory concentration (MIC) for many fungi. These concentrations can be maintained from one day to a few weeks, depending upon the tissue. Tissue accumulation is dose-dependent with drug clearance occurring most rapidly from the brain and slowest from the liver and spleen. LAmB localizes in lung epithelial lining fluid, within liver and splenic macrophages and in kidney distal tubules. LAmB has been used successfully in therapeutic and prophylactic animal models to treat many different fungal pathogens, significantly increasing survival and reducing tissue fungal burden.

Mechanisms of Acquired In Vivo and In Vitro Resistance to Voriconazole by Candida krusei following Exposure to Suboptimal Drug Concentration

Five Candida krusei isolates (susceptible and resistant) recovered from the urine of a kidney transplant patient treated with voriconazole (VRC) 200 mg twice daily for 20 days were studied. Eight unrelated clinical isolates of C. krusei were exposed in vitro to VRC 0.001 μg/ml for 30 days. Development of VRC transient resistance occurred in vivo, and induction of permanent resistance occurred in vitro Mostly, ABC1 and ERG11 genes were overexpressed, and a homozygous T418C mutation in the ERG11 gene was found.

Antifungal treatment administered in OPAT programs is a safe and effective option in selected patients

INTRODUCTION

Outpatient parenteral antimicrobial therapy (OPAT) has been recognised as a useful, cost-effective and safe alternative to inpatient treatment. Nevertheless, the most common antimicrobials used are antibiotics, and there is less information about the use of antifungal therapy (AT). The aim of this study is to analyse a cohort of patients treated with AT administered via OPAT and to compare them with patients from the rest of the cohort (RC) treated with antibiotics.

METHODS

Prospective observational study with post hoc (or retrospective) analysis of a cohort of patients treated in the OPAT program. We selected the patients treated with antifungals between July 2012 and December 2018. We recorded demographic and clinical data to analyse the validity of the treatment and to compare the differences between the AT and the RC.

RESULTS

Of the 1101 patients included in the OPAT program, 24 (2.18%) were treated with AT, 12 Liposomal Amphotericin B, 6 echinocandins and 6 fluconazole. This result is similar to other cohorts. There were differences between the AT vs RC in the number of patients with neoplasia (58.3% vs 28%; p=0.001), IC Charlson>2 (58.3% vs 38.8; p=0.053), duration of treatment (15 days vs 10.39 days; p=0.001) and patients with central catheters (54.2% vs 21.7%; p=0.0001). These differences are justified because there were more hematologic patients included in the AT group. Nevertheless, there were no differences in adverse reactions (25% vs 32.3%; p=0.45) or re-admissions (12.5% vs 10%; p=0.686) and OPAT with AT was successful in 21/24 patients (87.5%).

CONCLUSIONS

AT can be successfully administered in OPAT programs in selected patients, that are clinically stable and monitored by an infectious disease physician.

Increased Efficacy of Oral Fixed-Dose Combination of Amphotericin B and AHCC® Natural Adjuvant against Aspergillosis

Invasive pulmonary aspergillosis represents one of the most serious fungal infections among immunocompromised patients. In this study, we aimed to analyze the in vivo efficacy of prophylactic oral amphotericin B (AMB) encapsulated in modified chitosan-nanoparticles (Nanomerics’ Molecular Envelope Technology (MET)) supplemented with a standardized extract of cultured Lentinula edodes mycelia (AHCC^®) in a murine model of pulmonary aspergillosis. We determined fungal burden and survival of mice and additionally, we carried out a cytokine analysis in an attempt to understand the immunomodulation of the extract. Our results evidenced equivalent efficacy between orally administered AMB-MET and the intravenous liposomal AMB marketed formulation. Addition of the AHCC^® supplement significantly improved efficacy in terms of burden reduction and survival increase of both oral and intravenous AMB therapies compared to the untreated control group. Moreover, a protective effect of the extract was observed in terms of weight loss. Regarding the cytokine profiles, the Th1 immune response was stimulated in treated animals when compared to the control group. This response was marked by an enhancement in the MCP-1, GM-CSF, VEGF, RANTES and IL-17 levels and a decrease in the IL-6, a biomarker related to the severity of the infection.

Extended Dosing Regimens for Fungal Prophylaxis

Invasive fungal diseases carry high morbidity and mortality in patients undergoing chemotherapy for hematological malignancies or allogeneic hematopoietic stem cell transplantation. In order to prevent these life-threatening infections, antifungal chemoprophylaxis plays an important role in daily clinical practice. Broad-spectrum antifungal triazoles are widely used but exhibit disadvantages such as relevant drug-drug interactions. Therefore, amphotericin B products or echinocandins can be an alternative in selected patient populations. As these compounds are available as intravenous formulations only, there is growing interest in extended dosing regimens. Although not approved for these agents, this strategy is a rational option, as these compounds have properties suitable for this strategy, including dose-proportional pharmacokinetics, prolonged elimination half-life, and a large therapeutic window. As the use of extended dosing regimens in antifungal prophylaxis is expanding in clinical practice, we reviewed the pharmacokinetic and pharmacodynamic rationale for this strategy, animal model data, dose escalation studies, and clinical trials supporting this concept.

