Amphotericin B concentrations in healthy mallard ducks (Anas platyrhynchos) following a single intratracheal dose of liposomal amphotericin B using an atomizer

Aspergillosis is a fungal infection that primarily affects the respiratory tract. Amphotericin B has broad antifungal activity and is commonly used to treat aspergillosis, a fungal pneumonia that is a common sequela in oiled waterfowl as well as other birds in wildlife rehabilitation. Pharmacokinetic parameters of nebulized amphotericin B in an avian model have been reported, but those of direct intratracheal delivery have yet to be established. The objective of this study was to evaluate if a single 3 mg/kg dose of liposomal amphotericin B delivered intratracheally using a commercial atomizer would achieve plasma and lung tissue concentrations exceeding targeted minimum inhibitory concentrations (MIC) for Aspergillus species in adult mallard ducks (Anas platyrhynchos). Following intratracheal delivery, amphotericin B was present in lung parenchyma at concentrations above the targeted MIC of 1 μg/g for up to 9 days post-administration; however, distribution of the drug was uneven, with the majority of the drug concentrated in one lung lobe. Concentrations in the contralateral lung lobe and the kidneys were above the targeted MIC 1 day after administration but declined exponentially with a half-life of approximately 2 days. Plasma concentrations were never above the targeted MIC. Histological examination of the trachea, bronchi, lungs, heart, liver, and kidneys did not reveal any toxic changes. Using a commercial atomizer, intratracheal delivery of amphotericin B at 3 mg/kg resulted in lung parenchyma concentrations above 1 μg/ml with no discernable systemic effects. Further studies to establish a system of drug delivery to both sides of the pulmonary parenchyma need to be performed, and the efficacy of this treatment for disease prevention remains to be determined.

[Chemical and microbiological aspects of the quantitative analysis of amphotericin B]

Amphotericin B can be determined by chemical (HPLC, spectrophotometry) and microbiological (bioassay) methods. The utilization of both during a stability test can give more detailed information about the activity and concentration change of amphotericin B solutions. Previously published HPLC methods do not lay stress on the separation of by-constituents present in the substance. We have also observed that the bioassay conditions described in the Ph. Eur. 6. are not suitable for the measurement of concentration change experienced during a stability test. The aim of our study was to optimize the chemical and microbiological methods. We have improved the eluent system based on earlier HPLC methods for the separation of the main heptaene and the minor tetraene by-constituents in Fungizone (Bristol-Myers Squibb). The most optimal bioassay conditions were determined where a relatively wide concentration range can be measured. With the improved methods both chemical and microbiological changes can be more accurately measured in our future stability tests.

Penetration of amphotericin B lipid formulations into pleural effusion

The penetration of the amphotericin B (AMB) lipid formulations (liposomal AMB, AMB colloidal dispersion, and AMB lipid complex formulations) into pleural effusions in seven critically ill patients was assessed. AMB was detected in all pleural effusion samples at concentrations ranging from 0.02 to 0.43 microg/ml. The penetration ratio was 3 to 44%.

Development and characterization of amphotericin B bearing emulsomes for passive and active macrophage targeting

The antifungal and antileishmanial agent amphotericin B (AmB) has been complexed with lipids to develop a less toxic formulation of AmB. Because lipid particles are phagocytized by the reticuloendothelial system, lipid associated AmB should be concentrated in infected macrophages of liver and spleen and be very effective against visceral leishmaniasis (VL) and systemic fungal infections. Therefore, AmB was formulated in trilaurin based nanosize lipid particles (emulsomes) stabilized by soya phosphatidylcholine (PC) as a new intravenous drug delivery system for macrophage targeting. Emulsomes were prepared by cast film technique followed by sonication to obtain particles of nanometric size range. Formulations were optimized for AmB to lipid ratio, sonication time and PC to trilaurin ratio. Emulsomes were modified by coating them with macrophage-specific ligand (O-palmitoyl mannan, OPM). The surface modified emulsomes and their plain counterparts were characterised for size, shape, lamellarity and entrapment efficiency. Fluorescence microscopy study showed significant localization of plain and coated emulsomes inside the liver and spleen cells of golden hamsters. In vivo organ distribution studies in albino rats demonstrated that extent of accumulation of emulsome entrapped AmB in macrophage rich organs, particularly liver, spleen and lungs was significantly high when compared against the free drug (AmB-deoxycholate or AmB-Doc). The rate and extent of accumulation were found to increase further on ligand anchoring. Further, a significantly higher (P < 0.05) drug concentration in the liver was estimated over a period of 24 h for OPM coated emulsomes than for plain emulsomes. We concluded that OPM coated emulsomes could fuse with the macrophages of liver and spleen due to ligand-receptor interaction and could target the bioactives inside them. The proposed plain and OPM coated emulsome based systems showed excellent potential for passive and active intramacrophage targeting, respectively and the approach could be a successful alternative to the currently available drug regimens of VL and systemic fungal infections.

Safety of aerosolized liposomal versus deoxycholate amphotericin B formulations for prevention of invasive fungal infections following lung transplantation: a retrospective study

BACKGROUND

Nebulized amphotericin B deoxycholate (AmBd) has been used to prevent invasive pulmonary aspergillosis after lung transplantation.

METHODS

In this retrospective study we compared the safety and tolerability of nebulized AmBd and nebulized liposomal amphotericin B (L-AmB) in 38 consecutive lung transplant recipients. Progress notes, medication administration records, microbiology, and pulmonary function reports were reviewed. Histologic sections from lung tissue were examined. Plasma amphotericin B levels were measured.

RESULTS

A total of 1206 doses of AmBd and 1149 doses of L-AmB were administered. Eighteen patients received AmBd only, 11 received L-AmB only, and 9 received the medications sequentially. The total number of complaints vs. the number of doses administered was 1.0% for AmBd-treated patients and 1.2% for L-AmB-treated patients. No differences were observed between the treatment groups on lung biopsy specimens. Plasma amphotericin B levels were <0.2-0.9 microg/mL in AmBd-treated patients and <0.2 microg/mL in L-AmB-treated patients.

CONCLUSIONS

In lung transplant recipients, both inhaled AmBd and L-AmB were safe and well tolerated over a large number of medication exposures.

Serum and intraperitoneal levels of amphotericin B and flucytosine during intravenous treatment of critically ill patients with Candida peritonitis

OBJECTIVES

To study the relation between serum and peritoneal levels of amphotericin B and flucytosine during intravenous treatment in patients with abdominal sepsis due to a perforated gut.

PATIENTS AND METHODS

Included were consecutive patients with abdominal sepsis due to a perforated gut, who were treated intravenously with amphotericin B and/or flucytosine after surgery if an abdominal drain was present. Amphotericin B and flucytosine were measured from simultaneously collected serum and abdominal fluid samples.

RESULTS

Twenty-one consecutive patients were included. Five repeated samples were taken from three patients. The time interval between the start of the medication and the first sampling was median 4.0 days (range 2-7 days). The correlation coefficient (r(2)) between serum and peritoneal levels of amphotericin B was 0.79. In nine patients (43%) with a maximum serum level of 0.28 mg/L, amphotericin B in the peritoneal fluid was undetectable. The lowest serum level that was present with a detectable peritoneal level was 0.16 mg/L. A short duration of treatment (2 days) was associated with low serum and undetectable peritoneal levels. In seven patients, flucytosine levels were measured. Peritoneal flucytosine levels did not differ significantly from serum levels. Serum and peritoneal flucytosine levels correlated well with r(2)=0.88. Peritoneal amphotericin B level was inversely correlated with C-reactive protein level on the same day (r(2)=0.30).

CONCLUSIONS

It is shown, during continuous infusion, that peritoneal levels of amphotericin B are lower than serum levels. The amphotericin B serum levels should exceed 0.5 mg/L to obtain peritoneal levels above MIC values. Flucytosine levels in the abdominal fluid are comparable to serum levels and within MIC ranges.

