Amphotericin B and its delivery by liposomal and lipid formulations

Pharmacokinetic and pharmacodynamic profiling of generic amphotericin B colloidal dispersion in a rat model of invasive candidiasis

OBJECTIVES

We reported the pharmacokinetic/pharmacodynamic (PK/PD) targets of a biosimilar generic product of amphotericin B colloidal dispersion (G-ABCD) againstCandida albicans (MIC 1-2 μg/mL) in a rat model of invasive candidiasis (IC) to facilitate its precision administration.

METHODS

Single-dose plasma PKs of G-ABCD was studied in a rat IC model following intravenous administration at doses of 0.0625-10 mg/kg. Amphotericin B concentrations were determined and PK parameters were calculated based on the concentrations in plasma. The efficacy of G-ABCD was evaluated after single administration by the log reduction of CFU counts in kidney, liver, spleen and lung. The relationship between G-ABCD PK/PD index and log CFU reduction in kidney was calculated.

RESULTS

Following intravenous administration of G-ABCD at doses of 0.0625-10 mg/kg to rats, the maximum plasma concentration (C_max) was 0.05-0.82 mg/L and the area under the concentration-time curve from 0 to 24 h (AUC_0-24) was 0.50-5.29 mg h/L. G-ABCD showed potent antifungal activity against C. albicans C-13 with a maximum log CFU reduction of 2.1 in kidney. The mean AUC_0-24/MIC target of G-ABCD against C. albicans was 0.97 for stasis, 1.40 for 1-log kill and 3.34 for 2-log kill, and the mean C_max/MIC target was 0.063 for stasis, 0.097 for 1-log kill and 0.348 for 2-log kill.

CONCLUSIONS

The antifungal effect of G-ABCD was potent and correlated with AUC_0-24/MIC and C_max/MIC in this rat model of IC. The results of this study provide data for optimising G-ABCD dosing regimens and breakpoints for antifungals.

The synergistic fungicidal effect of low-frequency and low-intensity ultrasound with amphotericin B-loaded nanoparticles on C. albicans in vitro

It is difficult to effectively eradicate C. albicans using traditional antifungal agents, mainly because the low permeability of the C. albicans cell wall creates strong drug resistance. The aim of this study was to investigate the synergistic fungicidal effect and the underlying mechanisms of low-frequency and low-intensity ultrasound combined with a treatment of amphotericin B-loaded nanoparticles (AmB-NPs) against C. albicans. AmB-NPs were prepared by a poly(lactic-co-glycolic acid) (PLGA) double emulsion method. C. albicans was treated by AmB-NPs combined with 42 kHz ultrasound irradiation at an intensity of 0.30 W/cm² for 15 min. The results demonstrate that the application of ultrasound enhanced the antibacterial effectiveness of AmB-NPs (P < 0.01), and the antifungal efficiency increased significantly with increasing AmB concentration of drug-loaded nanoparticles under ultrasonic irradiation. Additionally, the mycelial morphology of C. albicans suffered from the most severe damage and loss of normal microbial morphology after the combined treatment of AmB-NPs and ultrasound, as revealed by electron microscope. Furthermore, we verified the safe use of low-frequency ultrasound on exposed skin and discussed the potential mechanism of ultrasound enhanced fungicidal activity. The results reveal that the mechanism may be associated with the ultrasound cavitation effect and an increase in intracellular reactive oxygen species.

Two-year Longitudinal Evaluation of Amphotericin B Lipid Complex Injection in a Tertiary Care Medical Center

A 2-year concurrent drug use evaluation was conducted in 156 patients to determine whether Abelcet (amphotericin B lipid complex injection) was being prescribed according to institution-approved guidelines and to characterize the patient population receiving Abelcet. Eighty-nine patients (57%) had fungal infections documented by chest x-ray, computed tomography, or fungal cultures. Sixty-seven (43%) had clinically suspected fungal infections. The Abelcet mean dose by weight was 5 mg/kg/day (actual body weight). Seventy-one patients (46%) met the established guidelines for use; 85 (54%) did not. Premedication was given to 64% of the patients; only 15 patients (10%) experienced documented fever and chills. A total of 72 patients (46%) died during therapy. Of the 75 patients who completed therapy in the hospital, 41 were switched to conventional amphotericin B, fluconazole, or itraconazole following a decrease in serum creatinine concentration, and 34 did not receive further antifungal therapy. The mean length of Abelcet therapy was 11 days. The mean increase in serum creatinine concentration at discontinuation of therapy was 0.2 mg/dL. Continued monitoring of Abelcet use was recommended and established guidelines were reaffirmed. Hydration with normal saline before and after dosing was suggested to help improve renal function, and dopamine was recommended to increase renal blood flow.

Antifungal activity of amphotericin B and voriconazole against the biofilms and biofilm-dispersed cells of Candida albicans employing a newly developed in vitro pharmacokinetic model

Background

Candida albicans is a common cause of a variety of superficial and invasive disseminated infections the majority of which are associated with biofilm growth on implanted devices. The aim of the study is to evaluate the activity of amphotericin B and voriconazole against the biofilm and the biofilm-dispersed cells of Candida albicans using a newly developed in vitro pharmacokinetic model which simulates the clinical situation when the antifungal agents are administered intermittently.

Methods

RPMI medium containing 1–5 X 10⁶ CFU/ml of C. albicans was continuously delivered to the device at 30 ml/h for 2 hours. The planktonic cells were removed and biofilms on the catheter were kept under continuous flow of RPMI medium at 10 ml/h. Five doses of amphotericin B or voriconazole were delivered to 2, 5 and 10 day-old biofilms at initial concentrations (2 and 3 μg/ml respectively) that were exponentially diluted. Dispersed cells in effluents from the device were counted and the adherent cells on the catheter were evaluated after 48 h of the last dose.

Results

The minimum inhibitory concentration of voriconazole and amphotericin B against the tested isolate was 0.0325 and 0.25 μg/ml respectively. Amphotericin B significantly reduced the dispersion of C. albicans cells from the biofilm. The log₁₀ reduction in the dispersed cells was 2.54-3.54, 2.30-3.55, and 1.94-2.50 following addition of 5 doses of amphotericin B to 2-, 5- and 10-day old biofilms respectively. The number of the viable cells within the biofilm was reduced by 18 (±7.63), 5 and 4% following addition of the 5 doses of amphotericin B to the biofilms respectively. Voriconazole showed no significant effect on the viability of C. albicans within the biofilm.

Conclusion

Both antifungal agents failed to eradicate C. albicans biofilm or stop cell dispersion from them and the resistance progressed with maturation of the biofilm. These findings go along with the need for removal of devices in spite of antifungal therapy in patients with device-related infection. This is the first study which investigates the effects of antifungal agents on the biofilm and biofilm-dispersion of C. albicans in an in vitro pharmacokinetic biofilm model.

