Liposomal amphotericin B (AmBisome): safety data from a phase II/III clinical trial

Do variations in molecular structure affect the clinical efficacy and safety of lipid-based amphotericin B preparations?

While amphotericin B is the drug of choice in the treatment of most fungal infections, systemic adverse reactions and dose-dependent nephrotoxicity associated with its use frequently render the conventional preparation of amphotericin unsuitable. A number of lipid-based formulations of amphotericin have been developed to overcome the limitations of the parent compound. These preparations, amphotericin B lipid complex (ABLC), amphotericin B colloid dispersion (ABCD) and liposomal amphotericin differ from one another significantly in their molecular structure. They are also considerably more expensive than the parent compound. Clinical data on their appropriate use are limited. This review looks at the differences in molecular structure of these preparations, and at the available clinical safety and efficacy data.

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.

Safety and efficacy of liposomal amphotericin B in allogeneic bone marrow transplant recipients

In a retrospective analysis, 79 allogeneic bone marrow recipients treated with AmBisome prophylactically or because of proven or suspected invasive fungal infection (IFI) were evaluated in 92 episodes. The median duration of treatment was 14 (range 1-112) days. The mean maximum dose given was 1.64 +/- 0.8 mg kg-1 day-1 and the mean total dose was 1.29 +/- 2.28 g. The overall incidence of reported adverse events was 194, of which none had a serious outcome. In six cases, the drug was withdrawn as a result of toxic or allergic reactions: dyspnoea and flush (3), urticaria (1), cholecystitis (1) and disorientation (one case, probably not related to AmBisome). No anaphylactoid reactions were seen. Laboratory findings, including low serum potassium (48% of the episodes), increased serum creatinine (38%) and increased serum sodium levels (7%), caused no major clinical problems. Thirteen cases of verified IFI were evaluated regarding the efficacy of AmBisome. Survival or cure of the mycotic infection occurred in 5/13 patients (38%). Two patients were treated with AmBisome (3.6 and 3.3 mg kg-1 day-1) because of verified IFI before BMT. One died of IFI. The other died of venoocclusive disease of the liver (VOD) without histological evidence of active IFI. We found a significant (P < 0.05) reduction in autopsy-proven IFI, 12/199 (6%) compared to the period when only conventional doses of amphotericin B were used, 26/227 (11%).

Rapid determination of amphotericin B in serum and urine by third-order derivative spectrophotometry

A derivative spectrophotometric method for rapid monitoring of amphotericin B in serum and urine down to 30 ng/mliters is described. Samples are treated with acetonitrile, and amphotericin B is directly quantified in the crude extracts on the basis of the intensity of the peak that appears at 402 nm when the normal absorption spectrum is submitted to third-order derivative processing. Accuracy data suggested recoveries in the range of 84.3-94.9% for serum and 85.6-93.4% for urine. The precision of the method was better than 11.3% for serum and 9.2% for urine when samples contained as low as 29.6 ng/mliters of amphotericin B. Ease of applicability, short analysis time, low cost, and reliability are the main advantages of the method.

Infections in neutropenic patients. II: Management

Improvement in supportive care including the introduction of new antibiotics, antiviral and antifungal agents and haematopoietic growth factors have all contributed to a decreased chemotherapy-related mortality and morbidity in cancer patients. However, infection during neutropenia is still a major complication and a great concern for the clinician responsible for the patient. Management of infectious complications in the neutropenic patient is reviewed.

Fungal endocarditis--a report on seven cases and a brief review

Candida endocarditis is an unusual but severe complication of systemic infection caused by Candida albicans and occasionally by other fungal species. We describe seven cases that occurred during a period of 20 years in western Sweden. In four cases infections were located on prosthetic valves and in three cases native valves were involved. Three patients died of the disease in the acute phase. A definite diagnosis was established in one of four survivors. This patient had an aortic valve endocarditis and a saddle embolisation and was treated with immediate surgery, followed by intensive treatment with liposomal amphotericin B+ flucytosine. Fungal endocarditis is still a serious disease with a high mortality and whenever the diagnosis is suspected, antifungal therapy must be started and transesophageal sonography should be performed to visualize vegetations. Immediate surgery should be considered.

