Types Of Suppository Bases

The release of drug from suppository bases is one of the important factors in the transmucosal absorption of drugs, since the orifice fluid is small in volume and is viscous compared with gastrointestinal (GI) fluid. Generally, the hydrophilic characteristics of base enhance the release of poorly water-soluble drugs from fatty bases because of the lesser interaction of the resultant complex with vehicles.

Suppository base

Properties Of An Ideal Suppository Base

The ideal suppository base should meet the following general specifications:

1. It should release the medicaments readily.

2. It should be compatible with a variety of drugs.

3. It should melt at body temperature or disperse in the body fluids.

4. It should be nontoxic and nonirritating to mucous membranes.

5. It should be stable on storage.

6. It should not bind or otherwise interfere with release or absorption of drug substances.

7. It should be stable if heated above its melting point.

9. It should be molded easily and should not adhere to the mold.

10. It should have wetting and emulsifying properties.

11. It should be able to incorporate a high percentage of water in it i.e., a high water number.

12. It should shrink sufficiently on cooling to release itself from mold and should be moldable by pouring or by cold compression.

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13. Fatty bases should have acid value below 0.2, saponification value in between 200 to 245, iodine value less than 7 and a small range between the melting and solidification points.

Type of Suppository Base

Suppository bases can be classified broadly into two types: Oleaginous (fatty) and water soluble or water miscible.

Fatty Bases

The traditional cocoa butter vehicle is immiscible with aqueous tissue fluids but melts at body temperature. They are also called lipophilic fat-based suppository. They readily solubilize typical insoluble small-molecule drugs and require no localized fluids to spread and release drug. Typically, such suppositories are ideal for the rectum where there is little available fluid in the lower large intestinal tract.

The most widely used fatty acid base is theobroma oil (cocoa butter). Theobroma oil is a triglyceride vegetable fat extracted from cocoa beans that is comprised primarily of palmitic acid, stearic acid and oleic acid. Theobroma oil is well tolerated by the rectal mucosa. At typical room temperatures of 15–25°C (59–77°F), theobroma oil is a hard, amorphous solid, but at 30–35°C (86–95°F) (i.e., body temperature) it melts to a bland, nonirritating oil. The two major disadvantages is that it changes shape and form above human temperature and it is expensive to produce. Adding an active ingredient or an excipient that increase the temperature of the mixture can damage the product. To overcome the first disadvantage, the active ingredient and excipient must be compatible and the final it must be stored in a refrigerator. To overcome the second disadvantage, newer synthetic triglycerides have been produced which consist of hydrogenated vegetable oils. Their advantage over cocoa butter is that they do not exhibit polymorphism. For example, Fattibase® is a single entity base that consists of triglycerides from palm, palm kernel, and coconut oils.

Water Bases

Water-soluble or water-miscible vehicles also have been used. They are also called hydrophilic water-based suppositories and are unaffected by body temperature and require water to dissolve the suppository and release the drug. In contrast to the fat-based suppositories, hydrophilic suppositories can more easily support drug delivery of soluble drug compounds and use the body fluids to dissolve the suppository to transport the drug into the body. Such water-based suppositories are appropriate for vaginal application where there is more local fluid.

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These include primarily glycerin, gelatin and water soluble polymers such as polyethylene glycol (PEG). Glycerine's mechanism as a suppository base is to draw moisture from the surrounding tissue to facilitate the dissolution of the suppository. As a result, gelatin suppositories dissolve slowly and provide long term release of active ingredients. This is desirable for indication like laxative. However, this can cause infection.

The choice of suppository base depends on the physicochemical properties of the drug as well as the compatibility between drug and base. Surfactants (e.g. Polysorbate 80, Tween 20) may be incorporated into the formulation to enhance the wetting properties of the suppository with the rectal fluid, thereby increasing dissolution rate.