Amphotericin B Lipid Complex (Abelcet) in the treatment of invasive mycoses: the North American experience

Abelcet, or Amphotericin B lipid Complex, is unique formulation, comprising an equimolar mixture of amphotericin B complexed with two lipids. In preclinical studies, Abelcet was clearly demonstrated to be less toxic than amphotericin B desoxycholate and to be effective in models where amphotericin B was ineffective at its maximum tolerated dose. Pharmacokinetic studies in animals also showed that the concentration of Abelcet in blood is similar or reduced compared to levels seen with conventional amphotericin B, with accumulation in the liver, lungs and spleen. Phase I clinical trials determined the optimum tolerated dose of Abelcet to be 5 mg/kg d-1. Data are now available for 228 cases (including 51 paediatric cases) of invasive fungal infection treated with Abelcet in an open-label emergency-release protocol. All patients had to have failed on previous amphotericin B or other conventional antifungals, or to have unacceptable toxicity on amphotericin B, or underlying renal disease, or nephrotoxicity due to other drugs. Abelcet was administered at a dose of 5 mg/kg d-1 for 4 wk. Approximately one-third of patients had candidiasis, one-third aspergillosis and one-third other infections, including fusariosis. Of 183 cases evaluable for response, 126 (69%) had a clinical response (cure or improvement) which was mycologically confirmed in 55% (61/110 tested). Results in paediatric cases were similar to or better than those seen in the group as a whole. When comparisons were made between cases with different types of infection, underlying disease/immunosuppressive disorder, and degree of neutropenia, the response rates were very consistent from group to group. Treatment with Abelcet was well tolerated and mean serum creatinine levels actually declined during therapy, particularly in patients with pre-existing renal dysfunction.

Biodegradable nanoparticles improve oral bioavailability of amphotericin B and show reduced nephrotoxicity compared to intravenous Fungizone

PURPOSE

Amphotericin B (AMB), an effective antifungal and antileishmanial agent associated with low oral bioavailability (0.3%) and severe nephrotoxicity, was entrapped into poly(lactide-co-glycolide) (PLGA) nanoparticles to improve the oral bioavailability and to minimize the adverse effects associated with it.

MATERIALS AND METHODS

The AMB-nanoparticles (AMB-NP) were prepared by nanoprecipitation method employing Vitamin E-TPGS as a stabilizer. In vitro release was carried out using membrane dialysis method. The in vitro hemolytic activity of AMB-NP was evaluated by incubation with red blood cells (RBCs). The acute nephrotoxicity profile and oral bioavailability of AMB-NP were evaluated in rats.

RESULTS

The prepared AMB-NP formulation contained monodispersed particles in the size range of 165.6 +/- 2.9 nm with 34.5 +/- 2.1% entrapment at 10% w/w initial drug loading. AMB-NP formulation showed biphasic drug release, an initial rapid release followed by a sustained release. The AMB-NP formulation exerted lower hemolysis and nephrotoxicity as compared to Fungizone. The relative oral bioavailability of the AMB-NP was found to be approximately 800% as compared to Fungizone.

CONCLUSION

Together, these results offer a possibility of treating systemic fungal infection and leishmaniasis with oral AMB-NP, which could revolutionize the infectious disease treatment modalities.

Amphotericin B-induced renal tubular cell injury is mediated by Na+ Influx through ion-permeable pores and subsequent activation of mitogen-activated protein kinases and elevation of intracellular Ca2+ concentration

Amphotericin B (AMB) is one of the most effective antifungal agents; however, its use is often limited by the occurrence of adverse events, especially nephrotoxicity. The present study was designed to determine the possible mechanisms underlying the nephrotoxic action of AMB. The exposure of a porcine proximal renal tubular cell line (LLC-PK1 cells) to AMB caused cell injury, as assessed by mitochondrial enzyme activity, the leakage of lactate dehydrogenase, and tissue ATP depletion. Propidium iodide uptake was enhanced, while terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling was not affected by AMB, suggesting a lack of involvement of apoptosis in AMB-induced cell injury. The cell injury was inhibited by the depletion of membrane cholesterol with methyl-beta-cyclodextrin, which lowered the extracellular Na(+) concentration or the chelation of intracellular Ca(2+). The rise in the intracellular Ca(2+) concentration may be mediated through the activation of the ryanodine receptor (RyR) on the endoplasmic reticulum and the mitochondrial Na(+)-Ca(2+) exchanger, since cell injury was attenuated by dantrolene (an RyR antagonist) and CGP37157 (an Na(+)-Ca(2+) exchanger inhibitor). Moreover, AMB-induced cell injury was reversed by PD169316 (a p38 mitogen-activated protein [MAP] kinase inhibitor), c-Jun N-terminal kinase inhibitor II, and PD98059 (a MEK1/2 inhibitor). The phosphorylations of these MAP kinases were enhanced by AMB in a calcium-independent manner, suggesting the involvement of MAP kinases in AMB-induced cell injury. These findings suggest that Na(+) entry through membrane pores formed by the association of AMB with membrane cholesterol leads to the activation of MAP kinases and the elevation of the intracellular Ca(2+) concentration, leading to renal tubular cell injury.

Assessing the Antifungal Activity of a New Oral Lipid-Based Amphotericin B Formulation Following Administration to Rats Infected withAspergillus Fumigatus

The purpose of this study was to assess the antifungal activity of a new oral amphotericin B (AmpB) lipid-based formulation following administration to rats infected with Aspergillus fumigatus. Aspergillus fumigatus inoculum (2.1-2.5 x 10(7) colony forming units [CFU]) were injected via the jugular vein; 48h later male albino Sprague-Dawley rats (350-400 g) were administered either a single oral dose of AmpB incorporated into Peceol (50 mg AmpB/kg), physiologic saline (nontreated controls) or Peceol alone (vehicle control) once daily for 4 days. To assess antifungal activity Brain, Lung, Heart, Liver, Spleen and Kidney sections were homogenized with normal saline (1 mL/g of tissue) and a 0.1-mL aliquot was spread plated onto a Sabourand dextrose agar plate. The plates were incubated for 48 hr at 37 degrees C, at which time the number of fungal CFU were determined and corrected for tissue weight. In addition, plasma galactomannan antigen concentrations were determined. Data was reported as mean +/- standard error of the mean. The AmpB-Peceol oral formulation significantly decreased total fungal CFU concentrations recovered in all the organs added together, brain CFU concentrations, spleen CFU concentrations and plasma galactomannan antigen concentrations compared to baseline. No significant differences in lung, heart, liver and kidney CFU concentrations between treatment and control groups were observed. Peceol vehicle control did not exhibit any antifungal activity. These findings suggest that a new oral lipid-based formulation of AmpB incorporated into Peceol can significantly decrease brain and spleen CFU concentrations and plasma galactomannan antigen concentrations compared to non-treated controls.

Amphotericin B Formulations and Drug Targeting

Amphotericin B is a low-soluble polyene antibiotic which is able to self-aggregate. The aggregation state can modify its activity and pharmacokinetical characteristics. In spite of its high toxicity it is still widely employed for the treatment of systemic fungal infections and parasitic disease and different formulations are marketed. Some of these formulations, such as liposomal formulations, can be considered as classical examples of drug targeting. The pharmacokinetics, toxicity and activity are clearly dependent on the type of amphotericin B formulation. New drug delivery systems such as liposomes, nanospheres and microspheres can result in higher concentrations of AMB in the liver and spleen, but lower concentrations in kidney and lungs, so decreasing its toxicity. Moreover, the administration of these drug delivery systems can enhance the drug accessibility to organs and tissues (e.g., bone marrow) otherwise inaccessible to the free drug. During the last few years, new AMB formulations (AmBisome, Abelcet, and Amphotec) with an improved efficacy/toxicity ratio have been marketed. This review compares the different formulations of amphotericin B in terms of pharmacokinetics, toxicity and activity and discusses the possible drug targeting effect of some of these new formulations.

