This document provides an overview of pharmaceutical gels. It defines gels as semisolid systems where liquid movement is restricted by a 3D network. Gels are classified as single-phase or two-phase systems. Key properties include swelling, syneresis, aging, and thixotropy. Gels are used to deliver drugs orally, topically, and via injection. They are formulated by choosing appropriate vehicles, gelling agents, and additives. Gels are prepared via thermal, flocculation, or chemical methods. Evaluation parameters include homogeneity, pH, drug content, viscosity, spreadability, extrudability, skin irritation, and in vitro diffusion studies.

1. A PRESENTATION
ON
PHARMACEUTICAL GELS
Prepared by
Karuna Raghuwanshi (M. Pharm)
Assist. Professor
Swami Vivekanand college of Pharmacy, Bhopal

2. CONTENT
• Introduction
• Classification
• Characteristics
• Properties
• Uses
• Formulation
• Methods of preparation
• Manufacture of Gels
• Evaluation Parameters

3. Introduction
Gels are semisolid preparations in which small or large molecules dispersed in a suitable liquid and rendered jelly like with the help of gelling
agent or gelator (proteins, starch, gelatin, cellulose derivatives, carbomers etc, or low molecular weight small molecules.
Definition
gels are defined as semi rigid systems in which the movement of the dispersing medium is restricted by an interlacing three-dimensional
network of particles or solvated macromolecules of the dispersed phase.
• Some times, gels are considered as colloidal dispersion because they contain particles of 1nm-0.5µm particle size.
• Structurally, gels having liquid phase which is constrained with polymeric matrix having a high degree of chemical or physical cross linking
and the twisted matted strands often bound together by stronger van der Waals force to form crystalline or amorphous region throughout the
system such as tragacanth and CMC.
• The rigidity of a gel arises from the presence of a network formed by the interlinking of particles gelling agent. The nature of the particles
and the type of force that is responsible for the linkages, which determines the structure of the network and the properties of the gel.
• During the gel formation, swelling occurs as a result of solvent penetration causing the polymer network to stretch and hold its shape and
entwine the drug particles in them. Viscosity plays an integral role in the formation of a gel.
Representations of gel structures. (a) Flocculated particles in a two-phase gel structure.(b) Network of elongated particles or rods forming a gel
structure. (c) Matted fibers as found in soap gels. (d) Crystalline and amorphous regions in a gel of carboxymethylcellulose.

4. Classification of Gels
Gels care mainly classified into two categories (based on colloidal phases):
a. Single phase system (Organic)
b. Two phase system (Inorganic )
• Single phase system (Organic)
Single phase gel consist of organic macromolecules distributed uniformly throughout a liquid in such a manner that no apparent boundaries
exist between the dispersed macromolecules and the liquid..
E.g. Organic gels consists of carbomer, tragacanth etc. as a gelling agent.
• Two phase system (Inorganic )
If the partition size of dispersed phase is relatively large and form the three-dimensional structure throughout gel, such a system consists of
floccules of small particles rather than larger molecules and gel structure, in this, system is not always stable. They must be thixotropic-forming
semisolid on standing and become liquid on agitation.
E.g. Aluminium hydroxide gel , bentonite magma

5. Swelling:
Swelling is taking up of a liquid by a gel with a rise in the volume. Only liquids that solvate a gel can cause swelling. Gels can swell, absorbing liquid
with an increase in volume. This can be looked on as the initial phase of dissolution.
Syneresis:
Many gel systems undergo contraction upon standing. The interstitial liquid is expressed, collecting at the surface of the gel. This process, referred to
as syneresis,.
Ageing:
Colloidal systems usually exhibit slow spontaneous aggregation. This process is referred to as ageing. In gels, gelling agent. ageing results in the
gradual formation of a dense network of the
Thixotropy:
Thixotropy is a reversible gel-sol formation with no change in volume or temperature, a type of non-Newtonian flow.
Characteristics
Properties
1. Ideally, the gelling agent must be inert, safe and cannot react with other formulation constituents.
2. The gelling agent should produce a sensible solid-like nature at the time of storage which is easily broken when exposed to shear forces produced
by squeezing the tube, trembling the bottle or at the time of topical application.
3. It should have suitable anti-microbial agent.
4. The topical gel must not be sticky.
5. The ophthalmic gel must be sterile.
6. The viscosity or gel strength increases with an increase in the effective crosslink density of the gel.
7. Each component is continuous throughout the system.
8. The gels remain equally uniform upon standing and doesn’t freely settle.

6. Uses
1. As delivery systems for orally administered drugs.
2. For topical drugs, applied directly to the skin, mucous membrane or the eye.
3. As long acting forms of drug injected intramuscularly or implanted into the body.
4. As binders in tablet granulation, protective colloids in suspensions, thickeners in oral liquid and suppository bases.
5. In cosmetics like shampoos, fragrance products, dentifrices and skin and hair care preparations.
6. Lubricant for catheters.
7. Bases for patch testing.
8. NaCl gel for electrocardiography.
9. As dental care prophylactic

7. Formulation Considerations for Pharmaceutical Gels
The choice of vehicle/solvent
E.g., alcohol, glycerol, PG, PEG 400, etc.
Inclusion of buffers
E.g., Phosphate, citrate, etc.
Gelling agents
E.g. gum tragacanth, starch, pectin, gelatin, clays, sod. Alginate, carbomers, PVC, cellulose derivatives ( HPMC, CMC).
Preservatives
E.g., Paraben, phenolics etc.
chelating agents
E.g. EDTA ethinyl diamine tetra acetic acid.
Antioxidants
E.g., Sodium metabisulphite, sodium formaldehyde sulfoxylate etc.
Flavours
E.g., Butterscotch, apricot, peach, vanilla, wintergreen mint, cherry, mint, anise, citrus flavours, raspberry
Sweetening agents
E.g., Sucrose, liquid glucose, glycerol, sorbitol, saccharin sodium, aspartame, etc.

