Colonic hydrogels

Attempts have been made to achieve colon-speeifie delivery of drugs. These include prodrugs and enteric coated polymers that are sensitive to degradation by bacterial enzymes, and matrices and hydrogels suseeptible to degradation by baeterial enzymes. 

Dextran hydrogels, cross-linked by diisocyanate, released drug only in the distal part of the colon, where the conditions for absorption are not as conducive as in the proximal part [96], The pH-sensitive dextran hydrogels were prepared by activation... 

Munjeri, O., Collet, J.H., and Fell, J.T., Hydrogel beads based on amidated pectins for colon-specific drug delivery Role of chitosan in modifying drug release, J. Contr. Rel., 46 273-278 (1997). 

Simonsen, L., Hovgaard, L., Mortensen, P.B., and Brondsted, H., Dextran hydrogels for colon-specific drug delivery. Degradation in human intestinal incubation models, Eur. J. Pharm. Sci., 3 329-337 (1995). 

Chiu, H.C., Hsiue, G.H., Lee, Y.P., and Huang, L.W., Synthesis and characterization of pH-sensitive dextran hydrogels as a potential colon-specific drug delivery system, J. Biomater. Sci. Polym. ed., 10 591-608 (1999). 

Brondsted, H. and Kopecek, J. (1992). Hydrogels for site-specific drug delivery to the colon— in vitro and in vivo degradation. Pharmaceut. Res., 9, 1540-1545. 

Proteus mirabilis bacteria was dispersed in agar before solidifying into a Petri dish, and colonization occurred which seems contradictory for an aerobic microorganism, but is understandable considering the gel structure is permeable to air, water vapor, and nutrients. The previous observation is further reason not to constmct a barrier dressing from an aqueous gel, hydrogel or other similar material containing more than about 20% water where protection from bacteria is a critical requirement. 

H. Brpndsted, and L. Hovgaard, A novel hydrogel system designed for controlled drug delivery to the colon, Proceed. Intern. Symp. Control. Rel. Bioact. Mater. 20 178-179 (1993). 

L. Hovgaard, and H. Brpndsted, Dextran hydrogels for colon-specific drug delivery, J. Controlled Release 36 159-166 (1995). 

Vervoort, D., Van den Mooter, G., Augustijns, P., Busson, R., Toppet, S., and Kinget, R., Inulin hydrogels as carriers for colonic drug targeting. I. Synthesis and characterization of methacrylated inulin and hydrogel formation, Pharm. Res., 14, 1730-1737, 1997. 

Colon LA, Guo Y, and Fermier A. Fritless packed columns for capillary electrochromatography Separation of uncharged compounds on hydrophobic hydrogels. Anal. Chem. 1996 68 2153-2151. 

Hydrogels that are based on natural products are more acceptable from the standpoint of toxicity-related issues and are therefore preferable to azo-based polymers. However, chemical derivatization, if performed without proper understanding, can lead to modifications of the hydrogels to products that will not degrade readily in the colon because it is possible that the new structures will not be recognized by the colonic bacterial enzymes for degradation. Also, bulk degradation is preferred to surface erosion because it... 

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