Clinical Pharmacokinetics of Systemically Administered Antileishmanial Drugs

This review describes the pharmacokinetic properties of the systemically administered antileishmanial drugs pentavalent antimony, paromomycin, pentamidine, miltefosine and amphotericin B (AMB), including their absorption, distribution, metabolism and excretion and potential drug–drug interactions. This overview provides an understanding of their clinical pharmacokinetics, which could assist in rationalising and optimising treatment regimens, especially in combining multiple antileishmanial drugs in an attempt to increase efficacy and shorten treatment duration. Pentavalent antimony pharmacokinetics are characterised by rapid renal excretion of unchanged drug and a long terminal half-life, potentially due to intracellular conversion to trivalent antimony. Pentamidine is the only antileishmanial drug metabolised by cytochrome P450 enzymes. Paromomycin is excreted by the kidneys unchanged and is eliminated fastest of all antileishmanial drugs. Miltefosine pharmacokinetics are characterized by a long terminal half-life and extensive accumulation during treatment. AMB pharmacokinetics differ per drug formulation, with a fast renal and faecal excretion of AMB deoxylate but a much slower clearance of liposomal AMB resulting in an approximately ten-fold higher exposure. AMB and pentamidine pharmacokinetics have never been evaluated in leishmaniasis patients. Studies linking exposure to effect would be required to define target exposure levels in dose optimisation but have only been performed for miltefosine. Limited research has been conducted on exposure at the drug’s site of action, such as skin exposure in cutaneous leishmaniasis patients after systemic administration. Pharmacokinetic data on special patient populations such as HIV co-infected patients are mostly lacking. More research in these areas will help improve clinical outcomes by informed dosing and combination of drugs.

The Viscoelastic Properties of the Fungal Cell Wall Allow Traffic of AmBisome as Intact Liposome Vesicles

The fungal cell wall is a critically important structure that represents a permeability barrier and protective shield. We probed Candida albicans and Cryptococcus neoformans with liposomes containing amphotericin B (AmBisome), with or without 15-nm colloidal gold particles. The liposomes have a diameter of 60 to 80 nm, and yet their mode of action requires them to penetrate the fungal cell wall to deliver amphotericin B to the cell membrane, where it binds to ergosterol. Surprisingly, using cryofixation techniques with electron microscopy, we observed that the liposomes remained intact during transit through the cell wall of both yeast species, even though the predicted porosity of the cell wall (pore size, ~5.8 nm) is theoretically too small to allow these liposomes to pass through intact. C. albicans mutants with altered cell wall thickness and composition were similar in both their in vitro AmBisome susceptibility and the ability of liposomes to penetrate the cell wall. AmBisome exposed to ergosterol-deficient C. albicans failed to penetrate beyond the mannoprotein-rich outer cell wall layer. Melanization of C. neoformans and the absence of amphotericin B in the liposomes were also associated with a significant reduction in liposome penetration. Therefore, AmBisome can reach cell membranes intact, implying that fungal cell wall viscoelastic properties are permissive to vesicular structures. The fact that AmBisome can transit through chemically diverse cell wall matrices when these liposomes are larger than the theoretical cell wall porosity suggests that the wall is capable of rapid remodeling, which may also be the mechanism for release of extracellular vesicles.IMPORTANCE AmBisome is a broad-spectrum fungicidal antifungal agent in which the hydrophobic polyene antibiotic amphotericin B is packaged within a 60- to 80-nm liposome. The mode of action involves perturbation of the fungal cell membrane by selectively binding to ergosterol, thereby disrupting membrane function. We report that the AmBisome liposome transits through the cell walls of both Candida albicans and Cryptococcus neoformans intact, despite the fact that the liposome is larger than the theoretical cell wall porosity. This implies that the cell wall has deformable, viscoelastic properties that are permissive to transwall vesicular traffic. These observations help explain the low toxicity of AmBisome, which can deliver its payload directly to the cell membrane without unloading the polyene in the cell wall. In addition, these findings suggest that extracellular vesicles may also be able to pass through the cell wall to deliver soluble and membrane-bound effectors and other molecules to the extracellular space.

A Young, Immunocompetent Woman with Small Bowel and Hepatic Mucormycosis Successfully Treated with Aggressive Surgical Debridements and Antifungal Therapy

A 24-year-old woman with coeliac disease and transient neutropenia developed mucormycosis with extensive involvement of the liver and small intestine. She was successfully treated with aggressive surgical debridements and long-term antifungal therapy with liposomal amphotericin B and posaconazole.

Biodistribution and In Vivo Antileishmanial Activity of 1,2-Distigmasterylhemisuccinoyl-sn-Glycero-3-Phosphocholine Liposome-Intercalated Amphotericin B

1,2-Distigmasterylhemisuccinoyl-sn-glycero-3-phosphocholine (DSHemsPC) is a new lipid in which two molecules of stigmasterol (an inexpensive plant sterol) are covalently linked via a succinic acid to glycerophosphocholine. Our previous study revealed that liposome (Lip)-intercalated amphotericin B (AMB) prepared from DSHemsPC (DSHemsPC-AMB-Lip) possesses excellent colloidal properties and in vitro antifungal and antileishmanial activities similar to those of the liposomal AMB preparation AmBisome. The aim of this study was to determine the biodistribution and evaluate the antileishmanial effects of DSHemsPC-AMB-Lip in Leishmania major-infected BALB/c mice. The serum profile and tissue concentrations of AMB were similar in DSHemsPC-AMB-Lip- and AmBisome-treated mice after intravenous (i.v.) injection. Multiple i.v. doses of the micellar formulation of AMB (Fungizone; 1 mg/kg of body weight), DSHemsPC-AMB-Lip (5 mg/kg), and AmBisome (5 mg/kg) were used in L. major-infected BALB/c mouse models of early and established lesions. In a model of the early lesions of cutaneous leishmaniasis (CL), the results indicated that the level of footpad inflammation was significantly (P < 0.001) lower in mice treated with DSHemsPC-AMB-Lip and AmBisome than mice treated with empty liposomes or 5% dextrose. The splenic and footpad parasite load was also significantly (P < 0.001) lower in these groups of mice than in control mice that received 5% DW or free liposome. The in vivo activity of DSHemsPC-AMB-Lip was comparable to that of AmBisome, and both provided improved results compared to those achieved with Fungizone at the designated doses. The results suggest that systemic DSHemsPC-AMB-Lip administration may be useful for the treatment of leishmaniasis, and because it costs less to produce DSHemsPC-AMB-Lip than AmBisome, DSHemsPC-AMB-Lip merits further investigation.

