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Chapter: Pharmaceutical Drugs and Dosage: Capsules

Capsules are the dosage forms in which the drug formulation in a powder, semisolid, or liquid form is enclosed in a shell.



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 hydroxypro-pyl methylcellulose (HPMC), polyvinyl alcohol (PVA), seaweed, or starch. Depending on the composition of the gelatin shell, the capsules can be hard or soft gelatin capsules. Soft gelatin capsules (also known as softgels) are made from a relatively more flexible, plasticized gelatin film than hard gela-tin 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. Figure 21.1 shows the common shapes of soft gelatin capsules. Table 21.1 shows the examples of commonly used capsule dosage forms.

Figure 21.1 Schematic diagrams illustrating different shapes of soft gelatin capsules. The range of fill volumes is also indicated.

Table 21.1 Typical sizes of hard gelatin capsules

The capsule shell dissolves rapidly on contact with gastrointestinal (GI) fluids, thus releasing the capsule’s contents. Drug’s bioavailability from capsules is usually high and similar to those of immediate-release (IR) tablets. Coating of capsule shell or drug particles (within the capsule) with sustained-release (SR) polymers can prolong drug release and affect bioavailability.

Hard gelatin capsules have a significant amount of bound water. These capsules are generally not physically stable in low humidity conditions, such as in the presence of desiccant in the packaged drug product. They tend to become fragile and crack at low humidity. On the other hand, HPMC capsules have lower equilibrium moisture contents than gelatin capsules and have better physical stability (i.e., do not become fragile and crack) on exposure to low humidity. The majority of capsule products manufactured today are hard gelatin capsules.

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