The capsule is just a coat or vest of the medicine. Of course, the purpose of using it is not only to make the medicine look good, but mainly to make the medicine easy to take and achieve the best effect.
The medicines taken when a person is sick must pass through the digestion and absorption of the gastrointestinal tract into the blood, and also pass through the liver to decompose. However, a considerable number of powders, granules, liquids and tablets are either bitter and irritating, or they are easily volatilized, or are easily broken down by saliva in the mouth. Some drugs can also be inhaled into the trachea, causing side effects. Therefore, putting the medicine into capsules can protect the oral cavity and digestive tract, is easy to swallow, and can also give the medicine the best effect. To make the drug play its best role, it is also necessary to prevent the drug from being destroyed by human stomach acid, because some drugs need to be dissolved and absorbed in the intestine, so they need to be made of special membrane materials (such as gelatin, cellulose, polysaccharides, etc.) Capsules, powder, liquid and other various drugs are packed into the capsule according to the dosage. In addition, drugs have a half-life, which refers to the time required for the highest concentration of the drug in the blood to decrease by half. The half-life of a drug reflects the speed at which the drug is eliminated in the body (excretion, biotransformation and storage, etc.), and shows the relationship between the time the drug is in the body and the blood drug concentration.
Therefore, it is the main basis for determining the dosage and frequency of administration. Drugs with a long half-life are slowly eliminated in the body and the interval between administrations are long; while drugs with a short half-life are eliminated in the body quickly and the administration time is short. For drugs with a short half-life, frequent medication is required to maintain the concentration of the drug in the blood. In order to avoid the trouble of frequent medication, it is necessary to wrap the medication with a special capsule, which is a sustained-release capsule. Sustained-release capsule drugs can also avoid the shortcomings of excessive fluctuations in blood drug concentration after frequent administration of general preparations and the occurrence of effective blood concentration fluctuations. At the same time, the toxic and side effects of sustained-release capsules are smaller than those of general preparations. Therefore, many drugs, such as ibuprofen, aspirin, Tylenol, etc., have sustained-release capsule preparations.