Amphotericin B lipid complex therapy of experimental fungal infections in mice

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.

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.

Amphotericin B and its new formulations: pharmacologic characteristics, clinical efficacy, and tolerability

Amphotericin B (amB) remains the gold standard for the treatment of invasive fungal infections. However, the efficacy is limited, with response rates from 10% to 80%. Moreover, amB is toxic, especially for the kidneys. New formulations have been developed in an attempt to improve both efficacy and tolerability. In an attempt to reduce toxicity, a number of investigators have reconstituted amB in a lipid emulsion, but few data are available on efficacy in documented infections. An improvement in immediate and renal tolerance was obtained with equivalent daily dose regimens, but the therapeutic index does not appear to be improved. This approach cannot be recommended at present. Three lipid formulations have been developed and are now available in most countries: amB colloidal dispersion (ABCD), amB lipid complex (ABLC), and liposomal amB (AmBisome). The efficacy of ABCD on various fungal infections has been assessed in open trials, with a response rate of 49% in aspergillosis, 70% in candidiasis, and 67% in mucormycosis. In two randomized trials comparing ABCD with amB in invasive aspergillosis and in persistent febrile neutropenia, the response rates were equivalent. ABCD was less nephrotoxic. In contrast, immediate reactions to ABCD were as frequent and severe as with amB. These immediate effects are more frequent during the first infusions and lessen as treatment continues. The recommended dose is 3-4 mg/kg/day. ABLC appeared to be effective as rescue therapy in various types of invasive mycoses, with a response rate of 42% in aspergillosis, 67% in candidiasis, and 82% in fusariosis. Efficacy identical to that of amB was demonstrated in a comparative randomized trial involving patients with invasive candidiasis. General and renal tolerability is improved compared with amB. The recommended dose regimen is 5 mg/kg/day. Liposomal amB (AmBisome) is the only truly liposomal formulation. The response rates in preliminary trials were 66% in aspergillosis and 81% in candidiasis. Several comparative studies have confirmed that this formulation has similar or superior efficacy relative to amB in various fungal infections and also in the empirical treatment of febrile neutropenia. Renal and general tolerability is excellent. The optimal dosing remains unclear but is generally between 3 and 5 mg/kg/day. A double-blind trial comparing the tolerance of liposomal amB and ABLC demonstrated that both infusion-related events and nephrotoxicity were significantly lower for liposomal amB. In sum, the new lipid formulations of amB are effective in various invasive fungal infections. The three formulations exhibit reduced nephrotoxicity compared with conventional amB. Large-scale comparative clinical trials may clarify issues of relative efficacy in various forms of mycotic infections.

Drug resistance in Cryptococcus neoformans

Cryptococcus neoformans has become a major opportunistic fungal pathogen worldwide. Successful treatment of invasive disease with this fungus has used amphotericin B, flucytosine and various azoles. However, treatment failures continue to occur for a variety of reasons including direct antifungal drug resistance. Issues and mechanisms for antifungal drug resistance in Cryptococcus neoformans are reviewed. Furthermore, approaches and strategies for prevention and treatment of antifungal drug resistance are identified and these include host immune modulation, dose optimization, prophylaxis/empirical regimens, improved drug delivery systems such as lipid preparations of amphotericin B, surgery, combination antifungal treatments and development of new antifungal agents. Copyright 1999 Harcourt Publishers Ltd.

Amphotericin B lipid complex in pediatric patients with invasive fungal infections

BACKGROUND

Lipid formulations of amphotericin B have been recently introduced for treatment of invasive fungal infections. However, little is known about their role in pediatric populations.

METHODS

We studied the safety and antifungal efficacy of amphotericin B lipid complex (ABLC, Abelcet) in 111 treatment episodes in pediatric patients through an open label, emergency use multicenter study. Patients with invasive fungal infections were enrolled if they had mycoses refractory to conventional antifungal therapy, if they were intolerant of previous systemic antifungal agents or concomitant nephrotoxic drugs or if they had preexisting renal disease.

RESULTS

All 111 treatment episodes were evaluable for safety and 54 were evaluable for efficacy. The mean serum creatinine for the study population did not significantly change between baseline (1.23 +/- 0.11 mg/dl) and cessation of ABLC therapy (1.32 +/- 0.12 mg/dl) during 6 weeks. There were no significant differences observed between initial and end-of-therapy levels of serum potassium, magnesium, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and hemoglobin. However, there was an increase in mean total bilirubin (3.66 +/- 0.73 to 5.31 +/- 1.09 mg/dl) at the end of therapy (P = 0.054). Among 54 cases fulfilling criteria for evaluation of antifungal efficacy, a complete or partial therapeutic response was obtained in 38 patients (70%) after ABLC therapy. Complete or partial therapeutic response was documented in 56% of cases with aspergillosis (n = 25) and in 81% (n = 27) with candidiasis. Among premature infants (n = 8) and allogeneic marrow recipients (n = 14), response rates were 88 and 57%, respectively. Response was similar in those patients enrolled because of intolerance to previous antifungal therapy or because of progressive infection.

