(i) Glycero Gelatin
It is a mixture of glycerin and water which is made
into a stiff jelly 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. To control the consistency, glycerin can be partially or wholly
substituted by propylene glycol and polyethylene glycol. The incompatibility of
some medicaments can be avoided by the use of either Pharmagel A (cationic) or
Pharmagel B (anionic). Glycerin suppositories are liable to mold growth, and preservatives
should be added.
Disadvantages
(a) Physiological effect: osmosis occurs during the dissolving of the mucous secretions of the rectum, producing a laxative effect.
(b) It can cause rectal irritation due to a small
amount of liquid present.
(c) Unpredictable solution time.
(d) Hygroscopic: So, they should be packaged in tight
containers and also have dehydrating effects on the rectal and vaginal mucosa
leading to irritation.
(e) Microbial contamination likely.
(f) Long preparation time.
(g) Lubrication of the mold is essential.
(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 the 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.
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.