Drug capsules serve as a widespread method for delivering medication, encompassing the active ingredients within a stable shell. This protective casing shields the compounds from external elements, such as light and oxygen, which can degrade their effectiveness. Capsules also make medicines easier to swallow and can mask unpleasant tastes or odors, enhancing patient acceptance. They allow for precise dosing and can be engineered to release their contents at specific rates within the digestive tract.
Understanding Capsule Types
Drug capsules fall into two main types: hard-shelled and softgel. Hard-shelled capsules consist of two interlocking cylindrical halves (body and cap) filled with medication. They are commonly used for powders or granules. Softgel capsules, in contrast, are single, hermetically sealed units, often seamless, flexible, and spherical or oval. Their forms dictate the drug formulations they can contain; softgels are typically suited for liquids or oils.
Materials for Hard Capsules
Gelatin, a protein derived from animal collagen (primarily from animal skin and bones), is the predominant material for hard-shelled capsules. It is favored for its non-toxic nature, broad acceptance in foodstuffs, and ability to dissolve readily at body temperature. It forms a strong, flexible shell encasing medication.
Hypromellose (HPMC), a plant-based polymer from cellulose, is a growing alternative to gelatin for hard capsules. HPMC capsules are vegetarian and vegan-friendly, suiting diverse dietary and religious preferences. They also have lower moisture content, advantageous for moisture-sensitive active ingredients, enhancing stability and shelf life.
Composition of Softgel Capsules
Softgel capsules primarily use gelatin, but include additional components for flexibility. Water is a significant component, initially 30-40% by weight, reduced to 5-8% in the dried shell. Plasticizers are incorporated into the gelatin mixture to impart elasticity and reduce brittleness.
Common plasticizers, like glycerin and sorbitol, contribute to their pliable texture. Glycerin is frequently used for oil-based formulations due to its low molecular weight and high hygroscopicity. Sorbitol is often preferred for formulations with polyethylene glycol (PEG) or volatile components, helping reduce their diffusion into the gelatin film.
Reasons Behind Material Choices
Material selection is influenced by dietary considerations and drug stability. Plant-based options like HPMC and Pullulan offer animal-free alternatives for vegetarian, vegan, and religious dietary needs. Material choice also impacts drug stability; the shell must protect the active ingredient from moisture, oxygen, and light. HPMC capsules, with lower moisture, benefit moisture-sensitive or hygroscopic formulations.
Dissolution properties—how quickly the capsule breaks down in the body—are another important consideration. Gelatin capsules typically dissolve rapidly at body temperature, allowing prompt medication release. However, HPMC capsule dissolution can be slower or more variable depending on formulation and pH. Compatibility between the capsule material and drug formulation is paramount, ensuring no undesirable chemical interactions that could compromise effectiveness or safety. HPMC capsules are often favored for highly reactive molecules due to their lower interaction potential.