DRUG ENCAPSULATION AND RELEASE FROM MULTILAMELLAR AND UNILAMELLAR LIPOSOMES

The concept of using liposomes as carriers for the delivery of drugs is well established, and the liposomal incorporation of various molecules, including peptides and proteins, has been described. In this study, propranolol (PPL) and atenolol (ATL) were used as model drugs to measure the encapsulation efficiency and release characteristics from multilamellar (MLV) and small unilamellar (SUV) liposomes. MLVs were prepared by hydration of thin lipid films and agitation using PPL and ATL solutions in phosphate-buffered saline (pH 7.4). Unilamellar liposomes were prepared by sonicating these MLVs. The non-encapsulated drug was separated either by centrifugation (MLV) or by size exclusion chromatography (SUV). The encapsulation of ATL and PPL was higher in small unilamellar liposomes. The encapsulation of PPL was higher than ATL in multi- as well as in unilamellar liposomes. The rate of drug efflux from liposomes was determined in vitro at 37-degrees-C and pH 7.4. The maximum release of both ATL and PPL was found with DSPC MLVs and DMPC: CHOL: DCP SUVs. The liposomal encapsulation and release of drug molecules are governed by the lipophilicity of drug molecules, type of liposomes and lipid composition.