Stability of liposomes on long term storage.

The effect of the lipid composition of liposomes on their storage for up to one year under different environmental conditions has been examined using 5,6-carboxyfluorescein as a model drug. When cholesterol and/or alpha-tocopherol were included in the liposomes, a significantly greater amount of dye was retained. The presence of alpha-tocopherol decreased the breakdown of phosphatidylcholine to lysophosphatidylcholine and also reduced the level of peroxidation. Carboxyfluorescein retention was further enhanced when liposomes were stored at 4 degrees C or at room temperature (20 degrees C) in an O2-free atmosphere. Lysophosphatidylcholine formation also slowed when the liposomes were kept at 4 degrees C, or in an O2-free atmosphere. It is concluded that egg yolk lecithin liposomes may be stored for long periods at low temperature in an O2-free atmosphere or with added stabilizers such as cholesterol and alpha-tocopherol.