Successful stepdown treatment of pulmonary histoplasmosis with thrice-weekly liposomal amphotericin B in a hospital-associated, outpatient infusion centre: A case report

WHAT IS KNOWN AND OBJECTIVE

Amphotericin is the preferred treatment for pulmonary histoplasmosis during pregnancy. The long half-life of amphotericin supports less than daily administration.

CASE SUMMARY

A 28-year-old pregnant woman diagnosed with recurrent pulmonary histoplasmosis was initiated on liposomal amphotericin 250 mg (4 mg/kg) intravenously daily. After 2 weeks, the patient was discharged and successfully received 250 mg thrice weekly at a hospital-associated outpatient infusion centre. After 6 weeks of outpatient treatment, a chest X-ray demonstrated no remaining disease and therapy was discontinued.

WHAT IS NEW AND CONCLUSION

Administration of thrice-weekly liposomal amphotericin in a hospital-associated, outpatient infusion centre may be a promising option for stepdown treatment in patients unable to take itraconazole.

Tissue pharmacokinetics and pharmacodynamics of AmBisome® (L-AmBis) in uninfected and infected animals and their effects on dosing regimens

By selecting a unique combination of lipids and amphotericin B, the liposome composition for AmBisome® (L-AmBis) has been optimized resulting in a formulation that is minimally toxic, targets to fungal cell walls, and distributes into and remains for days to weeks in various host tissues at drug levels above the MIC for many fungi. Procedures have been standardized to ensure that large scale production of the drug retains the drug's low toxicity profile, favorable pharmacokinetics and antifungal efficacy. Tissue accumulation and clearance with single or multiple intravenous administration is similar in uninfected and infected animal species, with tissue accumulation being dose-dependent and the liver and spleen retaining the most drug. The efficacy in animals appears to be correlated with drug tissue levels although the amount needed in a given organ varies depending upon the type of infection. The long-term tissue retention of bioactive L-AmBis in different organs suggests that for some indications, prophylactic and intermittent drug dosing would be efficacious reducing the cost and possible toxic side-effects. In addition, preliminary preclinical studies using non-intravenous routes of delivery, such as aerosolized L-AmBis, catheter lock therapy, and intravitreal administration, suggest that alternative routes could possibly provide additional therapeutic applications for this antifungal drug.

Experimental Models of Short Courses of Liposomal Amphotericin B for Induction Therapy for Cryptococcal Meningitis

Cryptococcal meningoencephalitis is a rapidly lethal infection in immunocompromised patients. Induction regimens are usually administered for 2 weeks. The shortest effective period of induction therapy with liposomal amphotericin B (LAMB) is unknown. The pharmacodynamics of LAMB were studied in murine and rabbit models of cryptococcal meningoencephalitis. The concentrations of LAMB in the plasma and brains of mice were measured using high-performance liquid chromatography (HPLC). Histopathological changes were determined. The penetration of LAMB into the brain was determined by immunohistochemistry using an antibody directed to amphotericin B. A dose-dependent decline in fungal burden was observed in the brains of mice, with near-maximal efficacy achieved with LAMB at 10 to 20 mg/kg/day. The terminal elimination half-life in the brain was 133 h. The pharmacodynamics of a single dose of 20 mg/kg was the same as that of 20 mg/kg/day administered for 2 weeks. Changes in quantitative counts were reflected by histopathological changes in the brain. Three doses of LAMB at 5 mg/kg/day in rabbits were required to achieve fungicidal activity in cerebrospinal fluid (cumulative area under the concentration-time curve, 2,500 mg · h/liter). Amphotericin B was visible in the intra- and perivascular spaces, the leptomeninges, and the choroid plexus. The prolonged mean residence time of amphotericin B in the brain suggests that abbreviated induction regimens of LAMB are possible for cryptococcal meningoencephalitis.

Suspected Pulmonary Infection with Trichoderma longibrachiatum after Allogeneic Stem Cell Transplantation

Aspergillus and Candida species are the main causative agents of invasive fungal infections in immunocompromised human hosts. However, saprophytic fungi are now increasingly being recognized as serious pathogens. Trichoderma longibrachiatum has recently been described as an emerging pathogen in immunocompromised patients. We herein report a case of isolated suspected invasive pulmonary infection with T. longibrachiatum in a 29-year-old man with severe aplastic anemia who underwent allogeneic stem cell transplantation. A direct microscopic examination of sputum, bronchoaspiration, and bronchoalveolar lavage fluid samples revealed the presence of fungal septate hyphae. The infection was successfully treated with 1 mg/kg/day liposomal amphotericin B.

Liposomal Amphotericin B (AmBisome(®)): A Review of the Pharmacokinetics, Pharmacodynamics, Clinical Experience and Future Directions

Liposomal amphotericin B (AmBisome(®); LAmB) is a unique lipid formulation of amphotericin B. LAmB is a standard of care for a wide range of medically important opportunistic fungal pathogens. LAmB has a significantly improved toxicity profile compared with conventional amphotericin B deoxycholate (DAmB). Despite nearly 20 years of clinical use, the pharmacokinetics and pharmacodynamics of this agent, which differ considerably from DAmB, remain relatively poorly understood and underutilized in the clinical setting. The molecular pharmacology, preclinical and clinical pharmacokinetics, and clinical experience with LAmB for the most commonly encountered fungal pathogens are reviewed. In vitro, experimental animal models and human clinical trial data are summarized, and novel routes of administration and dosing schedules are discussed. LAmB is a formulation that results in reduced toxicity as compared with DAmB while retaining the antifungal effect of the active agent. Its long terminal half-life and retention in tissues suggest that single or intermittent dosing regimens are feasible, and these should be actively investigated in both preclinical models and in clinical trials. Significant gaps remain in knowledge of pharmacokinetics and pharmacodynamics in special populations such as neonates and children, pregnant women and obese patients.