Targeting fungi: a challenge

Invasive fungal infections are more commonly identified in various categories of patients, mainly in cancer patients but also in those undergoing organ transplantation, patients in intensive care units, and those with AIDS. There is a great need to increase the awareness of practitioners who are still underestimating the morbidity and mortality relating to invasive fungal infections, and to stress the economic burden for the society and healthcare systems of invasive fungal infections. The list of fungal pathogens causing life-threatening complications has also increased recently, with the emergence of unusual fungi being more frequently identified in such settings. Early diagnosis of invasive fungal infections is still a major challenge for the clinician at the bedside. Identification of state-of-the-art management is also a difficult task for the clinical scientist involved in the assessment of optimal strategies to prevent and to treat those invasive fungal infections, although major progress has occurred in the last 5 years with the development of new, safe, and effective antifungal agents. Empiric therapy remains a very controversial issue that should be further investigated in high-quality clinical trials. Overall, clinical research in this difficult field requires independent and objective analysis; only large multicenter clinical trials can address these critical issues and rapidly provide convincing results leading to a better prognosis of patients with invasive fungal infections. These complications still represent too often an obstacle to successful control of severe underlying diseases. Clinical research on the appropriate ways to target fungi will not only define state-of-the-art management but also identify ineffective or redundant treatments. Such an approach will make a substantial contribution to the care of the high-risk patients within the next decade and will preserve our capacity for medical excellence.

Use of nebulised liposomal amphotericin B in the treatment of Aspergillus fumigatus empyema

A 28 year old man with asthma, bronchopulmonary aspergillosis, pulmonary thromboembolic disease, and pulmonary hypertension developed Aspergillus fumigatus empyema complicating a pneumothorax. His condition progressively deteriorated despite treatment with intravenous and intrapleural amphotericin B, but improved promptly after substituting nebulised liposomal amphotericin B and oral itraconazole. This experience suggests that nebulised liposomal amphotericin B is well tolerated and merits further assessment in the treatment of pulmonary fungal disease.

Treatment of invasive pulmonary aspergillosis in severely neutropenic children with malignant disorders using liposomal amphotericin B (AmBisome), granulocyte colony-stimulating factor, and surgery: report of five cases

Five children with malignancies developed invasive pulmonary aspergillosis during chemotherapy-induced neutropenia. All patients were treated with liposomal amphotericin B and human recombinant granulocyte colony-stimulating factor. Two patients did not recover from bone marrow aplasia and died from organ-infiltrating fungal invasion. Two patients who recovered from bone marrow aplasia survived after surgery of the pulmonary lesions. The fifth patient had a complete resolution of invasive pulmonary aspergillosis after neutrophil recovery without surgical intervention. We conclude that not only the antifungal treatment but also the recovery of granulocytes are important in localizing invasive forms of Aspergillus infections in patients with profound immunosuppression.

Infusion-related toxicity of three different amphotericin B formulations and its relation to cytokine plasma levels

A prospective study was performed to compare the infusion-associated toxicity of three different amphotericin B preparations and to correlate acute side-effects with plasma levels of tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-1 receptor antagonist (IL-1-RA) during and after the infusions. Six adult neutropenic patients with acute leukaemia suffering from suspected or documented systemic fungal infections were treated on three consecutive days with conventional amphotericin B (AmB), liposomal AmB (AmBisome) and AmB mixed in lipid emulsion (AmB/lipid). Drugs were given over 1-2 h. Drug-induced toxicity was monitored every 30 min for 4 h. Plasma levels of the three cytokines were determined using commercially available enzyme-linked immunosorbent assay (ELISA) techniques. Four of six patients showed toxicity after AmB and AmB/lipid infusions; only one patient reacted to liposomal AmB. Clinical toxicity was associated with increases in TNF-alpha plasma levels during two of four infusions of AmB and three of four infusions of AmB/lipid. Major increases in IL-6 occurred during three of four infusions of AmB and during all four AmB/lipid infusions associated with clinical toxicity. Three of four AmB infusions and all four AmB/lipid infusions accompanied by clinical toxicity were associated with major increases in IL-1-RA plasma concentrations. Liposomal AmB was better tolerated than AmB and AmB/lipid. This formulation also caused the lowest liberation of all three cytokines tested. The severity of clinical symptoms did not correlate closely with absolute cytokine plasma levels. The findings provide further evidence that expression of TNF-alpha, IL-6 and IL-1-RA plays an important role in mediating AmB-related acute toxicity in vivo.

