Drug delivery by liposomes

Abstract

In the past thirty years or so, considerable research has been directed towards utilizing lipid based vesicles as model membrane systems and drug delivery carriers. Liposomal drug delivery system has shown considerable promise with a better therapeutic outcome. In this report we will address critical reviews on their background and development of liposomes: methods of preparation, sizing, drug loading, as well as drug release study. In addition, stability of these carriers on shelf life will also be evaluated. Drug carriers were prepared from several types of lipids, namely Egg PC and DPPC. Egg PC is a type of lipid with unsaturated chains, which is found to possess less drug retention ability due to its higher drug permeability and less ordered, heterogeneous structure compared to DPPC. With incorporation of cholesterol in various proportions, the effect of cholesterol on permeability of phospholipid membranes was studied as well. Liposomes sizing was performed by sequential extrusion through polycarbonate filters to achieve liposomes of defined size with homogenous distribution of vesicles. Metoclopramide monohydrochloride was chosen as a model drug. Drug loading and release study were carried out in vitro mimicking in vivo condition. The encapsulation efficiency and released amounts were determined by UV spectroscopy. Egg PC 100% reached its complete release in 24 hours, Egg PC 80% in 48 hours, and Egg PC 60% in 96 hours. While in contrast DPPC 100% completely released its entrapped drug in 72 hours and DPPC 60% in 144 hours, suggesting the differences in the nature and types of the lipids led to the differences in the release behaviors in vitro. The particle sizes were monitored during the drug release studies and the size of liposomal vesicles were not altered significantly for cholesterol incorporated vesicles. Upon extrusion, dialysis and drug loading, there was no significant increase in size, not only in the liposomes added with cholesterol, but in plain liposomes as well. Upon storage, those liposomes with inclusion of cholesterol remain stable in size, but plain liposomes were aggregated indicating that cholesterol incorporated vesicles were more stable and sustained release behavior was shown.