Targeting of Liposomes: Study of Influencing Factors
A decade has now elapsed since liposomes were first proposed1–3 as vehicles for drug delivery in biology and medicine. During this time extensive studies have revealed a multitude of uses4 and at the same time established many of the principles governing the system’s behaviour within the biological milieu.5–7 Among the advantages that liposomes offer as a drug carrier system, versatility in structural characteristics is most prominent. For instance, appropriate choice of lipid composition, size, surface charge and also of surface ligands that can recognise and associate with, target cells selectively can all profoundly influence the fate and behaviour of the carrier and thus contribute towards optimising the action of its drug contents. One of the major objectives in the use of liposomes in vivo is interaction with accessible cells i.e. those in the blood circulation, lining the capillaries and, in certain cases, cells in extravascular areas separated from the circulation by leaky membranes. There is, therefore, a need for drugs to be retained by the carrier for periods of time necessary for effective access to, and association with the target. Here we have attempted to understand factors that influence (a) quantitative retention of drugs by liposomes in vitro and in vivo (b) rates of liposome clearance from the circulation and (c) targeting of liposomes to specific cells.
KeywordsCholesterol Content High Density Lipoprotein Drug Clearance Liposomal Drug Drug Retention
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