Stabilization of liposomes during drying.

INTRODUCTION: During the past 40 years, liposomes have been investigated intensively as drug carriers for anticancer drugs and as the adjuvant components of vaccines, for example. In this context, the development of dry formulations of liposomes is important to ensure a more stable drug product and to avoid the use of the 'cold chain' during distribution. AREAS COVERED: This review provides an overview of the technologies commonly used for the drying of liposomal formulations and the significance of formulation and processing parameters for the drying process. In addition, a review is provided of the protective mechanisms proposed to be responsible for stabilization during processing and in the dry state, with special emphasis on the techniques used for the characterization of the mechanisms. Parameters are discussed that critically influence the liposomal stability during drying and the underlying stabilization mechanisms, including the water replacement theory, vitrification and kosmotropic effects. EXPERT OPINION: Drying of liposomal formulations has contributed to the development of more stable products because liposomes can be dehydrated in the presence of appropriate stabilizing excipients, without affecting the size or the drug encapsulation efficiency. The key to the successful design and preparation of optimal liposomal dry powder formulations is an understanding of the significance of the drying process parameters, and the mechanisms responsible for the stabilization of liposomes during drying and in the dry state.