Encapsulated drugs

Exopolysaccharides are used in lotions and gel formation is exploited in encapsulated drugs. The latter application also takes advantage of the mouth feel and flavour neutrality, qualities also vital for the food industry. 

In conclusion, delivery of liposome-encapsulated drugs in eye drops can improve the extent of uptake and the residence time compared to the free drug. In particular, lipophilic substances seem to benefit from this approach. The exact mechanism behind the improved biopharmaceutical behavior still has to be unraveled. Intra-vitreal injection of drug-containing liposomes increases the residence times of both hydrophilic and lipophilic drugs. 

A number of aspects related to the potential toxicity of liposomes has to be considered. They include effects due to (1) their particulate nature, (2) the individual components, and (3) a changed distribution of the encapsulated drug. 

In view of the fact that large volumes have been administered to man without causing serious side effects (Zonneveld and Crommelin, 1988), it may be concluded that although liposomes can damage in vitro-cultured human cell lines (Nuzzo et al., 1985 Mayhew et al., 1987b), adverse effects observed in vivo are expected to be minimal. One should realize that liposomes reduce the toxicity of the encapsulated drug. Thus, the toxicity of liposomes may be of minor importance compared to the advantages of administration of certain chemotherapeutics encapsulated in liposomes. 

Allen, T. M., and Everest, J. M. (1983). Effect of liposome size and di ug release properties on pharmacokinetics of liposome-encapsulated drugs in rats, J. Pharmacol. Exp. Ther.. 226, 539-544. 

Therapy of leishmaniasis Superior efficacies of liposome-encapsulated drugs, Proc. Natl. Acad. Sci. USA, 75, 2959-2963. 

Juliano, R. L., and Stamp, D. (1975). Effect of particle size and charge on the clearance rates of liposomes and liposome encapsulated drugs, Biochlm. Biophys. Res. Commun.. 63, 651-658. 

Ohsawa, T., Matsukawa, Y., Takakura, Y., Hashida, M., and Sezaki, H. (1985). Fate of lipid and encapsulated drug after intramuscular administration of liposomes prepared by the freezethawing method in rats, Chem. Pharm. Bull., 5013-5022. 

Virosomes are virus-mimicking systems that contain liposomal bilayer and pH-dependent protein impregnated in the liposomal wall. Virosomes are produced by a detergent dialysis procedure. Many researchers have demonstrated that the virosomes facilitate the leakage of the encapsulated drugs from the endosomes into the cytoplasm. This is, however, complicated technology and, so far, no virosome products are used in the clinical practice. 

The fate of injected liposomes is drastically altered by administration route, dose and size, lipid composition, surface modification, and encapsulated drugs. Liposomes encapsulating drugs are often administered iv, therefore, the stability of liposomes in plasma is important. When liposomes composed of PC with unsaturated fatty acyl chains are incubated in the presence of serum, an efflux of internal solute from the liposomes is observed. This increase in permeability is caused by the transfer of phospholipids to high density lipoprotein (HDL) in serum (55). To reduce the efflux of liposomal contents, cholesterol is added as a liposomal component... 

T. Kato, Encapsulated drugs in targeted cancer therapy, in Controlled Drug Delivery (S. D. Bruck. ed.), CRC Press, Boca Raton, FL, 1983, p. 189. 

Encapsulation of small drugs in M S has also been demonstrated by a similar strategy [68]. In that work, the MS spheres were loaded with ibuprofen and then encapsulated within eight layers of PAH and PSS on the particle surface to cap the mesopore openings [68]. The encapsulated drug molecules were subsequently released from the MS particles under the influence of solution pH and salt concentration. 

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