Synergistic antifungal activity and reduced toxicity of liposomal amphotericin B combined with gramicidin S or NF.

Amphotericin B (AmpB) disrupts membrane integrity by binding to sterols in fungal and mammalian cell membranes. The gramicidins, which form pores in all membranes but exhibit poor antifungal activity, are too toxic to mammalian cells to be used systemically. This study demonstrated synergistic antifungal activity of free and liposomal forms of AmpB when combined with the free and liposomal forms of gramicidin S and gramicidin NF against five Candida strains. In vitro erythrocyte lysis was prevented by using the liposomal forms of all drugs tested alone or in combination. Presumably, AmpB increases accessibility of the fungal cell membrane to the gramicidins, while liposome encapsulation decreases the rate of transfer of the drugs to the mammalian cell membrane. Liposome encapsulation of inactive or toxic drugs, used in combination with liposomal AmpB, may give new life to drugs previously believed to be inactive or too toxic for therapeutic consideration.