Hemolytic and antifungal activity of liposome-entrapped amphotericin B prepared by the precipitation method.
A new method of preparing liposomes containing amphotericin B (AmB) was developed with the purpose of reducing the toxicity of AmB without causing a loss in its antifungal activity. The procedure involved the precipitation of AmB and egg phosphatidylcholine (PC) in phosphate buffered saline (PBS, pH 7.4) or tris buffered saline (TBS, pH 7.4) by evaporating methanol and chloroform, which had been previously mixed in the buffer solution, at 4 degrees C and 600 mm Hg. The in vitro toxicity of the precipitated liposomes containing 3, 6, 9, 12, and 15 wt% AmB was compared with that of the film-swollen liposomes containing the equivalent contents of the drug. The hemolytic ability of the precipitated liposomes at 37 degrees C was 50.3% at maximum of the film-swollen liposomes at a dose of 30 micrograms AmB/ml, as measured after 17-hr incubation. The significant reduction in the hemolysis effect may in fact be attributed to the reduced rate of drug release from the precipitated liposomes. The precipitated liposomes were multilayered and aggregates of AmB were embedded in the bilayers. These aggregates of AmB would be responsible for an intensive positive peak around 330 nm and reduced toxicity. Despite the decrease in toxicity, the activity of the precipitated liposomes against Candida albicans remained almost equipotent to that of the film-swollen liposomes. Therefore, liposomes prepared by the precipitation method are less toxic but equally as active.