CONCLUSIONS

These data support the use of ABLC for treatment of invasive fungal infections in pediatric patients who are intolerant of or refractory to conventional antifungal therapy.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

In vitro and in vivo activities of NS-718, a new lipid nanosphere incorporating amphotericin B, against Aspergillus fumigatus

We evaluated the in vitro and in vivo potencies of a new lipid nanosphere that incorporates amphotericin B (AmB), NS-718, against Aspergillus fumigatus. The in vitro activity of NS-718 (the MIC at which 90% of strains are inhibited [MIC90], 0.25 microgram/ml) against 18 isolates of A. fumigatus was similar to that of deoxycholate AmB (D-AmB; Fungizone; MIC90, 0.25 microgram/ml), but NS-718 was more potent than liposomal AmB (L-AmB; AmBi-some; MIC90, 1.0 microgram/ml). The in vivo efficacy of NS-718 in a rat model of invasive pulmonary aspergillosis was compared with those of D-AmB and L-AmB. A low dose (1 mg/kg of body weight) of L-AmB was ineffective (survival rate, 0%), although equivalent doses of D-AmB and NS-718 were more effective (survival rate, 17%). However, a higher dose of NS-718 (3 mg/kg) was more effective (survival rate, 100%) than equivalent doses of D-AmB and L-AmB (survival rate, 0%). To explain these differences, pharmacokinetic studies showed higher concentrations of AmB in the plasma of rats treated with NS-718 than in the plasma of those treated with D-AmB. Our results suggest that NS-718, a new preparation of AmB, is a promising antifungal agent with activity against pulmonary aspergillosis.

Antifungal agents. Part I. Amphotericin B preparations and flucytosine

Traditionally, amphotericin B has been the cornerstone of antifungal treatment. Toxicity, however, is a major dose-limiting factor of amphotericin B deoxycholate. Nevertheless, it continues to have a major role in the treatment of deep-seated mycotic infections. Recently, less nephrotic lipid formulations, including amphotericin B lipid complex, amphotericin B cholesteryl sulfate, and liposomal amphotericin B, have been introduced. The pharmacologic properties, main indications, recommended dosages, related costs, and adverse effects of these various preparations are summarized in this review. Orally administered flucytosine is useful in certain infections, particularly cryptococcal meningitis, but it should be used with caution in patients with renal insufficiency.

In vitro and in vivo antifungal activity of amphotericin B lipid complex: are phospholipases important?

Amphotericin B lipid complex for injection (ABLC) is a suspension of amphotericin B complexed with the lipids L-alpha-dimyristoylphosphatidylcholine (DMPC) and L-alpha-dimyristoylphosphatidylglycerol. ABLC is less toxic than amphotericin B deoxycholate (AmB-d), while it maintains the antifungal activity of AmB-d. Active amphotericin B can be released from ABLC by exogenously added (snake venom, bacteria, or Candida-derived) phospholipases or by phospholipases derived from activated mammalian vascular tissue (rat arteries). Such extracellular phospholipases are capable of hydrolyzing the major lipid in ABLC. Mutants of C. albicans that were resistant to ABLC but not AmB-d in vitro were deficient in extracellular phospholipase activity, as measured on egg yolk agar or as measured by their ability to hydrolyze DMPC in ABLC. ABLC was nevertheless effective in the treatment of experimental murine infections produced by these mutants. Isolates of Aspergillus species, apparently resistant to ABLC in vitro (but susceptible to AmB-d), were also susceptible to ABLC in vivo. We suggest that routine in vitro susceptibility tests with ABLC itself as the test material may not accurately predict the in vivo activity of ABLC and that the enhanced therapeutic index of ABLC relative to that of AmB-d in vivo may be due, in part, to the selective release of active amphotericin B from the complex at sites of fungal infection through the action of fungal or host cell-derived phospholipases.

Compassionate use of amphotericin B lipid complex (Abelcet) in life-threatening fungal infections: report of 30 courses

OBJECTIVE: To report a single-center experience of compassionate use of amphotericin B lipid complex (ABLC) in patients with proven or suspected fungal infection who were or would have been unable to tolerate conventional amphotericin B. METHODS: Twenty-eight patients receiving 30 courses of ABLC for 22 proven invasive mycosis episodes (11 aspergillosis, seven candidosis, four miscellaneous) and eight suspected episodes are described. Seven patients were given ABLC first-line therapy because of conditions precluding the use of amphotericin B deoxycholate (Am B). Twenty-one patients, initially given Am B, were shifted to ABLC because of failure in four, nephrotoxicity of AM B alone or in combination with another drug in 15, and acute side effects in two. The initial dose of ABLC was 5 mg/kg per day; this could be lowered to 3 mg/kg per day or transiently interrupted in cases of impairment of renal function. RESULTS: A mean cumulative dose of 6107 mg (660--16 050) was given over a mean duration of 22 days (4--49). Clinical response rate was 63% (14/22), with mycologic eradication in 37% (9/17) in proven infections. For proven aspergillosis, corresponding rates were 54% (6/11) and 20% (2/10), and in proven candidosis 71% (5/7) and 60% (3/5), respectively. Twenty-one courses were complicated by one or more side effects: fever and chills (11), impairment of renal function requiring a transient reduction of drug dosage (14), hypotension (1). However, for the whole group, creatinine clearance before and after 2, 4 and 6 weeks of treatment remained quite stable. CONCLUSIONS: ABLC, with its low toxicity, enabled us to treat patients who were or would have been unable to tolerate an efficacious dose of Am B. No conclusions about efficacy can be drawn from this small-size, compassionate study. Well-designed studies to compare efficacy and safety of conventional amphotericin B and the various lipidic formulations should be implemented.

