While many formulations have been experimentally prepared which rely upon a hydrophobic coating derived from an aqueous dispersion to provide controlled release of an active agent, such formulations have not proven to be commercially viable because of stability problems.Aqueous polymeric dispersions have been used to produce stable controlled release dosage forms, but this has only been possible by other methods such as incorporation of the same into the matrix of the dosage form, rather than via the use of a coating of the aqueous polymeric dispersion to obtain retardant properties. Hydrophobic polymers such as certain cellulose derivatives, zein, acrylic resins, waxes, higher aliphatic alcohols, and polylactic and polyglycolic acids have been used in the prior art to develop controlled release dosage forms. However, moisture content of a product can be controlled fairly successfully by controls in the processing method and proper packaging of the product.In particular, it is known that controlled release coatings of commercially available acrylic polymers such as those sold under the tradename Eudragit® by Rohm Pharma Gmb H are not stable when cured according to recommended curing conditions of 45° C. It is therefore an object of the present invention to provide a controlled release formulation of a substrate comprising an active agent, e.g.
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when the final coated product is stored for a period of time, during which time it may be exposed to elevated temperature and/or humidity above ambient conditions. The aging process brought about by storage under the above stress conditions impeded dissolution, irrespective of the nature of the polymeric film.
The stability data obtained with regard to a particular dosage form directly affects its shelf-life.