Evaluation of Resistant Starch from Eragrostis Tef as a Film Coating Material for Colon-Targeted Tablets

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Addis Abeba University


Targeting drug delivery into the colon is highly desirable with many advantages including local treatment of a variety of bowel diseases and systemic delivery of protein and peptide drugs. Research studies propose the use of resistant starch to serve as part of a targeted drug delivery system to the colon where it gets digested by the local bacterial enzymes. Considering this natural phenomenon, in this study Teff’s resistant starch has been evaluated as a film coating material for colon targeted drug delivery system (CTDDS) for the first time. Teff (Eragrostis tef) is a native cereal crop widely grown in Ethiopia. It has 73 % carbohydrates and out of the total starch around 30 % is resistant starch. The whole work includes the main steps of extraction of starch from teff and resistant starch from the total starch, preparation of a film coating material using the resistant starch and coating a sample tablet with the film-forming material, finally testing the film-coated tablet if it could pass the upper GIT intact to release the drug in the colon under simulated in vitro conditions. Different methods were used to achieve the above objectives including The methods by Bultosa et al. (2002) and Gebre-Mariam and Schmidt, (1998) for total starch isolation. While in the isolation of RS the AOAC official method 2002.02 and for the tablet coating process the method described by Siew et al, (2000) was used. In the preparation of the film coating material from the resistant starch for CTDDS, because of resistant starch dominant part amylose’s property of swelling when it gets in contact with water, a water-insoluble polymer Ethylcellulose (EC) was used and managed to control the premature film dissolution before reaching the colon. To get the optimum combination of amylose and EC for a film coating solution, their different ratios and film thickness (expressed in percentage total weight gain of the tablet) have been prepared and tested in a simulated gastrointestinal condition as per the standard pharmacopoeia of the model drug, Metronidazole tablet. In the study, as per the result of dissolution and fermentation data, the best film material proportions of amylose to EC and the corresponding thicknesses in percentage total weight gain identified were; the ratio of 1:1 with thickness 6%, ratio of 1:2 with thickness 4 % and 6%, and finally ratio of 1:3 with thickness 2% and 4%. These were found to be the optimum film thicknesses and combination of the film coating materials to release the drug in the colon but not in the upper GIT. The reason behind the site selected (targeted) drug release of the film material is due to bacterial enzyme digestion of the RS component of the film-coat in the colon. The digestion of RS produces pores through the EC scaffold of the film which brings a release of the drug content of the coated tablet only in the colon where these bacteria reside. Based on the above result, a film coating material from the local Teff’s resistant starch could be isolated, prepared and evaluated to use it as a CTDDS in the pharmaceutical industry.



Amylose, Colon targeted drug delivery, Ethylcellulose, Optimization of amylose, Resistant starch, Teff ,Eragrostis tef