Capsules are the dosage forms in which the drug formulation in a powder, semisolid, or liquid form is enclosed in a shell. This shell is generally made from gelatin but can be made from other polymers such as hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA), seaweed, or starch.
Capsules are usually colorless. A variety of colored capsules are now available in commerce. Colored capsules may be used to encapsulate ingredients that would appear unattractive in a colorless capsule.
Depending on the composition of the gelatin shell, the capsules can be hard or soft gelatin capsules. Soft gelatin capsules are made from a relatively more flexible, plasticized gelatin film than hard gelatin capsules.
Hard capsules, such as hard gelatin or HPMC capsules, are typically used for powder or solid fills, whereas soft gelatin capsules are used for semisolid or liquid fills. Lately, hard capsules have also been used for liquid or semisolid fills.
Most soft and hard capsules are intended to be swallowed as a whole. Some soft gelatin capsules are intended for rectal or vaginal insertion as suppositories. Some soft gelatin capsules are intended to be cut open by the patient to remove and externally apply the contained medicament, for example, ophthalmically.
Capsules cannot be used for substances that react with or dissolve gelatin, the major component of the capsule shell.
This article focuses on the differences between hard gelatin capsules and soft gelatin capsules.
The differences between hard gelatin capsules and soft gelatin capsules are summarized below
1. Hard gelatin capsules have two separate parts namely a body and a cap whereas soft gelatin capsules are hermetically sealed one-piece capsules and cannot be separated.
2. Hardshell capsules are manufactured in a two-step process; the shells are manufactured by one type of machine and the filling achieved by a different machine whereas the manufacture, feeding, and sealing of soft gelatin capsules are achieved by only one machine.
3. Hard gelatin capsules usually contain dry powders, slightly compressed plugs, granules, or tablets whereas soft gelatin capsules typically contain liquids and semisolids.
4. Hard gelatin capsules are cylindrical in shape while soft gelatin capsules are available in round, oval, and tubular shapes.
5. The ratio of plasticizer to gelatin is less in a hard gelatin capsule (0.4 : 1.0) than in soft gelatin capsule (0.8 : 1.0).