Liposome pharmaceutical formulation

The past decade has seen a dramatic increase in the number of reported applications of neural computing in pharmaceutical formulation [29-32]. Applications now cover a variety of formulations—for example, immediate and controlled release tablets, skin creams, hydrogel ointments, liposomes and emulsions, and film coatings. The following examples are by no means exhaustive, but they show where neural computing has been used successfully in modeling formulations. 

All together, these findings have encouraged the development of neutral and cationic lipospheres (CLS) as nonviral DNA-mediated gene transfer techniques because CLS enable the extemporaneous production of pharmaceutical formulations. Like emulsions and liposomes, lipospheres (LS) consist of physiologically well-tolerated ingredients that have often already been approved for pharmaceutical use... 

PEG is a widely used molecule as a component in pharmaceutical formulations. PEG is particularly useful thanks to its low cost and various simple synthetic methods (26). PEG-lipid has been developed as a means of stabilizing conventional liposomes. A lipid moiety has been linked to the large PEGylated head in order to anchor the molecule to the particles. Instead of shielding a direct layer of polymer PEG around the particle, which would be less stable, the idea is to favor hydrophobic interactions between the PEG-lipid and the particle bilayer lipids. This anchor had led to two conformations of the PEG on the particle surface commonly called mushroom and brush regimes (27), representing a more condensed or extended conformations... 

Part II starts with the possibilities of ACE for characterizing the relevant physicochemical properties of drugs such as lipophilicity/hydrophilicity as well as thermodynamic parameters such as enthalpy of solubilization. This part also characterizes interactions between pharmaceutical excipients such as amphiphilic substances (below CMC) and cyclodextrins, which are of interest for influencing the bioavailability of drugs from pharmaceutical formulations. The same holds for interactions of drugs with pharmaceutical vehicle systems such as micelles, microemulsions, and liposomes. 

Thus, liposomes are successfully utilized in all imaginable drug delivery approaches and their use to solve various biomedical problems is steadily increasing. At present, quite a number of various liposomal formulations has received clinical approval, or in advanced clinical trials. We are surely likely to see more liposomal pharmaceuticals on the market in the foreseeable future. 

Drugs that are highly lipophilic by their own nature, e.g., taxanes, epothilones, and cyclosporins, can only be used therapeutically by the addition of possibly toxic solubilizing agents (e.g., Cremophor EL) in complex pharmaceutical formulations [97-99]. One of several feasible means of obtaining nontoxic parenterally applicable formulations of such drugs is their incorporation into the bilayer matrix of phospholipid liposomes. 

The selective quantification of the PC degradation products 1-LPC, 2-LPC and GPC (Figure 3-43) makes P NMR spectroscopy the ideal method for testing the stability of liposome containing formulations in pharmaceutical products. The amount of the different phospholipids can be calculated from their integral areas. 

The ever-increasing demands on the performance of pharmaceutical formulations with respect to, e.g., storage stability, increased dosage levels, greater bioavailability, fewer side effects, controlled release, and biological response (e.g., tissue distribution) constitute the main motivation for drug delivery research. In the last few decades, this research has resulted in the development of, e.g., parenteral emulsions, liposomes with improved circulation in the bloodstream, cyclodextrins, and lipoprotein mimics for cancer therapeutics. 

Handbook of Polymers for Pharmaceutical Technologies Table.7.2 Liposomes herbal formulations [12]. 

The three commercially available AmB formulations differ in their morphology, their composition, and, consequently, their biological activity. AmBisome (developed by Nexstar Pharmaceuticals, commercially available from Gilead Sciences) is a true liposome formulation, consisting of small, unilamellar vesicles (9). Their small size confers a prolonged circulation time... 

Additional naturally occurring lipids may be minor components of oral lipid-based formulations. Terpenes such as peppermint oil (>50% menthol) are fairly hydrophobic but can provide some solvent capacity. Steroids such as cholesterol, while important in topical and in parenteral liposomal products, are not important as oral pharmaceutical adjuvants. Phospholipids (e.g., egg or soybean phosphatidylcholine) an essential component of cell membranes, are considered polar lipids, and have surfactant properties. 

Liposomes represent highly versatile drag carriers, offering almost infinite possibilities to alter structural and physicochemical characteristics. This feature of versatility enables the formulation scientist to modify liposomal behaviour in vivo and to tailor liposomal formulations to specific therapeutic needs. It has taken two decades to develop the liposome carrier concept to a pharmaceutical product level, but commercial preparations are now available in important disease areas and many more formulations are currently undergoing clinical trials. Examples of the different applications and commercial products of various types of liposomal systems are given below. 

Stability of Liposomes A shelf life of at least two years is requested for pharmaceutical products. Therefore, chemical stability and physical stability are important parameters for the overall performance of liposomal formulations. Additionaly, another very important factor is the retention of encapsulated drug. 

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