The formulation of capsule fill can be developed to fulfill the specifications and end-use requirements of the product.

Capsule content:
  • May be liquid or a combination of miscible liquids
  • Solution of a solid in a liquid or a suspension of a solid in a liquid
  • It can be a liquid like a volatile oil composition (e.g. Pudin hara)
  • Vegetable oils like arachis oil or aromatic or aliphatic hydrocarbons, ethers, eters, or alcohols.
  • Solid that are not Sufficiently soluble in liquids or in combination of liquids are capsulated as suspension
  • Suspending agents used are Lecithin, Soybean oil, Yellow wax.

Capsulation of liquids that are immiscible with water and non-volatile, such as vegetable oils and vitamin E, are easy and require little or no formulation. However, solids that are not sufficiently soluble in liquids are capsulated as suspensions. Such materials should have a particle size of 80 mesh or finer.

Capsulation of suspensions is the most common form for a large group of dietary products. Suspension formulation requires a suspending agent to prevent the settling of the solids and to maintain homogeneity throughout capsulation. The most widely used suspending agent for oil-based formulation is wax (e.g beeswax), and polyethylene glycols in a non-oil-base.

Powdered extracts are usually combined with soybean oil (as a carrier), yellow beeswax (as a suspension and thickening agent), and lecithin (as a lubricant) for formulation in soft gels. The relative amounts of the extract and the other ingredients depend upon the desired extract dose to be administered.

Some Limitations in Formulating Soft Gelatin Capsule

Filling of soft gel capsules with liquid and semi-solid materials is possible if the "fillings" selected do not dissolve the gelatin. Thus aqueous solutions would not be appropriate. But, substances in which gelatin is not soluble are suitable.

The following types of compounds may not be suitable candidates for soft gel encapsulation:
  • liquids that can easily migrate through the gelatin shell, such as water (more than 5 percent of the fill), and hygroscopic and volatile compounds
  • aldehydes, which have the ability to harden the shell and hence affect its dissolution property
  • acidic or alkaline solutions should be avoided, unless they are pictures on a blackboard. adjusted to become neutral; acids and alkalis can cause hydrolysis and leakage of the gelatin shell
  • water-soluble solid compounds that may affect the gelatin shell unless they are minor constituents of a formula or combined with a carrier that reduces their effect on the shell.