GENERAL CONSIDERATIONS

Liposome drug products are the most commonly used nanotechnology-based formulations. They contain a significant amount of intentionally produced spherical vesicles in the nanometer size range (between 1 and 1000 nm) with at least one lipid bilayer. Drug Products Containing Nanomaterials 〈1153〉 defines liposomes as lipid vesicles with at least one lipid bilayer that entraps at least one aqueous compartment. This chapter may also apply to vesicles that fall outside the nanometer size range. Some liposomal preparations can exceed the nanometer range beyond 1 micron. Some liposome preparations are converted to the dried state (e.g., after freeze-drying). Liposomes have been employed to formulate both water-soluble and water-insoluble drug substances (1). Water-soluble drug substances, due to their hydrophilic nature, can be incorporated into the internal aqueous compartment(s) of liposomes. Water-insoluble drug substances, due to their lipophilic nature, can be incorporated into the hydrophobic regions of the lipid bilayer of liposomes. Liposomes can be used to deliver drug substances via different administration routes including inhalation, mucosal, topical, oral, and parenteral. For each administration route, the requirements specified in the respective monographs (e.g., for parenteral or oral drug products) apply. This chapter focuses on the product quality tests that are generally necessary for liposomal preparations and on the selected specific requirements for liposomes not mentioned in other chapters. The terms "drug substance" and "active ingredient" can be used interchangeably; however, in this general chapter the term “drug substance” will be used. See Table 1 for types of liposomes categorized by route of administration.