ABSTRACT
There are numerous instances where drug delivery systems have to be further processed in order to obtain the complete drug formulation. In general, dry formulations are preferred when sufficient storage stability with liquid formulations is difficult or impossible to reach from a chemical and/or physicochemical perspective. For example, this is the case with essentially all protein and peptide drugs, which are generally not sufficiently stable when stored in an aqueous solution. In other cases, dry formulations are preferred for practical or patient compliance reasons. The latter is the case, e.g., with many tablet formulations used primarily for oral administration. Irrespective of the reason for the drying (‘‘lyophilization’’), however, it is important to note and control the effects of the lyophilization on the properties of both the drug and the drug delivery system. In this context, surfactants and other surface active compounds, such as polymers and proteins, offer possibilities which have only recently started to be investigated in a reasonably systematic way. In what follows, a few brief examples will be provided to illustrate the use of surfactants, polymers, and proteins in the context of lyophilization of drug delivery systems. In particular, the relationship between the lyophilization and the properties of these compounds in solution and at interfaces is considered. However, no discussion of solid state properties of these systems, or processes less straightforwardly connected to surface activity and self-assembly (e.g., crystallization and precipitation) is provided, since this is considered to be outside the scope of the present volume.
