Suppository bases can be broadly divided into following categories- A. Oleaginous bases. B. Aqueous bases. C. Emulsifying bases.

A. Oleaginous bases:

Theobroma oil or cocoa butter was introduced as base in 1852 and has been one of the most widely used bases. It satisfies most of the criteria of an ideal suppository base but it melts at 32°C i.e., below the body temperature.

Overheating alters its physical characteristics and it has a tendency to adhere to the mold when solidified. It may exist in 4 crystalline states.

α Form : This form is obtained by suddenly cooling the melted mass to 0 °C. Its melting point is 24°C. .

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β Form : This form is obtained when cocoa butter is melted at 35 to 36°C and slowly cooled. It melts at 18 to 23°C.

β’ Form : It reverts back to (3 form and melts at 34 to 35°C.

γ Form : It is obtained by pouring a cool (20°C) cocoa butter into a container before it is solidified and cooled at deep freeze temperature. It melts at 18°C.

All the four forms are unstable and are converted to stable form over a period of several days. Thus extreme care should be exercised while melting and cooling cocoa butter. As a general rule, the minimal use of heat during the melting process is recommended.

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Cocoa butter can take up to 20 to 30g of water per 100 g. The incorporation of emulsifiers such as Tween 61 (5 to 10%) increases the water absorption capacity of cocoa butter.

Drugs like volatile oils, cresol, phenol and chloral hydrate lower the melting point of cocoa butter considerably and hence some wax and spermaceti can be used to correct such a problem.

To overcome drawbacks of cocoa butter, hydrogenated palm kernel and soyabean oils have been suggested. Palm kernel oil is particularly suggested for use in tropical countries. Completely or partially hydrogenated cottonseed oil such as ‘Cotoflakes’ and ‘Cotomar’ together with hexanediol has also been suggested.

Edible hydrogenated vegetable oil in combination with some waxes has been worked out in India. Pas a major constituent of the official suppository bases.

B. Aqueous bases

(i) Glycero – gelatin:

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It is a mixture of glycerin and water made into a stiff jell by the addition of gelatin. The proportion of gelatin can be varied according to the intended use of the preparation.

Gelato-glycerin bases dissolve in the body fluids liberating contained medicaments Gelato-glycerin Mass BP contains 14% gelatin, 70% glycerin and water. USP formula contains 20% gelatin together with 70% of glycerin.

For dispensing purposes, good quality powdered gelatin should be used. In order to control the consistency, glycerin can be partially or wholly substituted by propylene glycol and polyethylene glycols. The incompatibility of some medicaments can be avoided by the use of either Pharmagel A (cationic) or Pharmagel B (anionic). Glycerin suppositories being liable to mould growth, preservatives should be added.

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(ii) Soap glycerin:

In this case, soap is employed instead of glycerin for hardening Sodium stearate can incorporate up to 95% of glycerin. Sodium stearate (soap) is produced in situ by interaction of sodium carbonate with stearic acid. Soap glycerin suppositories are however hygroscopic.

(iii) PEG bases:

Different mixtures of polyethylene glycols are marketed under the trade names of Postonals, Carbo waxes and Macrogols.

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Most of the drugs commonly administered in suppository form are compatible with these bases. Polyethylene glycols are however incompatible with phenols and reduce the antiseptic effects of quaternary ammonium compounds.

C. Emulsifying bases:

Massa Esterinum, Witepsol and Massupol are the trade names under which the emulsifying bases are marketed. Massa Esterinum is a mixture of the mono-, di- and tri-glycerides of the fatty acids having the formula C11H23COOH to C17H35COOH. Witepsol bases consist of hydrogenated triglycerides of lauric acid with added monoglycerides. These are available in 9 grades. Massupol consists of glyceryl esters namely of lauric acid and addition of very small quantity of glyceryl monostearate.

All these bases are free from the drawbacks of cocoa butter and don’t require any mold lubricant.

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Water-dispersible bases essentially consist of surfactants. They melt at body temperature. Some formulae of dispersible bases containing surfactants are outlined below.

Glyceryl monostearate 10 Glyceryl monostearate 15 Twenn 60 40 Tween 61 90 Tween61 85 Tween61 60