Amphotericin B dose optimization in children with malignant diseases

In this study, rational dosing guidelines for amphotericin B-deoxycholate (AmB) are proposed for children. AmB steady-state trough concentrations (C(ss,trough)) and plasma creatinine concentrations (C(creat)) were measured in 83 children (age: 10 months to 18 years) receiving prophylactic AmB therapy (1 mg/kg/day). Maximum tolerable AmB C(ss,trough) were identified by determining the probability of large (>24%, 75th percentile) increases in C(creat) after 6 days of AmB for a series of C(ss,trough) ranges. Dose requirements were determined using a concentration-targeting approach. The 0.76-1.05 mg/l C(ss,trough) range provided the maximum concentrations that still had a low probability (p < 0.29) of adverse renal effects. 1 mg/kg/day AmB produces C(ss,trough) within this range for children weighing 25-45 kg. Lighter children (10-25 kg) require higher AmB doses (1.25-1.5 mg/kg/day) to achieve target C(ss,trough), while heavier children (45-55 kg) require lower doses (0.75 mg/kg/day). These starting dose guidelines may require individualization and prospective evaluation.

Influence of the Progression of Cryptococcal Meningitis on Brain Penetration and Efficacy of AmBisome in a Murine Model

BACKGROUND

AmBisome is a small unilamellar vesicle containing amphotericin B. AmBisome is generally unable to pass through the blood-brain barrier, but the distribution of AmBisome in the brain is increased by inflammation, and in consequence, AmBisome exhibits activity against fungal meningitis. We investigated the influence of the progression of cryptococcal meningitis on the brain penetration and efficacy of AmBisome.

METHOD

Mice were infected intracerebroventricularly with Cryptococcus neoformans 4 h or 5 days prior to a single dose treatment.

RESULTS

The brain tissue level and efficacy of AmBisome when administered 5 days after infection were greater than 4 h after infection. An immunohistochemical study showed that AmBisome-derived amphotericin B was localized at the infected site in the subarachnoid space. When AmBisome was compared with Fungizone at the maximum tolerated dose, 10 mg/kg AmBisome exhibited greater efficacy than 1 mg/kg Fungizone in both regimens.

CONCLUSION

The brain penetration of AmBisome was enhanced by the progression of cryptococcal meningitis and correlated with the in vivo activity.

Evaluation of antifungal pharmacodynamic characteristics of AmBisome against Candida albicans

A liposomal formulation of Amphotericin B (AmBisome), with small unilamellar vesicles containing amphotericin B, shows characteristic pharmacokinetics as liposomes, and in consequence, has different pharmacological activity and toxicity from amphotericin B deoxycholate (Fungizone). In this study, we evaluated the antifungal pharmacodynamic characteristics of AmBisome against Candida albicans using the in vitro time-kill method and murine systemic infection model. A time-kill study indicated that the in vitro fungicidal activities of AmBisome and Fungizone against C. albicans ATCC 90029 increased with increasing drug concentration. For in vivo experiments, leucopenic mice were infected intravenously with the isolate 4 hr prior to the start of therapy. The infected mice were treated for 24 hr with twelve dosing regimens of AmBisome administered at 8-, 12-, 24-hr dosing intervals. Correlation analysis between the fungal burden in the kidney after 24 hr of therapy and each pharmacokinetic/pharmacodynamic parameter showed that the peak level/MIC ratio was the best predictive parameter of the in vivo outcome of AmBisome. These results suggest that AmBisome, as well as Fungizone, has concentration-dependent antifungal activity. Furthermore, since AmBisome can safely achieve higher concentrations in serum than Fungizone, AmBisome is thought to have superior potency to Fungizone against fungal infections.

Role of Phospholipid Transfer Protein on the Plasma Distribution of Amphotericin B Following the Incubation of Different Amphotericin B Formulations

PURPOSE

The purpose of this study was to investigate the role of phospholipid transfer protein (PLTP) on the plasma distribution of amphotericin B (AmpB) following incubation with different AmpB formulations in human plasmas with varying lipid profiles.

METHODS

In a first set of experiments, plasma distribution profiles of AmpB were determined following the incubation of Fungizone and lipid-based formulations (Abelcet and AmBisome) at a concentration of 20 microg AmpB/mL for 5-120 min at 37 degrees C in the plasma obtained from six different individuals (total cholesterol concentrations range between 62 and 332 mg/dL). In a second set of experiments, Abelcet, and AmBisome at a concentration of 20 microg AmpB/mL were incubated for 5 min at 37 degrees C in human plasma (total cholesterol = 163 mg/dL) that had been pretreated with an antibody raised up against PLTP (1:400 v/v dilution from stock solution) for 20 min at 37 degrees C. Following incubation, the human plasma was separated into its lipoprotein and lipoprotein-deficient fractions by density gradient ultracentrifugation and analyzed for AmpB content by high-performance liquid chromatography.

RESULTS

The majority of AmpB was covered in the lipoprotein-deficient plasma and high-density lipoprotein (HDL) fractions following incubation of Fungizone in human plasma. The majority of AmpB (48.7-87.2%) was recovered in the HDL fraction following incubation of Abelcet and AmBisome in human plasma. The presence of the PLTP antibody resulted in a 20% decrease in the percentage AmpB recovered in the HDL fraction following the incubation of Abelcet. However, the plasma distribution of AmpB remained unchanged following the incubation of AmBisome in plasma containing the PLTP antibody.

CONCLUSIONS

Taken together, these findings suggest indirect evidence that PLTP may play an important role in the plasma distribution profile of AmpB following the incubation of Abelcet and may be one of the factors responsible for the preferential association of AmpB with HDL when administered as Abelcet.

Population pharmacokinetics of liposomal amphotericin B in pediatric patients with malignant diseases

A population pharmacokinetic model of liposomal amphotericin B (L-AmB) in pediatric patients with malignant diseases was developed and evaluated. Blood samples were collected from 39 pediatric oncology patients who received multiple doses of L-AmB with a dose range from 0.8 to 5.9 mg/kg of body weight/day. The patient cohort had an average age of 7 years (range, 0.2 to 17 years) and weighed an average of 28.8 +/- 19.8 kg. Population pharmacokinetic analyses were performed with NONMEM software. Pharmacokinetic parameters, interindividual variability (IIV), between-occasion variability (BOV), and intraindividual variability were estimated. The influence of patient characteristics on the pharmacokinetics of L-AmB was explored. The final population pharmacokinetic model was evaluated by using a bootstrap sampling technique. The L-AmB plasma concentration-time data was described by a two-compartment pharmacokinetic model with zero-order input and first-order elimination. The population mean estimates of clearance (CL) and volume of distribution in the central compartment (V1) were 0.44 liters/h and 3.12 liters, respectively, and exhibited IIV (CL, 10%) and significant BOV (CL, 46% and V1, 56%). The covariate models were CL (liters/h) = 0.44 . e(0.0152.(WT-21)) and V1 (liters) = 3.12.e(0.0241.(WT-21)), where WT is the patient's body weight (kg) centered on the study population cohort median of 21 kg. Model evaluation by the bootstrap procedure indicated that the full pharmacokinetic model was robust and parameter estimates were accurate. In conclusion, the pharmacokinetics of L-AmB in pediatric oncology patients were adequately described by the developed population model. The model has been evaluated and can be used in the design of rational dosing strategies for L-AmB antifungal therapy in this special population.

Population pharmacokinetics of amphotericin B lipid complex in neonates

The pharmacokinetics of amphotericin B lipid complex (ABLC) were investigated in neonates with invasive candidiasis enrolled in a phase II multicenter trial. Sparse blood (153 samples; 1 to 9 per patient, 1 to 254 h after the dose) and random urine and cerebrospinal fluid (CSF) samples of 28 neonates (median weight [WT], 1.06 kg; range, 0.48 to 4.9 kg; median gestational age, 27 weeks; range, 24 to 41 weeks) were analyzed. Patients received intravenous ABLC at 2.5 (n = 15) or 5 (n = 13) mg/kg of body weight once a day over 1 or 2 h, respectively, for a median of 21 days (range, 4 to 47 days). Concentrations of amphotericin B were quantified as total drug by high-performance liquid chromatography. Blood data for time after dose (TAD) of <24 h fitted best to a one-compartment model with an additive-error model for residual variability, WT0.75 (where 0.75 is an exponent) as a covariate of clearance (CL), and WT as a covariate of volume of distribution (V). Prior amphotericin B, postnatal age, and gestational age did not further improve the model. The final model equations were CL (liters/h) = 0.399 x WT(0.75) (interindividual variability, 35%) and V (liters) = 10.5 x WT (interindividual variability, 43%). Noncompartmental analysis of pooled data with a TAD of >24 h revealed a terminal half-life of 395 h. Mean concentrations in the urine after 1, 2, and 3 weeks ranged from 0.082 to 0.430 microg/ml, and those in CSF ranged from undetectable to 0.074 microg/ml. The disposition of ABLC in neonates was similar to that observed in other age groups: weight was the only factor that influenced clearance. Based on these results and previously published safety and efficacy data, we recommend a daily dosage between 2.5 and 5.0 mg/kg for treatment of invasive Candida infections in neonates.

