Capsule Dosage Forms – Hard Gelatin, Soft Gelatin, Modified Release and Enteric

Capsules are a common form of dosage for oral administration of pharmaceutical and nutraceutical products. They are produced in various shapes, sizes and materials, each capsule generally containing a single dose of active ingredient. In addition to the active drug ingredient or principal nutrient, other excipients are incorporated into the fill material, including antimicrobial preservatives, fillers, flavouring agents, sweeteners and colouring agent. Branding and dosage information may be printed on the outer surface of the capsule.

Medication or ingredients inside the capsule may be in solid, liquid or paste form, depending on the drug component or, in the case of nutraceuticals, on the form of the main nutrient (for example liquid fish oil is encased in the widely available fish oil capsules). The API filled in the capsules may contain solvents or excipients but these do not affect the integrity of the capsule shell. Other than the modified release form, no capsule forms normally contain colouring agents.

Hard Gelatin Capsule

Hard gelatine capsules contain solid active ingredients. The capsules are formed by dipping finger-shaped pin forms into liquid gelatine solution and then extracting them and allowing the resulting surface film of gelatine to dry out. Once the film dries, each capsule is trimmed and then removed from the pins. The caps and body pieces of the capsule are supplied unlocked to be filled with the appropriate drug or nutraceutical ingredients.

More than one type of drug can be encased in a pharmaceutical capsule. In such a case, it is common to have the drugs in different forms, e.g., one as a tablet and one as a smaller capsule. Both drugs can then be encased in the larger capsule.

Soft Gelatin Capsule

Soft gelatin capsules, also called soft gels, are thicker than hard gelatin capsules and are sometimes the gelatine is plasticized by adding glycerin or sorbitol. The thickness of the gelatin is chosen by the manufacturer according to the requirements of the encased material and the environmental conditions outside the capsule (e.g, air temperature and humidity).

The composition of the gelatin used to prepare soft capsules may include preservatives, pigments and dyes. Flavourings and sweeteners may also be added. For example sucrose may be added at a level of about 5% to make the product palatable, and in some cases chewable. Soft gels generally contain between 6% and 13% by weight of water.

Soft gels can be filled with liquid or solid materials and solids can be dissolved or suspended in water to form a paste mixture. In other cases the capsule may simply be filled with granules or powder.

Modified Release Capsule

Both hard or soft gel capsules can be chemically modified to control the release of the active ingredient(s). Delivery of the active ingredient is usually effected by dissolution, degradation or disintegration of an excipient in which the active compound is formulated. In the case of capsules, the capsule body may be coated with a material through which the drug diffuses. Or it may be a slowly dissolving coat that slowly releases the drug over time. A more recent innovation is a system utilizing a semipermeable membrane that blocks the drug from diffusing out through the membrane, but where the water on the exterior of the membrane can diffuse into the formulation, allowing the drug to be released through channels within the membrane.

Enteric Capsule

Enteric capsules are another form of modified release capsule, and again they maybe in the hard or soft form. The encapsulating material is designed to resist the stomach acid until it reaches the intestinal fluid where at a higher pH it breaks down and releases the active ingredients.

It is important to observe during the manufacturing, packaging, storing and distribution of capsules that microbial contamination is possible as the capsules made of gelatine are susceptible to microbial attack and growth.

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