Comparison of fungizone, Amphotec, AmBisome, and Abelcet for treatment of systemic murine cryptococcosis

Three lipid-based formulations of amphotericin B have been approved for use in various countries. The aim of this study was to compare Amphotec (ABCD; Sequus), AmBisome (AmBi; Nexstar), Abelcet (ABLC; The Liposome Co.), and conventional deoxycholate amphotericin B (Fungizone; Bristol Meyers Squibb) for the treatment of experimental systemic cryptococcosis. A model was established in 10-week-old female CD-1 mice by intravenous (i.v.) injection of 6.25 x 10(5) viable Cryptococcus neoformans yeast cells. Therapy began 4 days later, with i.v. administration three times per week for 2 weeks. Mice received either no treatment, 1 mg of Fungizone per kg of body weight, or 1, 5, or 10 mg of ABCD, AmBi, or ABLC per kg. Ninety percent of control mice died between days 15 and 34. All treatment regimens except ABLC at 1 mg/kg prolonged survival compared with no treatment (P < 0.01 to 0.001). All mice receiving 5 or 10 mg of ABCD or AmBi per kg and 90% of mice given 10 mg of ABLC per kg survived, whereas < or =50% of those given other treatment regimens survived. Fungizone was the least effective of the four formulations, with 5 or 10 mg of ABCD, AmBi, or ABLC per kg resulting in a significantly better outcome than Fungizone (P < 0.001). Among the three formulations, ABCD and AmBi were equally effective, both being better than ABLC at equal 5- or 10-mg/kg doses (P < 0.001). Comparison of residual infectious burdens in various organs showed that each drug had some dose-responsive efficacy in three or more organs at escalating doses. In the brain, ABCD or AmBi at 5 or 10 mg/kg or ABLC at 10 mg/kg was more effective than Fungizone at 1 mg/kg or no treatment, while ABCD or AmBi at 1 mg/kg was as effective as ABLC at 10 mg/kg. Similar results were obtained for the kidneys and lungs. In the spleen, ABCD at 10 mg/kg cured all mice of infection and was superior to all other regimens. In the liver, AmBi at 5 mg/kg was superior to an equal dose of ABCD or ABLC. Overall, the efficacies of ABCD and AmBi were equal to that of Fungizone at 1 mg/kg and were about 10-fold better than that of ABLC, particularly in the brain; a comparative rank order of efficacies was ABCD approximately equal to AmBi > ABLC >> Fungizone. This is the first study that compared all four amphotericin B formulations.

Development of liposomal amphotericin B formulation

A considerable effort has been spent in the past three decades to investigate various aspects of liposomes as novel drug delivery systems. In 1990, the first amphotericin B (AmB) liposomal preparation (L-AmB) under the brand name AmBisome was introduced into the market by Vestar. The successful marketing of the product moved liposomes out of the stage of experimental obscurity to the realistic stage of clinical utility. The launch of AmBisome sparked off the introduction of other lipid-based AmB products marketed by Liposome Technology (Amphocil) and The Liposome Co. (Abelcet). The drive behind the development of a modified formulation of AmB was to improve the therapeutic index of this drug with respect to its major drawback associated with both acute and chronic toxic effects. In a 30-year-long experience with AmB, several reports were recorded in the literature of acute adverse effects, such as fever, rigors, vomiting, cardiotoxicity and hypotension occurring during infusion; while long-term therapy was reported to be associated with hypokalemia, renal dysfunction and hematological abnormalities. Another serious problem encountered with the drug had been the poor response obtained in immunocompromised patients like those with AIDS, neutropenia and cancer patients on chemotherapy. The encapsulation of amphotericin B in liposomal vesicles was hence targeted not only to obtain an improvement in the therapeutic index but also to see if it was useful in eradicating deep-seated fungal infections in immunocompromised patients. The liposomal AmB was found to have a better therapeutic index and lower toxicity than the commercial AmB preparations. The LD50 of AmBisome in mouse was 175 mg/kg compared with 3.7 mg/kg for Fungizone, the commercial preparation of AmB. Additionally, L-AmB has prolonged circulation time, and extravasates into the site of infection and delivers the drug directly to the site, with no nephrotoxicity and neurotoxicity as experienced with AmB. This review traces the course of development of L-AmB and discusses the rationale behind the development of its liposomal preparation. The results in in vitro, in vivo and clinical studies, mechanism of action, biodistribution, and formulation considerations of L-AmB are described. The clinical experience with the marketed preparation is reviewed.

Amphotericin B lipid complex

OBJECTIVE

To evaluate the published data on the effectiveness and safety of amphotericin B lipid complex (ABLC) for the treatment of invasive mycosis and to evaluate data describing the pharmacologic properties and pharmacokinetic behavior of ABLC in both animals and humans.

DATA SOURCE

A MEDLINE search was conducted to identify literature published from 1965 to January 1997 for amphotericin B deoxycholate (DCAB) and ABLC. In addition, preliminary data published as abstracts and presented at national conferences on infectious disease and hematology within the last 6 years were also included in this review.