In vitro evaluation of antifungal and cytotoxic activities as also the therapeutic safety of the oxidized form of amphotericin B

The aim of this study was to evaluate the antifungal and cytotoxic activities of the oxidized form of amphotericin B (AmB-Ox) as well as to determine whether oxidation process of AmB is therapeutically beneficial in vitro. The antifungal activity was estimated against Candida albicans ATCC 10231 and Candida parasilosis ATCC 22019 by broth microdilution method according to the NCCLS M27-A2 standards. The in vitro cytotoxicity was evaluated using normal green monkey kidney cells (GMK) by MTT assay. The obtained results demonstrated that AmB-Ox possesses 16-fold decreased antifungal properties against the two Candida strains and 5-fold lower cytotoxic activity towards GMK cells in comparison with AmB. The therapeutic safety in vitro assessed by calculating the ratio between cytotoxicity (CC50 value) to antifungal activity (MIC value) showed that oxidation of AmB is a very unfavourable process in vitro, because leads to formation of derivative (AmB-Ox) that lost antifungal properties much more rapidly than cytotoxic activity. Thus, the process of the oxidation of AmB in vivo (if it occurs) can be also highly harmful for patient.

Virulence and Resistance to Antifungal Therapies of Scopulariopsis Species

Scopulariopsisis an emerging opportunistic fungus characterized by its high resistance to antifungal therapies. We have developed a murine model of disseminated infection in immunosuppressed animals by intravenous inoculation ofScopulariopsis brevicaulisandScopulariopsis brumptii, the most clinically relevant species, in order to evaluate their virulence and their responses to conventional antifungal treatments. Survival and tissue burden studies showed thatS. brumptiiwas more virulent thanS. brevicaulis The three drugs tested, liposomal amphotericin B, posaconazole, and voriconazole, prolonged the survival of mice infected withS. brumptii, but none showed efficacy againstS. brevicaulis The different therapies were only able to modestly reduce the fungal burden of infected tissue; however, in general, despite the high serum levels reached, they showed poor efficacy in the treatment of the infection. Unfortunately, the most effective therapy forScopulariopsisinfections remains unresolved.

Intra-tumor distribution of PEGylated liposome upon repeated injection: No possession by prior dose

Liposomes have proven to be a viable means for the delivery of chemotherapeutic agents to solid tumors. However, significant variability has been detected in their intra-tumor accumulation and distribution, resulting in compromised therapeutic outcomes. We recently examined the intra-tumor accumulation and distribution of weekly sequentially administered oxaliplatin (l-OHP)-containing PEGylated liposomes. In that study, the first and second doses of l-OHP-containing PEGylated liposomes were distributed diversely and broadly within tumor tissues, resulting in a potent anti-tumor efficacy. However, little is known about the mechanism underlying such a diverse and broad liposome distribution. Therefore, in the present study, we investigated the influence of dosage interval on the intra-tumor accumulation and distribution of "empty" PEGylated liposomes. Intra-tumor distribution of sequentially administered "empty" PEGylated liposomes was altered in a dosing interval-dependent manner. In addition, the intra-tumor distribution pattern was closely related to the chronological alteration of tumor blood flow as well as vascular permeability in the growing tumor tissue. These results suggest that the sequential administrations of PEGylated liposomes in well-spaced intervals might allow the distribution to different areas and enhance the total bulk accumulation within tumor tissue, resulting in better therapeutic efficacy of the encapsulated payload. This study may provide useful information for a better design of therapeutic regimens involving multiple administrations of nanocarrier drug delivery systems.

New Insights Regarding Yeast Survival following Exposure to Liposomal Amphotericin B

In vitro resistance to amphotericin B is an extremely rare event among pathogenic yeasts. However, in vivo response is sometimes reduced, resulting in an unfavorable outcome. Such adverse outcomes might be related to subfungicidal plasma concentrations. We aimed to clarify the mechanisms of liposomal amphotericin B (AMB-L; AmBisome)-induced lesions and the mechanisms responsible for yeast cell recovery following exposure at plasma concentrations. The physiological statuses developing following exposure to AMB-L at simulated plasma concentrations (20 to 0.1 mg/liter) and at a constant concentration (3 mg/liter) were assessed in a 24-h time course assay. Time-kill experiments also were carried out under the same AMB-L treatment conditions. Our results suggest that yeast cells develop compensatory responses related to membrane polarization, metabolic activity, and reactive oxygen species (ROS) production after exposure to high plasma concentrations (20 to 5 mg/liter) during the first 6 h; in the remaining 18 h, when exposed to lower concentrations, cells reveal almost full recovery with no evidence of fungicidal activity. In contrast, whenever cells are exposed to a constant concentration above the MIC, despite initially exhibiting compensatory stress responses, soon afterwards they exhibit membrane depolarization, a decrease of metabolic activity, increasing ROS production, and lastly, programmed cell death and necrosis, resulting in succumbing to AMB-L fungicidal effects. This study may represent a step forward in the support of AMB-L use for clinical treatment of invasive fungal infections, since it demonstrates the importance of maintaining levels of AMB-L above the MIC in plasma and tissues to ensure it produces its fungicidal effects.

Synergistic enhancement of parasiticidal activity of amphotericin B using copaiba oil in nanoemulsified carrier for oral delivery: an approach for non-toxic chemotherapy

BACKGROUND AND PURPOSE

The aim of this study was to devise a nanoemulsified carrier system (CopNEC) to improve the oral delivery of amphotericin B (AmB) by increasing its oral bioavailability and synergistically enhance its antileishmanial activity with copaiba oil (Cop).

