Some drugs are prone to degeneration and decomposition of gastric acid, which has a strong stimulating effect on the gastric mucosa; some drugs must be absorbed in the intestinal tract. It is precisely because of the special properties and medical needs of some drugs that the development of enteric capsule materials is promoted.
Common materials for enteric capsules include shellac, cellulose acetate phthalate, alginate, polyvinyl acetate phthalate, acrylic resin, hydroxypropyl methylcellulose phthalate, and the like.
Shellac was the first material used for enteric capsules. It is the secretion of tropical and subtropical insects. Since it is a natural bioadhesive polymer, it is widely available, inexpensive, reliable in acid resistance, and uniform in the coating, making it suitable for a certain degree of application. But clothing is difficult to control in production and has not been put into use.
Cellulose acetate phthalate (CAP)
CAP is a cellulose polymer, insoluble in water, acidic, and soluble in buffers with pH > 6. Its main use in pharmacy is in enteric-coated formulations. CAP-based enteric coatings are resistant to acidic gastric juices but are soluble in the weakly alkaline media of the gut. There are two major drawbacks to this product. First, the coated enteric agricultural layer is susceptible to the pH of the drug in the heart during storage, slowly changing its dissolution rate. Second, the CAP layer is the thin film layer of the network structure. Its voids can slowly penetrate a small amount of water so that the disintegrant in the capsule/tablet absorbs water and loses its disintegration effect.
The active ingredient in the enteric coating material is sodium alginate. Sodium alginate is widely used in various industries such as food, textile printing, and pharmaceuticals. It is a natural macromolecular carbohydrate, non-toxic, non-flammable, and non-explosive. It decomposes when pH > 6. This material has good water resistance and stability, so it is not easy to crack, deform or mold under natural conditions.
In addition, there are polyvinyl acetate phthalate, acrylic resin, hydroxypropyl methylcellulose phthalate, zein, and the like. Generally, an enteric coating is indicated when the "EC" logo is printed near the drug name.
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