STUDY SELECTION

Both human and animal studies were reviewed. Animal and in vitro studies were selected to evaluate the pharmacologic and toxicologic properties of ABLC. For the evaluation of the efficacy, safety, and pharmacokinetic behavior of ABLC, large, well-controlled studies were reviewed. In addition, data from open-label and emergency use protocols were also included in the review.

DATA EXTRACTION

The study and analytical methods, results, and conclusions of the selected studies were evaluated. Pharmacokinetic data for both ABLC and DCAB that were derived from human subjects were also evaluated.

DATA SYNTHESIS

DCAB has been the cornerstone for the treatment of invasive mycosis, even though it has a narrow therapeutic index. Infusion-related toxicities (e.g., fever, chills, rigors) are likely due to DCAB stimulation of cytokine and prostaglandin synthesis. Conversely, nephrotoxicity, the primary non-infusion-related toxicity, likely results from the nonselective cytotoxic interaction between DCAB and cholesterol-containing mammalian cells. ABLC represents a new approach to improving the therapeutic index of DCAB. Mammalian cytotoxicity is attenuated by complexing amphotericin B to a mixture of phospholipids. This alters the affinity of amphotericin B and decreases its selective transfer from the complex to cholesterol-containing mammalian cells. Fungi also possess lipase, which improves the selective transfer from the complex to ergosterol-containing cell membranes. In humans, the lipid formulation increases the volume of distribution of amphotericin B. Thus, compared with DCAB, larger doses of ABLC can be administered for a longer duration with less nephrotoxicity. However, the prevalence of infusion-related toxicities associated with ABLC is similar to that of DCAB. Whether the alteration in distribution improves efficacy by improving tissue concentrations of amphotericin B has not been determined. The cost of this agent will limit its use.

CONCLUSIONS

ABLC has been shown to be at least as effective as DCAB, and it has been well tolerated in the clinical studies to date. Despite large dosages and extended courses of administration, there is little nephrotoxicity associated with its use. However, the cost of this agent will limit its use to the treatment of refractory mycosis or to cases where DCAB is contraindicated due to significant renal insufficiency.

Behavior of amphotericin B lipid complex in plasma in vitro and in the circulation of rats

Amphotericin B lipid complex (ABLC) shows reduced toxicity relative to that of amphotericin B deoxycholate (AmB-d) while maintaining antifungal activity. Rat blood or plasma was spiked with ABLC in vitro. Released amphotericin B was separated from the parent material by centrifugation. At early times (0 to 15 min) most (approximately 90%) of the amphotericin B was complexed. The amount of released amphotericin B increased gradually in a time- and temperature-dependent fashion. The released amphotericin B was associated with plasma lipoprotein and nonlipoprotein proteins. The area under the concentration-time curve from 0 to 24 h for total amphotericin B in whole blood of rats given a single intravenous bolus dose of 1 mg of ABLC per kg of body weight was fourfold lower than that in rats given 1 mg of AmB-d per kg. The complexed amphotericin B was rapidly removed from the circulation and was distributed to the tissues in these rats. Other rats were treated intravenously with ABLC (10 mg/kg/day) or AmB-d (0.5 mg/kg/day) daily for 15 days. Blood was collected at 15 and 180 min after administration of the last dose. The total levels of amphotericin B in the blood of the group given ABLC were about three to five times those in the group given AmB-d, and the concentration of released, protein-bound amphotericin B in the plasma of the group given ABLC was about one to two times that observed for the group given AmB-d, despite the 20-fold difference in dose. The relative protein distribution of amphotericin B in plasma was similar after ABLC or AmB-d administration under these steady-state conditions in vivo. The rapid uptake of complexed amphotericin B by tissues and the very low levels of circulating protein-bound amphotericin B in plasma after the administration of ABLC may explain, in part, the reduced toxicity and enhanced therapeutic index of this preparation.

Pulmonary delivery of beclomethasone liposome aerosol in volunteers. Tolerance and safety

STUDY OBJECTIVE

To test the tolerance and safety of single doses of beclomethasone dipropionate (Bec)-dilauroylphosphatidylcholine (DLPC) liposome aerosol in volunteers.

DESIGN

Single-dose inhalations of liposome preparations of Bec-DLPC and DLPC alone were administered for 15 min from a jet nebulizer (Puritan-Bennett, modified twin jet; mass median aerodynamic diameter of 1.6 microns) under close clinical and laboratory surveillance. Two dose levels (0.5 mg Bec/12.5 mg DLPC per milliliter, and 1.0 mg Bec and 25 mg DLPC per milliliter in the reservoirs, respectively) were administered. The Bec doses were selected to approximate the dosages of this glucocorticoid used with metered-dose inhalers (MDIs). First, four volunteers were exposed to an initial low dose; the mean (+/-SD) inhaled doses were 0.56 +/- 0.07 mg of Bec and/or 14.0 +/- 1.8 mg of DLPC. Subsequently, a second group of six volunteers was exposed to a higher dose; the mean (+/-SD) inhaled doses were 1.29 +/- 0.14 mg of Bec and/or 34.6 +/- 6.8 mg of DLPC.

