proteins oligonucleotides and other substances of biological origin and combinations thereof also encompassed by the terms u201c active ingredient s u201d u201c pharmaceutical ingredient s u201d and u201c active agents u201d are the drugs and pharmaceutically active ingredients described in mantelle u s pat no 5 234 957 in columns 18 through 21 that text of mantelle is hereby incorporated by reference alternatively or additionally the active ingredient can include drugs and other pharmaceutical ingredients vitamins minerals and dietary supplements as the same are defined in u s pat no 5 178 878 the disclosure of which is also incorporated by reference herein the dosage forms preferably contain materials that aid in releasing the drug in a specific section of the gastrointestinal tract thus promoting site specific delivery there are various mechanisms by which such materials promote site specific delivery and this invention is not limited to any one mechanism for example the material may be metabolized by enzymes present in a specific part of the gastrointestinal tract thus releasing the drug in that section the materials used to promote site specific absorption may preferably be included as coatings and or as matrix materials if a coating is used it may be applied to the entire dosage form or to the individual particles of which it consists coating materials may be used to prevent the release of the active agent before the.