Vesicular Phospholipid Gels

Abstract This chapter discusses some of the common limitations with small liposomes as drug carriers and how vesicular phospholipid gels can be used to circumvent them. The purpose of an intravenously injected liposomal drug carrier usually is to circulate in the bloodstream and carry the drug to the desired target organ or tissue. Under ideal circumstances the pharmacokinetics and biodistribution of the carrier-associated drug is merely dependent on the characteristics of the liposomes, not on the drug itself. Size and surface characteristics of the liposomes primarily determine the degree to which they are eliminated from the bloodstream by macrophages and end up in the RES organs spleen and liver (1, 2). Big liposomes (>200 nm) are rapidly eliminated, thus they are inappropriate for i.v. drug delivery. Smaller liposomes are more likely to escape the RES and may thus circulate long enough to reach targets within or nearby the vasculary bed (2). Smaller liposomes furthermore are more likely to extravasate.