Liposomal amphotericin B therapy of murine histoplasmosis

Liposomal amphotericin B (AmBisome) was compared with amphotericin B deoxycholate for the treatment of disseminated murine histoplasmosis. Liposomal amphotericin B was well tolerated and, milligram for milligram, was as potent as amphotericin B deoxycholate.

Efficacy and Toxicity of Amphotericin B Liposomal and Lipid Formulations

Objective:

To review the efficacy and toxicity of amphotericin B liposomal and various lipid formulations with conventional amphotericin B desoxycholate.

Data Sources:

Pertinent literature was identified via a MEDLINE search.

Study Selection:

English-language clinical trials.

Conclusions:

The incorporation of amphotericin B into liposomes or lipid formulations appears to be a novel method of administering amphotericin B for the treatment of serious systemic fungal infections for patients who have either failed therapy with, or are intolerant to, conventional amphotericin B desoxycholate.

Invasive central nervous system aspergillosis: cure with liposomal amphotericin B, itraconazole, and radical surgery--case report and review of the literature

Invasive aspergillosis of the central nervous system is a rare but well-described disease. There have been only a few reported survivors, and mortality exceeds 95% in the immunosuppressed host. We present a 2-year-old boy with acute lymphatic leukemia and multiple Aspergillus brain abscesses who was successfully treated with liposomal amphotericin B, itraconazole, and surgical excision of the abscesses. Liposomal amphotericin B is a new preparation that safely allows the attainment of significantly higher tissue levels with less toxicity than standard amphotericin B. The treatment of patients with invasive central nervous system aspergillosis is reviewed.

Liposomal amphotericin B for postoperative Aspergillus fumigatus endocarditis

A 10-month-old infant girl presented with Aspergillus fumigatus endocarditis localized to a Gore-Tex patch used as part of the repair for double-outlet right ventricle. A new liposomal preparation of amphotericin B combined with surgical vegectomy resulted in a successful outcome with no evidence of disease recurrence at 15 months' follow-up. Echocardiography provided an optimal modality for ongoing evaluation of therapeutic outcome.

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)

Pulmonary toxicity during infusion of liposomal amphotericin B in two patients with acute leukemia

Pulmonary toxicity with acute dyspnea occurred during infusion of a liposomal amphotericin B preparation (AmBisome) in two adult leukemic patients. The preparation was administered as a one hour infusion at a dose of 3 mg/kg body weight. Within 15 min after starting the infusion, both patients experienced sudden onset of dyspnea and chest tightness. Physical examination showed the patients to be anxious and restless with tachycardia and orthopnea but without other cardiopulmonary findings. No elevation of body temperature, rigors or chills were recorded. Symptoms disappeared within minutes after discontinuing the infusion. At present, the pathophysiologic mechanisms underlying these side effects are unknown.

Efficacy of AmBisome in murine coccidioidomycosis

ICR mice were infected intranasally with arthroconidia of Coccicioides immitis. Mice were treated intravenously with amphotericin B deoxycholate (Fungizone) or an amphotericin B-lipid vehicle (AmBisome). Doses ranged from 0.05 to 1.0 mg kg-1. Lung weight, which parallels disease severity and fungal burden in this infection, was used as the index of protection. Both Fungizone and AmBisome were significantly and equally protective at 0.3 and 1.0 mg kg-1 body weight.

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.