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.

Comparison of LNS-AmB, a novel low-dose formulation of amphotericin B with lipid nano-sphere (LNS), with commercial lipid-based formulations

Three lipid-based delivery systems (AmBisome, Amphocil, and Abelcet) for amphotericin B (AmB) have been marketed to overcome the disadvantages associated with the clinical use of AmB. However, to show their efficacy, they need to be administered at higher doses than the conventional dosage form, Fungizone. In this study, we compared LNS-AmB, our new low-dose therapeutic system for AmB using lipid nano-sphere (LNS), with these commercial formulations in terms of their pharmacokinetics and efficacy. The plasma AmB levels yielded by LNS-AmB after intravenous administration to rats were much higher than those yielded by Amphocil or Abelcet, and similar to those yielded by AmBisome, but in dogs LNS-AmB yielded plasma AmB concentrations about three times higher than did AmBisome. In a carrageenin-induced pleurisy model in rats, LNS-AmB yielded AmB levels in the pleural exudate over 20 times those yielded by Amphocil or Abelcet, and similar to those yielded by AmBisome. From these pharmacokinetic results, it is clear that Amphocil and Abelcet are based on a quite distinct drug-delivery concept from LNS-AmB. In a rat model of localized candidiasis, LNS-AmB significantly inhibited the growth of Candida albicans in the pouch, whereas AmBisome did not, even though the AmB concentrations in the pouch were similar. This difference in antifungal activity between LNS-AmB and AmBisome was also found in vitro. That is, the antifungal activity of LNS-AmB against C. albicans was similar to that of Fungizone and dimethyl sulfoxide-solubilized AmB, while AmBisome showed weaker antifungal activity than did other formulations. Based on these results, the release of AmB from AmBisome was judged to be slow and slight. In a mouse model of systemic candidiasis, LNS-AmB (1.0mg/kg) was much more effective than AmBisome (8.0mg/kg) or Fungizone (1.0mg/kg). These results suggest that LNS-AmB maintained the potent activity of AmB against fungal cells even though the AmB was incorporated into LNS particles. We conclude that LNS-AmB may offer an improved therapeutic profile at lower doses than Fungizone and commercial lipid-based formulations.

Pharmacokinetics of amphotericin B lipid complex in critically ill patients on continuous veno-venous haemofiltration

Pharmacokinetics of amphotericin B lipid complex (ABLC) was determined in two critically ill patients requiring continuous veno-venous haemofiltration (CVVH) because of acute renal failure. ABLC was administered at a mean daily dose of 4.94 mg/kg for suspected invasive mycosis. Mean C(max) was 0.56 microg/ml, the mean AUC(0-24 h) was 7.46 mgh/l, V(ss) 9.13 l/kg, and t(1/2) was 13.21 h. The haemofilter clearance accounted about 20% of the total ABLC clearance. In one patient sampling was repeated after CVVH had been discontinued. The concentration-time profiles were very similar on and off haemofiltration. Data on our two patients suggest, that pharmacokinetics of ABLC is not significantly affected by CVVH and that ABLC can be administered at the standard doses during CVVH.

A novel delivery system for amphotericin B with lipid nano-sphere (LNS®)

A low-dose therapeutic system with a lipid emulsion for amphotericin B (AmB), a potent antifungal drug, was studied. Lipid nano-sphere (LNS), a small-particle lipid emulsion, was taken up by the liver to a lesser extent than was a conventional lipid emulsion. As a result, LNS yielded higher plasma concentrations of a radiochemical tracer than did the conventional lipid emulsion. LNS was therefore judged to be a suitable carrier for a low-dose therapeutic system for AmB, and LNS incorporating AmB (LNS-AmB) was prepared. LNS-AmB was found to be a homogeneous emulsion with mean particle diameters ranging from 25 to 50 nm. LNS-AmB yielded higher plasma concentrations of AmB than did Fungizone, a conventional intravenous dosage form of AmB, after intravenous administration to mice, rats, dogs, and monkeys. This difference between LNS-AmB and Fungizone was also observed for constant intravenous infusion. In contrast to Fungizone, LNS-AmB showed a linear relationship between dose and AUC. These pharmacokinetic characteristics of LNS-AmB make it a suitable candidate for an effective low-dose therapeutic system for AmB.

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

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

Amphotericin B lipid formulations in critically ill patients on continuous veno-venous haemofiltration

OBJECTIVES

The pharmacokinetics of lipid-formulated amphotericin B (AMB), and of AMB that has dissociated from its lipid moiety and bound to lipoproteins in plasma, were separately determined in critically ill patients.

PATIENTS AND METHODS

Eleven patients required continuous veno-venous haemofiltration (CVVH). Five of them were treated with liposomal AMB (AmBisome) and seven with AMB colloidal dispersion (Amphocil). Six of the critically ill were not undergoing CVVH (three of them treated with liposomal AMB and three with AMB colloidal dispersion).

RESULTS

Significant amounts of AMB are liberated from liposomes or colloidal dispersion during circulation in plasma, where pharmacokinetics mimic that of AMB deoxycholate. Elimination of the remaining lipid-formulated fraction is different and differentially affected by CVVH. Plasma levels of lipid-formulated AMB were significantly higher in patients treated with liposomal AMB than in those treated with AMB colloidal dispersion; clearance of liposomal AMB is enhanced by haemofiltration, whereas elimination of AMB colloidal dispersion is not significantly affected.

CONCLUSIONS

The pharmacokinetics of AMB that has been liberated from its lipid moiety is similar under treatment with either liposomal AMB or AMB colloidal dispersion. Since no significant influence of haemofiltration on the pharmacokinetics of liberated AMB has been found, a standard dose of lipid-formulated AMB can be recommended for patients on haemofiltration.

Ocular distribution of intravenously administered lipid formulations of amphotericin B in a rabbit model

Little is known about the ocular penetration of amphotericin B (AMB) and its lipid formulations, the current drug of choice in fungal endophthalmitis. The ocular distribution of AMB lipid complex (ABLC), liposomal AMB (L-AMB), and AMB deoxycholate (D-AMB) was studied in a rabbit model. D-AMB (1 mg/kg of body weight/day), ABLC (5 mg/kg/day), or L-AMB (5 mg/kg/day) was given intravenously to rabbits as a single dose or as repeated daily doses on 7 consecutive days after induction of unilateral uveitis by intravitreal injection of endotoxin. AMB concentrations in aqueous humor, vitreous humor, and plasma were determined by high-pressure liquid chromatography 16 h after administration of a single dose or 24 h after the last of seven doses. After single-dose administration, L-AMB achieved at least eightfold-higher AMB concentrations in the aqueous of inflamed eyes than ABLC or D-AMB (1.21 +/- 0.58 micro g/ml versus 0.14 +/- 0.04 and 0.11 +/- 0.09 micro g/ml, respectively). At that time point no drug was detectable in the vitreous. After 7 days of treatment, the concentration of AMB in the vitreous was higher after treatment with L-AMB (0.47 +/- 0.21 micro g/ml) than after treatment with ABLC (0.27 +/- 0.18 micro g/ml) and D-AMB (0.16 +/- 0.04 micro g/ml). Similarly, AMB concentration in the aqueous was higher after repeated doses of L-AMB (0.73 +/- 0.43 micro g/ml) than after repeated doses of ABLC (0.03 +/- 0.02 micro g/ml) or D-AMB (0.13 +/- 0.06 micro g/ml). No AMB was detected in noninflamed eyes. Following systemic administration, AMB distribution to the eye is inflammation dependent and occurs sequentially, first to the aqueous and then to the vitreous. Compared to D-AMB and ABLC, L-AMB reaches higher drug concentrations in both ocular compartments.

