Intestine-soluble coatings are used for dosage forms that, when administered, are expected to delay the release of drugs, may be destroyed in the stomach (e.g., pancreatin, erythromycin), may cause nausea or bleeding, or may cause irritation of the gastric mucosa (e.g., aspirin, steroids). Such coatings can be used to re-release drugs in different parts of the GI tract. The action of intestine-soluble coating is due to the difference in properties of gastric and intestinal media due to different acidity and enzyme composition. Although some time ago there were attempts to create coatings that degrade under the action of intestinal enzymes, these developments were not popular, because enzymatic degradation of the film is a rather long process. Thus, most of the widely used intestine-soluble coatings are weak acids that do not dissociate at low pH values, but are easily ionized when the pH of the medium is increased to 5. The most effective enteric soluble polymers are polyacids. Enzyme-degradable coatings are currently used as protective coatings for delivery of polypeptide drug substances into the colon. One of the first synthetic polymers used for intestine-degradable coatings is phthalate cellulose acetate (PCA). However, pH>6 is required for dissolution of the coating, which significantly delays drug release. This polymer is relatively permeable to moisture and gastric juice compared to most enteric soluble polymers. In addition, it is highly susceptible to hydrolytic degradation, in which phthalic acid separates from acetic acid, leading to changes in the properties of the polymer and hence the action of the enteric coating.

Other useful polymers used in enteric coating formulations include: Polyvinyl acetate phthalate (PVAP), which is less permeable to moisture and gastric juice, more resistant to hydrolysis, and able to ionize at low pH values; hydroxypropyl methylcellulose phthalate (HPMCP), which has properties similar to those of PVAP; acrylic polymers such as methacrylic acid or methacrylic acid ester copolymer (some of which have a high dissociation constant); cellulose acetate trimellitate (ATC), which has properties similar to those of AFC; carboxymethyl ethyl cellulose (CMEC); hydroxypropyl methylcellulose acetate succinate (HPMCS).
In recent years, acrylic copolymers have been considered most suitable for the development of enteric coatings. A new type of film coatings has emerged, based on poly-methyl methacrylates (PMMA), polymers derived from acrylic acid, called Eudragit, which have the following properties: Excellent moisture-, heat- and light-protective properties, hence increasing the shelf life of drugs (far exceeding the corresponding properties of cellulose); complete neutralization of unpleasant taste and odor, which are often possessed by the active ingredients in the tablet; ease of swallowing large-sized tablets due to the sliding properties of the films; uniformly colored tablets of any shade when combined with pigments; delivery of the active ingredient to any part of the GI tract; use of Eudragit as a matrix for dosage forms with retarded