Hard gelatin capsule are actually easier and quicker to formulate and produce, whatever the batch size, compared with other solid oral dosage forms. Indeed, by using hard gelatin capsules it is possible to produce small or very small batch sizes on manual or semi-automatic filling machine.

Hard gelatin capsules usually require between one and four excipients. In fact there is drug in capsule form that contains only the active ingredient, which means there is no excipient.

Some excipients might have several functions. Talcum, for instance, serves as a lubricant in concentrations below 5%. At higher concentrations, it is mainly considered as filler. Microcrystalline cellulose also serves as a disintegrant besides filler.

The functions of excipients in hard gelatin capsules can be different their functions in tablets. Starch, which is commonly added to tablets as a disintegrant owing to its macerating properties of 5% to 10%, might be used as a filler in hard gelatin capsules because the macerating properties are not strong enough to really disintegrate the lightly compressed substances in hard gelatin capsules.

Here are the list of excipients used in formulating drug in hard gelatin capsule

Diluents : improved plug formation and compression
• Mannitol
• Lactose
• Corn starch
• Microcrystalline Cellulose
• Starch 1500

Lubricatns : Improved properties and reduced powder adhesion to metal parts
• Magnesium Stearate
• Stearic acid
• Glyceryl monostearate

Glidants : improved powder properties, improved flow characteristics and reduced adhesion of the substance to metal parts in the filling machine
• Aerosil/ Silicon Dioxide
• Talcum

Disintegrants : to ensure disintegration of powder mixture
• Croscarmellose
• Crospovidone
• Sodium starch glycolate
• Corn starch
• Starch 1500/pregelatinized starch
• Alginic acid

Wetting agents : improved penetration into powder mixture
• Sodium lauryl sulfate
• Tween 80

The characteristic of many excipients depend on storage conditions such as temperature or humidity. Excipients that show hysteresis in their sorption-isotherms-as, for example, gelatin starch or microcrystalline cellulose-might show different levels of absorbed water on their surfaces even when subject to the same humidity in the controlled conditions of the production room. That’s why it is advisable to dry these excipients before use. To optimize product stability, the excipients need to be selected according to their surface acidity in the dry state (pH eq) rather than to add buffer agents.

When formulating hard gelatin capsules for immediate release, attention should be paid to establishing a reproducible product dissolution profile. In the fluid environment of the stomach, the shell of the capsule starts to soften and dissolve within one or two minutes, and comes apart at its weakest point, the capsule shoulder.

Consequently, the uncompressed or only lightly compacted content comes into contact with water. If the capsule formulation is sufficiently hydrophilic or contains disintegrant or a wetting agent, water can penetrate the powder. The capsule disintegrated and its contents are released. Hard gelatin capsule are fully disintegrated within about 10 minutes.