Enhancing drug absorption using lipids: a case study presenting the development and pharmacological evaluation of a novel lipid-based oral amphotericin B formulation for the treatment of systemic fungal infections

The development of a safe and efficacious drug involves a balance between bioavailability, toxicity and disposition within the body. If the drug is hydrophobic or acid labile, oral administration may lead to poor systemic exposure, necessitating a parenteral treatment regime. Amphotericin B (AmpB) is one example of a well established, highly efficacious drug that has a 50 year history of intravenous therapy. AmpB formulated as a micellar dispersion (Fungizone; FZ) for IV use, remains one of the most effective agents in the treatment of systemic fungal infections, yet no oral formulations are currently commercially available. Recently, our laboratory has developed new oral lipid-based AmpB formulations with enhanced gastrointestinal (GI) tract absorption and antifungal activity with minimum renal toxicity. This review article will discuss these findings and present data to support two potential mechanisms for the enhanced GI tract absorption of AmpB when formulated in this oral lipid-based delivery system, namely an increase in lymphatic drug transport and a decrease in pre-systemic transporter-mediated drug efflux.

Effect of heat-treatment and the role of phospholipases on Fungizone®-induced cytotoxicity within human kidney proximal tubular (HK-2) cells and Aspergillus fumigatus

The objectives of this study were to determine the effects of heat-treatment on Fungizone (FZ)-induced cytotoxicity in human kidney (HK-2) cells and fungal isolates of Aspergillus fumigatus, and to determine the possible role of phospholipases (PLA2 and PLC) on heat-treated FZ (HFZ)-associated renal cell toxicity. HK-2 cells were grown at 37 degrees C in T75 flasks and seeded in 96-well plates at 20,000 cells/well. FZ and HFZ concentrations of 10, 25 and 50 microg/mL of AmpB were prepared. Snake venom PLA2 and PLC (2.15 U/mL) were pre-incubated with HFZ for 1h prior to addition to the cells. After 18 h of incubation, an MTS assay was performed to assess cell viability through mitochondrial respiration. A spore suspension of A. fumigatus was prepared and 96-well plates were seeded at 500,000 spores/well. HFZ and FZ were prepared as above and incubated with the fungi at 35 degrees C. After 72 h, the minimum inhibitory concentration (MIC) was determined as the lowest concentration of drug that inhibited visible growth. Student-Newman-Keuls multiple comparisons tests were conducted to determine statistical significance. FZ-induced cytotoxicity was significantly greater than for HFZ in HK-2 cells at amphotericin B (AmpB) concentrations between 10 and 50 microg AmpB/mL (n = 5-9, p < 0.05). HFZ and FZ were found to have similar minimum inhibitory concentration (MIC) ranges for A. fumigatus (0.225-0.25 microg) AmpB/mL; (n = 6). The addition of PLA2 and PLC to 50 microg heat-treated AmpB/mL significantly enhanced the cytotoxicity compared to controls (n = 6, p < 0.05). The presence of the phospholipases did not alter FZ-associated renal cell toxicity. Taken together, these findings suggest heat-treatment significantly decreased FZ-induced cytotoxicity in HK-2 cells without altering toxicity against a reference strain of A. fumigatus. In addition, PLA2 and PLC enhanced the renal toxicity associated with HFZ, but not that of FZ.

Amphotericin B

Invasive fungal infections are a major cause of morbidity and mortality in immunodeficient individuals (such as AIDS patients) and in transplant recipients or tumor patients undergoing immunosuppressive chemotherapy. Amphotericin B is one of the oldest, yet most efficient antimycotic agents. However, its usefulness is limited due to dose-dependent side-effects, notably nephrotoxicity. In order to improve its safety margin, new pharmaceutical formulations of amphotericin B have been designed especially to reduce its detrimental effects on the kidneys. Since the 1980s, a wide variety of new amphotericin B formulations have been brought forward for clinical testing, many of which were approved and reached market value in the 1990s. This review describes and discusses the molecular genetics, pharmacological, toxicological, and clinical aspects of amphotericin B itself and many of its innovative formulations.

Potential mechanisms by which Peceol increases the gastrointestinal absorption of amphotericin B

PURPOSE

The purpose of this study was to ascertain how the incorporation of AmpB into a glyceride-rich excipient Peceol significantly increased Amphotericin B's (AmpB) gastrointestinal absorption in white male Sprague-Dawley rats. Based on preliminary studies, our working hypothesis was that incorporation of AmpB into mixed micelles composed of Peceol would significantly enhance gastro-intestinal (GI) tract absorption by increasing lymphatic drug transport and decreasing P-glycoprotein (PGP)-mediated drug efflux.

METHODS

I. Lymphatic Transport

STUDIES

Following an overnight fast (12-16 hr) and 48 hr postsurgery, rats were divided into two treatment groups and received a single-dose oral gavage (1 mL total volume) at 0700 h of either desoxycholate (DOC)-AmpB (5 mg AmpB/kg; n = 6 at each time point) or AmpB incorporated into 100% Peceol (Peceol-AmpB; 5 mg AmpB/kg; n = 6 at each time point). Mesenteric lymph samples were obtained prior to and at 0-4-hr, 4-6-hr, and 6-8-hr intervals post oral gavage. An equal volume of normal saline (1 mL) was administered intravenously to the animal following each blood draw to prevent fluid depletion throughout the duration of the study. Lymph was immediately harvested by centrifugation and analyzed for drug by high-performance liquid chromatography (HPLC). II. Multidrug Resistance 1 (mdr-1) STUDIES: Caco-2 cells were seeded at 10,000 cells/cm2 in T-75 flasks. When the cells reached 80% confluency, they were treated for 1 day and 7 days with 0.1% to 1.0% (v/v) Peceol or media alone (control). Following treatment, total RNA was isolated using TRIzol reagent, followed by reverse transcription into single-stranded cDNA. Polymerase chain reactions (PCR) were performed with specific primers for mdr-1. The PGP protein was determined by Western Blot Analysis.

RESULTS

Mean weight of rats was not significantly different prior to and following drug administration. Similarly, kidney, liver, lung, spleen, and heart weights were not different between DOC-AmpB and Peceol-AmpB treatment group. A significantly greater amount of AmpB was transported through the mesenteric lymph duct for all the time intervals used following the administration of Peceol-AmpB treatment group compared to the administration of DOC-AmpB (suspension). A significant lower mdr-1 mRNA and PGP protein expression within Caco-2 cells was observed following 1 and 7 days treatment with Peceol 0.1% to 1.0% (v/v) compared to nontreated controls.

CONCLUSIONS

Taken together, these findings suggest that Peceol increases the gastrointestinal absorption of AmpB by increasing the amount of drug that is transported through the mesenteric lymph duct and by decreasing mdr-1 mRNA and PGP protein expression, resulting in lower PGP-mediated AmpB efflux.

Development and characterization of liposomal disodium ascorbyl phytostanyl phosphates (FM-VP4)

The specific objectives of this project were (1) to develop liposomal disodium ascorbyl phytostanyl phosphate (FM-VP4) formulations, (2) to develop a liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) assay for quantification of FM-VP4 in liposomal formulations and plasma sample, and (3) to characterize liposomal FM-VP4 formulations by finding optimal drug-to-lipid ratios and determining the degradation of FM-VP4 in liposomes. Section 2 describes an LC/MS/MS assay developed for the identification and quantification of FM-VP4 in liposomal formulations to provide estimates of drug concentrations and encapsulation efficiency. The extra step of removing plasma proteins prior to LC/MS/MS assay yields an analysis of FM-VP4 in plasma samples. Section 3 describes experiments designed to find the optimal drug-to-lipid ratio for liposomal FM-VP4 formulations by comparing encapsulation efficiencies and varying the lipid compositions. Additionally, this section details our degradation studies to determine if liposomes have any protective effects on FM-VP4; these studies tested various lipid compositions at 37 degrees C in rabbit plasma. The mechanism of how FM-VP4 lowers low-density lipoprotein (LDL) cholesterol and total cholesterol levels in various animal models is presently unknown. However, before the mechanism of action could be studied, FM-VP4 first had to be delivered efficiently into plasma or cultured cell. The low systemic bioavailability and cellular uptake of FM-VP4 further suggested the importance of finding an efficient delivery vehicle for this drug. This project proposed a framework for such delivery and paves the way for further investigation into how FM-VP4 works in vivo and in vitro.