A comparative study of plasma concentrations of liposomal amphotericin B (L-AMP-LRC-1) in adults, children and neonates

Amphotericin B (AmpB) incorporated into small unilamellar liposomes prepared from soya phosphatidylcholine and cholesterol (L-AMP-LRC-1) has been shown to be safe and effective in patients with systemic fungal infections. In this report, we compared the plasma levels of AmpB in adults, children and neonates following administration of L-AMP-LRC-1. A 1.0 mg/kg dose of L-AMP-LRC-1 in adult patients resulted in peak concentrations of 1.02+/-0.14 mg/l (mean+/-S.D.) on day 1, which increased to 1.66+/-0.19 mg/l on day 28 after continued therapy. The area under the plasma concentration-time curve also increased from 13.05+/-1.52 on day 1 to 19.85+/-5.41 mg h/l on day 28. In children, the peak plasma concentration following 1.0 mg/kg per day dose of L-AMP-LRC-1 increased from 0.63+/-0.20 on day 1 to 1.10+/-0.53 mg/l on day 28. While in neonates, the levels increased from 0.54+/-0.17 on day 1 to 0.73+/-0.29 mg/l on day 28. These levels of AmpB in children and neonates were found to be significantly lower than in adults. This may be due to higher volume of distribution, since 1.0 mg/kg per day dose of L-AMP-LRC-1 was found to be effective in neonates.

Pharmacokinetics and tissue distribution of a new partricin A derivative (N-dimethylaminoacetyl-partricin A 2-dimethylaminoethylamide diaspartate) in mice

A single-dose trial in mice (1.25 mg/kg SPA-S-753 or 1 mg/kg amphotericin B [AmB] by intravenous route) was performed to study the pharmacokinetics, tissue distribution, and urinary excretion of a new polyene, SPA-S-753 (N-dimethylaminoacetyl-partricin A 2-dimethylaminoethylamide diaspartate), in comparison with AmB. Antibiotic concentrations were determined by microbiological assay (agar diffusion method). The elimination half-lives in serum were 15.1 and 19.8 h, respectively, for SPA-S-753 and AmB; the area under the curve from 0 to infinity values were 49.3 for SPA-S-753 and 23.6 microg. h/mL for AmB, because of the higher serum levels of SPA-S-753 found just after administration. The tissue concentrations of SPA-S-753 were lower than those of AmB in liver and lungs but higher in the kidneys. The urine concentrations of SPA-S-753 and the percent of the administered dose recovered from the urine were quite low in mice, whereas those of AmB were higher.

Plasma protein binding of amphotericin B and pharmacokinetics of bound versus unbound amphotericin B after administration of intravenous liposomal amphotericin B (AmBisome) and amphotericin B deoxycholate

Unilamellar liposomal amphotericin B (AmBisome) (liposomal AMB) reduces the toxicity of this antifungal drug. The unique composition of liposomal AMB stabilizes the liposomes, producing higher sustained drug levels in plasma and reducing renal and hepatic excretion. When liposomes release their drug payload, unbound, protein-bound, and liposomal drug pools may exist simultaneously in the body. To determine the amounts of drug in these pools, we developed a procedure to measure unbound AMB in human plasma by ultrafiltration and then used it to characterize AMB binding in vitro and to assess the pharmacokinetics of nonliposomal pools of AMB in a phase IV study of liposomal AMB and AMB deoxycholate in healthy subjects. We confirmed that AMB is highly bound (>95%) in human plasma and showed that both human serum albumin and alpha(1)-acid glycoprotein contribute to this binding. AMB binding exhibited an unusual concentration dependence in plasma: the percentage of bound drug increased as the AMB concentration increased. This was attributed to the low solubility of AMB in plasma, which limits the unbound drug concentration to <1 microg/ml. Subjects given 2 mg of liposomal AMB/kg of body weight had lower exposures (as measured by the maximum concentration of drug in serum and the area under the concentration-time curve) to both unbound and nonliposomal drug than those receiving 0.6 mg of AMB deoxycholate/kg. Most of the AMB in plasma remained liposome associated (97% at 4 h, 55% at 168 h) after liposomal AMB administration, so that unbound drug concentrations remained at <25 ng/ml in all liposomal AMB-treated subjects. Although liposomal AMB markedly reduces the total urinary and fecal recoveries of AMB, urinary and fecal clearances based on unbound AMB were similar (94 to 121 ml h(-1) kg(-1)) for both formulations. Unbound drug urinary clearances were equal to the glomerular filtration rate, and tubular transit rates were <16% of the urinary excretion rate, suggesting that net filtration of unbound drug, with little secretion or reabsorption, is the mechanism of renal clearance for both conventional and liposomal AMB in humans. Unbound drug fecal clearances were also similar for the two formulations. Thus, liposomal AMB increases total AMB concentrations while decreasing unbound AMB concentrations in plasma as a result of sequestration of the drug in long-circulating liposomes.

Suspected infection in children with cancer

A common complication of the intensive therapy that children with cancer receive is infection. The Oncology Unit of The Children's Hospital at Westmead maintains a comprehensive database of all admissions for suspected sepsis. From July 1994 to June 1999 broad-spectrum antibiotics were commenced in 2331 episodes. With early and aggressive use of empirical amphotericin B, 545 courses were given. Bacteraemia was documented in 701 episodes and invasive fungal disease in 73. Trends seen during the study included: (i) the proportion of febrile neutropenic patients receiving granulocyte colony stimulating factor increased from 40% to 60%; (ii) the mean neutrophil count at cessation of antibiotics fell from 0.97 to 0.63 x 10(9) cells/L for patients not receiving growth factors; (iii) the proportion of non-albicans Candida species infections increased. In addition, an outbreak of infection caused by Scedosporium sp. was documented; (iv) first-line empirical antibiotic combinations containing vancomycin fell from 20% to 7%; and (v) the ability to maintain or escalate anti-fungal therapy with reduced nephrotoxicity through use of lipid formulations of amphotericin was increasingly apparent in high-risk patients. During the study, infection was the primary cause of death in 11 non-bone marrow transplant (BMT) patients (five fungal, four viral, one bacterial infection and one sepsis syndrome) and five BMT patients (two bacterial and three viral). A prospective randomized study of toxicity due to amphotericin B given in either lipid emulsion or dextrose showed no significant difference, but both groups showed a lower incidence of amphotericin B intolerance in comparison with the adult series. The inability to reduce toxicity of amphotericin B by simple mixing with lipid emulsion has led to increasing use of commercially available lipid formulations of amphotericin B.

Determination of amphotericin B, liposomal amphotericin B, and amphotericin B colloidal dispersion in plasma by high-performance liquid chromatography

Amphotericin B is a potent polyene antifungal drug for intravenous treatment of severe infections. It is used as amphotericin B-deoxycholate and in order to reduce amphotericin B toxicity as lipid-formulated complex (liposomal or colloidal dispersion). A sensitive and specific analytical method is presented for the separation of lipid-complexed and plasma protein-bound amphotericin B in human heparinized plasma. This separation, which is required for pharmacokinetic studies, is achieved by solid-phase extraction (SPE) via Bond Elut C18. The protein-bound amphotericin B has a higher affinity to the SPE material and is therefore retained, whereas the lipid-complexed amphotericin B is eluted in the first step. The recovery of the SPE was >75% for high concentrations and >95% for low concentrations. Quantification was performed by reversed-phase HPLC using a LiChrosorb-RP-8 column, UV detection (lambda=405 nm) and a mixture of acetonitrile-methanol-0.010 M NaH2PO4 buffer (41:10:49, v/v) as mobile phase. The retention time for amphotericin B under the given conditions was 6.7 min. The calibration curves were found to be linear (r > or = 0.999) in two different ranges (5.0-0.50 microg/ml and 0.50-0.005 microg/ml). Intra- and inter-day precision and accuracy fulfilled the international requirements. No interference from other drugs (typical broad medication for intensive-care patients) or common plasma components was detected in >400 samples analyzed.