SETTING

Outpatient and inpatient.

PATIENTS

Normal male (n = 6) and female (n = 4) adult volunteers.

INTERVENTIONS

Inhalation of Bec-DLPC and DLPC liposome aerosols in a single-dose tolerance study involving 10 normal volunteers.

MEASUREMENTS AND RESULTS

Spirometry, clinical observations, clinical chemistry, and hematology were monitored. No adverse clinical or laboratory events were observed.

CONCLUSIONS

Bec-DLPC liposome aqueous aerosol was well tolerated in doses equivalent to those currently administered by MDIs and dry powder inhalers for treatment of asthma.

Efficacy of prophylactic aerosol amphotericin B lipid complex in a rat model of pulmonary aspergillosis

Invasive pulmonary aspergillosis remains an important cause of morbidity and mortality among transplant recipients and patients receiving cancer chemotherapy. The lipid-associated formulation of amphotericin B (AmB), AmB lipid complex (ABLC), was evaluated for its prophylactic efficacy when it was administered as an aerosol in a rat model of pulmonary aspergillosis. Aerosol ABLC (aero-ABLC), in doses from 0.4 to 1.6 mg/kg of body weight given 2 days before infection, significantly delayed mortality compared to the mortality of rats given placebo (P < 0.001). At day 10 postinfection, 50% of rats in the 0.4-mg/kg group and 75% of rats in the 1.6-mg/kg group were alive, while all control animals had died. In a second trial aero-ABLC was more effective than an equivalent dose of aerosol AmB (aero-AmB) in prolonging survival, with 100% survival at day 14 postinfection in the ABLC group, compared to 62.5% survival in the AmB group. Mean concentrations of AmB in lungs were 3.7 times higher at day 1 (P < 0.002) and almost six times higher at day 7 (P < 0.001) after treatment with aero-ABLC than after treatment with a similar dose of aero-AmB. We conclude that aero-ABLC provided higher and more prolonged levels of the parent compound in the lungs than aero-AmB and was more effective in delaying mortality from aspergillosis in this model.

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 deoxycholate (Fungizone): old drug, new versions]

Amphotericin B-deoxycholate (Fungizone) remains the main treatment of systemic mycoses. However, its toxicity, especially renal impairment, limits its use. The chemical properties of this molecule led to its association with lipidic structures. Among the three so-called liposomal formulations of amphotericin B, only one (AmBisome) is a true liposome. Its tolerance is good, along with high blood concentrations. The two others formulations, either in disk or ribbon form, are not true liposomes and these formulations are not as well tolerated as the former. These three forms of amphotericin are very expensive, thus limiting their use. The association of amphotericin B with other lipidic structures is of great interest. The direct solubilization of Fungizone in an emulsion (Intralipid 20%) is inexpensive and easily prepared extemporaneously; this preparation of Fungizone leads to a strong reduction of side effects and its efficacy is at least equivalent to conventional Fungizone. In the future, the association with triglycerides or lecithins is probable: possibly providing promising formulations.

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.

Lipid formulations of amphotericin b in the treatment of experimental visceral leishmaniasis due to Leishmania infantum

Despite significant antileishmanial activity of amphotericin B (AmB) in vitro, the use of the deoxycholate formulation (Fungizone) is limited because of serious side effects. Lipid formulations of AmB have been proposed to reduce this toxicity. We compared the tolerance and efficacy of the conventional AmB prepared with deoxycholate, AmB emulsified in Intralipid 20%, amphotericin B lipid complex (Abelcet), and liposomal AmB (AmBisome) in a murine model of visceral leishmaniasis induced by Leishmania infantum. Control groups included untreated mice and mice treated with the pentavalent antimonial (Glucan-time). Balb/C mice were infected intravenously on day 0 with 10(7) promastigotes of L. infantum, then treated from days 7 to 17 (early treatment group) or from days 60 to 70 (delayed treatment group). Glucan-time was administered daily by intraperitoneal injection, whereas AmB formulations were administered intravenously on alternate days. On days 20, 60 and 120 in the early treatment group and 72 and 125 in the delayed treatment group, parasite burdens were determined in liver, spleen, and lungs by subculturing using a microtitration method. Abelcet (12 mg/kg) and AmBisome (12 mg/kg) completely eradicated the parasites from the tissues. Both of these lipid formulations enabled higher dosages to be tolerated, and were remarkably more effective than Fungizone (0.8 mg/kg) and AmB diluted in Intralipid 20% (1.2 mg/kg) in the treatment of murine visceral leishmaniasis due to L. infantum.

Is there a therapeutic or pharmacokinetic rationale for amphotericin B dosing in systemic Candida infections?

OBJECTIVE

To review the literature regarding the dosage of amphotericin B in Candida infections. The correlation or rationale of current dosing practices is assessed in light of the literature.

DATA SOURCES

A MEDLINE search encompassing the years 1968-1995 was used to identify pertinent literature. Additional references were obtained from the articles retrieved from MEDLINE.

STUDY SELECTION

Studies that directly assessed amphotericin B dosage and/or duration, pharmacokinetic literature dealing with plasma concentrations and amphotericin B disposition, and literature dealing with dose and/or concentration as well as clinical outcome were selected for inclusion. Additional relevant citations were used in the introductory material and discussion.

