Dosage Forms - Gels

Front 1

What is a gel?

Back 1

• Are semisolid systems
• The movement of the dispersing medium is
restricted by an interlacing 3D-network of particles

Front 2

What is caused by the interlacing of 3D-network particles?

Back 2

Viscosity

Front 3

Gel Applications

Back 3

Oral
Topical
Intranasal
Vaginal
Rectal

Front 4

What are the phase systems of gels?

Back 4

Two-Phase System

Single Phase System

Front 5

What is a Two-Phase System?

Back 5

If the gel mass consists of a network of small
inorganic discrete particles

EX: AlOH3

Front 6

What is a Single Phase System?

Back 6

If the gel mass consists of a network of large
organic particles

EX: Carbomer

Front 7

What are the two class systems of gels?

Back 7

Hydrogel - Water Disp Diapers

Organogel - Oils, Cosmetics, Foods

Front 8

Descriptions of Hydrogels

Back 8

Inorganic

Natural & Synthetic Gums

Organic

Front 9

Inorganic Hydrogels

Back 9

Silica

Bentonite

Aluminum

Front 10

Natural & Synthetic Hydrogels

Back 10

Pectin

Sodium Alginate

Front 11

Organic Hydrogels

Back 11

Methylcellulose

Front 12

Descriptions of Organogels

Back 12

Hydrocarbon Types

Soap Base

Hydrophilic Gels

Front 13

Hydrocarbon Types

Back 13

Mineral Oil

PEG

Front 14

Soap Base Types

Back 14

Aluminum Stearate

Front 15

Hydrophilic Organogels

Back 15

Carbowax Bases

Front 16

What are characteristics of gels?

Back 16

Can be clear or turbid

To appeal to the consumer, gels should
have clarity and sparkle

•Most gels are water washable, greaseless

Front 17

Why use a gel?

Back 17

useful as liquid formulations in oral,
topical, intranasally, vaginal, and rectal
administration.

Cooling effect

moisturize

Front 18

What is a disadvantage of a gel?

Back 18

Bacterial/Mold Growth

Front 19

Swelling and Gels

Back 19

Soaking up liquid WITH a volume increase

Front 20

Syneresis and Gels

Back 20

Gels exudes fluid causing shrinkage

Elastic contraction of the polymer

In H2O phase

Front 21

Imbibition and Gels

Back 21

Soaking up liquid volume WITHOUT a marked increase in volume - like a sponge

Front 22

Thixotropy and Gels

Back 22

viscous during storage but
loses consistency and become
fluid upon shaking.

Front 23

Xerogel

Back 23

Liquid is removed from a gel, only the
framework remains

Front 24

Gelling Agents

Back 24

Alginic Acid
Carbomer
Cellulose Derivates
Gums
Gelatine
Plastibase
Poloxamers

Front 25

Alginic Acid

Back 25

• Obtained from seaweed
• Tasteless, odorless
• Swells in water ~ 200 – 300
times its own weight
• Most common alginate:
calcium alginate gel
• Used in food industry (ice
cream, yogurt)

Front 26

Carbomer (Carbopol)

Back 26

• acrylic acid based polymers
• gel viscosity is pH dependent
• form acidic aqueous solutions (pH ~ 3), thicken at
a higher pH (5-6) (NaOH, KOH)
• a maximum of electrolytes (3%) can be added
before a rubbery mass form
• Addition of alcohol: viscosity decreases
• Used for: oral suspensions, topical gels

Front 27

Cellulose Derivates

Back 27

• Methylcellulose, hydroxyethylcellulose,
hydroxypropylcellulose, hydroxypropylmethylcellulose,
carboxymethylcellulose (CMC)
• Viscosity of all derivatives is maintained over a wide pH
range (3-11), except CMC
•Compatible with water and alcohol

Front 28

Carboxymethyl Cellulose (CMC)

Back 28

A cellulose Derivate
• Soluble in water at all temperatures
• Sensitive to pH, viscosity  < pH5
• Stable between pH 7-9
• 30 producers make over 300 types of CMC
• Anhydroglucose polymer with 100 to 3,500 units
(Degree of polymerization = DP)
• CMC has broad food usage (salad dressings, ice
cream)

