1.  Field of the Invention
This invention relates to controlled-release, drug-delivery compositions, and, more particularly, to compositions which contain a hydrogen-bonded complex between two polymers for predetermining the dissolution of the drug therein in acid and alkaline solutions. 
2.  Description of the Prior Art
Controlled-release, drug-delivery compositions are well-known in the art.  However, controlled-release tablets which can deliver a drug to the intestine without disintegrating in the gastric area require a specially designed gastric-resistant coating.  Thereon typically, application of such coatings involves several processes using expensive equipment. 
Accordingly, it is an object of this invention to provide a drug-delivery composition which is insoluble in aqueous acidic solution and dissolves only slowly under alkaline conditions. 
Another object herein is to provide a tableted compositions having such controlled release of drugs therein, which can be made conveniently by direct compression or wet granulation techniques. 
A composition such as described herein is considered pH sensitive and can be modified effectively to release the drug contents either immediately or in a controlled manner, under alkaline conditions. 
Specifically, the system described herein, can function in two modes: (a) substantially no drug-release is exhibited in acidic, conditions (&lt;20% of the drug is released in 2 hours) and controlled release of the drug occurs in alkaline conditions, (an additional 60% of the drug is released in 8 hours or more); (b) a pH-immediate mode wherein some of the drug is released in acid (&lt;20% in 2 hours) and immediate release of the drug in alkaline conditions (an additional 60% in 2-3 hours or less). 
These and other objects and features of the invention will be made apparent from the following description.