DATA EXTRACTION

Although there was a large number of articles related to amphotericin B, surprisingly few large studies were designed to address the issues in question. The description of the methods and results of these heterogeneous articles are the basis of this review. Although additional controlled studies with more subjects need to be performed, the results to date provide a foundation from which to make some inferences regarding optimal use of this therapeutic modality until more definitive data become available.

DATA SYNTHESIS

Despite numerous articles addressing the pharmacokinetics of amphotericin B, little is known about its tissue distribution, the rate of transfer of the drug from vascular to peripheral sites, or its terminal disposition. Less information is available regarding the relevance of pharmacokinetic parameters or serum concentrations to clinical outcome. Most of the articles mentioning dosing provide little or no justification for the doses employed. The variety of the dosages used and the heterogeneity of the populations studied make determination of dose-outcome relationships difficult.

CONCLUSIONS

From the available clinical data, it appears that early initiation of amphotericin B therapy is crucial to a favorable outcome. Daily dosing initially followed by every-other-day administration of twice the daily dose is better tolerated by the patient than daily dosing and produces a similar therapeutic outcome. The drug should be continued until therapeutic endpoints have been achieved, rather than until a specific total dosage has been administered. The nephrotoxicity that occurs with amphotericin B administration is apparently reversible and should not be used as an endpoint for therapy if total dosages do not exceed 4 g. Additional well-designed, controlled trials evaluating standardized dosing methods of amphotericin B with predetermined dosing regimens and/or definitive therapeutic endpoints are needed to determine the optimal dosing approach for this agent.

Recent progress and current problems in treatment of invasive fungal infections in neutropenic patients

Invasive fungal infections, including disseminated candidiasis and invasive pulmonary aspergillosis, are important causes of morbidity and mortality in neutropenic patients. The recent development of fluconazole, itraconazole, lipid formulations of amphotericin B, and recombinant cytokines have expanded our therapeutic armamentarium. Clinical trials have elucidated new strategies for utilizing these compounds in the prevention and treatment of opportunistic mycoses. The population of more severely immunocompromised patients, however, continues to expand and the spectrum of drug-resistant fungi, including but not limited to Candida spp, Fusarium spp, Zygomycetes, and dematiaceous moulds, continues to evolve, thus presenting new challenges to recent therapeutic advances. Development of new antifungal chemotherapeutic agents and novel approaches for augmentation of host response will be required to meet these new mycologic challenges.

Cryptococcosis in the era of AIDS--100 years after the discovery of Cryptococcus neoformans

Although Cryptococcus neoformans and cryptococcosis have existed for several millennia, a century has passed since the discovery of this encapsulated yeast and its devastating disease. With the advent of the AIDS pandemic, cryptococcal meningitis has emerged as a leading cause of infectious morbidity and mortality and a frequently life-threatening opportunistic mycosis among patients with AIDS. Both basic and clinical research have accelerated in the 1990s, and this review attempts to highlight some of these advances. The discussion covers recent findings, current concepts, controversies, and unresolved issues related to the ecology and genetics of C. neoformans; the surface structure of the yeast; and the mechanisms of host defense. Regarding cell-mediated immunity, CD4+ T cells are crucial for successful resistance, but CD8+ T cells may also participate significantly in the cytokine-mediated activation of anticryptococcal effector cells. In addition to cell-mediated immunity, monoclonal antibodies to the major capsular polysaccharide, the glucuronoxylomannan, offer some protection in murine models of cryptococcosis. Clinical concepts are presented that relate to the distinctive features of cryptococcosis in patients with AIDS and the diagnosis, treatment, and prevention of cryptococcosis in AIDS patients.

Successful treatment of invasive aspergillosis complicating prolonged treatment-related neutropenia in acute myelogenous leukemia with amphotericin B lipid complex

Herein we report the successful treatment of invasive aspergillosis with the liposomal amphotericin B (AMB) formulation, Amphotericin B Lipid Complex (ABLC). This investigational compound was employed in a 50-year-old patient with acute myelomonocytic leukemia complicated by prolonged, treatment-induced granulocytopenia and documented Aspergillus flavus sinusitis with signs of disseminated aspergillosis. The patient demonstrated radiographic signs of pulmonary aspergillosis and biochemical signs of hepatic involvement that were resistant to a 23 day course of conventional AMB (Fungizone) therapy. Following therapy with ABLC her fever abated, her chest X-ray findings improved, and her hepatic function tests improved with eventual resolution.