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.

Pharmacokinetics, excretion, and mass balance of 14C after administration of 14C-cholesterol-labeled AmBisome to healthy volunteers

Amphotericin B (AmB) in small unilamellar liposomes (AmBisome) provides higher plasma concentrations and greater safety than the conventional deoxycholate formulation. The authors compared the disposition of the liposome's drug and cholesterol components by measuring AmB and radioactivity in plasma, urine, and feces for 1 week after a single 2-hour infusion of 14C-cholesterol-labeled AmBisome (2 mg/kg, 1 microgCi/kg) in healthy adults (4 males, 1 female). The plasma profile of 14C-cholesterol differed from that of AmB, lacking an initial rapid disappearance phase, having a lower total clearance, and having a volume of distribution (0.13 L/kg) close to that of the plasma compartment. The biphasic disappearance and long plasma half-life (147 h) of 14C-cholesterol were similar to those of other low-clearance liposomes. This and the low clearance of 14C-cholesterol from the plasma compartment suggest that it served as a liposome marker. The plasma drug-lipid ratio fell during the study, showing that AmB was cleared from plasma more rapidly than cholesterol or liposomes and suggesting that the composition of the liposomes changed over time. 14C-radioactivity was recovered mainly in the feces (9.5% of dose), consistent with the catabolism of cholesterol to bile salts. Combined fecal and renal clearances were < 18% of total clearance, suggesting that most of the liposomal drug and lipid remained in the body 1 week after dosing. Thus, AmBisome remains in the circulation for an extended period of time while releasing AmB, resulting in its markedly altered pharmacokinetic and safety profiles.

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.

Administration and clearance of amphotericin B during high-efficiency or high-efficiency/high-flux dialysis

Administration and clearance of amphotericin B infused during high-efficiency or high-efficiency/high-flux dialysis were studied in two end-stage renal disease patients requiring systemic antimycotic treatment for fungal peritonitis. Amphotericin B concentrations were measured in the arterial and venous dialysis ports as well as in the ultrafiltrate. Amphotericin B is poorly dialyzable while administered during hemodialysis sessions with high-efficiency (CA 210) or high-efficiency/high-flux (CT 190 G) membranes. Amphotericin B infusion during hemodialysis was well tolerated and can be administered conveniently in an outpatient dialysis setting, avoiding prolonged hospitalization for parenteral antifungal therapy.

Determination of amphotericin B in human plasma using solid-phase extraction and high-performance liquid chromatography

A rapid and selective HPLC method is described and validated for measuring amphotericin B (AB) in plasma. The procedure involves the solid phase extraction of AB from plasma by incorporating 1-amino-4-nitronaphthalene as an internal standard during the last elution step in extraction followed by HPLC analysis with UV detection at 407 nm. The chromatographic separation is achieved in less than 10 min on a reversed-phase C-18 column using acetonitrile-disodium edetate (20 mM) (45:55, v/v) at pH 5.0 as eluent. A linear response over the concentration range of 0.0100--2.00 microg ml(-1) is obtained having a detection limit of 0.00500 microg ml(-1) for AB. The mean extraction recovery is found to be 98.1+/-1.1% (n=15). The within-day and day-to-day R.S.D. were less than 2% (n=15) and 6.54% (n=45) respectively. This method is applied for quantifying AB trough levels in the plasma of cancer patients who have been on antifungal therapy with AmBisome. It can further be applied either for AB therapeutic monitoring or single/multiple pharmacokinetic analysis of AB in plasma.

Pharmacokinetics of liposomal amphotericin B in neutropenic cancer patients

This study was conducted to characterise the pharmacokinetics of a liposomal pharmaceutical product of amphotericin B (LAB) in three neutropenic cancer patients complicated by suspected fungal infections. LAB was administered at a constant dose of 50 mg/day over 1--6 h by intravenous infusion, and blood samples were obtained between two infusion intervals without complicating the systemic therapy of the patients. Quantitative analysis of amphotericin B (AB) in plasma was established by a validated reversed-phase high-performance liquid chromatographic (HPLC) assay. Model independent pharmacokinetic parameters were estimated using area and moment analysis. Administration of LAB to the first patient (day 1) diagnosed as malignant melanoma resulted in a mean maximum concentration (C(max)) of 679+/-6 ng/ml and a mean minimum concentration (C(min)) of 139+/-9 ng/ml of AB. Pre-dose, C(max) and C(min) values of AB, after multiple LAB dosing to the other two patients both having acute myeloblastic leukemia were found to be 440+/-6, 1140+/-10, 409+/-11 ng/ml (day 19) and 408+/-3, 1180+/-10, and 283+/-1 ng/ml (day 9), respectively. The area under the plasma concentration-time curve (AUC) and the mean residence time (MRT) calculated between the two infusion intervals were 6180 ngh/ml, 7.79 h (day 1) for the first patient; 13,700 ng.h/ml, 10.5 h (day 19) and 14,000 ng.h/ml, 9.93 h (day 9) for the other two patients, respectively. The pharmacokinetic profiles and non-compartmental parameters calculated were comparable for both patients diagnosed with acute myeloblastic leukemia after multiple dosing at steady state, which also demonstrated a twofold increase in their AUC values compared with the AUC of the first patient. Although C(min) values supported the assumption that there was AB accumulation in plasma and this accumulation could be increased at high doses, LAB was administered safely to these patients and well tolerated at the doses given.

Ligand directed macrophage targeting of amphotericin B loaded liposomes

Two types of ligand anchored multilamellar liposomes (MLVs) containing amphotericin B (Amp B) were prepared. The MLVs consisting of soya phosphatidylcholine (PC) and cholesterol (Chol) were coated with O-palmitoyl mannan (OPM). Similarly, the MLVs with the same Amp B content consisting of soya PC, Chol and phosphatidylethanolamine (PE) were prepared and covalently anchored with p-aminophenyl-mannopyranoside (PAM). The surface modified MLVs and their plain counterparts were characterised for size, shape, lamellarity, entrapment efficiency and ligand density. The stability in serum and in vivo bio-distribution in albino rats were also determined. It was observed that extent of accumulation of liposomal Amp B in macrophage rich organs, particularly liver, spleen and lungs was significantly high when compared against the free drug. The rates and extent of accumulation were found to increase further on ligand anchoring. In either of the cases, the macrophagic uptake of ligand anchored liposomes was inhibited significantly on pre-injection of hydrolysed mannan, being suggestive of receptor mediated uptake of ligand anchored liposomes. Comparison of biodistruibution pattern of ligand anchored MLVs revealed that PAM linked liposomes exhibited a higher hepato-splenic accumulation where as drug accumulation in lungs was highest in the case of OPM coated liposomes. It was thus observed that mannopyranoside is a specific ligand for targeting bioactives to the macrophages of liver and spleen while OPM could preferentially negotiate the targeting of bioactives to the alveolar macrophages.

Biodistribution of amphotericin B when delivered through cholesterol hemisuccinate vesicles in normal and A. fumigatus infected mice

PURPOSE

This study compared the biodistribution of two amphotericin B formulations in normal and Aspergillus infected mice. Amphotericin B cholesterol hemisuccinate vesicles (ABCV) which reduces the toxicity of amphotericin B and thereby enhances its therapeutic efficacy in a murine model of aspergillosis was compared with conventional amphotericin B deoxycholate suspension (AmB(DOC)).

METHODS

ABCV (12 mg/kg wt) and AmB(DOC) (2 mg/kg wt) were intravenously administered to normal and A. fumigatus infected mice. The concentration of amphotericin B in plasma and other organs was determined at different time points.

