ABSTRACT
Liposomal drug products are defined as drug products containing drug substances (active pharmaceutical ingredients) encapsulated in liposomes [1]. A liposome is a microvesicle composed of a bilayer of lipid amphipathic molecules enclosing an aqueous compartment [1]. Liposome drug products are formed when a liposome is used to encapsulate a drug substance within a lipid bilayer of lipid amphipathic molecules enclosing an aqueous compartment [1]. Liposomal drug products are a relatively new “class” of drugs. Doxil (liposomal doxorubicin), for example, was only approved in late 1995 and there are only a handful of approved products (Ambisome, Abelcet, Amphotec, Daunosome, Depocyt, Doxil), and a limited number of newer products are at various stages of development. As a result, regulatory thinking on these types of products is not as well evolved as it is for more traditional oral or intravenous formulations. However, the Guidances for Industry for orally administered products, and the concepts that underlay them, are also useful guides for our approach to evaluating liposomal products [2-4]. Although these agents are generally administered intravenously, they also share many characteristics with peroral drugs, and especially orally administered modified-release (MR) drugs [4]. As with MR drugs, often the purpose of the liposome is to provide slower drug release and provide a more prolonged circulatory life of the active drug molecule. This approach has apparently been successful for Doxil, which may reduce the cardiotoxicity that is usually associated with doxorubicin [5, 6]. Therefore, many of the concepts used to characterize MR oral formulations can be adapted to liposomal formulations.