Therapeutic monitoring of experimental invasive pulmonary aspergillosis by ultrafast computerized tomography, a novel, noninvasive method for measuring responses to antifungal therapy

Pulmonary infiltrates in neutropenic hosts with invasive aspergillosis are due to vascular invasion and hemorrhagic infarction. In order to measure the effect of antifungal compounds on this organism-mediated tissue injury, we monitored the course of pulmonary infiltrates by serial ultrafast computerized tomography (UFCT) in persistently granulocytopenic rabbits with experimental invasive pulmonary aspergillosis. The course of pulmonary lesions measured by serial UFCT scans was compared with those measured by conventional chest radiography, histopathological resolution of lesions, and microbiological clearance of Aspergillus fumigatus. Treatment groups included either amphotericin B colloidal dispersion in dosages of 1, 5, and 10 mg/kg of body weight per day intravenously or conventional desoxycholate amphotericin B at 1 mg/kg/day intravenously. Therapeutic monitoring of pulmonary lesions by UFCT demonstrated a significant dose-response relationship. Lesions continued to progress in untreated controls, whereas lesions in treated rabbits initially increased and then decreased in response to antifungal therapy in a dosage-dependent manner (P < or = 0.05 to P < or = 0.005, depending upon the groups compared). This same trend of resolution of lesions in response to antifungal therapy was also demonstrated by postmortem examination and by microbiological clearance of the organism. These data indicated that amphotericin B colloidal dispersion at 5 and 10 mg/kg/day exerted a more rapid rate of clearance of lesions than conventional amphotericin B. UFCT was more sensitive than conventional chest radiography in detecting lesions due to invasive pulmonary aspergillosis (P < 0.05 to P < 0.005, depending upon the groups compared). These findings establish a correlation among UFCT-defined lesions, microbiological response, and resolution of pathologically defined lesions in experimental invasive pulmonary aspergillosis. Serial monitoring of UFCT-defined lesions of aspergillosis provides a novel system for determining the antifungal response of organism-mediated tissue injury.

Comparative tissue distribution and elimination of amphotericin B colloidal dispersion (Amphocil) and Fungizone after repeated dosing in rats

The pharmacokinetic profiles of amphotericin B (AmB) after administration of Amphocil, an AmB/cholesteryl sulfate colloidal dispersion (ABCD) and the micellar AmB/deoxycholate (Fungizone) were compared after repeated dosing in rats. After administration of ABCD and Fungizone at an equal AmB dose (1 mg/kg), AmB concentrations in plasma and most tissues were lower for the ABCD dose, especially in the kidneys where reduced drug concentration correlated with reduced nephrotoxicity. In contrast, AmB concentrations in the liver were substantially higher when ABCD was administered; however, without an accompanying increase in hepatotoxicity. Daily administration of ABCD for 14 days did not lead to AmB accumulation in plasma; while a slight accumulation was observed after multiple administration of Fungizone. AmB was eliminated more slowly from the plasma and various tissues and urinary and fecal recoveries of AmB were reduced after ABCD administration. These results suggest that ABCD may be stored in tissues in a form that is less toxic and is eliminated from the systemic circulation by a different mechanism than the free and protein-bound AmB in plasma. AmB accumulation in the spleen was observed when higher, doses of ABCD (5 mg/kg) were administered, which could be due to saturation of hepatic uptake of AmB. Comparison of spleen concentrations of AmB between ABCD and Fungizone at 5 mg/kg AmB doses was not possible because of Fungizone's toxicity in rats. In all other organs, AmB concentrations reached or approached a steady state within two weeks of dosing with ABCD. Urinary and fecal clearences of AmB were not different between ABCD and Fungizone administration.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Efficacy of escalating doses of liposomal amphotericin B (AmBisome) against hematogenous Candida lusitaniae and Candida krusei infection in neutropenic mice

Immunosuppressed CF1 mice were infected intravenously with two strains of Candida krusei and four strains of Candida lusitaniae (two of which were resistant to amphotericin B). Mice were treated with 1 or 2 mg of amphotericin B desoxycholate per kg of body weight per day or escalating doses of liposomal amphotericin B (8 to 30 mg/kg/day) or were left untreated. Higher doses of liposomal amphotericin B were as effective as standard dose of amphotericin B desoxycholate in prolonging survival but were significantly more effective in reducing the fungal burden in the kidneys of animals infected with both C. krusei strains and the C. lusitaniae strains that were susceptible to amphotericin B desoxycholate. This advantage of liposomal amphotericin B therapy could not be demonstrated in mice infected with the C. lusitaniae strains that were resistant to amphotericin B desoxycholate.

In vitro and in vivo antifungal activities of liposomal amphotericin B, and amphotericin B lipid complex

The in vitro and in vivo antifungal activities of liposomal amphotericin B (L-AMPH) and amphotericin B lipid complex (ABLC), which is composed of amphotericin B and the phospholipids dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol, were compared with those of conventional amphotericin B (Fungizone, AMPH). The acute intravenous toxicity was markedly lower in BALB/c mice; 50% lethal doses (LD50s) were 2.75 mg/kg in AMPH, 32.9 mg/kg in L-AMPH and > 75 mg/kg in ABLC. In vitro antifungal activities against Candida albicans, C. parapsilosis, C. tropicalis, C. glabrata, and C. krusei were evaluated by the agar plate dilution method. The activities were unchanged against C. albicans, but MICs increased more than four fold in 18 of the 20 strains other than C. albicans in L-AMPH and in 9 of the 20 in ABLC. L-AMPH and ABLC were as efficacious as AMPH in the treatment of mice infected with C. albicans, and at a dose of 0.5 and 1.0 mg/kg of body weight, ABLC was more efficacious on survival A ten-times larger dose (10 mg/kg) of L-AMPH and ABLC was administered to mice with 100% survival, suggesting improved tolerability as compared to amphotericin B.