Effects of lipid-based oral formulations on plasma and tissue amphotericin B concentrations and renal toxicity in male rats

The purpose of this study was to determine the effects of various lipid and mixed-micelle formulations on the oral absorption and renal toxicity of amphotericin B (AMB) in rats. The maximum concentration of AMB in plasma and the area under the concentration-time curve for 0 to 24 h for AMB were elevated in rats administered triglyceride (TG)-rich AMB formulations in comparison to those in rats given (i) AMB preformulated as a micelle containing sodium deoxycholate with sodium phosphate as a buffer (DOC-AMB), (ii) an AMB-lipid complex suspension, or (iii) AMB solubilized in methanol. Furthermore, our findings suggest that AMB incorporated into TG-based oral formulations has less renal toxicity than DOC-AMB.

Effect of heat-treated amphotericin B on renal and fungal cytotoxicity

The purpose of this investigation was to determine the cytotoxicity of amphotericin B (AMB; trade name Fungizone [FZ]) following the administration of FZ and a heat-treated form of FZ (HFZ) to LLC-PK(1) pig kidney cells and Cryptococcus neoformans var. gattii cells. HFZ was significantly less toxic to kidney cells than FZ at all concentrations tested. For both FZ and HFZ, the concentration range which resulted in a 50% reduction of the growth of fungal cells was 0.125 to 1 mg/ml. These findings suggest that heat treatment decreases AMB's renal cytotoxicity without modifying its antifungal activity.

Physicochemical properties of amphotericin B liposomes prepared by reverse-phase evaporation method

The physicochemical properties of phosphatidylcholine-cholesterol liposomes containing amphotericin B and prepared by reverse-phase evaporation method were studied. Uniformly dispersed liposomal suspensions were obtained by employing 3:1 ratio (by volume) of diethyl ether to normal saline, 5 min sonication time at 7 degrees C, and evaporation of diethyl ether at 25 degrees C. Microscopic examination showed that the prepared liposomes were spheroids with unilamellar, oligolamellar, or multilamellar structure. The liposomes containing amphotericin B 2.0 mol% of total lipid led to the highest percentage of drug entrapment. Liposomes with maximum entrapment efficiency were obtained from using 250 micromol of total lipid. The liposomal amphotericin B possessing the highest drug entrapment efficiency (approximately 95%) with particle size range of 1307-1451 nm was the one composed of 1:1 molar ratio of phosphatidylcholine to cholesterol.

Amphotericin B interactions with a DOPC monolayer. Electrochemical investigations

A model lipid membrane consisting of a monolayer of dioleoyl phosphatidylcholine (DOPC) adsorbed onto a Hg electrode has been used to study the interaction between the lipid and different formulations of Amphotericin B (AmB) [Fungizone (FZ), Heated Fungizone (HFZ), and Abelcet]. The lipid organizational order was measured by electrochemical methods [capacitance and metal ion (Tl(+)) reduction], characterizing the change in lipid order due to interaction with the drug. The mean size and number density of pores formed in the monolayer were estimated by fitting the reduction current transients to a random array of microelectrode model. This method was shown sensitive for investigation of the interaction of drugs with the DOPC monolayer. Abelcet was found to have a smaller disruptive effect on lipid order than FZ and HFZ. The formulations used to solubilize the AmB were also studied. Sodium deoxycholate used as a solubilizer in FZ displayed significant influence on lipid order similar to that observed for Abelcet. The lipid complex, used in Abelcet, did not significantly perturb the DOPC monolayer order. The lipid complex used in Abelcet may have an annealing or healing effect that buffers the disruption possible due to AmB.

Differences in the method by which plasma is separated from whole blood influences amphotericin B plasma recovery and distribution following amphotericin B lipid complex incubation within whole blood

A previous investigation suggested that the use of plasma as the biological fluid for measurement of amphotericin B (AmpB) concentrations greatly underestimates the concentrations of AmpB in the total blood circulation following amphotericin B lipid complex (ABLC) administration to humans. The purpose of this study was to determine if differences in the method used to obtain plasma from whole blood influences the percentage of AmpB recovered in plasma following ABLC incubation in whole blood. ABLC (5 microg AmpB/ml; peak blood concentration observed in rabbits following intravenous bolus of ABLC at a dose of 1 mg/kg) was incubated in whole blood for 5 min at 25 degrees C. These conditions were used to mimic the sample retrieval conditions used when blood is obtained from animals and human patients. Following incubation, plasma was obtained from whole blood using five different methods: (A) Whole blood was centrifuged for 5 min at 23 degrees C, and the plasma was separated; (B) whole blood was stored at 4 degrees C for 18 h, and the plasma was separated by gravity; (C) whole blood was stored at 23 degrees C for 18h, and the plasma was separated by gravity; (D) whole blood was stored at 37 degrees C for 18 h in a water bath, and the plasma was separated by gravity; and (E) whole blood was stored at 30 degrees C for 18 h in a water bath, and the plasma was separated by gravity. All samples were protectedfrom light throughout the duration of the experiment. AmpB concentration in each plasma sample was determined by high-performance liquid chromatography (HPLC) using an external calibration curve. The whole blood:plasma Amp B concentration ratio and the percentage of AmpB partitioned into plasma following incubation of ABLC in whole blood for each plasma separation procedure was as follows: (A) 6.5:1 blood:plasma AmpB concentration ratio, 15.4% +/- 1.6% AmpB in plasma; (B) 2.98:1 blood:plasma AmpB concentration ratio, 33.6% +/- 7.7% AmpB in plasma; (C) 1.5:1 blood:plasma AmpB concentration ratio, 67.6% +/- 10.3% AmpB in plasma; (D) 1.5:1 blood : plasma concentration ratio, 68.1% +/- 1.1% AmpB in plasma; and (E) 1.2 : 1 blood:plasma AmpB concentration ratio; 83.4% +/- 5.5% AmpB in plasma. These findings suggest that when measurement of AmpB in plasma is required following ABLC administration, incubation of whole blood at 30 degrees C for 18 h appears to be the most effective method.

Heat treatment of amphotericin b modifies its serum pharmacokinetics, tissue distribution, and renal toxicity following administration of a single intravenous dose to rabbits

The purpose of this investigation was to determine the serum pharmacokinetics, tissue distribution, and renal toxicity of amphotericin B (AmpB) following administration of a single intravenous dose (1 mg/kg of body weight) of Fungizone (FZ) and a heat-treated form of FZ (HFZ) to New Zealand White female rabbits. FZ solutions were heated at 70 degrees C for 20 min to produce HFZ. Blood samples were obtained before drug administration and serially thereafter. After collection of the 48-h blood sample, each rabbit was humanely sacrificed and the right kidney, spleen, lungs, liver, and heart were harvested for AmpB analysis. Serum creatinine levels were measured before and 10 h after drug administration. AmpB concentrations in the serum and tissues were analyzed using high-performance liquid chromatography. FZ administration to rabbits resulted in a greater-than-50% increase in serum creatinine concentrations compared to baseline. However, HFZ administration resulted in no difference in serum creatinine concentrations compared to baseline. The AmpB area under the concentration-time curve (AUC) after HFZ administration was significantly lower than the AmpB AUC in rabbits administered FZ. However, AmpB systemic total body clearance was significantly greater in rabbits administered HFZ than in rabbits administered FZ without any differences in volume of distribution at steady state. Kidney tissue AmpB concentrations, although not significantly different, were greater in rabbits administered FZ than in rabbits administered HFZ. Likewise, lung and spleen AmpB concentrations, although not significantly different, were greater in rabbits administered FZ than in rabbits administered HFZ. However, liver AmpB concentrations were significantly lower in rabbits administered FZ than in rabbits administered HFZ. No significant differences in heart AmpB concentration between rabbits administered FZ and those given HFZ were found. These findings suggest that the pharmacokinetics, tissue distribution, and renal toxicity of AmpB are modified following administration of HFZ. HFZ could be an improved low-cost AmpB drug delivery system that has a potentially higher therapeutic index than FZ.

