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

Liposomal and lipid formulations of amphotericin B. Clinical pharmacokinetics

Amphotericin B remains a very important drug for the treatment of fungal infections despite its toxicity. Encapsulation of amphotericin B into liposomes appears to reduce the toxic effects and to improve the clinical efficacy, allowing higher dosages to be given. The exact mechanism behind the reduced toxicity is not yet known. Amphotericin B is widely distributed after intravenous administration as the deoxycholate solubilisate. The highest concentrations are found in the liver, spleen and kidney. Protein binding and binding to the tissues is very high. The fate of the drug in the body is not known in detail. Renal and biliary excretion are both low and no metabolites have been identified. The drug is still detectable in the liver, spleen and kidney for as long as 1 year after stopping therapy. The pharmacokinetics of the different liposomal amphotericin B or lipid complexes of amphotericin B, which were recently developed, are quite diverse. A number of these preparations, such as amphotericin B lipid complex (ABLC), 'AmBisome' and amphotericin B colloidal dispersion (ABCD) are in clinical development. Their pharmacokinetics depend to a large extent on the composition and particle size of the liposomes or lipid complexes. Relatively large structures such as ABLC are rapidly taken up by the mononuclear phagocyte system, whereas smaller liposomes remain in the circulation for prolonged periods. In all studies only the total amphotericin B (both free and liposome- or lipid-associated) concentrations were determined. There is a need for studies correlating clinical efficacy and tolerability of liposomal amphotericin B with the pharmacokinetic properties of these formulations.

High-performance liquid chromatographic analysis of amphotericin B in plasma, blood, urine and tissues for pharmacokinetic and tissue distribution studies

A sensitive and reproducible high-performance liquid chromatographic method was developed to assay ampherotericin B in plasma, blood, urine and various tissue samples. Amphotericin B was isolated from each sample matrix by solid-phase extraction (Bond-Elut). The eluate from Bond-Elut containing amphotericin B was injected onto a reversed-phase C18 column (Waters, mu Bondpak, 10 microns, 300 mm x 3.9 mm I.D.) with a mobile phase of 45% acetonitrile in 2.5 mM Na2EDTA at 1 ml/min. Detection of amphotericin B was by ultraviolet absorption at 382 nm. Blood and tissues were homogenized and extracted with methanol prior to Bond-Elut extraction. The extraction efficiencies of amphotericin B from plasma, blood and tissues were approximately 90, 70 and 75%, respectively. The sensitivity of the assay was less than or equal to 5 ng/ml for plasma, less than or equal to 25 ng/ml for blood, 2.5 ng/ml for urine and 50 ng/g for tissues. The linearity of the assay method was up to 2.5 micrograms/ml for plasma, 5 micrograms/ml for blood, 500 ng/ml for urine and 500 micrograms/g for tissues. The assay was reproducible with an intra-day coefficient of variation (C.V., n = 3) of less than 5% in general for plasma, blood and tissues. The inter-day C.V. of the assay was less than 5% for plasma (n = 5), less than 10% for blood (n = 4) and less than 5% for tissues (n = 3). The overall variability in the urine assay was generally less than 10%. This method has demonstrated significant improvement in the sensitivity and reproducibility in assaying amphotericin B in plasma and especially in blood, urine and tissues. We have employed this assay to compare the pharmacokinetic and tissue distribution profiles of amphotericin B in rats and dogs following administration of Fungizone and ABCD (amphotericin B-cholesteryl sulfate colloidal dispersion), a lipid-based dosage form. In addition, the assay method for plasma and urine samples can also be applied to pharmacokinetics studies of amphotericin B in man.

A retrospective clinical comparison between antifungal treatment with liposomal amphotericin B (AmBisome) and conventional amphotericin B in transplant recipients

Invasive fungal infections are an important cause of morbidity and mortality in immunosuppressed bone marrow and solid organ transplant recipients. Treatment with amphotericin B, the drug of choice for these infections, is however often limited by toxicity. Ten transplant patients receiving a liposomal amphotericin B formulation (AmBisome) were compared to ten retrospective control patients given conventional amphotericin B. Each group included bone marrow (8), kidney (1), and liver transplant (1) recipients. Conventional amphotericin B treatment was instituted due to nine Candida infections, and one Aspergillus fumigatus infection. In the AmBisome group treatment was instituted due to eight Candida infections, one infection caused by Saccharomyces cerevisiae and in one case as prophylactic treatment. In the amphotericin B group, maximal daily doses ranged from 0.1 to 0.65 mg kg-1 and cumulative doses were 21-836 mg kg-1 and were given over 3-32 days. In the AmBisome group, maximal daily doses ranged from 0.9 to 2.3 mg kg-1 and cumulative doses ranged from 225 to 3525 mg kg-1 over 8-28 days. All patients in the amphotericin B group experienced severe toxicity, especially nephrotoxicity which in four cases caused withdrawal of the drug. In contrast, the only adverse reaction in the AmBisome group was cholestasis in one patient. Only three out of ten patients in the amphotericin B group responded to treatment, seven patients died and six patients still had evidence of invasive fungal infection at autopsy. In contrast, eight out of nine patients in the AmBisome group responded to treatment, and the patient that received prophylaxis had a successful course.