The fabrication of hard capsules is a complex process requiring precise calculations. Once the capsules are manufactured, their performance might also vary. Let’s take a look at some key technical considerations of hard capsules.
The fabrication of hard gelatin capsules is a complex process requiring precise calculations. Once the capsules are manufactured, their performance might also vary. Let’s take a look at some key technical considerations of hard capsules.
Compared to alternative excipients, gelatin is the most cost-efficient. The ingredients for first-generation HPMC hard capsules cost around four times more than gelatin and HPMC capsules cost around three times more to manufacture. This of course has an impact on the costs charged to the healthcare systems, the consumers, and the taxpayers.
This is the rate at which the hard gelatin capsule dissolves in the stomach allowing the active ingredient to be absorbed by the body. Gelatin, for example, has one of the best API dissolution rates, enabling the API to be quickly available for absorption by the body. It’s one of the most important considerations for pharmaceutical manufacturers.
Usually, the dissolution process occurs smoothly in the body. However, exposure to inappropriate heat or humidity conditions, or the presence of certain aldehydes, can cause capsule shells to cross-link. Because of its low humidity, HPMC is not subject to the problems of crosslinks. The gelatin used to be susceptible to this phenomenon but a new generation of gelatins have been developed to significantly decrease and slow down possible cross-linking issues.
Capsules have to be strong enough to cope with mechanical stress. Any weakness can lead to defects. When compared to HPMC, gelatin is by far the most resistant.
Gelatin has a high level of machinability, which means it can tolerate the mechanical process really well, and therefore no additional ingredients or machines are needed. HPMC has a lower level of machinability: first-generation HPMC requires secondary gelling agents, while second-generation HPMC doesn’t need gelling agents but does require machine adaptation.
Another consideration is moisture penetration. Vapor can have different impacts depending on the capsule type. HPMC has a lower water content than gelatin. However, it’s inconclusive as to whether HPMC actually performs better than gelatin in the area of water permeability.
Some APIs have complex profiles making them sensitive to oxidation. For these formulations, hard gelatin capsules are the best option as they offer the best protection. Because it has low oxygen permeability, gelatin is the best excipient when dealing with oxygen-sensitive APIs. The alternative, HPMC, has a high potential for oxygen penetration which means other ingredients (such as antioxidants) have to be used, which increases the overall costs. So, wherever possible, manufacturers will always opt for gelatin capsules when oxygen sensitivity is a consideration.
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