Preparation of liposomes by reverse-phase evaporation using alternative organic solvents

The organic solvents employed in liposome preparation, such as chlorinated solvents, diethyl ether or methanol, although usually removed by evaporation, may remain as traces in the final formulation representing a possible risk for human health and influencing the stability of the vesicles. In order to solve the above mentioned disadvantages, this paper describes the use of different organic solvents, namely ethanol, ethyl acetate and two mixtures of ethanol/ethyl acetate, for the production of liposomes by the reverse phase evaporation technique. After preparation, liposomes were extruded through polycarbonate filters and then characterized by size and encapsulation efficacy. As model drugs retinyl acetate and sodium cromoglycate have been used. The association yield for the hydrophilic drug and the encapsulation yield for the hydrophilic model drug were found, in all the liposome preparations, to be satisfactory. In particular, the use of more polar organic solvents (with respect to diethyl ether) appear to enhance the encapsulation of the hydrophilic drug, sodium cromoglycate. The use of alternative organic solvents to diethyl ether can be proposed with the aim of reducing the toxic problems associated with the presence of residual traces of organic solvents in the final liposome formulation.