Evaluation of Resistant Starch from Eragrostis Tef as a Film Coating Material for Colon-Targeted Tablets
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Date
2020-02
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Addis Abeba University
Abstract
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.
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Keywords
Amylose, Colon targeted drug delivery, Ethylcellulose, Optimization of amylose, Resistant starch, Teff ,Eragrostis tef