Liposomal Drug Delivery System

Liposomal Drug Delivery System

1. Definition & overview

• 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 (Shargel 8e Ch.28, p.792; Ch.10, p.815).
• They are the prototypical nanomedicine-class particulate carrier — a colloidal drug-delivery system engineered to alter one or more of the four pharmacokinetic properties (absorption, distribution/biodistribution, metabolism, elimination) of an encapsulated drug rather than the drug's intrinsic pharmacology (Golan 4e Ch.55, p.978).
• The defining advantage is high drug-carrying capacity per particle compared with single-chain polymer–drug conjugates, which can accommodate only small amounts of drug per molecule — making liposomes an attractive circulating reservoir for IV delivery (Golan 4e Ch.55, p.984).
• A liposome can carry both hydrophilic and hydrophobic payloads simultaneously: water-soluble drug partitions into the aqueous core, lipophilic drug intercalates within the bilayer membrane, governed by the drug's hydrophobicity / effective partition coefficient (Shargel 8e Ch.10, pp.815, 819; Ch.28, p.808).
• The principal therapeutic rationale, especially for cytotoxic anticancer agents, is to improve biodistribution — enhance deposition in tumour tissue, prolong circulating half-life, and reduce drug exposure to healthy tissue (lowering dose-limiting toxicity) (Shargel 8e Ch.10, pp.816–17).
• Liposomes are complex drug products under FDA classification; they account for ~30% of the nanomedicine market share, and most have no approved generic because bioequivalence of a complex particulate is hard to demonstrate (Shargel 8e Ch.28, pp.695, 810).
• FDA regulatory definition of "nanotechnology" product: a material/end-product engineered to have ≥1 external dimension or internal/surface structure in the nanoscale (~1–100 nm), OR engineered to exhibit dimension-attributable properties up to 1 μm (1000 nm); the FDA applies the same quality/safety/efficacy standards as for non-nanomaterial medicines (no separate framework) (Shargel 8e Ch.28, pp.690–93).