Antifungal drugs on the horizon

In the past 10 years there has been a major expansion in the development of antifungal drugs, but there are still weaknesses in the range and scope of current antifungal chemotherapy. New developments have included the modification of existing drug molecules to eliminate toxicity and improve activity, for instance, the development of the lipid formulations of the polyene antifungal agent amphotericin B. Three different amphotericin B derivatives, a unilamellar liposome (AmBisome), a colloidal dispersion (ABCD--Amphocil), and a lipid complex (ABLC) are undergoing evaluation. New triazoles with broad-spectrum antifungal activity, such as saperconazole, are also being assessed. The development of groups of drugs with novel modes of action such as cell wall biosynthesis inhibitors has been slower, although a number of molecules with activity against key enzymes, including chitin or glucan synthase, have been found. The morpholine antifungal amorolfine, a sterol biosynthesis inhibitor, has been developed for the topical treatment of fungal nail infections. The assessment of these drugs is a major challenge because it will be necessary to show that they have some advantage over existing compounds in efficacy, speed of action, or lack of toxicity.

Modulation of amphotericin B activity by association with mannose ester

The biological and molecular properties of a new formulation of Amphotericin B complexed with the surfactant palmitoyl mannose were studied in in vitro as well as in in vivo situations. The properties analyzed include toxicity towards two types of mammalian cells and four fungi strains, effect on macrophage activity, inflammatory properties, acute toxicity in mice and spectral behavior in presence of foetal calf serum or 6% propanol. The results demonstrate that, in presence of palmitoyl mannose, the cytotoxicity of AmB is decreased towards both, fungal and mammalian cells while its fungistatic potential is increased, its inflammatory properties are conserved and its acute toxicity is significantly diminished. These effects can be potentially explained by the formation of a complex between AmB and the sugar ester that impedes the interaction of the drug with either serum components or cell membrane constituents. The overall properties of AmB in the complex would be expected to favor an increase in the immunoadjuvant properties of the drug, a more localized inflammation during fungal infection and consequently a better therapeutic efficiency.

Alternative modalities of administering amphotericin B: current issues

Numerous studies performed in the field of antifungal therapy during the last decade have resulted in major developments in new modalities of administering amphotericin B including liposomes or other lipid vehicles. Current data available are very encouraging and several preparations are already commercially available in some countries. An improved therapeutic index has been shown in humans but large comparative trials are still needed to establish the definite role and indications of the various preparations as well as the optimal therapeutic regimens. These studies will make a significant contribution to improving the prognosis of patients predisposed to life threatening invasive fungal infections.

Liposomal amphotericin B, AmBisome

The unilamellar liposomal formulation of amphotericin B, AmBisome, is composed of hydrogenated soy phosphatidylcholine, distearoyl phosphatidylglycerol and cholesterol. Early studies of its efficacy in an open design showed that remissions could be induced in candidosis and aspergillosis and that doses of up to 5 mg/kg could be used. Adverse events were infrequent, with the main abnormality seen being hypokalaemia in about 18% of patients. Subsequent developments have extended this work. AmBisome has been used in two open studies of patients with invasive aspergillosis; in one of these remission was achieved in 77% of 17 patients with confirmed infection who had failed to respond to conventional amphotericin B. In AIDS patients with cryptococcosis AmBisome given for 6 weeks at 3 mg/kg daily produced mycological remission of meningitis in 67%. Other infections treated with the drug include zygomycete (mucormycosis) and Fusarium infections. AmBisome has also been used as preventative therapy in bone marrow transplant recipients and was found to reduce fungal colonisation rates. There were fewer systemic fungal infections in the treated versus placebo groups although this did not achieve statistical significance. Lack of renal and liver toxicity or anaemia has been confirmed in subsequent studies. In addition febrile reactions to the AmBisome are rare. The drug has also been used effectively in children, including infants, with systemic fungal infections. In visceral leishmaniasis patients, including HIV positive individuals, remissions have been obtained using drug regimens of 1-2 mg/kg of 2.1 days and 3 mg/kg for 10 days.

