Although gelatin hollow capsules can also be coated, it is not suitable to use ethanol and other substances that easily denature gelatin. Organic solvents and the use of water-based coatings will have a greater impact on the gelatin hollow capsules and their contents. HPMC hollow capsules are chemically inert and can be coated with both aqueous and organic solvents such as ethanol.
In addition, gelatin hollow capsules will become brittle when the water content is less than 10%, while HPMC hollow capsules will not become brittle even if the water content reaches 1%. Excessive water content has a great influence on the stability of moisture-sensitive drugs. For highly hygroscopic contents, if gelatin hollow capsules are used, water will migrate from the gelatin hollow capsules to the contents, the water content of the hollow capsules will decrease, and the hollow capsules will become hard and brittle, resulting in delayed disintegration. However, there is no such phenomenon when HPMC hollow capsules are used for the contents with strong hygroscopicity. HPMC hollow capsules are chemically inert and will not become hard and brittle under low humidity conditions, resulting in delayed disintegration. In contrast, gelatin hollow capsules become brittle in a low-humidity environment, and the hollow capsules appear to stick in a high-humidity environment.