Colon specific

The aim of this chapter is to summarize some of the research findings on xylan, a natural polymer extracted from corn cobs, which presents a promising application in the development of colon-specific drug carriers. Physicochemical characterization of the polymer regarding particle size and morphology, composition, rheology, thermal behavior, and crystallinity will be provided. Additionally, research data on its extraction and the development of microparticles based on xylan and prepared by different methods will also be presented and discussed. 

Ribeiro, A. J., Neufeld, R. Arnaud, P. Chaumeil, J. C. (1999). Microencapsulation of lipophilic drugs in chitosan-coated alginate microspheres. International Journal of Pharmaceutics, Vol. 187,1, (September 1999), pp. (115-123), ISSN 0378-5173 Rubinstein, A. (1995). Approaches and opportunities in colon-specific drug-delivery. Critical Reviews in Therapeutic Drug Carrier Systems, Vol 12, 2-3,1995), pp. (101-149), ISSN 0743-4863... 

KRISHNAIAH Y S, SEETHA DEVI A, NAGESWARA RAO L, BHASKAR REDDY P R, KARTHIKEYAN R S, SATYANARAYANA V (2001) Guat gum as a carrier for colon specific delivery influence of metronidazole and tinidazole on in vitro release of albendazole from guar gum matrix tablets. J Pharm Pharm Sci. 4 235-43. 

DR Friend. Colon-specific drug delivery. Adv Drug Del Rev 7 149-199, 1991. 

Saffran, M., Oral Colon-Specific Drug Delivery With Emphasis on Insulin, in Oral Colon-Specific Drug Delivery (D. R. Friend Ed.), pp. 115-142. CRC Press, Boca Raton (1992). 

Gardner N, Haresign W, Spiller R, Farraj N, Wiseman J, Norbury H, Ilium L (1996) Development and validation of a pig model for colon-specific drug delivery. J. Pharm. Pharmacol 48 pp 689-693. 

A second example is the colon-specific delivery of glucocorticoids linked to dextran via a succinic acid or glutaric acid spacer [256a]. Such conjugates resist hydrolysis in the upper gastrointestinal tract, but are rapidly degraded by bacteria in the colon and caecum where little drug absorption occurs. 

K. Uekama, K. Minami, F. Hirayama, 6A-0-[(4-Biphenylyl)-acetyl]-a-, -/3-, and y-cy-clodextrins and 6A-Deoxy-6A-[[(4-biphenylyl)-acetyl]amino]-a-, -/T, and y-cyclodex-trins Potential Prodrugs for Colon-Specific Delivery ,./. Med. Chem. 1997, 40, 2755-2761. 

The same strategy was applied in colon-specific delivery of two corticosteroids used to treat inflammatory bowel disease [20][21], Indeed, budeso-nide /3-D-glucuronide and dexamethasone /3-D-glucuronide underwent ready hydrolysis in the luminal contents of rat colon and caecum. Rat mucosal homogenates were less active, and hydrolysis in human fecal samples was quite low. Based on these and other studies, the prodrugs were found to be suitable candidates for delivery of corticosteroids to the large intestine. 

B. Haeberlin, W. Rubas, H. W. Nolen III, D. R. Friend, In vitro Evaluation of Dexa-methasone-/ -D-glucuronide for Colon-Specific Drug Debvery , Pharm. Res. 1993, 10, 1553 - 1562. 

Colon-specific drug delivery is primarily dependent on two physiological factors, the pH and the transit time. 

Comparison of their rate of onset and recovery of a treated mucosa has been made [37]. Fatty acids have strong and fast reactivity and allow for a fast recovery of the barrier function. Bile salts and salicylates are moderate, fast-acting agents with fast barrier-function recovery. Strong surfactants and chelators have strong or moderate reactivity and a slow recovery of barrier function. Solvents like dimethylsulfoxide and ethanol have moderate reactivity and act primarily as agents to improve drug miscibility in an aqueous environment. The enhancers listed above are also effective in the small intestine [22]. Enhancers that are more colon specific include ethylaceto-acetate, which must be first metabolically transformed to enamine [38]. 

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