Stabilized controlled release substrate having a coating derived from an aqueous dispersion of hydrophobic polymer

DETAILED DESCRIPTION Ethylcellulose, which is a cellulose ether that is formed by the reaction of ethyl chloride with alkaline cellulose, is completely insoluble in water and gastrointestinal juices, and therefore to date has been considered not to be suitable by itself for tablet coating.
It has, however, been commonly used in combination with hydroxypropyl methylcellulose and other film-formers to toughen or influence the dissolution rate of the film.
Due to the solubility characteristics of ethylcellulose, this polymer has been mainly applied to the above-mentioned formulations from organic solutions.
Many polymers have been investigated for use in film-coating.
Most film-coats are prepared by deposition of one or more film-forming polymers resulting in coats that usually represent no more than about 2-5% by weight of the final coated product.
The film-coating has been used in conjunction with the preparation of tablets, pills, capsules, granules, and powders.
The characteristics of the polymer used in the film-coating is governed by the structure, size and properties of its macromolecules.
Common film-formers used in pharmaceuticals as nonenteric materials include hydroxypropyl methylcellulose, methyl hydroxyethylcellulose, hydroxypropylcellulose, sodium carboxymethylcellulose, ethylcellulose, and others.
In order to obtain a controlled release formulation, it is usually necessary to overcoat the substrate comprising the therapeutically active agent with a sufficient amount of the aqueous dispersion of ethylcellulose to obtain a weight gain level from about 5 to about 15 percent, although the overcoat may be lesser or greater depending upon the physical properties of the therapeutically active agent and the desired release rate, the inclusion of plasticizer in the aqueous dispersion of ethylcellulose and the manner of incorporation of the same, for example.
An example of a suitable controlled release formulation pursuant to the present invention will provide a dissolution rate in vitro of the dosage form, when measured by the USP Paddle Method at 100 rpm in 900 ml aqueous buffer (pH between 1