EXPERIMENTAL APPROACH

The AmB encapsulated NEC (CopNEC-AmB) comprised of Cop, d-α-tocopheryl polyethylene glycol 1000 succinate and phosphatidylcholine was prepared by high-pressure homogenization method. Stability study of CopNEC-AmB was carried out in simulated gastric fluid and simulated intestinal fluid. The CopNEC-AmB and plain AmB were compared as regards their in vitro antileishmanial activity, pharmacokinetics, organ distribution and toxicity.

KEY RESULTS

The optimal CopNEC-AmB had a small globule size, low polydispersity index, high ζ potential and encapsulation efficiency. The high resolution transmission electron microscopy illustrated spherical particle geometry with homogeny in their sizes. The optimal CopNEC-AmB was found to be stable in gastrointestinal fluids showing insignificant changes in globule size and encapsulation efficiency. The AUC0-48 value of CopNEC-AmB in rats was significantly improved showing 7.2-fold higher oral bioavailability than free drug. The in vitro antileishmanial activity of CopNEC-AmB was significantly higher than that of the free drug as Cop synergistically enhanced the antileishmanial effect of AmB by causing drastic changes in the morphology of Leishmania parasite and rupturing its plasma membrane. The CopNEC-AmB showed significantly less haemolytic toxicity and cytotoxicity and did not change the histopathology of kidney tissues as compared with AmB alone.

CONCLUSIONS AND IMPLICATIONS

This prototype CopNEC formulation showed improved bioavailability and had a non-toxic synergistic effect on the antileishmanial activity of AmB.

Tissue penetration of antifungal agents

Understanding the tissue penetration of systemically administered antifungal agents is critical for a proper appreciation of their antifungal efficacy in animals and humans. Both the time course of an antifungal drug and its absolute concentrations within tissues may differ significantly from those observed in the bloodstream. In addition, tissue concentrations must also be interpreted within the context of the pathogenesis of the various invasive fungal infections, which differ significantly. There are major technical obstacles to the estimation of concentrations of antifungal agents in various tissue subcompartments, yet these agents, even those within the same class, may exhibit markedly different tissue distributions. This review explores these issues and provides a summary of tissue concentrations of 11 currently licensed systemic antifungal agents. It also explores the therapeutic implications of their distribution at various sites of infection.

Amphotericin B-copper(II) complex as a potential agent with higher antifungal activity against Candida albicans

Amphotericin B (AmB) is a polyene antibiotic produced by Streptomyces nodosus used for more than 50 years in the treatment of acute systemic fungal infections. It exhibits a broad spectrum of activity against fungal and protozoan pathogens with relatively rare resistance. The aim of this study was to prepare and evaluate the utility of the AmB-Cu(2+) complex as a potential compound with a high fungicidal activity at lower concentrations, compared with conventional AmB. It was hypothesized that insertion of copper ions into fungal cell membranes, together with the AmB-Cu(2+) complex bypassing the natural homeostatic mechanisms of this element, may contribute to the increased fungicidal activity of AmB. The analysis of results indicates the increased antifungal activity of the AmB-Cu(2+) complex against Candida albicans in comparison with the pure AmB and Fungizone. Additionally, it was stated that the increased antifungal activity of the AmB-Cu(2+) complex is not the sum of the toxic effects of AmB and Cu(2+) ions, but is a result of the unique structure of this compound.

Prospective phase II single-center study of the safety of a single very high dose of liposomal amphotericin B for antifungal prophylaxis in patients with acute myeloid leukemia

Some preclinical and pharmacokinetic studies suggested the variable safety and the potential efficacy of an antifungal prophylaxis with a single high dose of liposomal amphotericin B (L-AmB) in high-risk patients. An open-label, prospective study was conducted with 48 adults receiving induction chemotherapy for acute myeloid leukemia (AML). Patients received a single infusion of 15 mg/kg of body weight L-AmB and, eventually, a second dose after 15 days of persistent neutropenia. The primary objective was tolerability and safety. Efficacy was also evaluated as a secondary endpoint. A pharmacokinetic study was performed with 34 patients in order to evaluate any association of plasma L-AmB levels with toxicity and efficacy. Overall, only 6 patients (12.5%) reported Common Toxicity Criteria (CTC) grade 3 hypokalemia, which was corrected with potassium supplementation in all cases, and no patient developed clinically relevant nephrotoxicity. Mild infusion-related adverse events occurred after 6 of 53 (11.3%) total infusions, with permanent drug discontinuation in only one case. Proven invasive fungal disease (IFD) was diagnosed in 4 (8.3%) patients. The mean AmB plasma levels at 6 h, 24 h, and 7 days after L-AmB administration were 160, 49.5, and 1 mg/liter, respectively. The plasma AmB levels were higher than the mean values of the overall population in 3 patients who developed CTC grade 3 hypokalemia and did not significantly differ from the mean values of the overall population in 3 patients who developed IFD. Our experience demonstrates the feasibility and safety of a single 15-mg/kg L-AmB dose as antifungal prophylaxis in AML patients undergoing induction chemotherapy.

Development of amphotericin B-loaded cubosomes through the SolEmuls technology for enhancing the oral bioavailability

The oral administration of amphotericin B (AmB) has the major drawback of poor bioavailability. The aim of this work was to evaluate the potential of AmB-loaded cubosomes as an oral formulation with improved bioavailability. This manuscript firstly developed AmB-loaded cubosomes by using the SolEmuls technology. The encapsulation efficiency, the in vitro release, and stability studies in simulated gastrointestinal fluid were used to evaluate AmB-loaded cubosomes. The acute nephrotoxicity, bioavailability, and tissue distribution study of AmB-loaded cubosomes were assayed upon oral administration to rats. SAXS and cryo-TEM exhibited AmB-loaded cubosomes as a bicontinuous cubic liquid crystalline phase with Pn3m geometry. The encapsulation efficiency and the results of in vitro release and stability studies in simulated gastrointestinal fluid further demonstrated that AmB was successfully encapsulated in cubosomes. AmB-loaded cubosomal formulation orally administrated in rats did not show nephrotoxicity and its relative bioavailability was approximately 285% as compared to Fungizone®. The AmB-loaded cubosomal formulation presented an effective potential approach for enhancing the oral bioavailability of AmB.

