Bilayer vesicles encapsulated drugs

Injection, Suspension, Liposomal A liquid preparation, suitable for injection, which consists of an oil phase dispersed throughout an aqueous phase in such a manner that liposomes (a lipid bilayer vesicle usually composed of phospholipids which is used to encapsulate an active drug substance, either within a lipid bilayer or in an aqueous space) are formed. 

A liquid crystal is a general term used to describe a variety of anisotropic structures formed by amphiphilic molecules, typically but not exclusively at high concentrations. Hexagonal, lamellar, and cubic phases are all examples of liquid crystalline phases. These phases have been examined as drug delivery systems because of their stability, broad solubilization potential, ability to delay the release of encapsulated drug, and, in the case of lamellar phases, their ability to form closed, spherical bilayer structures known as vesicles, which can entrap both hydrophobic and hydrophilic drug. This section will review SANS studies performed on all liquid crystalline phases, except vesicles, which will be considered separately. Vesicles will be considered separately because, with a few exceptions, generally mixed systems, vesicles (unlike the other liquid crystalline phases mentioned) do not form spontaneously upon dispersal of the surfactant in water and because there have been many more SANS studies performed on these systems. 

Interesting and practically relevant materials for stud5dng the behavior of smart polymers attached to lipid membranes are liposomes, self-assembled 50-200 nm vesicles that have one or more (phospho)lipid bilayers which encapsulate a fraction of the solvent. Liposomes are stable in aqueous suspension because of the repulsive forces that appear when two liposomes approach each other. Liposomes are widely used for drug delivery and in cosmetics (96). 

Sustained Release. Depending on permeation coefficient, vesicle radius, and bilayer thickness, encapsulated low molecular weight solutes will be released on timescales of minutes to days. This can be used for the controlled release of drugs, where the dose can be predicted from the encapsnlated volume and the initial drug concentration in the vesicle using eqnation 21. Large ionic solutes, in particular proteins, will have low release rates and are practically permanently encapsulated until the vesicle is ruptured. 

Based on these prior studies, a liposome-encapsulated drug carrier system has been developed in order to overcome fentanyls short dilation of action. Liposomes are microscopic vesicles composed of an aqueous compartment surroimded by a phospholipid bilayer that acts as a permeable barrier to entrap molecules. Incorporation of a drug within a hposome provides a controlled, sustained release system. 

Vesicles are utilized today to encapsulate drugs and other agents for protection and targeted delivery. They are made of closed fluid bilayers, typically a single one, but sometimes several or many. Lipid vesicles are often called liposomes, especially when multilamellar. A book on liposomes written by D. D. Lasic and geared to their medical applications has just been published [1]. 

Like the liposomes, niosomes can be used as carriers for both hydrophilic and lipophilic drugs. The release of the encapsulated drug is influenced by the composition, the size and the number of bilayers in the vesicles. The properties of liposomes and niosomes are therefore largely similar however, niosomes present several advantages over the phospholipids-based liposomes ... 

Liposomes are vesicles with an aqueous core surrounded by lipid bilayer walls. Drugs may be encapsulated into the liposomes, either in the bilayers or into the aqueous core of the liposomes. Liposomes have been widely investigated by systemic and local drug delivery in different cavities of the body. 

The polar character of the liposomal core makes the encapsulation of polar drug molecules possible. Amphiphilic and lipophilic molecules are solubilized within the phospholipid bilayer according to their affinity toward the phospholipids. Participation of nonionic surfactants instead of phospholipids in the bilayer formation results in Niosomes . The term sphingosomes is suggested for vesicles from sphingolipids. However, the nomenclature is not consistent, and the term liposomes is used as a general term, although vesicles would be the better choice. 

---