FORMULATION OF GELS
Following agents are used for the preparation of pharmaceutical gels
a) Gelling Agents
These are organic hydrocolloids polymers. Sometimes hydrophilic inorganic substance are used as gelling agent.
Natural Polymers
- Gum tragacanth
- Starch
- Pectin
- Gelatin
- Clays
- Sod. Alginate
- Carrageenan
Semi-synthetic polymer
- Micro-crystalline HPMC,
- CMC
- Na. CMC
Synthetic/Acrylic polymers
- Polyacrylic acids
The Polymers such as Alginic acid (seaweed), Gelatin, Bentonite, veegum (magnesium aluminum silicate), Agar, natural gum/mucilage, Pectin, Tragacanth, Alginic acid, Carrageen, and synthetic, semi-synthetic material, MethylCellulose, Hydroxy methylcellulose, Carboxymethylcellulose (CMC), and the carbopols is used to prepare pharmaceutical gels.
b) PRESERVATIVES
Since gels are most susceptible to microbial growth due to high water content
Example: Methy paraben & Propyl paraben; Benzoic acid, Chlorocresol; Chlorhexidine acetate.
b) other ingredients
Hygroscopic substances:
After applying the gel on skin, water quickly evaporate from gels, lead to formation of flakes on skin, To prevent this hygroscopic agents are added.
Example: Glycerin, Propylene glycol, Sorbitol
Chelating agents
By formation of complex with heavy metals, chelating agent inactivates the heavy metal which result into prevention of degradation of medicament sensitive to heavy metals.
Example: EDTA (ethylene diamine Tetra acetic acid)
METHODS OF PREPARATION OF GELS
Gels are prepared by mixing suitable thickening agent and aqueous vehicles. Drug is dispersed in aqueous vehicle and thickening agent is added by triturating in a mortar. Trituration is carried out until a homogenous preparation is formed.
- Fusion Method
- Cold Method
- Dispersion Method
1. Fusion Method
In this method various waxy materials employed as gellant in non polar media. Drug was added when waxy materials melted by fusion, stirred slowly until uniform gel formed.
2. Cold Method
Water was cooled to 4-100c and placed it in mixing container. Gelling agent was slowly added and agitating until solution is complete. Maintained temperature below 100oc . Drug was added in solution form slowly with gentle mixing. Immediately transfer to container & allow to warm to room temperature where upon liquid becomes clear gel.
3. Dispersion Method
Gelling agent was dispersed in water with stirring at 1200 rpm for 30 min . Drug was dissolved in non-aqueous solvent with preservative. This solution was added in above gel with continuous stirring.
Also Read…
Pharmaceutical Gels & its Classification | Pharmacy Notes
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