Low water content – about 60% lower than gelatin hollow capsules
The water content of gelatin hollow capsules is generally 12.5%-17.5%. No matter in the process of production, transportation, use and storage of hollow capsules, the temperature and humidity of the environment should be controlled within a suitable range. The suitable temperature is 15-25°C and the relative humidity is 35%-65%, so that the performance of the product can be maintained for a long time. The water content of HPMC membrane is very low, generally 4%-5%, which is about 60% lower than the water content of gelatin hollow capsules. The exchange of moisture with the environment during long-term storage will increase the moisture content of HPMC hollow capsules in the specified packaging, but will not exceed 9% within 5 years.
The low water content of HPMC hollow capsules makes them suitable for filling hygroscopic or moisture-sensitive contents to extend the shelf life of the product.
In a 2005 study by DSM Nutraceuticals, the effects of HPMC hollow capsules (Vcaps®) and gelatin hollow capsules on the stability of probiotics (Lactobacillus® acidophilus L-10) were compared. Probiotics are a class of live microorganisms, and oral administration of sufficient amounts of probiotics can improve the balance of the host's intestinal microbiota and be used to treat intestinal diseases. However, probiotics are very sensitive to moisture, and too much water can lead to the death of live bacteria [12]. DSM filled Lafti® L-10 and its excipients into HPMC capsules and gelatin hollow capsules at different humidity conditions, and their stability was investigated. The results showed that compared with gelatin hollow capsules, HPMC hollow capsules could better maintain the number of viable bacteria in the product and prolong the validity period of the probiotic product.
High toughness, no brittleness
As mentioned above, gelatin film has a specified moisture content, and if it is below this limit, the gelatin film will become significantly brittle. Ordinary gelatin hollow capsules without any additives have a risk of more than 10% brittle when the moisture content is 10%, and 100% brittle when the moisture content is continuously reduced to 5%. In comparison, HPMC hollow capsules are much tougher and maintain good performance even when the ambient humidity is low. Of course, the incidence of brittle crushing at low humidity will vary greatly between different prescriptions of HPMC hollow capsules.
On the contrary, when gelatin hollow capsules are placed in a high humidity environment, the capsule shell will become soft, deformed, or even collapse after absorbing water. HPMC hollow capsules retain good form and performance even under high humidity conditions. Therefore, HPMC hollow capsules are highly adaptable to the environment, and this advantage is particularly significant when the sales area of the product covers a variety of climatic zones or the storage conditions are relatively poor.
Strong chemical stability
The cross-linking reaction of gelatin capsules is a thorny problem for capsule formulations. Because the aldehyde group of the content reacts with the amino group of the amino acid in the gelatin to form a network structure, the capsule shell is difficult to dissolve under the condition of in vitro dissolution, thus affecting the release of the drug. Hypromellose is a cellulose derivative, chemically inert, and has excellent compatibility with most substances, so HPMC hollow capsules have no risk of cross-linking reaction and are chemically stable.
Good coating properties
Enteric-coated capsules should be used for drugs that are susceptible to gastric acid destruction, irritating to the gastric mucosa, or require targeted administration. The internationally accepted enteric-coated capsule process is enteric-coated pellets and capsule overall coating. HPMC hollow capsules show unique advantages in the overall coating of the capsule.
The results show that due to the rough surface of HPMC hollow capsules, the affinity with most enteric coating materials is significantly higher than that of gelatin, and the speed and uniformity of the attachment of the coating materials are significantly better than those of gelatin, especially the reliability of the coating of the body-cap junction is significantly improved. In vitro dissolution testing showed that the permeability in the stomach was lower after HPMC capsule coating, and there was good release in the intestine.
