Theobroma oil (Cocoa butter): It is obtained from whole and roasted seeds of cocoa bean. It occurs as a yellowish-white solid with chocolate-like odor. It contains a mixture of glyceryl esters of stearic acid and palmitic, oleic, and other unsaturated fatty acids.

The advantages of this base are as follows:

1. It is solid at normal room temperature but melts in the body as the melting point range is 30–36°C.
2. It liquefies readily on warming and sets rapidly on cooling.
3. It has got good miscibility with many ingredients.
4. It is physicochemically inert, nontoxic and nonirritant.

The following are its disadvantages:

1. It undergoes polymorphism at various preparation temperatures. If cocoa butter is melted and cooled, it solidifies in different crystalline forms depending on the melting temperature, rate of cooling and size or bulk of the mass. The four main polymorphic forms are α, β, β¹, and γ. If melted at a temperature less than 36°C and slowly cooled, it forms stable beta crystals with normal melting point. However, if over-heated, it may produce on cooling unstable gamma crystals, which melt at about 15°C, or alpha crystals, which melt at about 20°C.
2. Cocoa butter contracts enough on cooling to loosen the suppositories in the mold. Sticking may occur, particularly if the mold is inadequately lubricated. This can be overcome by sufficient lubrication of the mold before use.
3. The softening point of cocoa butter is too low for hot climates. To raise the softening point, white beeswax may be added if intended for use in tropical and subtropical countries.
4. Chloral hydrate, which dissolves in theobroma oil, lowers its melting point so that the suppositories are too soft for use. To restore or increase the melting point, a controlled quantity of white beeswax may be added.
5. Slow chemical oxidation of the unsaturated glycerides present in the theobroma oil takes place, leading to rancidification.
6. The base is hydrophobic in nature and has poor water-holding capacity. The water absorption capacity can be improved by the addition of emulsifying agents.

Synthetic fats: A number of hydrogenated oils, such as hydrogenated edible oil, arachis oil, coconut oil, palm kernel oil, and a mixture of oleic and stearic acids are recommended as a substitute of theobroma oil.

The advantages of these synthetic fats over theobroma oil are as follows:

1. They are unaffected by overheating.
2. They have good resistance to oxidation because their unsaturated fatty acids have been reduced.
3. They possess good emulsifying and water-absorbing capacities.
4. Mold lubricant is not required.
5. They produce colorless, odorless and elegant suppositories.

Their main disadvantage is that they should not be cooled in refrigerator because they become brittle if cooled quickly. Certain additives such as 0.05% polysorbate 80 can be used as the remedy.

Water-soluble and Water-miscible Bases

Glycero-gelatin base: The base consists of a mixture of glycerol and water made into a stiff jelly by adding gelatin. It is mainly used for the preparation of suppositories and pessaries. The stiffness of the mass depends upon the proportion of gelatin used, which is adjusted according to its immediate or sustained drug release use. It is hydrophilic in nature and is a tailor-made base for suppositories containing belladonna extract, boric acid, chloral hydrate, iodoform or opium.

Glycero-gelatin base suppositories are less commonly used than the fatty base suppositories because of its following disadvantages:

1. Glycerol exerts laxative action.
2. They are hygroscopic in nature and hence must be carefully stored.
3. Gelatin is incompatible with drugs those precipitate with protein such as tannic acid, ferric chloride and gallic acid.
4. They are more prone to microbial contamination as gelatin is obtained from the animal source.

Soapglycerin suppositories: In this type of suppositories, gelatin is replaced with curd soap or sodium stearate, which makes the glycerin sufficiently hard for suppositories; moreover, a large quantity of glycerin, up to 95% of the mass, can be incorporated. Furthermore, the soap helps in the evacuation of glycerin. The striking disadvantage is that they are very hygroscopic; therefore, they must be protected from atmosphere and wrapped in waxed paper or tin foil.

Emulsifying Bases

These are synthetic bases and a number of proprietary bases of very good quality are available as desired.

 

Witepsol: It consists of triglycerides of saturated vegetable acids (chain length C₁₂ to C₁₈) with varying proportions of partial esters.

 

Massa esterium: The base consists of a mixture of mono-, di-, and triglycerides of saturated fatty acids with chain lengths of C₁₁ to C₁₇.

 

Massuppol: It consists of glyceryl esters, mainly of lauric acid, to which a small amount of glyceryl monostearate has been added to improve its water-absorbing capacity.

The following are the advantages of this base:

1. Physical characteristics do not alter on overheating.
2. It does not stick to the mold.
3. Prelubrication of the mold is not necessary
4. It solidifies rapidly.
5. It is less liable to get rancid.
6. It absorbs fairly large amount of aqueous liquids.