Capsules are drug delivery systems that come under the category of solid dosage forms.
They are single unit dosage forms used to administer a drug or medicament in solid or liquid form.
Capsules are made of two shells which fit into each other by holding an internal space.
Any substance can be held within that internal space. Capsules are of many types, but prominently two types are used.
Types of capsules
- Hard gelatin capsules.
- Soft gelatin capsules.
- Enteric-coated capsules.
- Sustained-release capsules.
- Rectal capsules.
Among the above, hard gelatin and soft gelatin capsules are routinely used.
Hard gelatin capsules
These capsules are hard by external touch.
They incorporate a solid powder form of drug ingredients. They are filled in the space held by gelatin shells.
These shells are cylindrical in shape. One of the shells is of a larger diameter than the other. But the other with a shorter diameter is usually longer.
The former is known as the cap, and the latter is called a body. These two shells can be separated to expose the contents inside.
Soft gelatin capsules
These as soft to touch, elastic, and a bit flexible.
They incorporate a liquid form of drug ingredients. Hence they are soft to touch. They are mostly used to administer essential oils, vitamins, etc.
Unlike hard gelatin type, their shells can’t be opened. These capsules are completely sealed by the heat process. They can only be ruptured and dissolved.
These are capsules that are designed to release the drug in the intestine. They resist degradation in the stomach and stay intact until they reach the intestine. Once they reach the intestine, they release their contents.
This is due to their insolubility in acidic pH in the stomach. But again, they are soluble in basic pH, which is present in the intestine.
These are capsules designed to release drug ingredients slowly over a period of hours. So they are long-acting types and release drugs gradually for a prolonged effect. A single such capsule can be taken once in the day instead of multiple times of normal capsules.
These are capsules that are meant to be inserted into the rectum for local effect. The drug is released in the rectum region for immediate effect.
Also, the drug can escape the first-pass metabolism by the liver.