Capsules offer certain benefits over tablets for oral-solid dosage drugs, and several types of capsules are available
Oral-solid dosage (OSD) drugs can be formulated in tablet or capsule form. Some drugs are available only as capsules or tablets, and some are available as both. Various types of capsules, with shells made of different materials, are available. When choosing a capsule type, formulators should consider factors such as the shell’s barrier to water and oxygen, reactivity, and the material it is made of.
Selecting a capsule type
The most widely used capsules can be classified as shown in Figure 1 and discussed in the following sections. Dry-filled capsules include mainly hard gelatin and hard hydroxypropyl methylcellulose or hypromellose (HPMC) capsules. Liquid-filled capsules include hard capsules (gelatin or HPMC) and softgel gelatin capsules.
The larges size (000) is mainly used in veterinary practice. Fill weights increase with the size of the capsule as well as with the bulk density of the filled material, which can range from 0.3–1.5 g/cc. Fill weights in the smallest capsules might be 39 mg, for example; the largest may weigh 1425 mg.
The shell of hard gelatin capsules contain 13–16% water. Storage of hard-gelatin capsules at very low humidity can cause them to turn brittle. Gelatin capsules do not protect hygroscopic materials from atmospheric water vapor because moisture can diffuse through the gelatin wall. If stored at high humidity, the capsules become flaccid. In such cases, primary packaging material such as aluminum strip packing, moisture barrier blister foil (e.g., Aclar), or bottle packs should be used.
Oct 02, 2017
By Milind K. Biyani 
Volume 41, Issue 10, pg 36–41