Capsules: These are drug delivery systems which come under the category of solid dosage forms.
Capsules 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 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 larger diameter than other. But the other with shorter diameter is usually longer.
The former is known as cap and the latter is called as 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 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 heat process. They can only be ruptured and dissolved.
Enteric coated capsules: These are capsules which are designed to release the drug in the intestine. They resist degradation in the stomach and stay intact till they reach intestine. Once they reach intestine, they release their contents. This is due to their insolubility in acidic pH in stomach. But again they are soluble in basic pH which is present in intestine.
Sustained release capsules: These are capsules designed to release drug ingredients slowly over a period of hours. So they are long acting types and release drug gradually for prolonged effect. A single such capsule can be taken once in day instead multiple times of normal capsules.
Rectal capsules: These are capsules which are meant to be inserted into rectum for local effect. The drug is release in the rectum region for immediate effect. Also the drug can escape first pass metabolism by liver.