Liposomal amphotericin B in the treatment of fungal infections in neutropenic patients: a single-centre experience of 133 episodes in 116 patients

Liposomal amphotericin B (AmBisome) was used for suspected or confirmed fungal infection complicating 133 neutropenic episodes in 116 patients not tolerating, or not responding to, conventional amphotericin. Adverse effects were infrequent and no significant renal impairment resulted. Acute reactions occurred in five patients, reversible hepatic dysfunction in 23, and hypernatraemia in 17. The putative mycosis resolved with AmBisome treatment in 81 episodes (61%) and progressed with fatal outcome in 25 (19%), but the diagnosis was equivocal in most, and in 27 episodes (20%) evidence indicating nonfungal pathogenesis emerged. Treatment efficacy is, however, evaluable in those with proven aspergillosis. 13/17 patients with confirmed invasive aspergillosis responded to AmBisome (77%), conventional amphotericin having failed in 11. Treatment was successfully discontinued when the neutrophil count was < 1 x 10(9)/l in eight responders (61%). In four further patients treated for suspected aspergillosis, disseminated infection was documented at post-mortem, but the true incidence is unknown. This analysis confirms that AmBisome is well tolerated and effective against invasive mycoses in neutropenic patients, and may salvage patients when conventional amphotericin proves excessively toxic or ineffective.

Pharmacokinetics and safety of a unilamellar liposomal formulation of amphotericin B (AmBisome) in rabbits

A unilamellar liposomal formulation of amphotericin B (LAmB) known as AmBisome was safely administered intravenously to 20 rabbits at 0.5, 1.0, 2.5, 5, or 10 mg/kg of body weight, whereas of 12 rabbits given desoxycholate amphotericin B (DAmB) intravenously at 0.5, 1.0, or 1.5 mg/kg, 2 died of acute cardiac toxicity when DAmB was administered at the highest dose. Single-dose LAmB (1 mg/kg) achieved a maximum concentration in serum (Cmax) of 26 +/- 2.4 micrograms/ml and an area under the curve to infinity (AUC0-infinity) of 60 +/- 16 micrograms.h/ml, while single-dose DAmB (1.0 mg/kg), by comparison, achieved a lower Cmax (4.7 +/- 0.2 micrograms/ml; P = 0.001) and a lower AUC0-infinity (30.6 +/- 2.2 micrograms.h/ml; P = 0.07). Following administration of a single dose of LAmB (10 mg/kg), a disproportionately higher Cmax (287 +/- 14 micrograms/ml) and AUC0-infinity (2,223 +/- 246 micrograms.h/ml) occurred, indicating saturable elimination. After chronic dosing (n = 4) with LAmB at 5.0 mg/kg/day for 28 days or DAmB at 1.0 mg/kg/day for 28 days, LAmB achieved daily peak levels of 122.8 +/- 5.8 micrograms/ml and trough levels of 34.9 +/- 1.8 micrograms/ml, while DAmB reached a peak of only 1.76 +/- 0.11 microgram/ml and a trough of 0.46 +/- 0.04 microgram/ml (P < or = 0.001). Significant accumulations of amphotericin B into reticuloendothelial organs were observed, with 239 +/- 39 micrograms/g found in the liver after chronic LAmB dosing (5 mg/kg/day), which was seven times higher than the 33 +/- 6 micrograms/g after DAmB dosing (1 mg/kg/day) (P = 0.002). Accumulation in kidneys, however, remained 14-fold lower (P =0.04) following LAmB dosing (0.87 +/- 0.61 microgram/g) than after DAmB dosing (12.7 +/- 4.6 microgram/g). Nephrotoxicity occurred in only one of four LAmB treated animals, while it occurred in all four chronically DAmB-treated animals: mild hepatozicity with transaminase elevations was seen in one LAmB-treated rabbit. We conclude that LAmB safely achieved higher Cmax(s) and AUC0-infinity(s) and demonstrated saturable, nonlinear elimination from plasma via reticuloendothelial organ uptake. Take reduced nephrotoxicity of LAmB correlated with diminished levels of amphotericin B in the kidneys.

Lipid-based amphotericin B in the treatment of cryptococcosis

Amphotericin B is the only antifungal drug which, despite its dose-limiting toxicity, can be given intravenously when an aggressive treatment is required. In an attempt to reduce the drug toxicity while retaining its therapeutic efficacy, new formulations of amphotericin B have been developed. The most promising have employed lipid vehicles such as liposomes. Three lipid-based amphotericin B formulations have been developed by pharmaceutical companies and are under active clinical investigation. Efficacy and safety data of these derivatives in animals and humans are reviewed, with particular concern to cryptococcal infection. The authors' experience with a small unilamellar liposomal amphotericin B formulation, AmBisome, in the primary therapy of cryptococcosis is reported. Nine AIDS patients affected with cryptococcosis, seven of whom had meningitis, were given AmBisome (3 mg/kg/day) for 3-6 weeks. Complete response was obtained in six patients, marked improvement in two, and failure in one. AmBisome was well tolerated and shortened the time to clinical and mycological response suggesting a further improvement in the management of cryptococcosis in AIDS patients.