Amphotericin B lipid complex or amphotericin B multiple-dose administration to rabbits with elevated plasma cholesterol levels: pharmacokinetics in plasma and blood, plasma lipoprotein levels, distribution in tissues, and renal toxicities

The purpose of the present study was to determine if a relationship exists between the plasma cholesterol concentration, the severity of amphotericin B (AmpB)-induced renal toxicity, and the pharmacokinetics of AmpB in plasma in hypercholesterolemic rabbits administered multiple doses of amphotericin B (AmB) deoxycholate (Doc-AmB) and AmB lipid complex (ABLC). After 7 days of administration of a cholesterol-enriched diet (0.50% [wt/vol]) or a regular rabbit diet, each rabbit was administered a single intravenous bolus of Doc-AmB (n = 8) or ABLC (n = 10) (1.0 mg/kg of body weight) daily for 7 consecutive days (a total of eight doses). Blood samples were obtained daily before and 24 h after the administration of each dose and serially thereafter following the administration of the last dose for the assessment of pharmacokinetics in plasma, kidney toxicity, plasma lipoprotein levels, and drug distribution in tissue. The pharmacokinetics of AmB in blood following the administration of ABLC were also determined in rabbits fed cholesterol-enriched and regular diets (n = 3 each group). Before drug treatment, cholesterol-fed rabbits demonstrated marked increases in total, low-density lipoprotein (LDL), and triglyceride-rich lipoprotein (TRL) cholesterol levels in plasma compared with the levels in rabbits on a regular diet. No significant differences in total plasma triglyceride levels were observed. Significant increases in plasma creatinine levels were observed in rabbits fed a cholesterol-enriched diet (P < 0.05) and rabbits fed a regular diet (P < 0.05) when administered AmB. However, the magnitude of this increase was twofold greater in rabbits fed a regular diet than in rabbits fed a cholesterol-enriched diet. An increase in plasma creatinine levels was observed only in rabbits on a cholesterol-enriched diet administered ABLC. The pharmacokinetics of AmB were significantly altered in rabbits on a cholesterol-enriched diet administered Doc-AmB or ABLC compared to those in rabbits on a regular diet administered each of these compounds. The pharmacokinetics of AmB in blood were significantly different following ABLC administration but not following Doc-AmB administration in both rabbits fed cholesterol-enriched diets and rabbits fed regular diets compared to their corresponding pharmacokinetics in plasma. An increased percentage of AmB was recovered in the TRL fraction when Doc-AmB was administered to rabbits fed a cholesterol-enriched diet than when it was administered to rabbits fed a regular diet. Furthermore, an increased percentage of AmB was recovered in the LDL and TRL fractions when ABLC was administered to rabbits fed a cholesterol-enriched diet rabbits fed a regular diet. These findings suggest that an increase in plasma cholesterol levels modifies the pharmacokinetics of AmB and renal toxicity following the administration of multiple intravenous doses of Doc-AmB and ABLC.

A pharmacokinetic study of amphotericin B lipid complex injection (Abelcet) in patients with definite or probable systemic fungal infections

This study describes a pharmacokinetic evaluation of amphotericin B (AMB) lipid complex injection (ABLC or Abelcet) in 17 patients with systemic fungal infection administered 5 mg/kg of body weight/day by infusion for 10 to 17 days. The results showed that AMB exhibited multiexponential disposition with high clearance, large volume of distribution at steady state, and long apparent elimination half-life but no evidence of accumulation in the blood after multiple daily doses. The results confirm previous observations and further reinforce the suggestion that ABLC may exist as a depot in the tissues from which free AMB is slowly released to limit exposure.

Antifungal activity of amphotericin B-lipid admixtures in experimental systemic candidosis in naive mice

We have shown previously that admixtures of amphotericin B (AMB) and Intralipid (AMB-IL) obtained by vigorous and prolonged agitation are stable and can be standardized. These preparations exhibited in-vitro activity against various Candida spp., and had significantly lower toxicity. The present study was undertaken to evaluate the activity of AMB-IL admixtures in vivo in comparison with the conventional formulation of AMB (Fungizone), using a murine model of experimental systemic candidosis. ICR female mice (4-6 weeks old) were injected iv with 5 x 10(4) Candida albicans CBS 562. The animals developed a lethal infection (100%) within 10 days. Systemic candidosis was demonstrated by the presence of fungal elements in kidneys and spleen tissue, and by enumeration of cfu of Candida in the tissue homogenates. AMB-IL or AMB was administered iv 48 h post-Candida inoculation for 5 consecutive days. Four experiments with 108 mice treated with AMB 5 x 0.4 mg/kg and followed up for 6 weeks, showed that the mean survival percentages at the end of the experiment were 0, 24.9 and 52.5% for the untreated group, conventional AMB-treated and AMB-IL-treated groups, respectively. The mean survival time (MST) was 7.4, 25 and 30 days for the untreated, conventional AMB-treated and AMB-IL-treated groups, respectively. Use of increased doses of AMB showed that conventional AMB at doses greater than 5 x 1 mg/kg caused immediate animal death. AMB-IL was used at doses of AMB up to 5 x 2 mg/kg. Experiments with 104 mice revealed that the mean survival percentage at the end of the experiment was 0, 34.5, 58.6 and 97% for the untreated, conventional AMB-treated (5 x 1 mg/kg), AMB-IL-1-treated (5 x 1 mg/kg) and AMB-IL-2-treated (5 x 2 mg/kg) groups, respectively. The MST was 7, 27.8, 34.8 and 41.4 days for the untreated, conventional AMB-treated, AMB-IL-1-treated and AMB-IL-2-treated groups, respectively. The results of this study reveal that AMB-IL is significantly more effective in treating systemic murine candidosis than conventional AMB.

Encapsulation characteristics of nystatin in liposomes: effects of cholesterol and polyethylene glycol derivatives

In this study, we characterized the encapsulation of amphipathic nystatin into liposomes with or without cholesterol (CH) and a polyethylene glycol derivative, distearoyl-N-(monomethoxy poly(ethylene glycol)succinyl)phosphatidylethanolamine (DSPE-PEG). The highest encapsulation efficacy of nystatin into liposomes (151 microg nystatin/mg lipid) was obtained with a cholesterol-free lipid composition containing 6 mol% of DSPE-PEG. The encapsulation efficacy was decreased by the incorporation of CH and improved by the incorporation of DSPE-PEG. In liposomes composed of dipalmitoylphosphatidylcholine (DPPC)/CH (2:1, mol/mol), the highest encapsulation efficacy of nystatin liposomes (84 microg/mg lipid) was achieved by the addition of DSPE-PEG and hydration with 9% sucrose solution, as compared with 13 microg/mg lipid without DSPE-PEG. The encapsulated amount increased with increasing amount of DSPE-PEG used and plateaued at 6 mol% of DSPE-PEG. The optimum molecular weight of PEG in DSPE-PEG was 2000 and a larger molecular weight resulted in lower encapsulation. The incorporation of CH affected the self-association of nystatin with lipid membranes, which was detected by fluorescence measurement. The molecular interaction between an amino group in nystatin and a phosphate group in DSPE-PEG plays an important role in efficient encapsulation of nystatin. Finally, the encapsulation characteristics of nystatin were compared with those of amphotericin B (AmB). Nystatin more readily associated with CH-free lipid membranes, but, AmB more readily interacted with DSPE-PEG. The results indicated that the differences in the molecular association of AmB or nystatin with lipids or DSPE-PEG are reflected in the encapsulation characteristics in liposomes.