RESULTS

It was observed that ABCV had a significantly different pharmacokinetic profile compared to conventional amphotericin B. In comparison to AmB(DOC) significantly lower levels of amphotericin B were observed in kidneys and plasma, the major target organs of toxicity. Animals receiving ABCV demonstrated high levels of amphotericin B in liver (38% retention till 48 h) and spleen (2.6% retention till 48 h) in comparison to AmB(DOC) (7.3% and 0.21% retention in liver and spleen respectively till 48 h). Biodistribution studies of ABCV in infected mice demonstrated that there was a moderate enhancement in levels of amphotericin B in liver, spleen, lungs and kidneys as compared to normal mice and the plasma levels were reduced. However, such observations were not made after AmB(DOC) administration to infected mice except for kidneys in which there was a marked increase in uptake as compared to normal mice.

CONCLUSIONS

Our results suggest that prolonged retention of high concentrations of ABCV in reticuloendothelial system organs is the reason for its reduced toxicity. Enhanced localization of the drug at the infected site may lead to improvement in therapeutic efficacy.

Pulmonary extraction and accumulation of lipid formulations of amphotericin B

OBJECTIVE

To compare single-dose first pass uptake and accumulation of conventional amphotericin B (cAmB), liposomal amphotericin B (L-AmB), and amphotericin B lipid complex (ABLC) by the intact feline lungs.

DESIGN

Prospective, controlled animal study.

SETTING

Experimental laboratory in a university teaching hospital.

SUBJECTS

A total of 31 spontaneously breathing, anesthetized cats.

INTERVENTIONS

The pulmonary uptake of cAmB, L-AmB, and ABLC during a single passage through the pulmonary circulation, and the pulmonary retention of these drugs were studied after a bolus [cAmB, L-AmB, and ABLC, 1 mg/kg (n = 9 each) and ABLC, 5 mg/kg (n = 4)] administration into the right ventricle. The amount of drug taken up by the lung during the first pass was measured from double indicator-dilution outflow curves. Animals were killed 30 mins (cAmB, n = 4; L-AmB, n = 4), 1 hr (cAmB, n = 5; L-AmB, n = 5; ABLC, n = 5), or 6 hrs (ABLC, 1 mg/kg, n = 4; 5 mg/kg, n = 4) after drug administration.

MEASUREMENTS AND MAIN RESULTS

The first-pass uptake of cAmB, L-AmB, and ABLC (mean +/- sD) by the lung was 73%+/-5%, 69%+/-8%, and 82%+/-6% of the injected dose (1 mg/kg), respectively (p > .05). ABLC (1 mg/kg) exhibited prolonged retention in the lung; 23% and 15% of the injected dose of ABLC remained in the lung 1 hr and 6 hrs after its administration, respectively. In contrast, cAmB and L-AmB exhibited rapid back diffusion of the drug out of the lung. After 30 mins, only 4% of the administered cAmB and L-AmB remained in the lung and after 1 hr only 1% to 2% was retained. Increasing the dose of ABLC from 1 mg/kg to 5 mg/kg did not alter pulmonary extraction of the drug; however, compared with the lower dose (1 mg/kg), higher concentrations of the drug were found in the lung 6 hrs after its administration.

CONCLUSIONS

The results demonstrate a substantial extraction and accumulation of ABLC by the lung. This affinity for the lungs may have clinical implications for treating fungal infections that primarily involve the lung. Further studies are required to confirm the potential clinical relevance of these data.

Comparative efficacy and distribution of lipid formulations of amphotericin B in experimental Candida albicans infection of the central nervous system

The central nervous system (CNS) distribution and antifungal efficacy of all 4 approved formulations of amphotericin B (AmB) were investigated in a rabbit model of hematogenous Candida albicans meningoencephalitis. Treatment with AmB deoxycholate (1 mg/kg/day) or liposomal AmB (5 mg/kg/day) yielded the highest peak plasma concentration (C(max)), area under concentration versus time curve from zero to 24 h (AUC(0-24)), and time during dosing level tau Ttau>minimum inhibitory complex (MIC) values and led to complete eradication of C. albicans from brain tissue (P<.05 vs. untreated controls). By comparison, AmB colloidal dispersion and AmB lipid complex (5 mg/kg/day each) were only partially effective (not significant vs. untreated controls). There was a strong correlation of C(max), AUC(0-24), C(max)/MIC, AUC(0-24)/MIC, and Ttau>MIC with clearance of C. albicans from brain tissue (P</=.0002). Although pharmacodynamic parameters derived from the MIC of free AmB were highly predictive of antifungal efficacy, parameters derived from MICs of individual formulations were not predictive. AmB deoxycholate and liposomal AmB had the greatest antifungal efficacy. This activity was concentration and time dependent.

Itraconazole oral solution for primary prophylaxis of fungal infections in patients with hematological malignancy and profound neutropenia: a randomized, double-blind, double-placebo, multicenter trial comparing itraconazole and amphotericin B

Systemic and superficial fungal infections are a major problem among immunocompromised patients with hematological malignancy. A double-blind, double-placebo, randomized, multicenter trial was performed to compare the efficacy and safety of itraconazole oral solution (2.5 mg/kg of body weight twice a day) with amphotericin B capsules (500 mg orally four times a day) for prophylaxis of systemic and superficial fungal infection. Prophylactic treatment was initiated on the first day of chemotherapy and was continued until the end of the neutropenic period (>0.5 x 10(9) neutrophils/liter) or up to a maximum of 3 days following the end of neutropenia, unless a systemic fungal infection was documented or suspected. The maximum treatment duration was 56 days. In the intent-to-treat population, invasive aspergillosis was noted in 5 (1.8%) of the 281 patients assigned to itraconazole oral solution and in 9 (3.3%) of the 276 patients assigned to oral amphotericin B; of these, 1 and 4 patients died, respectively. Proven systemic fungal infection (including invasive aspergillosis) occurred in 8 patients (2.8%) who received itraconazole, compared with 13 (4.7%) who received oral amphotericin B. Itraconazole significantly reduced the incidence of superficial fungal infections as compared to oral amphotericin B (2 [1%] versus 13 [5%]; P = 0.004). Although the incidences of suspected fungal infection (including fever of unknown origin) were not different between the groups, fewer patients were administered intravenous systemic antifungals (mainly intravenous amphotericin B) in the group receiving itraconazole than in the group receiving oral amphotericin B (114 [41%] versus 132 [48%]; P = 0.066). Adequate plasma itraconazole levels were achieved in about 80% of the patients from 1 week after the start of treatment. In both groups, the trial medication was safe and well tolerated. Prophylactic administration of itraconazole oral solution significantly reduces superficial fungal infection in patients with hematological malignancies and neutropenia. The incidence of proven systemic fungal infections, the number of deaths due to deep fungal infections, and the use of systemic antifungals tended to be lower in the itraconazole-treated group than in the amphotericin B-treated group, without statistical significance. Itraconazole oral solution is a broad-spectrum systemic antifungal agent with prophylactic activity in neutropenic patients, especially for those at high risk of prolonged neutropenia.

A sensitive amphotericin B immunoassay for pharmacokinetic and distribution studies

Since currently used assays of amphotericin B (AMB) lack sensitivity or are not easily adaptable in all laboratories, we have developed an enzyme immunoassay for AMB in biological fluids and tissues. Antibodies to AMB were raised in rabbits after administration of an AMB-bovine serum albumin conjugate. The enzymatic tracer was obtained by coupling AMB via its amino group to acetylcholinesterase (EC 3.1.1.7). These reagents were used for the development of a competitive immunoassay performed on microtitration plates. The limit of quantification was 100 pg/ml in plasma and 1 ng/g in tissues. The plasma assay was performed directly without extraction on a minimal volume of 0.1 ml. The intra- and interassay coefficients of variation were in the range of 5 to 17%, and the recoveries were 92 to 111% for AMB added to human plasma. The assay was applied to a pharmacokinetic study with mice given AMB intraperitoneally at the dose of 1 mg/kg. The drug distribution in selected compartments (plasma, liver, spleen, lung, and brain) was monitored until 72 h after administration. In conclusion, our assay is at least 100-fold more sensitive than previously described bioassays or chromatographic determinations of AMB and may be useful in studying the tissue pharmacokinetics of new AMB formulations and in drug monitoring in clinical situations.

