Biol. Pharm. Bull. 28(2) 387—390 (2005)

systems, having been investigated for delivery of chemotherapeutic agents for cancer, vaccines for immunological protection, radiopharmaceuticals for diagnostic imaging, and nucleic acid-based medicines for gene therapy. As is observed for colloidal drug delivery systems, however, the physico-chemical stability of liposomes varies with their compositions and structures. In most cases liposomes tend to aggregate and fuse with or leak entrapped drugs, especially highly hydrophilic small molecules. Likewise, during storage, the phase state transition of lipids induces the release of their content. We supposed that if the intraliposomal segment was solid instead of liquid, leakage from the liposome would decrease dramatically for drug must be released from the solid-core before diffusing across the lipid membrane. Additionally, the solid core could facilitate controlled or sustained-release. In the present study, chitosan and the oppositely charged, highly hydrophilic small molecule, fluorescein sodium (FS) were selected to form the solid cores, which were encapsulated in liposomes. Preparation, size and zeta potential of this nanocombination were investigated and the biopharmaceutical applicability and pharmacokinetics of this system was assessed in vitro and in rats.