Efficacy and tolerance of amphotericin B in a lipid emulsion in the treatment of visceral leishmaniasis in AIDS patients

Overview of treatment options for invasive fungal infections

The introduction of several new antifungals has significantly expanded both prophylaxis and treatment options for invasive fungal infections (IFIs). Relative to amphotericin B deoxycholate, lipid-based formulations of amphotericin B have significantly reduced the incidence of nephrotoxicity, but at a significant increase in drug acquisition cost. Newer, broad-spectrum triazoles (notably voriconazole and posaconazole) have added significantly to both the prevention and treatment of IFIs, most notably Aspergillus spp. (with voriconazole) and the treatment of some emerging fungal pathogens. Finally, a new class of parenteral antifungals, the echinocandins, is employed most frequently against invasive candidal infections. While the role of these newer agents continues to evolve, this review summarizes the activity, safety and clinical applications of agents most commonly employed in the treatment of IFIs.

Liposomal amphotericin B: clinical experience and perspectives

While amphotericin B deoxycholate (Fungizone, Apothecon Pharmaceuticals) has been considered by many to be the gold standard for the treatment for numerous invasive fungal infections for over 45 years, toxicities associated with its use often necessitate treatment modification or discontinuation. Lipid-based formulations, including liposomal amphotericin B (AmBisome, Fujisawa Healthcare, Inc.), were developed to decrease many of these toxicities while retaining broad antifungal spectrum and potency of amphotericin B. In clinical trials, liposomal amphotericin B has demonstrated efficacy comparable to that of amphotericin B deoxycholate while reducing the incidence of treatment-related nephrotoxicity, electrolyte-wasting, and infusion-related reactions. In addition, recent clinical trials have also compared liposomal amphotericin B with other antifungal classes. Acquisition costs of liposomal amphotericin B are substantially higher than those of amphotericin B deoxycholate and other antifungals. While pharmacoeconomic analyses consider outcomes and other treatment-related costs, they have yet to clearly demonstrate the cost-effectiveness of liposomal amphotericin B when compared with amphotericin B deoxycholate or other antifungal agents. This review will focus primarily on recent liposomal amphotericin B experience and attempt to put its use into perspective considering other available antifungal agents.

Formulation and biopharmaceutical issues in the development of drug delivery systems for antiparasitic drugs

The development of really new antiparasitic drugs to market level is a very rare event. A large number of lead structures have already been screened and discarded, the market is large but poor, and the administrative barriers are increasingly high and costly. Novel antiparasitics must not only be better, they must also be substantially safer than the existing repertoire. There are two major aspects to drug development. One is the strategy of pathogen-specific biochemical intervention, the other the strategy of optimal formulation and application. This review focuses on the latter. In finding and adapting innovative and "intelligent", i.e. parasite- and disease-specific formulations and delivery systems, established but deficient drugs might be optimised, enhancing their efficiency and reducing negative side effects at relatively low cost. Further, many promising new ideas are severely hampered by the low water solubility of the antiparasitic drug. Here as well, some of the innovative drug formulation and delivery systems discussed below might offer highly efficient, while technologically simple, solutions.

The effect of serum albumin on amphotericin B aggregate structure and activity

PURPOSE

Mild heat treatment of Fungizone (FZ, an amphotericin B:deoxycholate preparation) leads to a new self-associated form (HFZ) that demonstrates improved therapeutic index in vivo. The origin of the improvement may lie in the differential stability in the presence of serum proteins. The purpose of this study is to assess the effect of human serum albumin (HSA) on the structure and stability and in vitro channel forming ability of these two preparations against model fungal and mammalian membrane vesicles.

METHODS

Kinetic absorption and CD spectroscopy were used to assess the kinetic and equilibrium stability of the characteristic amphotericin B complexes in the presence of HSA. Kinetic fluorescence spectroscopy of pyranine entrapped in model fungal and mammalian membrane vesicles was used to measure the cation-selective channel forming ability of HZ and HFZ delivered from HSA.

RESULTS

It is shown that FZ is rapidly converted from its aggregated form to a protein-bound monomer in the presence of HSA, whereas HFZ demonstrates greater stability by persisting as a stable inactive aggregate. Fluorescence measurements of ion currents show that HSA attenuates the membrane-activity of both preparations. However, the activity of both HFZ and FZ remains significant against ergosterol-containing membranes. This is the first direct measurement of the intrinsic channel forming abilities of these amphotericin B preparations in the presence of serum proteins.

CONCLUSION

These data provide a mechanistic rationale for the similar efficacy and lower toxicity of HFZ.

Treatment of visceral leishmaniasis (kala-azar): a decade of progress and future approaches

In 1990, there was essentially one treatment regimen in use for visceral leishmaniasis (kala-azar) around the world: 20 to 28 days of daily injections of pentavalent antimony (Sb). During the past 10 years, however, new agents have been tested alone or in combination, in more than 50 studies carried out worldwide. This renewed clinical effort was spurred by a variety of factors, including the emergence of large-scale Sb unresponsiveness in India, where up to one-half of the world's cases of kala-azar now are found. As this new decade opens, the success of this clinical research effort is tangible: three additional, highly effective parenteral regimens now are available (amphotericin B, lipid formulations of amphotericin B, aminosidine), and an active oral agent, a long sought after objective in kala-azar, has been identified (miltefosine). This report reviews the evolution of treatment of visceral leishmaniasis, considers the interaction of the immune response and chemotherapy, highlights therapeutic successes and failures, examines advantages and disadvantages of current treatments, and looks at future therapeutic approaches to the management of this disseminated intracellular protozoal infection.

Short-course, cost-effective treatment with amphotericin B-fat emulsion cures visceral leishmaniasis

Although short-course therapy with new lipid formulations of amphotericin B represents an advance over lengthy traditional treatments in visceral leishmaniasis (kala-azar), high cost has rendered these agents largely irrelevant in developing countries where the disease is endemic. Therefore, we tested standard amphotericin B deoxycholate mixed with a commercial fat emulsion as short-course treatment for Indian visceral leishmaniasis in Bihar in 1997/98. Seventy children and adults with splenic aspirate-documented infection, 23 of whom had failed prior antimony (Sb) therapy, received 5 alternate-day infusions of 2 mg/kg. Apparent cure, which required a parasite-free splenic aspirate smear, was assessed 20 days after treatment (day 30); definitive cure was determined at 6 months. Other than anticipated infusion-related fever and/or chills, treatment was safe and well tolerated. One patient required dose modification because of mild, reversible renal insufficiency. Sixty-nine patients (98.6%, CI 92.3-100%) had apparent cures; during follow-up, there were 4 treatment failures (relapses, 3; unrelated death, 1), yielding definitive cures in 65 of 70 patients (92.9%, CI 84.1-97.6%). Including retreatment costs for patients in Bihar (who now often fail initial Sb therapy), the final per patient cost of the tested regimen (US $260) was 59% and 43% less than treatment with Sb or conventional amphotericin B alone, respectively. Short-course treatment with amphotericin B-fat emulsion is active, cost-effective treatment for patients with visceral leishmaniasis including those with Sb-unresponsive infection.