Jellies are transparent or translucent non-greasy, semisolid preparations meant for external application to the skin or mucous membrane. They may be prepared by using gums such as tragacanth, pectin, sodium alginates, methyl cellulose and sodium carboxymethyl cellulose.
Types of jellies:
There are three types of jellies
1) Medicated jellies: These are chiefly used on mucous membrane and skin for their spermicidal, local anaesthetics and antiseptic properties. These jellies contain sufficient water.
After evaporation of water, jellies provide a local cooling effect and residual film gives protection. Ex: Ephedrine sulphate jelly is used as a vasoconstrictor (to arrest the bleeding of nose). Phenyl mercuric nitrate jelly is used as spermicidal contraceptive.
2) Lubricating jellies: These jellies are used for lubrication of diagnostic equipment such as, surgical gloves, cystoscopes, fingerstalls, catheters, rectal thermometers etc. These jellies should be thin, transparent and water soluble.
These jellies should be sterile because these are used as lubricants for articles to be inserted into sterile regions of the body such as urinary bladder etc.
3) Miscellaneous jellies:
i) Patch testing: These jellies are used as a vehicle for allergens which are applied on to check the sensitivity. On drying, the residual film is formed which helps to keep the patches separate and avoid confusing results.
ii) Electro-cardiography: The jelly is applied on the electrode to reduce the electrical resistance between the patient’s skin and the electrode. They jelly contains sodium chloride, pumice powder and glycerine. The sodium chloride is a good conductor of electricity where glycerine acts as humectants.
Formulation of jellies:
1. Gelling agents: These are usually organic hydrocolloids. Some inorganic hydrocolloids are also used as gelling agents.
i) Tragacanth: It is used for the preparation of lubricating, medicated and contraceptive jellies. The concentration of gum required for the preparation of jellies varies from 2-5%. The jelly prepared with tragacanth usually contains lumps which can be avoided by using a dispensing agent like alcohol, glycerine and volatile oil.
The tragacanth jellies are becoming less popular because of the following reasons:
a) They cannot be stored for a long time.
b) They are prone to microbial growth.
c) They vary in viscosity because the gum is obtained from natural sources.
d) The residual film formed after the evaporation of jelly tends to flake.
e) They lose viscosity beyond pH range 4.5-7.
ii) Sodium alginate: Sodium alginate jellies are used as lubricants (1.5-2%) and dermatological vehicles (5-10%).
The viscosity of sodium alginate jelly can be increased by adding trace of soluble calcium salt.
iii) Pectin: Pectin is a valuable gelling agent for acid products. Pectin jelly is prone to microbial growth, so a suitable preservative is needed to preserve it properly during its storage
iv) Starch: Starch mucilage is prepared with water alone lead to bacterial growth, so a suitable preservative must be added.
Starch in combination with other substances like gelatin and glycerine is commonly used for the preparation of jellies.
V) Gelatin: Gelatin is soluble in hot water. A 2% gelatin solution in hot water forms a jelly on cooling. Very stiff medicated jelly can be prepared by incorporating about 15% gelatin.
Vi) Cellulose derivative: Methyl cellulose and sodium carboxymethyl cellulose are widely used for the preparation of jellies. These substances produce natural jellies of very stable viscosity and afford good resistance. Sodium carboxymethyl cellulose is used for the preparation of lubricating jellies as well as used for sterile jellies.
2. Preparation of jellies:
The pharmaceutical jellies are usually prepared by adding a thickening agent, such as tragacanth, carboxymethyl cellulose etc. to an aqueous solution of drug. The mass is triturated in a mortar until a uniform product is obtained. The glass pestle and mortar is used in case of dark coloured drug.
3. Preservation of jellies:
The jellies contains large amount of water so these are prone to bacterial and fungal growth. The jellies must be
suitably preserved by adding a preservative like Ex: Methyl p-hydroxybenzoate (0.1- 0.2% w/v), Propyl
p-hydroxybenzoate (0.05 %), Chlorocresol (0.1- 0.2%), Benzalkonium chloride (0.02%)
4. Storage of jellies:
Jellies are stored in well filled and well closed containers to minimise the evaporation of water. Jellies are stored in a cool place to prevent drying out. The sterile jellies, such as catheter lubricants are packed in collapsible tubes.
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