Evaluation of the in-line filters for the intravenous infusion of amphotericin B fluid

OBJECTIVE

To evaluate the effects of four types of in-line filters on filtration rate, amphotericin B concentration and particulate matter.

METHODS

Filtration rates of amphotericin B fluid through in-line filters under maximum gravity flow were examined. The concentrations of amphotericin B and the particulate matter in the non-filtered and filtered amphotericin B fluid at the flow rate of 500 ml/24 h were measured.

RESULTS

Filtration through a 1.2 microm or 0.2 microm polyethersulphone (PES) filter under maximum gravity flow took less than 40 min. The 0.2 microm positively charged nylon 66 and 0.2 microm nylon 66 filters took 70 and 100 min, respectively, to filter 500 ml of amphotericin B fluid. The 0.2 microm positively charged nylon 66 filter and the 0.2 microm nylon 66 filter, but not the PES filter (1.2 and 0.2 microm), decreased the concentrations of amphotericin B in the filtered fluid by 100% within 1 h and by 66% within 24 h after the start of filtration, respectively. The particulate count in the non-filtered amphotericin B fluid was 27+/-5 particles/ml, exceeding the limit defined by USP XXIII. The 1.2 microm and 0.2 microm PES filters significantly decreased particulate matter by 83 and 97%, respectively, just after filtration.

CONCLUSION

The present results indicate that the 0.2 microm PES filter is optimal for intravenous infusion of amphotericin B fluid to minimize the introduction of particulate matter, microbial contaminants and endotoxin into patients.

Pharmacokinetics, distribution in serum lipoproteins and tissues, and renal toxicities of amphotericin B and amphotericin B lipid complex in a hypercholesterolemic rabbit model: single-dose studies

The purpose of this study was to determine if a relationship exists among total serum and lipoprotein cholesterol concentration, the severity of amphotericin B (AmpB)-induced renal toxicity, and the serum pharmacokinetics of AmpB in hypercholesterolemic rabbits administered AmpB and AmpB lipid complex (ABLC). After 10 days of cholesterol-enriched diet (0.50% [wt/vol]) or regular rabbit diet (control), each rabbit was administered a single intravenous bolus of AmpB or ABLC (1.0 mg/kg of body weight). Blood samples were obtained before administration and serially thereafter for the assessment of serum pharmacokinetics, kidney toxicity, and serum lipoprotein distribution. Rabbits were humanely sacrificed after all blood samples were obtained, and tissues were harvested for drug analysis. Before drug treatment, cholesterol-fed rabbits demonstrated marked increases in total serum cholesterol and low-density lipoprotein (LDL) cholesterol levels compared with levels in rabbits on a regular diet. No significant differences in triglyceride levels were observed. A significant increase in serum creatinine levels was observed in cholesterol-fed and regular diet-fed rabbits administered AmpB. However, the magnitude of this increase was 2.5-fold greater in cholesterol-fed rabbits than in regular diet-fed rabbits. No significant differences in triglyceride levels were observed. A significant increase in serum creatinine levels was observed in cholesterol-fed and regular diet-fed rabbits administered ABLC. Whereas AmpB pharmacokinetics were significantly altered in cholesterol-fed rabbits administered free AmpB, similar AmpB pharmacokinetics were observed in both rabbit groups administered ABLC. Renal AmpB levels were significantly increased in cholesterol-fed rabbits administered AmpB compared with those in all other groups. Hepatic and lung AmpB levels were elevated in cholesterol-fed rabbits administered free AmpB compared to controls. In addition, hepatic, lung, and spleen AmpB levels were significantly decreased in cholesterol-fed rabbits administered ABLC compared to controls. An increased percentage of AmpB was recovered in LDL-very-low-density lipoprotein fraction when free AmpB was administered to cholesterol-fed rabbits compared with those in all other groups. These findings suggest that increases in cholesterol, specifically, LDL cholesterol levels, modify the disposition and renal toxicity of free AmpB. However, the pharmacokinetics and renal toxicity of ABLC were independent of elevations in total and LDL cholesterol levels.

Enhanced encapsulation of amphotericin B into liposomes by complex formation with polyethylene glycol derivatives

PURPOSE

A highly efficient method was developed for the encapsulation of amphotericin B (AmB) in liposomes, and the mechanism involved was characterized.

METHODS

AmB was encapsulated in dipalmitoylphosphatidylcholine/ cholesterol (DPPC/CH, 2:1) liposomes after complex formation with distearoyl-N-(monomethoxy poly(ethylene glycol)succinyl) phosphatidylethanolamine (DSPE-PEG). Hydration of lipids was done with 9% sucrose solution.

RESULTS

The encapsulated amount of AmB was 111 microg/mg lipid, which was much higher than that obtained by the same method without DSPE-PEG (14 microg/mg lipid). The amount encapsulated increased with amount of DSPE-PEG used and with PEG molecular weight. Encapsulation efficacy was also influenced by the type of PEG derivatives used and by the modification of AmB, suggesting the involvement of complex formation between AmB and DSPE-PEG. Absorption and 31P-NMR spectral analyses indicated that interactions between the amino and phosphate groups and between the polyene and PEG moieties in AmB and DSPE-PEG, respectively, play an important role in the complex formation.

CONCLUSIONS

Complex formation of AmB with DSPE-PEG allows the highly efficient encapsulation of the drug in liposomes. This simple technique should be applicable to other hydrophobic drugs.

Quality evaluation by capillary electrophoresis of amphotericin B injection after filtration through various membrane filters

The determination of amphotericin B, an antifungal agent, was developed using micellar electrokinetic capillary chromatography (MEKC) with a diode array detector. Repeatability and intermediate precision of MEKC analysis were acceptable. A high correlation was found between amphotericin B levels in pharmaceutical solutions obtained by MEKC and those by high-performance liquid chromatography (HPLC) (r = 0.994). This MEKC method is therefore useful for the determination of amphotericin B. The concentration of amphotericin B did not significantly change after filtration through polyethersulfone (PES, 0.2 microm) and polyvinylidene difluoride (PVDF, 0.45 microm) membrane filters. When the Fungizone injection was filtered through PES (0.2 microm) and added to 5% dextrose for injection (500 mL), particulate matters larger than 10 microm decreased by 64% to a level under the standard defined by United States Pharmacopoeia (USP XXIII). PVDF filtration (0.45 microm) did not have this effect. Our results suggest that filtration of Fungizone injection through PES (0.2 microm) membrane filters is recommended for the preparation of intravenous amphotericin B fluid.

