Messi Biology states that magnesium oxide, as an excipient, plays an important role in hard capsules by absorbing moisture, maintaining a dry environment, and slowing drug degradation. Compared to other moisture-absorbing materials, it is mild and safe, making it particularly suitable for drug formulations with highly moisture-sensitive contents. Proper selection and addition of magnesium oxide will greatly improve product stability and quality reliability.
I. Overview of Drug Moisture Absorption Problems
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 clumping, resulting in poor flowability.
- 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 Moisture Absorption Performance
- Structural characteristics: Magnesium oxide is an alkaline inorganic oxide with a porous surface, providing good physical moisture absorption capabilities.
- Large specific surface area (especially light or active magnesium oxide) can effectively absorb free water in the air.
- After moisture absorption, it forms magnesium hydroxide and does not release free water, so its impact on the drug system is more gentle.
III. Typical Application Scenarios
- Traditional Chinese Medicine Compound Hard Capsules: Such as those containing baicalin, aloe extract, and other moisture-absorbing ingredients, magnesium oxide is often added as a drying protective agent.
- Vitamin and Mineral Capsules: Such as vitamin C and ferrous sulfate, adding magnesium oxide can slow down oxidation and hydrolysis.
- Probiotic Hard Capsules: Blending with magnesium oxide can stabilize the content of viable bacteria and extend shelf life.
IV. Usage and Key Points of the Process
- Addition method: It is often evenly mixed into the powder as a filler or glidant.
- Addition ratio: Generally 0.5%~5%, which is adjusted according to the powder’s water content and target humidity control requirements.
- Process requirements:
- Mix evenly to avoid moisture absorption concentration.
- No significant chemical reaction with the main drug components.
- Avoid excessive amounts to prevent the capsule pH from being too alkaline.
Further details regarding Magnesium Oxide as a desiccant
- Magnesium oxide (MgO) is a commonly used desiccant in pharmaceutical formulations, particularly in solid dosage forms like capsules and tablets, due to its ability to absorb moisture and maintain a dry environment.
- Magnesium oxide exists in different forms, including light and heavy magnesium oxide, which vary in their specific surface area and density. Light magnesium oxide has a higher specific surface area, making it more effective at absorbing moisture compared to heavy magnesium oxide.
- The amount of magnesium oxide used in a formulation depends on factors such as the moisture sensitivity of the active ingredients and the desired level of protection. Typically, it is used in concentrations ranging from 0.5% to 5% w/w.
- In addition to its desiccant properties, magnesium oxide can also function as a pH modifier, buffering agent, and diluent in pharmaceutical formulations. Its alkaline nature helps neutralize acidic environments, which can degrade certain drugs.
- Magnesium oxide can interact with certain drugs or excipients, potentially affecting their stability or bioavailability. Compatibility studies should be performed to ensure that there are no adverse interactions.
- The particle size of magnesium oxide can influence its performance as a desiccant. Smaller particles have a larger surface area, leading to better moisture absorption.
- Magnesium oxide should be stored in a dry, airtight container to prevent it from absorbing moisture from the environment before use.