Freeze-drying of liposomes using tertiary butyl alcohol/water cosolvent systems

The objective of this study was to obtain dehydrated liposomes using a novel procedure that involves freeze-drying (FD) of liposomes with TBA/water cosolvent systems. The effects of TBA on the integrity/stability of vesicles of HSPC (or SPC):Cholesterol (4: 1) were investigated. TBA used as a cosolvent was detrimental to SPC liposomes, leading to increased particle size and leakage of trapped calcein. However, this was not the case for HSPC liposomes. The vesicle size and the retention of trapped calcein after lyophilization from cosolvents were similar to those after FD from water alone. Moreover, the addition of TBA can significantly enhance the sublimation of ice resulting in short FD cycles. The resulting lyophilized cake can form a loose powder upon agitation, which flowed well enough to be easily poured from the vial. Thus FD of HSPC liposomes using TBA/water cosolvent systems can provide sterile powder for specialized applications. In addition, in conjunction with a modified injection method, this FD technology might be used to produce dehydrated HSPC liposomes on a large scale. (c) 2006 Elsevier B.V. All rights reserved.