Toxicological profile and pharmacokinetics of a unilamellar liposomal vesicle formulation of amphotericin B in rats

AmBisome (ABLP) is a unilamellar liposomal preparation of amphotericin B that has demonstrated an improved safety profile compared to conventional amphotericin B. Single- and multiple-dose pharmacokinetics were determined by using noncompartmental methods for rats administered ABLP at 1, 3, 9, and 20 mg/kg/day. The toxicological profile was evaluated following 30 consecutive days of intravenous ABLP administration. Mean plasma amphotericin B concentrations reached 500 and 380 microg/ml (males and females, respectively) following 30 days of ABLP administration at 20 mg/kg. The overall apparent half-life was 11.2+/-4.5 h (males) or 8.7+/-2.2 h (females), and the overall clearance (CL) was 9.4+/-5.5 ml/h/kg (males) or 10.2+/-4.1 ml/h/kg (females). ABLP appears to undergo saturable disposition, resulting in a non-dose-proportional amphotericin B area under the curve and a lower CL at higher doses. Histopathological examination revealed dose-related transitional-cell hyperplasia in the transitional epithelium of the urinary tract (kidney, ureters, and urinary bladder) and moderate hepatocellular necrosis at the 20 mg/kg/day dose. Administration of ABLP in doses of up to 20 mg/kg/day resulted in 100-fold higher plasma amphotericin B concentrations, with significantly lower toxicity than that reported with conventional amphotericin B therapy.

Pharmacokinetic profile of ABELCET (amphotericin B lipid complex injection): combined experience from phase I and phase II studies

Amphotericin B (AmB) has been the most effective systemic antifungal agent, but its use is limited by the dose-limiting toxicity of the conventional micellar dispersion formulation (Fungizone). New formulations with better and improved safety profiles are being developed and include ABELCET (formerly ABLC), but their dispositions have not been well characterized; hence, the reason for their improved profiles remains unclear. This report details the pharmacokinetics of ABELCET examined in various pharmacokinetic and efficacy studies by using whole-blood measurements of AmB concentration performed by high-pressure liquid chromatography. The data indicated that the disposition of AmB after administration of ABELCET is different from that after administration of Fungizone, with a faster clearance and a larger volume of distribution. It exhibits complex and nonlinear pharmacokinetics with wide interindividual variability, extensive distribution, and low clearance. The pharmacokinetics were unusual. Clearance and volume of distribution were increased with dose, peak and trough concentrations after multiple dosings increased less than proportionately with dose, steady state appeared to have been attained in 2 to 3 days, despite an estimated half-life of up to 5 days, and there was no evidence of significant accumulation in the blood. The data are internally consistent, even though they were gathered under different conditions and circumstances. The pharmacokinetics of ABELCET suggest that lower concentrations in blood due to higher clearance and greater distribution may be responsible for its improved toxicity profile compared to those of conventional formulations.

Diversity of lipid-based polyene formulations and their behavior in biological systems

Patients with cancer and infectious disease often display dyslipidemias that result in changes in their plasma lipoprotein-lipid composition. It is likely that the interactions of liposomal polyenes with plasma lipoproteins may be responsible for the far different pharmacokinetics and pharmacodynamics of these compounds when they are administered to infected patients rather than to animals or healthy volunteers. Amphotericin B (AmpB) and nystatin are examples of such polyenes. Amphotericin B initially distributes with the high-density lipoprotein (HDL) fraction upon incubation in plasma. Over time, AmpB redistributes from HDLs to low-density lipoproteins (LDLs). This redistribution appears to be regulated by lipid transfer protein. However, when AmpB is incorporated into liposomes composed of negatively or positively charged phospholipids, not only is the capability of LTP to transfer AmpB from HDL to LDL diminished, but AmpB remains retained with only the HDL fraction. However, when liposomal nystatin is incubated in plasma, over 50% of nystatin distributes with HDLs. Over time, nystatin redistributes from HDL to the lipoprotein-deficient plasma fraction, which is composed of mainly aqueous plasma proteins. The lipid composition selected for the drug appears to be a vital constituent in regulating the drug's interaction with biological fluids. Furthermore, liposome (or liposomal particle) size, fluidity, and other physiochemical characteristics also play a role in altering the pharmacokinetics and pharmacological effects of lipid-based drug formulations. Armed with this understanding, a rational approach to clinical development of these formulations could be facilitated.

Amphotericin B: new life for an old drug

Interest in amphotericin B has undergone a renaissance of sorts over the past few years despite the advent of the newer less-toxic azole antifungal drugs. This is, in part, owing to the unfortunate increase in fungal diseases worldwide. It is also, however, owing to the reduction of toxicity via innovative liposomal delivery systems, better understanding of drug mechanism and distribution and a surprising expansion of the antibiotic spectrum of amphotericin B to include select virus, parasite and possibly prion infections. In this article, Scott Hartsel and Jacques Bolard summarize the recent leaps in pharmaceutics, spectrum and molecular mechanistic knowledge of this surprising molecule.

A high-performance liquid chromatographic assay for the determination of amphotericin B serum concentrations after the administration of AmBisome, a liposomal amphotericin B formulation

A sensitive and selective high-performance liquid chromatographic (HPLC) method has been developed for the determination of amphotericin B in human serum. After methanol deproteinization, amphotericin B and 3-nitrophenol (internal standard) are separated by reversed-phase chromatography and detected by ultraviolet absorbance. The analysis of human serum after the standard addition of amphotericin B (0.05-200.0 micrograms/mL) demonstrated excellent precision and accuracy over a five-day period. The HPLC assay uses two standard curve ranges. The high sensitivity curve range for low AmBisome dosage (1.0 mg/kg) is 0.05-20.0 micrograms/mL (curve 1), and the second curve range for the higher AmBisome dose regimens (2.5-5.0 mg/kg) is 0.5-200 micrograms/mL (curve 2). The intraday and interday coefficients of variations for standard curve 1 were 0.5-4.6% and 3.0-11.5%, respectively. The limit of quantitation was 0.05 microgram/mL. The intraday and interday coefficients of variation for standard curve 2 were 2.0-3.6 and 6.9-10.1, respectively. No interfering peak at the retention time for Amphotericin B and the internal standard were present in blank serums or serum samples spiked with fifteen potential co-administrated drugs with Amphotericin B treatment. The method was used to quantitate serum concentrations of amphotericin B in patients after the administration of AmBisome, a liposomal formulation of amphotericin B.

Carrier effects on biological activity of amphotericin B

Amphotericin B (AmB), the drug of choice for the treatment of most systemic fungal infections, is marketed under the trademark Fungizone, as an AmB-deoxycholate complex suitable for intravenous administration. The association between AmB and deoxycholate is relatively weak; therefore, dissociation occurs in the blood. The drug itself interacts with both mammalian and fungal cell membranes to damage cells, but the greater susceptibility of fungal cells to its effects forms the basis for its clinical usefulness. The ability of the drug to form stable complexes with lipids has allowed the development of new formulations of AmB based on this property. Several lipid-based formulations of the drug which are more selective in damaging fungal or parasitic cells than mammalian cells and some of which also have a better therapeutic index than Fungizone have been developed. In vitro investigations have led to the conclusion that the increase in selectivity observed is due to the selective transfer of AmB from lipid complexes to fungal cells or to the higher thermodynamic stability of lipid formulations. Association with lipids modulates AmB binding to lipoproteins in vivo, thus influencing tissue distribution and toxicity. For example, lipid complexes of AmB can be internalized by macrophages, and the macrophages then serve as a reservoir for the drug. Furthermore, stable AmB-lipid complexes are much less toxic to the host than Fungizone and can therefore be administered in higher doses. Experimentally, the efficacy of AmB-lipid formulations compared with Fungizone depends on the animal model used. Improved therapeutic indices for AmB-lipid formations have been demonstrated in clinical trials, but the definitive trials leading to the selection of an optimal formulation and therapeutic regimen have not been done.