Experimental central nervous system aspergillosis therapy: efficacy, drug levels and localization, immunohistopathology, and toxicity

We have shown previously that high-dose lipid amphotericin preparations are not more efficacious than lower doses in aspergillosis. We studied toxicity, drug concentrations and localization, and quantitative infection concurrently, using a 4-day model of central nervous system (CNS) aspergillosis to assess early events. Mice given Aspergillus fumigatus conidia intracerebrally, under a cyclophosphamide immunosuppressive regimen, were treated for 3 days (AmBisome at 3 or 10 mg/kg of body weight, Abelcet at 10 mg/kg, amphotericin B deoxycholate at 1 mg/kg, caspofungin at 5 mg/kg, or voriconazole at 40 mg/kg). Sampling 24 h after the last treatment showed that AmBisome at 3 but not at 10 mg/kg, as well as Abelcet, caspofungin, and voriconazole, reduced brain CFU. All regimens reduced renal infection. Minor renal tubular changes occurred with AmBisome or Abelcet therapy, whereas heart, lung, and brain showed no drug toxicity. Amphotericin B tissue and serum concentrations did not correlate with efficacy. Endothelial cell activation (ICAM-1 and P-selectin in cerebral capillaries) occurred during infection. Amphotericin B derived from AmBisome and Abelcet localized in activated endothelium and from Abelcet in intravascular monocytes. In 10-day studies dosing uninfected mice, minor renal tubular changes occurred after AmBisome or Abelcet at 1, 5, or 10 mg/kg with or without cyclophosphamide treatment; nephrosis occurred only with Abelcet in cyclophosphamide-treated mice. Hepatotoxicity occurred with AmBisome and Abelcet but was reduced in cyclophosphamide-treated mice. Marked CFU reduction by AmBisome at 3 mg/kg occurred in association with relatively more intense inflammation. Abelcet renal localization appears to be a precursor to late nephrotoxicity. Hepatotoxicity may contribute to high-dose Abelcet and AmBisome failures. Our novel observation of endothelial amphotericin localization during infection may contribute to amphotericin mechanism of efficacy.

Central nervous system toxicity associated with liposomal amphotericin B therapy for cutaneous leishmaniasis

AmBisome (liposomal amphotericin B) is used for prophylaxis and treatment of fungal infections, treatment of visceral leishmaniasis, and more recently, treatment of cutaneous leishmaniasis. Although the package insert cites neurologic toxicities in up to 20% of cases, review of the literature did not reveal any specific cases describing this side effect, particularly in a patient without comorbidities. We describe a healthy 38-year-old male treated with liposomal amphotericin B for cutaneous leishmaniasis acquired during military duties in Iraq. Shortly after completion of his treatment course, he reported memory difficulties and confusion. Further evaluation revealed no other source, and his cognitive issues were attributed to liposomal amphotericin B toxicity. These issues resolved over a few weeks, which is consistent with data about the drug's tissue penetration and metabolism available in the literature. This is a potential side effect of liposomal amphotericin B that can be observed in otherwise healthy patients.

Differences in tissue drug concentrations following intravenous versus intraperitoneal treatment with amphotericin B deoxycholate or liposomal amphotericin B

Amphotericin B formulations were compared in preclinical models by using intraperitoneal (ip) and intravenous (iv) delivery of amphotericin B deoxycholate (DAMB) or liposomal amphotericin B. We examined the effects on drug tissue penetration and retention resulting from different routes of drug administration. Mice were treated with equivalent total doses of AmBisome (AmBi) or DAMB (i.e.,15 mg/kg) given ip (3 mg/kg/day for 5 days) or iv (3 mg/kg/day AmBi for 5 days or 1 mg/kg/day DAMB for 15 days), with tissues collected 24 h post-treatment. For drug retention studies, mice were given iv or ip total doses of 30 mg/kg AmBi (10 mg/kg/day 3 x /week) or 60 mg/kg AmBi (20 mg/kg/day 3 x /week) with tissue collection 24 h or 7 days post-treatment. Blood samples were collected at 0.5 h, 2 h, 8 h, 12 h and 24 h after ip or iv drug dosing. A Paecilomyces variottii bioassay was used to determine drug concentrations. AmBi and DAMB were detected in the kidneys following iv, but not ip dosing. Significantly more DAMB than AmBi was detected in the lungs with ip dosing (P = 0.008), and more AmBi than DAMB (P = 0.056) was present with iv dosing. Unlike the lungs, the spleen and liver retained the AmBi for up to one week post-treatment regardless of the route of drug administration. Thus, there are significant differences in AmBi and DAMB tissue distribution depending upon the drug route and these differences could effect how the drugs perform in fungal infection models.