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.

Liposomal amphotericin-B (AmBisome) for treatment of cutaneous widespread candidosis in an infant with methylmalonic acidaemia

In a 10-week-old infant with vitamin B12-unresponsive methylmalonic acidaemia, cutaneous candidosis (Candida albicans) progressed rapidly despite topical antifungal treatment. After 1 week of intravenous therapy with liposomal amphotericin-B (AmBisome) the dermatitis disappeared completely and blood cultures were sterile. No side-effects were observed. This is one of the first experiences in the treatment of infants with this new antifungal agent.

Amphotericin B and its delivery by liposomal and lipid formulations

In recent years, new formulations of the original amphotericin B preparation (Fungizone) have been devised in order to overcome toxicity problems that frequently occur. These preparations represent an improved method of drug delivery, with an increased therapeutic index and a decrease in toxicity to mammalian cell membranes. The new formulations have different physico-chemical characteristics and differ in pharmacokinetic parameters. Their effects must be compared with conventional amphotericin B to ascertain potential roles in future antifungal therapy.

Liposomal amphotericin B (AmBisome) treatment of invasive fungal infections in immunocompromised children

Thirteen children were treated for 16 cases of proven (8 cases) or suspected (8 cases) invasive fungal infections caused by Candida spp. (9 cases), Aspergillus spp. (3 cases) and mycetoma (1 case). The type of fungal infection was not identified in 3 cases. Liposomal amphotericin B (AmBisome) was instituted because of the failure of previous treatments in 9 cases, toxicity-associated amphotericin B therapy in 4 cases and renal insufficiency in 3 cases. AmBisome was given for a median of 19 days (range 3-55) with a mean cumulative dose of 1.8 +/- 1.3 g (+/- SD). Acute toxic side-effects were not seen in any patients. Slight increases in serum creatinine were seen in 3 cases during AmBisome therapy. No other side-effects were observed. Among 8 cases with proven invasive fungal infection, 6 were clinically cured, one had persistent fungi and one died after only 3 days of AmBisome therapy. Eradication of fungi was documented in 5 out of 6 cases. Among the 8 cases with presumed fungal infections, 6 were clinically cured, one improved and one died after 6 days of treatment. To conclude, AmBisome can safely be given to children with invasive fungal infections; side-effects are minimal and among those treated for at least a week, the overall cure rate was 86% (12 out of 14).

Liposomes in drug delivery. Clinical, diagnostic and ophthalmic potential

Liposomes (phospholipid-based vesicles) have been investigated since 1970 as a system for the delivery or targeting of drugs to specific sites in the body. Because of their structural versatility in terms of size, composition, surface charge, bilayer fluidity and ability to incorporate almost any drug regardless of solubility, or to carry on their surface cell-specific ligands, liposomes have the potential to be tailored in a variety of ways to ensure the production of formulations that are optimal for clinical use. This includes controlled retention of entrapped drugs in the presence of biological fluids, controlled vesicle residence in the blood circulation or other compartments in the body, and enhanced vesicle uptake by target cells. Accumulated in vivo evidence, particularly in areas such as cancer chemotherapy, antimicrobial therapy, vaccines, diagnostic imaging and the treatment of ophthalmic disorders has indicated clearly that some liposome-entrapped drugs and vaccines exhibit superior pharmacological properties to those observed with conventional formulations. Such work has encouraged the application of liposomes in the treatment of diseases in humans. A large number of trials in patients with cancer or infections suggest that certain liposomal drug formulations are likely to prove clinically useful.