8. Methods of preparation
Gels can be prepared by following methods:
1. Thermal changes
Solvated polymers (lipophilic colloids) when subjected to thermal changes causes gelatin. Many hydrogen formers are more soluble in hot than
cold water. If the temperature is reducing, the degree of hydration is reduced and gelatin occurs. E.g., Gelatin, agar sodium oleate, guar
gummed, cellulose derivatives, etc.
2. Flocculation
Here gelation is produced by adding just sufficient quantity of salt to precipitate to produce age state, but inadequate to bring about complete
precipitation. It is essential to ensure quick mixing to avoid local high concentration of precipitant.
E.g., E.g.: Solution of ethyl cellulose, polystyrene in benzene can be gelled by rapid mixing with suitable amounts of a non-solvent such as
petroleum ether. The addition of salts to hydrophobic solution brings about coagulation and gelation is rarely observed.
3. Chemical reaction
In this method gel is produced by chemical interaction between the solute and solvent.
E.g., Aluminum hydroxide gel can be prepared by interaction in aqueous solution of an aluminum salt and sodium carbonate, an increased
concentration of reactants will produce a gel structure.

9. Manufacture of Gels
Generally, the, in a mixing vessel by To prevent aggregation. The excessive stirring results in entrapment of air. The mixing rate must not
be extreme or a mixing vessel may be used to which a vacuum may be pulled, to prevent the entrapment of air
water soluble excipients are dissolved in vehicle
using mechanical stirrer.
add hydrophilic polymer to the stirred mixture slowly
Stirring is continued until the dissolution of the polymer has occurred.

10. Evaluation Parameters of the Formulated Gels
1. Homogeneity
All developed gels are tested for homogeneity by visual inspection after the gels have been set in the container. They are tested for their appearance
and presence of any aggregates.
2. Grittiness
All the formulations are evaluated microscopically for the presence of particles if any no appreciable particulate matter seen under light microscope.
3. Measurement of pH
One gram of gel dissolved in 100 ml of distilled water and stored for two hours. The measurement of pH of each formulation is done in triplicate and
average values are calculated.
4. Drug content
1 g of the prepared gel is mixed with 100ml of suitable solvent. After suitable dilution, absorbance recorded by using UV- visible spectrophotometer
(UV – 1700 at 222 nm). Drug content is determined using slope of standard curve.
5. Viscosity study
The viscosity of the different gel formulations determined at 25°C using a cone and
plate viscometer or Brookfield Viscometer. The gels are rotated at 0.3, 0.6 and 1.5 rotations per minute. At each speed, the corresponding dial reading
are noted.

11. 6. Spreadability
Spreadability is expressed in terms of time in seconds taken by two slides to slip off from gel and placed in between the slides under the direction of
certain load, lesser the time taken for separation of two slides, better the spreadability. It is calculated by using the formula:
S = M. L / T
Where M = weight tied to upper slide
L = length of glass slides
T = time taken to separate the slide
7. Extrudability study
The formulations are filled in the collapsible tubes after the gels set in the container. Extrudability are based upon the quantity of gel in percentage and
gel extruded from collapsible tube on application of weight in grams required to extrude at least 0.5 cm ribbon of gel in 10 seconds.
8. Skin irritation study
The albino mice of either sex weighing 20-22gms used for this test. The intact skin is used. The hairs are removed from the back of the mice 3 days
before the experiment. The animals are divided into two batches and each batch is again divided into two groups. The gel containing drug is used on
test animal. A piece of cotton wool soaked in saturated drug solution is placed on the back of albino mice taken as control. The animals are treated
daily upto seven days and finally the treated skin examined visually for erythema and edema
9. In-vitro Diffusion study
The In-vitro technique for studying skin penetration involves use of some variety of a diffusion cell like Franz cell and Flow through cell in which
animal or human skin is fastened to a holder and the passage of compounds from the epidermal surface to a fluid bath is measured.
10. Stability
It was carried out by freeze-thaw cycling. Here, the product to a temperature of 4°C for 1 month, then at 25°C for 1 month and then at 40°C for 1
month, syneresis was observed. Then the gel is exposed to ambient room temperature.

12. References
1. Kaur L.P., Garg R. and Gupta G.D. Topical Gels: A Review. Research Journal of Pharmacy and Technology. 2010; 3(1): ISSN
0974-360X .
2. Rathod H. J., Mehta D.P. A Review on Pharmaceutical Gel. Acta Scientifica International Journal of Pharmaceutical Science. 2015; 1(1): 33-47.
3. https://www.pharmatutor.org/articles/pharmaceutical-gels-in-summarized-form [Accessed 5th June 2022]
4. J. Alemán, A. V. Chadwick, J. He, M. Hess, K. Horie, R. G. Jones, P. Kratochvíl, I. Meisel, I. Mita, G. Moad, S. Penczek and R. F. T. Stepto. Gel
Aging. De Gruyter. 2016; [https://doi.org/10.1515/iupac.79.2386] [Accessed 5th June 2022].
5. Bhakar N. Gels in Pharmaceuticals: Types of Gels and Standard Test. Pg pharma manufacturing guidelines. 2021; [https://pharmaguddu.com/gels-
pharmaceuticals-types-of-gels-and-standard-test/].
6. Patil P.B., Datir S.K., Saudagar R. B. A Review on Topical Gels as Drug Delivery System. Journal of Drug Delivery and Therapeutics. 2019; 9(3): 989-
994.

13. Thank you