Messi Biology states that magnesium oxide, as an excipient, plays an important role in hard capsules by absorbing moisture, maintaining a dry environment, and delaying drug degradation. Compared to other hygroscopic materials, it has gentle properties and high safety, making it especially suitable for drug formulations containing contents that are highly sensitive to moisture. Proper selection and addition will significantly improve product stability and quality reliability.
I. Overview of Drug Moisture Absorption Issues
Hard capsules are often used to fill powdered drugs, but many raw materials are hygroscopic, such as Traditional Chinese Medicine extracts, organic acid salts, amino acids, and vitamins.
Moisture absorption can lead to:
- Powder caking and poor fluidity.
- Hydrolysis and degradation of chemical components, affecting efficacy.
- Softening and deformation of the capsule shell, affecting appearance and disintegration behavior.
II. Advantages of Magnesium Oxide’s Hygroscopic Performance
- Structural Characteristics: Magnesium oxide is an alkaline inorganic oxide with a porous surface and good physical moisture absorption capabilities.
- Large Specific Surface Area: Especially in light or active magnesium oxide, it can effectively adsorb free moisture from the air.
- Gentle Impact: Upon absorbing moisture, it forms magnesium hydroxide without releasing free water, thus having a gentler impact on the drug system.
III. Typical Application Scenarios
- TCM Compound Hard Capsules: For ingredients prone to moisture absorption, such as Baicalin and Aloe extracts, magnesium oxide is often added as a drying protective agent.
- Vitamin and Mineral Capsules: For ingredients like Vitamin C and Ferrous Sulfate, adding magnesium oxide can slow down oxidation and hydrolysis.
- Probiotic Hard Capsules: Formulating with magnesium oxide can stabilize the content of active bacteria and extend shelf life.
IV. Usage Methods and Process Points
- Method of Addition: It is often mixed uniformly into the powder as a filler or glidant.
- Addition Ratio: Generally 0.5% to 5%, specifically adjusted according to the moisture content of the powder and target humidity control requirements.
- Process Requirements:
- Mix uniformly to avoid concentrated moisture absorption.
- Ensure no significant chemical reaction with the main drug ingredients.
- Avoid excessive amounts to prevent the capsule pH from becoming too strongly alkaline.