Liposomal amphotericin B and echinocandins as monotherapy or sequential or concomitant therapy in murine disseminated and pulmonary Aspergillus fumigatus infections

Monotherapy and combination therapy were compared using optimal doses of liposomal amphotericin B, micafungin, or caspofungin in Aspergillus fumigatus pulmonary and disseminated infections. Mice were challenged intravenously (2.8 x 10(4) to 5.7 x 10(4) conidia) or intranasally (5.8 x 10(7) conidia) with A. fumigatus. Drugs (5, 10, or 15 mg/kg of body weight) were given for 3 or 6 days as single, concomitant, or sequential therapy (i.e., days 1 to 3 and then days 4 to 6). Mice were monitored for survival, and tissues were assayed for fungal burden and drug concentrations. Treatments starting 24 h postchallenge significantly prolonged survival in disseminated aspergillosis (P < 0.002), but only liposomal amphotericin B treatments or treatments beginning with liposomal amphotericin B increased survival to 100% in the pulmonary aspergillosis model. Fungi in kidneys and spleens (disseminated) and lungs (pulmonary) were significantly decreased (P < or = 0.04) by liposomal amphotericin B, liposomal amphotericin B plus echinocandin, or liposomal amphotericin B prior to echinocandin. In the disseminated infection, liposomal amphotericin B and micafungin (10 or 15 mg/kg) had similar kidney drug levels, while in the spleen, 5 and 15 mg/kg liposomal amphotericin B gave higher drug levels than micafungin (P < 0.02). In the pulmonary infection, drug levels in lungs and spleen with 5-mg/kg dosing were significantly higher with liposomal amphotericin B than with caspofungin (P < or = 0.002). In summary, treatment of A. fumigatus infections with liposomal amphotericin B plus echinocandin or liposomal amphotericin B prior to echinocandin was as effective as liposomal amphotericin B alone, and a greater decrease in the fungal burden with liposomal amphotericin B supports using liposomal amphotericin B prior to echinocandin.

Candida glabrata persistence in mice does not depend on host immunosuppression and is unaffected by fungal amino acid auxotrophy

Candida glabrata has emerged as an important fungal pathogen of humans, causing life-threatening infections in immunocompromised patients. In contrast, mice do not develop disease upon systemic challenge, even with high infection doses. In this study we show that leukopenia, but not treatment with corticosteroids, leads to fungal burdens that are transiently increased over those in immunocompetent mice. However, even immunocompetent mice were not capable of clearing infections within 4 weeks. Tissue damage and immune responses to microabscesses were mild as monitored by clinical parameters, including blood enzyme levels, histology, myeloperoxidase, and cytokine levels. Furthermore, we investigated the suitability of amino acid auxotrophic C. glabrata strains for in vitro and in vivo studies of fitness and/or virulence. Histidine, leucine, or tryptophan auxotrophy, as well as a combination of these auxotrophies, did not influence in vitro growth in rich medium. The survival of all auxotrophic strains in immunocompetent mice was similar to that of the parental wild-type strain during the first week of infection and was only mildly reduced 4 weeks after infection, suggesting that C. glabrata is capable of utilizing a broad range of host-derived nutrients during infection. These data suggest that C. glabrata histidine, leucine, or tryptophan auxotrophic strains are suitable for the generation of knockout mutants for in vivo studies. Notably, our work indicates that C. glabrata has successfully developed immune evasion strategies enabling it to survive, disseminate, and persist within mammalian hosts.

Comparison between concentrations of amphotericin B in infected lung lesion and in uninfected lung tissue in a patient treated with liposomal amphotericin B (AmBisome)

Generally, the primary lesion of a mold infection is in the airway, an extravascular site. Therefore, the antifungal drug concentration at the actual tissue lesion of a mold infection is as important as in the blood compartment. Although our antifungal armamentarium has expanded recently, polyenes are still often needed in clinical practice because of their potent fungicidal activity and the rarity of resistance. Nevertheless, the distribution of amphotericin B (AmB) in infected lung tissue has not yet been evaluated. Using high-performance liquid chromatography analysis, we determined the concentrations of AmB in plasma and infected and uninfected tissues of resected lung simultaneously, in a patient with pulmonary aspergillosis treated with liposomal amphotericin B (L-AmB). The AmB concentration in the infected lesion of the lung was approximately 5.2 times higher than that in plasma and 3.7 times higher than in uninfected lung tissue. L-AmB accumulated in the infected lesion of the lung at a higher concentration. Although our data are from only one patient, they may be useful in helping to develop better strategies for the use of L-AmB against pulmonary fungal infections.

Pulmonary epithelial lining fluid concentrations after use of systemic amphotericin B lipid formulations

Amphotericin B (AMB) concentrations were determined in pulmonary epithelial lining fluid (ELF) of 44 critically ill patients, who were receiving treatment with liposomal AMB (LAMB) (n = 11), AMB colloidal dispersion (ABCD) (n = 28), or AMB lipid complex (ABLC) (n = 5). Mean AMB levels (+/- standard errors of the means) in ELF amounted to 1.60 +/- 0.58, 0.38 +/- 0.07, and 1.29 +/- 0.71 microg/ml in LAMB-, ABCD-, and ABLC-treated patients, respectively (differences are not significant).

A safety and feasibility study comparing an intermittent high dose with a daily standard dose of liposomal amphotericin B for persistent neutropenic fever

A high intermittent dose regimen (group A: 10 mg kg(-1) on day 1, 5 mg kg(-1) on days 3 and 6) was compared with standard dosing (group B: 3 mg kg(-1) per day for 14 days) of liposomal amphotericin B (LAB) for empirical treatment of persistent febrile neutropenia. A total cumulative dose of 1275 mg (group A) and 2800 mg (group B) was administered. Infusion-related adverse drug events, mainly rigors/chills, occurred more frequently with group A (11/45, 24 % infusions) than with group B (12/201, 6 % infusions) (P=0.002), which extended the mean infusion time by 20 min (P=0.001). Creatinine levels were similar in the two regimens: the A : B ratio of the area under the curve for creatinine (AUC(CREATININE)) for days 2-7 was 1.09 (P=0.27) and for days 2-14 was 1.05 (P=0.51). Rises in creatinine were mild (clinical toxicity criteria 1) in all patients with elevations. Hypokalaemia tended to be less severe in group A with a lower proportion of hypokalaemic days [57/143 (39 %) vs 80/137 (58 %), P=0.21], a higher AUC(POTASSIUM) (A : B ratio of 1.06, P=0.12), a lower proportion of patients with hypokalaemia at the end of study (10 vs 61 %, P=0.01) and fewer potassium-supplemented days [12/210 (6 %) vs 41/210 (19.5 %), P<0.1]. There were mildly elevated median levels of serum bilirubin, alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase, which were similar for the two regimens and were usually associated with other co-existing co-morbid conditions. The AUC for these enzymes was also similar in the two groups. No patient had discontinuation of the study drug due to toxicity. Composite success was identical for each regimen (11/15 patients, 73 %). Three of the fifteen patients in group B and none in group A developed invasive fungal infections (IFIs). Beta-D-Glucan levels were similar in both groups for patients without an IFI [AUC(GLUCAN) of 362 and 683 (P=0.36) for groups A and B, respectively]. The rate of defervescence was similar for each regimen (P=0.75). This feasibility study suggests that a short intermittent high-dose course of 10/5/5 mg LAB kg(-1) on days 1, 3 and 6 may be as safe and effective as a standard 14 day course of 3 mg kg(-1) per day, with drug-acquisition cost savings and reduced drug exposure. A larger study is indicated for confirmation of this.

