Leong, Chuei Wuei; (1996) Low temperature coatings with aqueous formulations for oral colonic delivery of thermolabile materials. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

Targeted oral delivery to the colon has previously been achieved with aqueous coatings of amylose and ethylcellulose applied at temperatures above 60°C. Such a high processing temperature may damage certain thermolabile drugs. Therefore, this study sets out to develop aqueous amylose-containing coating formulations which are suitable for use at temperatures below 37°C. The coating materials used were aqueous coating dispersions of an experimental grade of amylose blended with each of two commercial brands of ethylcellulose. In general, aqueous coating dispersions applied at low temperatures have the increased risk of incomplete film formation due to insufficient energy to ensure fusion of the polymer. Also, aqueous amylose-butanol complex coating dispersion has the increased risk of retaining butanol within the film. The quality of the film formed from the aqueous coating dispersions were assessed as cast isolated free films and as films sprayed onto pellets. Studies using free films showed that successful fusion of the films could be achieved using high quantities of effective plasticizers. The possible presence of residual butanol within the film was found to be minimal. The specific colon release performance of coating materials were assessed as spray-coats onto pellets containing 5-ASA and glucose pellets and tested in vitro. The ratio of ethylcellulose to amylose, the thickness of the films and the contents of plasticizer were all important influencing factors to ensuring the resistance of the spray-coats to premature drug release. Formulations containing (33.33 - 40)% of amylose, with (28 - 36)% of dibutyl sebacate as plasticizer, applied to 10% total weight gain, showed minimal 5-ASA release in the simulated upper gastrointestinal tract condition with significantly larger drug release in simulated colonic test conditions. However, these same coating formulations were not successful in preventing premature glucose release from the pellets. The success of these low temperature coating formulations appeared to be influenced by the solubility of the drug.

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