Efficacy evaluation of a novel submicron amphotericin B emulsion in murine candidiasis

A submicron amphotericin B (AmB) sterile emulsion with a mean droplet size of approximately 100 nm was prepared. The emulsion was stable at 4 degrees C over a period of 4 months. The acute toxicity results showed that the maximum tolerated dose of the AmB emulsion was 2.0 mg kg-1 as compared to 0.5 mg kg-1 for a commercial deoxycholate suspension, Fungizone. Efficacy evaluations of submicron AmB emulsion compared to Fungizone were performed in a murine candidiasis model using either a single or a multiple daily dose administration of 0.4 mg kg-1. Survival (100%) was observed up to 15-18 days post-infection in mice treated with AmB emulsion or Fungizone, while all control non-treated animals had died after 9 days in both single and multi-treatment experiments. Survival (50%) was obtained after 35 days in the single treatment, and 40 days in the multi-treatment, experiment with AmB emulsion, while treatment with Fungizone gave 50% survival after 15 and 20 days, respectively. The overall results indicate that in murine candidiasis, treatment with AmB submicron emulsion was more effective than Fungizone, suggesting a potential therapeutic application.

Liposomes as carriers of antimicrobial agents or immunomodulatory agents in the treatment of infections

Targeting of antimicrobial agents by means of liposomes is under investigation and may be of importance in the treatment of infections that prove refractory to conventional forms of antimicrobial treatment. The ability to achieve a significantly longer residence time of liposomes in plasma and limited uptake of liposomes by the mononuclear phagocyte system opens up new areas of investigation and potential therapeutic application. By manipulating the liposomal composition, rates of uptake and intracellular degradation can be influenced and thereby the rates at which liposome-encapsulated agents are released and become available to exert their therapeutic action. With respect to the targeting of macrophage modulators at the mononuclear phagocyte system by means of liposomes for maximal stimulation of the nonspecific antimicrobial resistance, experimental evidence is now available of the potential usefulness of liposomes as carriers of these agents. This approach may also be of importance for the potentiation of treatment of severe infections.

Clinical experience with multilamellar liposomal amphotericin B in patients with proven and suspected fungal infections

Over a 3-year period, an unsonicated multilamellar vesicle preparation containing a low ratio of amphotericin B (5 mole %) was used as a routine alternative to amphotericin B-deoxycholate in treating 17 patients with a variety of systemic fungal infections representative of those commonly encountered on a tertiary care centre infectious disease service. Patient acceptability and convenience of administration were noteworthy. In 6/7 patients who had been given the liposomal drug after experiencing severe side effects (primarily hypokalemia and marked elevation of serum creatinine) on the non-liposomal form, the problems that had led to institution of the liposomal drug were reversed during treatment. However, multilamellar liposomal amphotericin B at conventional dosage was not without detectable toxicity in this patient population. Three transplant patients receiving cyclosporin at the same time as liposomal amphotericin B experienced a rise in serum creatinine, and 4 patients became hypokalemic during treatment: none of these effects was severe or required discontinuation of therapy. One or more liver enzymes rose measurably in 7 patients during treatment with liposomal amphotericin B, but remained unchanged or actually decreased in the remaining patients.

Effects of the aggregation state of amphotericin B on its toxicity to mice

Amphotericin B (AmB) is a very effective antifungal agent for most systemic fungal infections. However, the relatively high toxicity of this drug imposes limits on its clinical usefulness. Most of the current work in this field is devoted to the search for less-toxic formulations of the drug. Here we describe the effects of three surfactants, one anionic and the other two nonionic, on the aggregation state of AmB in solutions which were injected intravenously into mice. The degree of aggregation of AmB was monitored spectroscopically and by light scattering. The toxicity was expressed as percentage of survivors. These results were compared with those obtained with doses of AmB the same as those present in a commercial formulation of AmB, Fungizone. Two surfactants, lauryl sucrose and sodium deoxycholate, used at concentrations which induced monomerization of AmB, substantially decreased the acute toxicity of AmB to mice. Conversely, the third surfactant, Tween 80, showed a synergistic potentiation of the toxicity of the antibiotic. A good correlation was found between the in vivo toxicity and the aggregation state of AmB in injected solutions. Solutions in which AmB was almost entirely monomeric were half as toxic after 24 h and about six times less toxic after 1 week than the corresponding solutions of Fungizone.