Efficacy of liposomal amphotericin B with prolonged circulation in blood in treatment of severe pulmonary aspergillosis in leukopenic rats

The therapeutic efficacy of long-circulating polyethylene glycol-coated liposomal amphotericin B (AMB) (PEG-AMB-LIP) was compared with that of AMB desoxycholate (Fungizone) in a model of severe invasive pulmonary aspergillosis in persistently leukopenic rats as well as in temporarily leukopenic rats. PEG-AMB-LIP treatment (intravenous administration) consisted of a single, or double (every 72 h), or triple (every 72 h) dose of 10 mg of AMB/kg of body weight, a double dose (every 72 h) of 14 mg of AMB/kg, or a 5-day treatment (every 24 h) with 6 mg/kg/dose. AMB desoxycholate was administered for 10 consecutive days at 1 mg of AMB/kg/dose. Treatment was started 30 h after fungal inoculation, at which time mycelial growth was firmly established. Both persistently and temporarily leukopenic rats died between 4 and 9 days after Aspergillus fumigatus inoculation when they were left untreated or after treatment with a placebo. In persistently leukopenic rats, a single dose of PEG-AMB-LIP (10 mg/kg) was as effective as the 10-day treatment with AMB desoxycholate (at 1 mg/kg/dose) in significantly prolonging the survival of rats infected with A. fumigatus and in reducing the dissemination of A. fumigatus to the liver. Prolongation of PEG-AMB-LIP treatment (double or triple dose or 5-day treatment) did not further improve efficacy. For temporarily leukopenic rats no major advances in efficacy were achieved compared to those for persistently leukopenic rats, probably because the leukocyte numbers in blood were restored too late in the course of infection.

Distribution of lipid formulations of amphotericin B into bone marrow and fat tissue in rabbits

The distribution of the three currently available lipid formulations of amphotericin B (AmB) into bone marrow and fat tissue was evaluated in noninfected rabbits. Groups of four animals each received either 1 mg of AmB deoxycholate (D-AmB) per kg of body weight per day or 5 mg of AmB colloidal dispersion, AmB lipid complex, or liposomal AmB per kg per day for seven doses. Plasma, bone marrow, fat, and liver were collected at autopsy, and AmB concentrations were determined by high-performance liquid chromatography. At the investigated dosages of 5 mg/kg/day, all AmB lipid formulations achieved at least fourfold-higher concentrations in bone marrow than did standard D-AmB at a dosage of 1 mg/kg/day. Concentrations in bone marrow were 62 to 76% of concurrent AmB concentrations in the liver. In contrast, all AmB formulations accumulated comparatively poorly in fat tissue. The results of this study show that high concentrations of AmB can be achieved in the bone marrow after administration of lipid formulations, suggesting their particular usefulness against disseminated fungal infections involving the bone marrow and against visceral leishmaniasis.

Interaction between fluconazole and amphotericin B in mice with systemic infection due to fluconazole-susceptible or -resistant strains of Candida albicans

The interaction between fluconazole (Flu) and amphotericin B (AmB) was evaluated in a murine model of systemic candidiasis for one Flu-susceptible strain (MIC, 0.5 microg/ml), two strains with intermediate Flu resistance (Flu mid-resistant strains) (MIC, 64 and 128 microg/ml), and one highly Flu-resistant strain (MIC, 512 microg/ml) of Candida albicans. Differences in fungal densities in kidneys of infected mice after 24 h of therapy and in survival rates at 62 days of mice treated with an antifungal drug or a combination of antifungal drugs for 4 days were compared. For the Flu-susceptible and Flu mid-resistant strains, the combination of Flu and AmB was antagonistic, as shown by both quantitative culture results and survival. The interaction was additive for the highly Flu-resistant strain. These results suggest that the combination of Flu and AmB should be used with caution in infections due to fungi that are usually susceptible to both antifungal agents and as empirical antifungal drug therapy.

Preferential distribution of amphotericin B lipid complex into human HDL3 is a consequence of high density lipoprotein coat lipid content

The purpose of this study was to determine the plasma lipoprotein (LP) distribution of amphotericin B (AmpB) and amphotericin B lipid complex [ABLC; Abelcet composed of dimyristoyl phosphatidylcholine (DMPC) and dimyristoyl phosphatidylglycerol (DMPG)] and define the relationship between LP lipid concentration and composition and the distribution of AmpB and ABLC in human plasma with varying total and lipoprotein cholesterol and triglycerides. AmpB and ABLC at a concentration of 20 microg amphotericin B/mL were incubated in plasma obtained from different human subjects (n = 7) for 60 min at 37 degrees C. Following these incubations plasma samples were separated into their high-density lipoprotein (HDL), triglyceride-rich lipoprotein (TRL; which contains very low-density lipoproteins and chylomicrons), low-density lipoprotein (LDL), and lipoprotein-deficient (LPDP) fractions by density-gradient ultracentrifugation (UC) and each fraction was assayed for AmpB using high-pressure liquid chromatography (HPLC). The HDL fraction was further separated into its HDL3 and HDL2 subclasses by UC and assayed for AmpB using HPLC. Separation of HDL into its subclasses was confirmed by gel electrophoresis. To assess the influence of modified lipoprotein concentrations and lipid composition on the plasma distribution of AmpB and ABLC, these compounds were incubated in plasmas from human subjects with varying total and lipoprotein lipid concentrations. In addition, to demonstrate that alterations in HDL lipid composition influence the plasma distribution of ABLC, ABLC (20 microg amphotericin B/mL) was incubated in plasma pretreated with dithionitrobenzoate (DTNB, a compound which inhibits lecithin:cholesterol acyltransferase conversion of HDL3 free cholesterol to esterified cholesterol) 18 h prior to the experiment or in untreated plasma for 60 min at 37 degrees C. Total plasma and lipoprotein cholesterol (TC), free cholesterol (fC), esterified cholesterol (CE), triglyceride (TG), phospholipid (PL), and protein (TP) concentrations in each human sample were determined by enzymatic assays. When AmpB was incubated in human plasmas of varying lipid concentrations, the majority of the drug was recovered in the LPDP fraction. However, the majority of AmpB was recovered in the HDL3 fraction following the incubation of ABLC. Differences in lipid coat content (fC and PL) carried by HDL influenced the distribution of ABLC within plasma of different human subjects. These findings were confirmed by the DTNB treatment experiments. These findings suggest that the association of AmpB with DMPC and DMPG to form drug-lipid complexes modifies the plasma distribution of the AmpB. In addition, the distribution of ABLC among plasma lipoproteins of different human subjects is defined by the HDL lipid coat content and is possibly an important consideration when evaluating the pharmacokinetics, toxicity, and activity of these compounds following administration to humans with differing plasma lipid concentrations.

Safety and toxicokinetics of intravenous liposomal amphotericin B (AmBisome) in beagle dogs

PURPOSE

Amphotericin B (AmB) in small, unilamellar liposomes (AmBisome) has an improved therapeutic index, and altered pharmacokinetics. The repeat-dose safety and toxicokinetic profiles of AmBisome were studied at clinically relevant doses.

METHODS

Beagle dogs (5/sex/group) received intravenous AmBisome (0.25, 1, 4, 8, and 16 mg/kg/day), empty liposomes or vehicle for 30 days. AmB was determined in plasma on days 1, 14, and 30, and in tissues on day 31. Safety parameters included body weight, clinical chemistry, hematology and microscopic pathology.

RESULTS

Seventeen of twenty animals receiving 8 and 16 mg/kg were sacrificed early due to weight loss caused by reduced food intake. Dose-dependent renal tubular nephrosis, and other effects characteristic of conventional AmB occurred at 1 mg/kg/day or higher. Although empty liposomes and AmBisome increased plasma cholesterol, no toxicities unique to AmBisome were revealed. Plasma ultrafiltrates contained no AmB. AmBisome achieved plasma levels 100-fold higher than other AmB formulations. AmBisome kinetics were non-linear, with clearance and distribution volumes decreasing with increasing dose. This, and nonlinear tissue uptake, suggest AmBisome disposition was saturable.

