Vesicular carriers liposomes

Dermal and transdermal delivery requires efficient penetration of compounds through the skin barrier, the bilayer domains of intercellular lipid matrices, and keratin bundles in the stratum corneum (SC). Lipid vesicular systems are a recognized mode of enhanced delivery of drugs into and through the skin. However, it is noteworthy that not every lipid vesicular system has the adequate characteristics to enhance skin membrane permeation. Specially designed lipid vesicles in contrast to classic liposomal compositions could achieve this goal. This chapter describes the structure, main physicochemical characteristics, and mechanism of action of prominent vesicular carriers in this field and reviews reported data on their enhanced delivery performance. 

Since the discovery of vesicular structures, termed liposomes, by Alec Bangham, a tremendous amount of work on applications of liposomes has emerged. The use of small unilamellar liposomes as carriers of drugs for therapeutic applications has become one of the major fields in liposome research. The majority of these applications are based on the encapsulation of water-soluble molecules within the trapped volume of the liposomes. Long circulating poly(ethylene glycol) (PEG) modified liposomes with cytotoxic drugs doxorubicin, paclitaxel, vincristine, and lurtotecan are examples of clinically applied chemotherapeutic liposome formulations (1,2). 

Liposomes, as carriers for diagnostic or therapeutic drugs, have been the focus of extensive studies over the past decades. Liposomes are vesicular particles that are composed of a membrane formed out of lipids with a polar head group and one or preferentially two long non-polar side-chains (Figs. 3,4). Typical lipids... 

In conclusion, we have designed a synthetic vesicular DNA carrier that physically and functionally mimics an enveloped virus particle. To achieve an acceptable degree of encapsulation within the vesicle, we use a process that is essentially inverse to the preparation of cationic lipid-DNA complexes. A suitable DNA condensing agent is introduced that, at a certain critical concentration, conveys a weak net cationic charge to the condensed DNA that then interacts spontaneously with a liposome containing one or more anionic components. These DNA formulations behave distinctly different from classic cationic liposome DNA complexes in vitro in as much as they have been shown to be nontoxic, to display a traditional linear dose response, and to be serum-insensitive. 

Liposomal systems also can form an effective drug reservoir in the upper layers of the skin. This is particularly useful for local skin therapy. Ethosomal carriers composed of phospholipid vesicular systems with alcohols are also effective at enhancing tran -dermal delivery of both lipophilic and hydrophilic compounds. The use of these ethosomes has been used in the delivery of minoxidil to the pilo-sebaceous section of the skin with better results than conventional liposomes. Similar results are reported in clinical studies with acyclovir in a topical therapy treatment of recurrent herpes labialis. Other application reports with ethosomes are patches containing testosterone (37). 

Therefore, alternative carrier substances have been investigated in recent years. Among them, lipidic materials have garnered growing attention. Successful peptide or protein incorporation and delivery has been reported for liposomes [7], multi-vesicular liposome preparations [8], cubic phase gels [9], hollow lipid microparticles [10], hollow lipid microcylinders [11], microparticles [12,13], and sohd lipid nanoparticles (SLN) for intravenous applications [14,15],... 

DepoDur is a sterile, non-pyrogenic, white to olf-white, preservative-free suspension of multi-vesicular lipid-based particles containing morphine sulfate, USP. The lipid carrier is a proprietary drug delivery system known as DepoFoam . After the administration of DepoDur into the epidural space, morphine sulfate is released from the multivesicular liposomes over a period of time [1-3] (Figures 44.2 and 44.3). 

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