Front 29

Gum Arabic (Acacia Senegal)

Back 29

• Highly branched with b-Galactose backbone
• Molecular weight 250,000 - 750,000
• Water soluble, fat insoluble
• Low viscosity gum
• Viscosity affected by pH and salts

Front 30

Food Uses for Gum Arabic

Back 30

– Stabilizer for flavor emulsions
– Encapsulated flavors
– Water binding
– Inhibit sugar crystallization

Front 31

Gum Tragacanth (Astragalus Gummifer)

Back 31

• sap of several species of Middle
Eastern legumes
• Polymer of Galacturonic Acid +
Galactose + Galactose + Arabinose
+ xylose

• Viscosity (varies with grade) 600 -
4,000 CPS at 1%
• Acid stable at pH 4-8
• Less common
• High cost
Burns External

Front 32

Gelatine

Back 32

• Gelatin is a protein produced by partial hydrolysis of collagen
extracted from the bones and connective tissues of animals
• Forms a solution of high viscosity in hot water, which sets to a gel on cooling

Alcohol will decrease viscosity

Front 33

Plastibase

Back 33

• Mixture of 5% low-molecular weight
polyethylene and 95% mineral oil.
• Mineral oil is immobilized by in the network of
entangled insoluble polyethylene chains
• Gel can be heated up to 60°C (140°F) without
substantial loss of viscosity

Front 34

Poloxamers

Back 34

 Poloxamers, trade name Pluronics

 nonionic block copolymers: central hydrophobic
chain of polyoxypropylene (poly-propylene oxide)
flanked by two hydrophilic chains of polyoxyethylene
(poly-ethylene oxide)

Front 35

Poloxamers (cont)

Back 35

 Form thermoreversible gels: liquids at cool, gels at
room or body temperature.

 Commonly named with the word Poloxamer
followed by a number to indicate which polymer is
being discussed (e.g. Poloxamer 407).

 Low toxicity products

Front 36

Magmas

(Bentonite Magma)

Back 36

Bentonite (50g) and Purified Water (1000 mL)

Two phase system, larger particles

Ex - Cat Litter

Front 37

Magmas (cont)

Back 37

Bentonite:
-hydrated aluminum silicate
-Bentonite usually forms from weathering of
volcanic ash, most often in the presence of water.
- preparation of 5% bentonite in water
-- thixotropic gel, swells approx. 12 times its
volume

Front 38

What is gel composition?

Back 38

• Gelling agent
• Water
• Cosolvents
• Preservatives
• Stabilizers

Front 39

How do gels form?

Back 39

The the tangling of polymer strands

Front 40

When do gels tend to clump?

Back 40

• If gelling agent is added to the dispersing medium: agent tends to “clump”
– Fix: sieve the agent onto the surface of the medium as medium is stirring

Front 41

Tips and Tricks for Gels

Back 41

• Some gelling agents require neutralizer to create gel
• Most gelling agents require 24 – 48hrs to completely
hydrate and reach max. viscosity
• Only Carbopol® 934P, methylcellulose,
hydroxypropylmethylcellulose and CMC are
recommended for oral use

Front 42

When should the drug be added to the gel?

Back 42

Drug should be added before the gel is formed

Drug should not interfere with gel formation

Front 43

Which agents are more soluble in Hot water?

Tepid water?

Back 43

-Hot: gelatine

- Tepid:carbomers, alginic acid

Front 44

Which gelling agents are more soluble in Cold Water?

Back 44

Poloxamers methylcellulose

Front 45

Packaging, Storage, and Labeling

Back 45

• Tight containers (tubes, jars,
squeeze bottles)
• Room or Refrigerated Temperatures,
as appropriate
• Prior to use….store in tight
containers.

Front 46

Example Preperation:

Lubricating Jelly

Back 46

• Methylcellulose 4000 cps 0.8%
• Carbopol 934 0.24%
• Propylene glycol 16.7%
• Methylparaben 0.015%
• Sodium hydroxide qs ad pH 7
• Purified water qs ad 100%
• Used for: insertion of medical devices