The capsule should not react with the contents. Some groups containing aldehydes, reducing sugar-based compounds, and vitamin C in the content will react with amino or carboxyl groups in gelatin, which will affect both the disintegration of the hollow capsule and the stability of the drug. Therefore, this type of drug is not suitable for use. Empty gelatin capsules. HPMC is an inert material that has no interaction with the contents and can be widely used.
There are polar groups such as amino and carboxyl groups in gelatin, while water molecules are polar small molecules that can be drilled into between polypeptide chains and combined with polar groups. With the continuous entry of water molecules in the air, the structural gap of gelatin continues to expand, resulting in an increase in oxygen permeability, which is very unfavorable for oxygen-sensitive drugs. HMPC is a part of methyl and part of polyhydroxypropyl ether of cellulose, with stable chemical properties and little effect of moisture on the permeability of hollow capsules. Therefore, HPMC hollow capsules are suitable for filling oxygen-sensitive contents.
As capsules for dry powder inhalers, higher requirements are placed on the moisture resistance of the capsules to avoid moisture has a great influence on the powder properties of dry powder inhalers, making the preparation unusable. Compared with gelatin hollow capsules, HPMC hollow capsules have stronger moisture resistance and better stability, and are more suitable as capsules for dry powder inhalation.