How to Store Hard Empty Capsules Properly?

　　Capsules are solid dosage forms in which medicinal agents are enclosed in a small shell. Depending on the composition capsules may be hard or soft. Hard gelatin capsules are made from gelatin (Gelatin is a translucent, colorless, brittle (when dry), flavorless solid substance, derived from the collagen- an animal protein). Empty Hard Gelatin Capsules contain 12 - 16% moisture. But the moisture content can vary up on the storage conditions.

　　Recommended Storage conditions for Hard Gelatin Capsules

　　• Store capsules away from direct sunlight (e.g. windows and skylights)

　　• Store capsules away from hot water/air radiators, hot water pipes and steam pipes.

　　• Store capsules on pallets off the ground.

　　• Store capsules away from potential sources of water condensation e.g. under water pipes.

　　• Do not store empty capsules in freezers.

　　Hard gelatin capsules shall be stored between 15-25oC (68-75oF) and 45-55% relative humidity to maintain the 12-16% moisture content of capsules. It is important that this moisture content is maintained and exposure to high temperatures or cycling between high/low temperatures is avoided. When humidity is low capsules become brittle, if stored at high humidity, the capsules become flaccid and the excess moisture content can interact with encapsulated product and can cause stability problems.

　　If capsules stored at high temperature following defects can occur

　　1. Stucking of capsules together in lumps and do not come apart.

　　2. Brittle or shatter capsules.

　　3. Capsules with distorted shape.

　　4. Stucking of capsule cap to body and resists separation.

　　After gelatine, hypromellose (HPMC) is also used to produce capsules. Its plant-based ingredients pose few dietary objections than animal-based gelatines, and it is well-suited to fillings that are sensitive to moisture or that may not work well with the residual moisture found in gelatine capsules (e.g. powders used in inhalers).

　　Moisture content of finished capsules

　　Empty gelatine capsules have a moisture content between 13% and 16% — they will become brittle if the moisture content falls below this limit, and will soften if it increases above it.

　　Empty HPMC capsules have a moisture content of 3% to 6%. These capsules can be dried down to less than 1% moisture without losing their mechanical strength and becoming brittle. Regardless of the material used, this fluctuation can lead to some degree of compromised capsule strength and overall quality, so it needs to be considered from the very outset of production.

　　Moisture content of gelatine and HPMC capsules will vary depending on the ambient conditions as the moisture content will gradually reach equilibrium with the surrounding relative humidity level.

　　Therefore, humidity must be considered when capsules are stored to ensure the required moisture content is maintained, particularly if water vapor exchange between the capsule and the filling may also contribute to the overall available moisture content.

　　Packaging and storage — how gelatine reacts to relative humidity

　　When capsules are packaged, attention should be given to the ambient conditions, as a small quantity of the surrounding air will be sealed in with the product. Depending on the volume of the packing container, this could introduce a quantity of water vapor that may affect the capsules.

　　In general, HPMC capsules are not as vulnerable to this water vapor as gelatine capsules are, so from this point on only gelatine capsules will be considered.

　　HPMC capsules contain less water than gelatine alternatives, and changes in moisture content has less effect on capsule dimensions.

　　In conclusion

　　Relative humidity can impact the quality of both gelatine and, to a lesser degree, HPMC capsules during production and storage. If the air is too dry, the gelatine capsules become brittle, particularly if they are kept in their unfilled, open state.