Management of deep Candida infection in surgical and intensive care unit patients. British Society for Antimicrobial Chemotherapy Working Party

Deep Candida infections are increasing in incidence, especially in non-neutropenic, intensive care patients including neonates. The attributable mortality of candidaemia and candida peritonitis is 37-38% with a 57% overall mortality. The BSAC set up a working party to develop recommendations for management in the absence of controlled trials. These recommendations focus on the role of the microbiology laboratory, management strategies, the respective roles of amphotericin B, flucytosine and fluconazole and long-term maintenance therapy. The indications for initiation of therapy are given special consideration.

Dose-dependent antifungal activity and nephrotoxicity of amphotericin B colloidal dispersion in experimental pulmonary aspergillosis

We investigated the safety and efficacy of amphotericin B colloidal dispersion (ABCD) for the treatment of invasive pulmonary aspergillosis in persistently granulocytopenic rabbits. Treatment groups included ABCD in dosages of 1, 5, and 10 mg/kg/day intravenously or conventional desoxycholate amphotericin B (DAmB) at 1 mg/kg/day intravenously. Antifungal activity was directly related to increasing dosage of ABCD as determined by the concentration of Aspergillus fumigatus organisms in lungs and the frequency of hemorrhagic pulmonary lesions. At 5 and 10 mg/kg/day, there was a significant reduction in the tissue burden of A. fumigatus as measured by percent culture-positive lobes and CFU per gram of tissue (P < or = 0.001), whereas at 1 mg/kg/day measured by percent culture-positive lobes and CFU per gram of tissue (P < or = 0.001), whereas at 1 mg/kg/day the tissue burden of A. fumigatus was not significantly different from that in untreated controls. Microbiological clearance was significantly greater at 1 mg of DAmB per kg per day than at 1 mg of ABCD per kg per day (P < or = 0.001). There was no difference in microbiological clearance of bronchoalveolar lavage fluid among the treatment groups as measured by CFU per milliliter. As determined by survival, ABCD at 5.0 mg/kg/day was more effective than DAmB at 1.0 mg/kg/day and ABCD at 10 mg/kg/day. ABCD at 10 mg/kg/day was more nephrotoxic than the lower dosages of ABCD and resulted in higher mortality. Impairment of glomerular filtration developed as a direct function increasing the ABCD dosage (r = 0.77; P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosolized amphotericin B-liposomes for treatment of systemic Candida infections in mice

Mice lethally infected with Candida albicans were exposed to small-particle aerosols containing amphotericin B-liposomes. The drug, when administered twice daily for 2 h (0.58 mg/kg of body weight per day) on days 1, 2, and 3 postinoculation, significantly reduced the numbers of Candida organisms in the kidneys. Aerosol treatment increased the survival time of mice given 2 2-h treatments once a week for 4 weeks. A twice-weekly, 2-h small-particle aerosol administration of amphotericin B-liposomes for 1, 2, or 3 weeks significantly increased both the mean time of survival and percent survival.

Treatment of murine candidiasis and cryptococcosis with amphotericin B incorporated into egg lecithin-bile salt mixed micelles

Amphotericin B (AmB) with deoxycholate (Fungizone) and AmB incorporated into mixed micelles (AmB-mixMs) composed of egg lecithin with glycocholate, deoxycholate, or taurocholate were compared as treatments for murine infections. For mice infected with Candida albicans, treatment consisted of a single intravenous injection; for mice infected with Cryptococcus neoformans, treatment consisted of two intravenous injections. The maximal tolerated doses of AmB as Fungizone were 1.25 mg/kg of body weight in mice with candidiasis and 2.5 mg/kg of body weight in mice with cryptococcosis. The AmB-mixMs were nontoxic to mice at doses of 80 and 100 mg/kg of body weight and were therapeutically more active than the maximal tolerated dose of Fungizone in both models of infection. However, when Fungizone or AmB-mixMs were administered at equivalent doses of AmB, AmB-mixMs were more active in treating murine candidiasis, whereas Fungizone was more active in treating murine cryptococcosis.

Liposomes in the treatment of infections

The use of liposomes in the treatment of severe infections is under investigation. Classical liposomes which localize in cells of the mononuclear phagocyte system (MPS) can be exploited in two ways. First for targeting of macrophage modulators such as muramyl peptides or IFN-gamma, to stimulate the cells of the MPS to maximal blood clearance capacity. This enhanced nonspecific anti-infectious resistance is important as in immunocompromised patients micro-organisms frequently appear in the blood from a local infection. Secondly, classical liposomes are successfully used as carriers of antibiotics in experimental intracellular parasitic-, viral-, fungal- or bacterial infections in MPS tissues. Based on these data extensive studies in patients with severe fungal infections have demonstrated successful treatment with liposomal or lipid-complexed amphotericin B. More recently, liposomal amphotericin B appeared to be effective in patients with drug-resistant visceral leishmaniasis. For the treatment of Mycobacterium avium complex infection in AIDS patients the efficacy of liposomal gentamicin is under investigation. With respect to infections in non-MPS tissues the applicability of Stealth liposomes characterized by long circulation half-lives is under investigation. Substantial localization of these liposomes in infected lung tissue of rats was demonstrated. Preliminary data in experimental bacterial lung infection showed superior efficacy of antibiotic encapsulated in Stealth liposomes.