Amphotericin B lipid complex treatment of a leukemic child with disseminated Fusarium solani infection

We report a case of Fusarium solani infection in a 2 1/2-year-old girl with acute lymphoblastic leukemia and severe neutropenia. The infection, initially limited to her sinuses, became disseminated, as evidenced by the development of a characteristic cutaneous lesion on her left leg after a cumulative dose of amphotericin B of 18.3 mg/kg. Amphotericin B lipid complex (ABLC), 5 mg/kg/day, in conjunction with repeated surgical debridement of the sinuses and correction of neutropenia with granulocyte colony stimulating factor (GCSF), led to clinical and mycologic cure.

Pharmacokinetics of conventional formulation versus fat emulsion formulation of amphotericin B in a group of patients with neutropenia

The pharmacokinetics of amphotericin B administered in a conventional 5% dextrose (glucose) (5% D) solution and in a 20% fat emulsion formulation (Intralipid; 20% IL) were compared in 16 patients (mean age, 42 years [range, 18 to 70 years]) who had been hospitalized for hematological malignancies and with proven or suspected fungal infections. All of the patients received 50 mg (approximately 1 mg/kg of body weight per day) of amphotericin B daily in random order, either as a 50-ml lipid emulsion (20% IL) (group I) or in 500 ml of 5% D (group II). Five serum samples were taken during the 24 h after drug administration, and the levels of amphotericin B were measured by high-pressure liquid chromatography. Serum amphotericin B concentrations declined rapidly during the first 6 h, and subsequent measurements revealed a slow terminal elimination phase in both groups. The maximum serum amphotericin B concentration was significantly lower when the drug was administered in 20% IL (1.46 +/- 0.61 versus 2.83 +/- 1.17 micrograms/ml; P = 0.02). The area under the concentration-time curve from 0 to 24 h was also much lower in group I (17.22 +/- 11.15 versus 28.98 +/- 15.46 micrograms.h/ml). The half-life of the distribution phase was approximately three times longer in group I (2.92 +/- 2.34 h versus 0.64 +/- 0.24 h; P = 0.011). Conversely, the half-lives of the elimination phase were approximately equal in the two groups (11.44 +/- 5.18 versus 15.23 +/- 5.25 h). The mean residence times were also similar in both groups (19.41 +/- 11.13 versus 19.65 +/- 7.86 h). The clearance and the steady-state volume of distribution of amphotericin B in group I were about twice as great as those in group II (62.97 +/- 35.51 versus 33.01 +/- 14.33 ml/kg/h and 1,043.92 +/- 512.10 versus 562.32 +/- 152.05 ml/kg [P = 0.034], respectively). Finally, the volume of distribution in the central compartment was greater in group I than in group II (618.17 +/- 231.80 versus 328.19 +/- 151.71 ml/kg; P = 0.013), but there were no differences in the volume of distribution in the peripheral compartment (425.75 +/- 352.87 versus 234.14 +/- 75.92 ml/kg). These results suggest that amphotericin B has a different pharmacokinetic profile when it is administered in 20% IL than when it is administered in the standard 5% D form and that the main difference is due to a clear-cut difference in the steady-state volume of distribution, especially that in the central compartment.

Administration of lipid-emulsion versus conventional amphotericin B in patients with neutropenia

OBJECTIVE

To evaluate the usefulness of a 20% lipid emulsion as a delivery system for amphotericin B (1 mg/mL) administered over 1 hour to patients with neutropenia with hematologic malignancies compared with amphotericin B (0.1 mg/mL) administered in dextrose 5% solution over the same time.

DESIGN

A prospective, comparative, randomized, labeled study.

SETTING

Hematology unit, pharmacy service, university general hospital.

PARTICIPANTS

Twenty patients with neutropenia with hematologic malignancies and proven or suspected fungal infections, 10 in the fat emulsion group (group 1) and 10 in the dextrose 5% group (group 2).

MAIN OUTCOME MEASURES

Clinical tolerance (i.e., fever, shaking chills, nausea, blood pressure, pulse rate) and biologic tolerance (i.e., urea, creatinine, sodium, potassium).

RESULTS

Clinical tolerance was comparable in both groups although amphotericin B in fat emulsion was better tolerated. Medication for symptoms related to the administration of amphotericin B was given in 6 cases in group 1 and in 8 cases in group 2. There was a statistically significant difference in the urea concentrations between the 2 groups (p = 0.023); there was an observed increase between the initial and the final serum urea (56.8 mg/d in group 1, 79.8 mg/dL in group 2). Statistically significant differences in creatinine serum concentrations (84.9 mumol/L in group 1, 123.8 mumol/L in group 2) (p = 0.047) were found. No differences were found in the antifungal efficacy of the treatment. However, as amphotericin B was started in the majority of cases (75%) as empiric treatment for fever unresponsive to antibiotic therapy, it is difficult to compare the efficacy of both preparations.

CONCLUSIONS

The clinical tolerance of lipid-emulsion infusions is similar to that of conventionally administered amphotericin B therapy. Renal toxicity appears to be decreased when the drug is administered in a fat emulsion. This type of preparation permits the reduction of the volume and the time of administration for amphotericin B therapy.

Amphotericin B liposomes with prolonged circulation in blood: in vitro antifungal activity, toxicity, and efficacy in systemic candidiasis in leukopenic mice

Pegylated amphotericin B (AmB) liposomes (PEG-AmB-LIP) were compared with laboratory-prepared nonpegylated AmB liposomes (AmB-LIP), a formulation with a lipid composition the same as that in AmBisome, as well as with industrially prepared AmBisome regarding their in vitro antifungal activities, toxicities, blood residence times, and therapeutic efficacies. Killing of Candida albicans (> 99.9%) during short-term (6-h) incubation was observed at 0.2 mg of AmB per liter for AmB desoxycholate, 0.4 mg of AmB per liter for PEG-AmB-LIP, 0.8 mg of AmB per liter for AmB-LIP, and 12.8 mg of AmB per liter for AmBisome. The maximum tolerated doses of PEG-AmB-LIP, AmB-LIP, and AmBisome were 15, 19, and > 31 mg of AmB per kg of body weight, respectively. In contrast to AmB-LIP, the blood residence time of PEG-AmB-LIP was prolonged and dose independent. In a model of systemic candidiasis in leukopenic mice at a dose of 5 mg of AmB per kg, PEG-AmB-LIP was completely effective and AmB-LIP was partially effective, whereas AmBisome was not effective. AmB-LIP at 11 mg of AmB per kg was partially effective. AmBisome at 29 mg of AmB per kg was completely effective. In conclusion, the therapeutic efficacies of AmB liposomes can be improved by preparing AmB liposomes in which a substantial reduction in toxicity is achieved while antifungal activity is retained. In addition, therapeutic efficacy is favored by a prolonged residence time of AmB liposomes in blood.

Liposomes as delivery systems in the prevention and treatment of infectious diseases

Research on the potential application of liposomes in the prevention and treatment of infectious diseases has focussed on improvement of the therapeutic index of antimicrobial drugs and immunomodulators and on stimulation of the immune response to otherwise weak antigens in vaccines composed of purified micro-organism subunits. In this review current approaches in this field are outlined. The improved therapeutic index of antimicrobial drugs after encapsulation in liposomes is a result of enhanced drug delivery to infected tissue or infected cells and/or a reduction of drug toxicity of potentially toxic antibiotics. Liposomal encapsulation of immunomodulators that activate macrophages aims at reducing the toxicity of these agents and targeting them to the cells of the mononuclear phagocyte system in order to increase the nonspecific resistance of the host against infections. Studies on the immunogenicity of liposomal antigens have demonstrated that liposomes can potentiate the humoral and cell mediated immunity to a variety of antigens.