Pharmaceutical Gels | Pharmacy Notes

GELS, PHARMACY NOTES

DEFINITION OF GELS

Gels are transparent or translucent, non-greasy, semisolid systems preparation consisting of dispersions of small or large molecules in an aqueous liquid vehicle, which has been thickened with a gelling agent. Gels can be a single phase or a biphasic system.

Jels & Jellies both are semi-solid system dosage form but jellies have soften consistency than gels.

Gels, Xerogels, Aerogels, types of Gels, Preparation of Gels, Pharmacy Notes
Pharmaceutical Gels

CLASSIFICATION OF GELS

According to solubility of gelling agent into dispersion liquid, gels are classified into two classes.

A. One-Phase/monophasic gel system

  • When the gelling agent is soluble in dispesing liquid, get single phase gel system.
  • Example; Hydrophillic polymers (Hydrophillic pomymer is soluble in aqueous).
  • Appearance: Clear
  • Rheology- Pseudoplastic flow
  • Single-phase gels use high molecular weight hydrophilic polymers as gelling agents. Examples of such polymers include carbomers (cross-linked acrylic acid polymers). These gels are considered to be one-phase systems because no definite boundaries exist between the dispersed macromolecules and the liquid.
  • According to dispersing liquid medium, One-Phase gel system is further classified into following two class.

a) Hydrogels

b) Organogels

B. Biphasic/ two phase gel system

  • Gelling agent is insoluble in dispersion liquid, we get biphasic gel system.
  • Example: Aluminum hydroxide gel, Bentonite gel.
  • Biphasic Gel system show Thixotropic flow behavior.
  • Appearance- Turbid
  • Biphasic gels could contain a gelatinous, cross-linked precipitate of one substance in the aqueous phase. For example, magma or milk of magnesia consists of a gelatinous precipitate of magnesium hydroxide.

Jellies are generally applied externally. They are used for medication, lubrication and some miscellaneous applications.

Jellies are used as lubricants for surgical gloves, catheters, and rectal thermometers. Lidocaine Hydrochloride Jelly is used as a topical anesthetic. Therapeutic vaginal jellies are available, and certain jelly-like preparations are used for contraceptive purposes, which often contain surface-active agents to enhance the spermatocidal properties of the jelly.

One base contains sodium alginate, glycerin, calcium gluconate, and water. The calcium ions cause a cross-linking with sodium alginate to form a gel of firmer consistency.

TYPES OF GELS

  • 1. HYDROGELS
  • 2. XEROGELS
  • 3. ORGANOGELS

1. HYDROGELS

  • A hydrogel is a network of polymer chains that are hydrophilic, sometimes found as a colloidal gel in which WATER/AQUEOUS is the dispersion medium.
  • Hydrogels are highly absorbent(they can contain over 90% water) natural or synthetic polymeric networks.
  • Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their significant water content. 
  • Common ingredients include polyvinyl alcohol, sodium polyacrylate, acrylate polymers and copolymers with an abundance of hydrophilic groups.

Uses

  • As scaffolds in tissue engineering.
  • As environment sensitivity detector.
  • Sustained release DDS.
  • Contact lenses.
  • ECG medical electrode.
  • Glue

2. XEROGELS

Xerogels can be described as dried gels. Open network formed by the removal of all swelling agents from a gel. Xerogels usually retain high porosity (15–50%) and enormous surface area, along with very small pore size (1–10 nm). When solvent removal occurs under supercritical conditions, the network does not shrink and a highly porous, low-density material known as an aerogel is produced.

Xerogels, aerogels, gels, pharmacy notes, pharmaceutics
Xerogels & aergels

3. ORGANOGELS

An organogel is a non-crystalline, non-glassy thermo reversible (thermoplastic) solid material composed of a liquid organic phase entrapped in a three-dimensionally cross-linked network. The liquid can be, for example, an organic solvent, mineral oil, or vegetable oil. These systems are based on self-assembly of the structuring molecules.

CHARACTERISTIC OF GELS

  • Jells have large proportion of water and water act as a vehicle for solubility of the drug.
  • Gels are commonly used as topical preparations or used in body cavities.
  • They are clear and turbid preparation depending upon solubility of ingredients.
  • Gels may thicken upon long stand so gel should be shaken prior to use.

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

  1. Gum tragacanth
  2. Starch
  3. Pectin
  4. Gelatin
  5. Clays
  6. Sod. Alginate
  7. Carrageenan

Semi-synthetic polymer

  1. Micro-crystalline HPMC,
  2. CMC
  3. Na. CMC

Synthetic/Acrylic polymers

  1. 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

Gents 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.

  1. Fusion Method
  2. Cold Method
  3. 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.


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