Liposomal Drug Delivery System

Definition & rationale

• Liposomes are microscopic, spherical lipid vesicles enclosing an aqueous internal core within one or more synthetic phospholipid bilayer membranes; size ranges from ~30 nm to several micrometres — the prototypical nanomedicine-class particulate carrier.
• Core rationale — a colloidal carrier engineered to alter biodistribution (and the other PK properties) of the encapsulated drug rather than its intrinsic pharmacology; for cytotoxic anticancer agents it enhances tumour deposition, prolongs circulating half-life and reduces drug exposure to healthy tissue (lowering dose-limiting toxicity).
• Dual-payload capacity — carries both hydrophilic and hydrophobic drugs simultaneously — water-soluble drug partitions into the aqueous core, lipophilic drug intercalates within the bilayer; high drug-carrying capacity per particle makes it an attractive circulating reservoir for IV delivery.
• Regulatory status — liposomes are complex drug products (FDA), account for ~30% of the nanomedicine market, and most have no approved generic because bioequivalence of a complex particulate is hard to demonstrate. FDA defines a "nanotechnology" product by a nanoscale (~1–100 nm, up to 1000 nm) dimension and applies the same quality/safety/efficacy standards as for non-nanomaterial medicines.