The characteristics of capsules are closely related to their uses. There are generally three types of capsules in clinical practice. One is ordinary capsules, which means that drugs or some excipients are packed into ordinary capsules, so as to avoid the unpleasant taste of the drug and effect taking. It can be directly filled into capsules and swallowed. There is also an enteric-coated capsule, mainly because some drugs have an obvious stimulating effect on the gastrointestinal tract, or some drugs encounter gastric acid in the gastrointestinal tract. Pepsin will be destroyed, and it must avoid the environment of the stomach. It can be disintegrated and released in the environment of the small intestine, and the drug can be absorbed, so it is made into enteric-coated capsules.

    In addition, there is also a kind of capsule that is the slow-release or controlled-release capsule, that is, using certain characteristics of the capsule shell to ensure the slow release of the drug in the body, so as not to disintegrate and release all at once, resulting in a high local concentration and sustained release. Capsules can achieve the slow release of drugs and have a very long action time in the body. Therefore, the characteristics of capsules are roughly divided into three types, namely ordinary capsules, enteric-coated capsules, and sustained-release capsules, which are characterized by dissolution and release in the intestinal tract. The drug can be slowly released into the gastrointestinal tract to be absorbed.

    But capsules also have some disadvantages. The main capsule material of the capsule shell is water-soluble gelatin, so the capsule core cannot be an aqueous solution or a dilute ethanol solution to prevent the capsule wall from melting. For example, when filled with easily weathered drugs, the vaporization of water will soften the capsule material, and the easily deliquescent drugs will dry and crack the capsule wall due to the drug’s absorption of water. Therefore, drugs of this nature are generally not suitable for capsules. After the capsule shell is melted in the body, the local drug dose is very large. Therefore, easily soluble irritant drugs should not be made into capsules.