Drug delivery, carriers liposomes

Their mode of appearance in the lumen of the intestine is rather complicated and involves activation of trypsinogen secretion by enterokinase. Once trypsin is formed it activates chymotrypsinogen. Pancreatic lipase is also secreted into the lumen with the pancreatic fluid. The digestion process of fatty acids by their lipase-mediated hydrolysis is completed by bile salts, which are also secreted in the duodenum and are crucial for micellization of lipophilic compounds. The micelles formed in the duodenum enable the absorption of hydro-phobic drugs such as steroids. They pose, however, a serious constraint for the stability of drug delivery carriers such as liposomes and emulsions. 

V. V. Ranade, Drug delivery systems. 1. Site-specific drug delivery using liposomes as carriers, J. Clin. Pharmacol. 29 685 (1989). 

Among the several drug delivery systems, liposomes - phospholipid nanosized vesicles with a bilayered membrane structure - have drawn a lot of interest as advanced and versatile pharmaceutical carriers for both low and high molecular weight pharmaceuticals. At present, liposomal formulations span multiple areas, from clinical application of the liposomal drugs to the development of various multifunctional liposomal systems to be used in therapy and diagnostics. This chapter provides a brief overview of various liposomal products currently under development at experimental and preclinical level. 

Figure 15.6 Illustration of various pharmaceutical drug delivery carriers (a) Microspheres, (b) Nanospheres, (c) Emulsions, (d) Liposomes, (e) Micelles, (f) Injectibles, (g) Thermoplastic elastomers,...

A variety of other clinically important infections, such as brucellosis, listeriosis, salmonellosis, and various Mycobacterium infections, are of interest as these are often localized in organs rich in MPS cells. Liposome encapsulation has been demonstrated to improve therapeutic indices of several drugs in a number of infectious models. The natural avidity of macrophages for liposomes can also be exploited in the application of the vesicles as carriers of immunomodulators to activate these cells to an microbicidal, antiviral, or tumoricidal state. These studies were recently reviewed by Emmen and Storm (1987), Popescu et al. (1987), and Alving (1988). In addition to the treatment of "old" infectious diseases, the concept of MPS-directed drug delivery is of considerable interest for the therapy AIDS, possibly enabling control of human immunodeficiency virus replication in human macrophages. 

Gabizon, A. (1989). Liposomes as a drug delivery system in cancer chemotherapy, in Drug Carrier Systems Horizons in Biochemistry and Biophysics, Vol. 9 (F. H. Roerdink and A. M. Kroon, eds.), John Wiley and Sons, Chichester, pp. 185-211. 

Liposomes represent an important class of carrier vehicles other than polymers for drug delivery. This paper provides an introduction and general review of liposomes with emphasis on their classifications, their constituent materials, their preparation and characterizaton, and their stability and biodistribution in the body. Liposomes with specific characteristics are also described in this general introduction. 

Several types of dmg carriers such as microspheres, liposomes, and polymer have been investigated to achieve targetable drug delivery, especially for anticancer drugs. However, nonselective scavenging of such carriers by the reticuloendothelial system (RES) is a serious problem even when monoclonal antibodies are used to carry the dmg [15,16]. 

Reszka, R. (1998). Liposomes as drug carrier for diagnostics, cytostatics and genetic material. In Future Strategies for Drug Delivery with Particulate Systems, eds. J. E. Diederichs and R. H. Muller. Medpharm GmbH Scientific Publishers. 

---