Pharmacokinetics and buccal mucosal concentrations of a 15 milligram per kilogram of body weight total dose of liposomal amphotericin B administered as a single dose (15 mg/kg), weekly dose (7.5 mg/kg), or daily dose (1 mg/kg) in peripheral stem cell transplant patients

The pharmacokinetics and safety of extended-interval dosing of prophylactic liposomal amphotericin B (L-AMB) in peripheral stem cell transplant recipients were evaluated. The patients received L-AMB daily at 1 mg/kg of body weight or weekly at 7.5 mg/kg or received L-AMB as a single dose (15 mg/kg). The buccal mucosal tissue concentrations of L-AMB were measured. Of the 24 patients enrolled, 5 withdrew after the initial dose due to an infusion-related reaction (n = 2) or significant increases in the serum creatinine (Scr) levels (n = 3). Weekly L-AMB dosing (7.5 mg/kg) produced mean plasma concentrations of >0.300 microg/ml for the first 7 days and >0.220 microg/ml for 7 days after the second dose. A single L-AMB dose (15 mg/kg) produced mean plasma concentrations of >0.491 microg/ml for at least 7 seven days. These concentrations are within the range of the MICs reported in the literature for susceptible strains of Candida and are at the lower limits of the MICs for Aspergillus spp. Extended-interval dosing produced buccal mucosal tissue concentrations well in excess of the MICs reported in the literature for susceptible strains of Candida and Aspergillus spp. Infusion-related reactions occurred in 24% of the patients. Baseline and end-of-study Scr, electrolyte (K+, Mg2+, PO4), and serum transaminase levels were similar across the dosage groups. Five (31%) patients met the nephrotoxicity definition prior to completion of the study. Patients in the weekly or single-dose groups experienced nephrotoxicity significantly faster than the patients in the daily dosing cohort. A weekly L-AMB dose (7.5 mg/kg) or a single L-AMB dose (15 mg/kg) produced sufficient concentrations in plasma and highly vascular tissue to warrant further studies of the safety, efficacy, and practicality of the weekly prophylactic administration of L-AMB.

Pharmacokinetics and biodistribution of amphotericin B in rats following oral administration in a novel lipid-based formulation

OBJECTIVES

To assess the pharmacokinetics and biodistribution of amphotericin B (AmB) following oral administration in a novel mono/diglyceride-phospholipid formulation and to compare with intravenous (iv) administrations using commercial formulations.

METHODS

Rats were allocated into the following treatment groups: oral gavage of AmB dispersed in mono/diglyceride-phospholipid formulation at doses of 4.5 and 10 mg/kg; iv bolus administration of 0.8 mg/kg Fungizone; iv bolus of 5 mg/kg Abelcet and iv bolus of 5 mg/kg AmBisome. Blood was sampled from jugular vein cannula at certain time points. The animals were sacrificed 72 h following administration of AmB and multiple tissues were harvested. The concentration of AmB in plasma and tissues was determined by means of HPLC. The plasma creatinine concentrations were determined using an enzymatic kit.

RESULTS

The pharmacokinetics and tissue distribution of AmB following iv administrations of the commercial formulations were found to be highly formulation dependent. The terminal half-life and biodistribution of orally administered AmB in a mono/diglyceride-phospholipid formulation resembled those of Fungizone. The larger volume of the co-administered lipid-based formulation in the case of the higher dose of orally administered AmB resulted in flip-flop kinetics and in preferential distribution into the kidneys. No nephrotoxicity was detected for any formulation and route of administration.

CONCLUSIONS

Oral administration of AmB in a mono/diglyceride-phospholipid formulation to rats resulted in significant intestinal absorption into the systemic circulation with pharmacokinetic and biodistribution properties similar to a micellar iv preparation.

Amphotericin B lipid preparations: what are the differences?

To reduce the in-vivo toxicity of the broad-spectrum antifungal drug amphotericin B, various lipid formulations of amphotericin B, ranging from lipid complexes to small unilamellar liposomes, have been developed and subsequently commercialized. These structurally diverse formulations differ in their serum pharmacokinetics as well as their tissue localisation, tissue retention and toxicity. These differences can affect the choice of formulation for a given infection, the time of initiation of treatment, and the dosing regimen. Although preclinical studies have shown similarities in the in-vitro and in-vivo antifungal activity of the formulations with comparable dosing, their acute and chronic toxicity profiles are not the same, and this has a significant impact on their therapeutic indices, especially in high-risk, immunosuppressed patients. With the recent introduction of new antifungal drugs to treat the increasing numbers of infected patients, the amphotericin B lipid formulations are now being studied to evaluate their potential in combination drug regimens. With proven efficacy demonstrated during the past decade, it is expected that amphotericin B lipid formulations will remain an important part of antifungal drug therapy.