Soft capsules can be filled with various oils or liquid drugs or suspensions that have no dissolving effect on gelatin, or solid drugs, and the filled liquid contents can be divided into three categories:
1) Volatile or non-volatile liquids immiscible with water, such as vegetable oil or aromatic oil.
2) Non-volatile liquids that are miscible with water, such as polyethylene glycol and nonionic surfactants.
3) Compounds that can be miscible with water and have little volatility such as glycerol, propylene glycol and isopropanol.
Usually the drug may absorb water, often cause changes in the water in the soft capsule shell, if the drug is hydrophilic, the drug should be kept 5% water, oil is generally used as the drug solvent or suspension medium, oil-filled soft capsule although there is no water, but moisture or water in the capsule shell can penetrate the cyst wall and enter it. If the drug is hydrophilic, 3% water should also be retained. Volatile solvents such as ethanol, acetone, amines, acids and esters that contain more than 50% water in the chemical solution or low molecular weight and water miscible can soften or dissolve soft capsules, so it is not suitable to be made into soft capsules; When filling liquid drugs, PH should be controlled between 2.5~7.5, otherwise soft capsules can leak due to acid hydrolysis of gelatin during storage, strong alkalinity can denature gelatin and affect the solubility of soft capsules, soft capsule equipment in the production of soft capsules raw material gelatin iron content can not exceed 0.0015%, so as to avoid iron-sensitive drug deterioration.