CONCLUSIONS

AmBisome has the same toxic effects as conventional AmB, but they appear at much higher plasma exposures. AmBisome's non-linear pharmacokinetics are not associated with increased risk, as toxicity increases linearly with dosage. Dogs tolerated AmBisome with minimal to moderate changes in renal function at doses (4 mg/kg/day) producing peak plasma concentrations of 18-94 microg/mL.

Activity and kinetics of dissociation and transfer of amphotericin B from a novel delivery form

Recently it has been demonstrated that moderate heat treatment of Amphotericin B/deoxycholate solutions (HAmB-DOC ) leads to a therapeutically interesting supramolecular rearrangement that can be observed by significant changes in light scattering, CD, and absorbance. In this study, we continue the investigation of the physical properties of this new form by evaluating the activity and kinetics of dissociation and dispersion of HAmB-DOC and AmB-DOC in saline, serum, and in model mammalian or fungal lipid biomimetic membrane vesicles. Stopped-flow spectrophotometry combined with singular value decomposition (SVD) and global analysis were used to resolve the components of this process. The dissociation kinetics for both states are complex, requiring multi-exponential fits, yet in most cases SVD indicates only two significant changing species representing the monomer and the aggregate. The kinetic mechanism could involve dissociation of monomers from coexisting spectroscopically similar but structurally distinct aggregates or sequential rearrangements in supramolecular structure of aggregates. Rate constants and amplitudes of dissociation from aggregates to monomer in buffer, whole serum, 10% cholesterol, and ergosterol membrane vesicles are generally greater for AmB-DOC, demonstrating its greater kinetic instability. In addition, at comparable low concentrations, HAmB-DOC and AmB-DOC are nearly equally active at promoting cation selective permeability in ergosterol-containing membranes; however, HAmB-DOC is much less active against mammalian mimetic cholesterol-containing vesicles, despite a higher level of self-association, supporting previous observations that there exists a specific "toxic aggregate" structure.

High-performance liquid chromatographic determination of amphotericin B in plasma and tissue. Application to pharmacokinetic and tissue distribution studies in rats

A sensitive HPLC method with piroxicam as internal standard was developed for assaying amphotericin B in plasma and tissue. An Ultrabase-C18 column and a simple mobile phase consisting of an acetonitrile-acetic acid (10%)-water (41:43:16) mixture were used. The flow-rate was 1 ml/min and the effluent was monitored at 405 nm. The linearity of the assay method was up to 1000 ng/ml and 100 micrograms/g for plasma and tissue, respectively. Intra-day and inter-day RSDs were below 10% for all the sample types. This HPLC assay has been applied to determine amphotericin B in plasma and tissue samples taken during pharmacokinetic and tissue distribution studies in rats.

Lack of a nitric-oxide response during the course of Leishmania infantum infection in the golden hamster (Mesocricetus auratus), with or without treatment with liposomal amphotericin B

Liver and spleen volumes and serum concentrations of nitrate (the end-product of NO in vivo), albumin, gamma-globulin, protein, creatine and urea were measured during the course of progressive infections with Leishmania infantum MON-1 (MHOM/PR/93/CRE29) in 10 Syrian golden hamsters. Each hamster was infected by intraperitoneal injection with 4 x 10(7) promastigotes. Five of the infected animals were treated, with 6 mg liposomal amphotericin B (L-AmB)/kg given by intracardiac injection, on day 107 post-infection (p.i.). Compared with those in the uninfected hamsters used as controls, the liver volumes in the infected animals became significantly enlarged by day 40 p.i. (38% larger than the controls; P < 0.001) whereas significant enlargement of the spleen was first detected on day 72. Each infected animal had detectable serum levels of antileishmanial antibodies on day 72. There were significant elevations in gamma-globulin concentration as early as day 40 (P < 0.05) but significant falls in albumin concentrations were only detected from day 107 (P < 0.001). Nitrate, creatinine and urea concentrations remained unchanged during the course of infection, even after L-AmB treatment. Serum nitrate levels were not enhanced by L. infantum infection nor by the L-AmB treatment which induced a 98.2% decrease in parasite burden. The lack of NO production in visceral leishmaniasis, with or without L-AmB treatment, points to the unresponsiveness of inducible nitric oxide synthase in this rodent model.

Activity of liposomal amphotericin B with prolonged circulation in blood versus those of AmBisome and fungizone against intracellular Candida albicans in murine peritoneal macrophages

Activity against intracellular Candida albicans was assessed in C. albicans-infected murine peritoneal macrophages exposed to long-circulating pegylated amphotericin B liposomes (PEG-AMB-LIP), AmBisome, or Fungizone. The level of antifungal activity of Fungizone is much higher than that of AmBisome or PEG-AMB-LIP, while PEG-AMB-LIP and AmBisome show equivalent activity levels. Previous exposure of uninfected macrophages to PEG-AMB-LIP or AmBisome is advantageous for intracellular antifungal activity.

Superior efficacy of liposomal amphotericin B with prolonged circulation in blood in the treatment of severe candidiasis in leukopenic mice

In leukopenic mice with severe systemic candidiasis, single-dose treatment (5 mg of amphotericin B [AMB]/kg of body weight) with long-circulating polyethylene glycol-coated AMB liposomes (PEG-AMB-LIP) resulted in zero mortality and a significant reduction in the number of viable Candida albicans in the kidney, whereas 70% mortality was seen in mice treated with five daily doses of AmBisome (5 mg of AMB/kg . day). When the first of five daily doses of AmBisome was combined with a single low dose of Fungizone (0.1 mg of AMB/kg), the efficacy was equal to that of PEG-AMB-LIP.

Pharmacokinetic evaluation of amphotericin B in lung tissue: lung lymph distribution after intravenous injection and airspace distribution after aerosolization and inhalation of amphotericin B

We have studied the pharmacokinetics of amphotericin B (AmB) in lung lymph circulation and bronchial-wash fluid after intravenous infusion and inhalation, respectively. For two experiments with awake sheep, we used lung lymph fistulas and tracheotomy. In experiment 1, AmB concentrations in plasma and lung lymph after intravenous infusion of AmB (1 mg/kg of body weight) over 1.5 h were measured. The mean peak in plasma level was 756.0 +/- 188.8 ng/ml at 3 h after the start of infusion, and the level then decreased gradually to 194.8 +/- 28.9 ng/ml at 24 h. The stable and maximal levels in lung lymph last 5 to 9 h after the start of AmB infusion. The concentrations in lung lymph after 9 h were slightly higher than those in plasma. Thus, the lung lymph-to-plasma ratio of AmB concentrations increased gradually during infusion, and the ratio was more than 1.0 after the end of infusion, suggesting that AmB could be easily moved from plasma to pulmonary interstitium and/or lung lymph circulation. In another experiment, 5 or 30 mg of aerosol AmB was inhaled, and the concentration of AmB in the bronchial-wash fluid was determined by bronchoalveolar lavage. The peak AmB concentration in the fluid was observed at 0.5 h. After that, AmB was slowly eliminated over 24 h. The area under the concentration-time curve for 30 mg of inhaled AmB was higher than that for 5 mg, but maximum concentrations of AmB in serum for 5 and 30 mg were almost similar. These observations identify the pharmacokinetic characteristics of AmB in the lung and may provide a new insight into the strategy for clinical treatment of fungal pneumonia.

Quantitation of amphotericin B in plasma by second-derivative spectrophotometry

A method is described for determining amphotericin B in plasma using second-derivative spectrophotometry after deproteinization. The assay was based on the absorbance at 407.5 nm. The second-derivative spectrum recorded between 350 and 450 nm allowed identification of the analyte and showed absence of drug interference. Only bilirubin interfered at high concentration (> or = 50 mumol l-1. The linear concentration ranges were 0.05 -5.0 mg l-1 (r = 0.999, slope = 2.731, intercept = 0.008). Between-day CV < or = 9.7%, within-day CV < or = 5.5%, analytical recovery close to 100% were suitable for clinical investigations. This method provides better specificity than direct absorbance, is simpler and faster than a high performance liquid chromatography assay and can be used routinely by any laboratory possessing a spectrophotometer with a derivative accessory.