Pharmaceutical chemistry II TEHSEEN MALIK WOMEN UNIVERSITY MULTAN tehseenmalik2003@gmail.com

1. PASTES AND GELS

2.  Introduction
 Properties
 Uses
 Method of preparation
 Prescription
 Packaging
 Labeling
 dispensing
Topic outlines

3.  Pastes are semisolid preparations, containing high
proportion of finely divided solid (usually 20_50%)
dispersed in a suitable vehicle such as water,
glycerin or oils.
 Pastes have a stiff consistency but are not as firm
as ointments.
Examples:
 Zinc oxide paste
 Starch paste
 Dental impression pastes
 Toothpastes etc
Pastes

4.  Pastes are stiffer than other semisolid dosage forms such as
ointments and creams, hence they remain stable at site of
application.
 Because of high powder contents, pastes are porous , hence
perspiration can escape..
 They do not interfere with the non infected areas of the skin.
 They are considerably less greasy compared to ointments.
 They are mostly applied over moist lesions as they posses
good adhesive property to the skin.
 Most of the pastes are unsuitable for treating scalp
conditions because they are difficult to be removed from
hair.
Properties of pastes

5.  Based on the type of the base used in
formulation, pastes are classified as follows:
 Fatty pastes: consisting of fatty oleaginous
bases. eg: zinc oxide paste
 Aqueous gel paste: These are prepared with
water miscible bases. eg :cellulose paste and
titanium dioxide paste.
 Hydrocolloid pastes: consist of hydrocarbon
bases. Eg: zinc oxide gelatin paste, tooth paste etc
Types of pastes

6. Various types of bases are used in the preparation of
pastes;
A. Hydrocarbon bases: (soft paraffin and liquid
paraffin are commonly used bases)
Formulation of pastes
Name of preparation Active
ingredient
base use
Compound zinc paste
B. P
Zinc oxide Soft paraffin Eczema , psoriasis
Compound zinc and
salicylic acid paste B.P
Zinc oxide and
salicylic acid
Soft paraffin Eczema , psoriasis
Coal tar paste Coal tar Soft paraffin eczema
Aluminium paste Aluminium oxide Liquid
paraffin
protectant

7. B. Water miscible base
Water miscible bases include emulsifying
ointments and emulsifying wax used for the
preparation of pastes.
Name of preparation Base used uses
Resorcinol & sulfur
paste B.P.C
Emulsifying ointment Treatment of dandruff
Zinc and coal tar paste Emulsifying wax eczema
Magnesium sulfate
paste B.P.C
Magnesium sulfate -
45% phenol in glycerol
Used to treat boils

8. C. Water soluble base
Water soluble bases are prepared from mixture of
high and low molecular weight polyethylene glycols.
Name of the
preparation
base use
Water soluble
dental paste
Neomycin sulfate Sterilizing infected
root canal
Triamcinolone
dental paste
Triamcinolone acetonide in
an adhesive paste(sodium
carboxy methyl cellulose,
pectin + gelatin
Anti inflammatory

9. Ingredient type Typical percentage
Liquid base White 30, Gel : up to 80
Fillers and abrasives White 2-50 , Gel : 15 to 80
Rheology modifiers 0.5 _ 2
Detergent 0.5_2.5
Active ingredient 0.3
flavor 0.5 _ 2
Sweetener 0.2
Commonly used additives in
pastes

10. Ingredients used in medicated tooth paste
 Potassium citrate
 Potassium nitrate
 Sodium monoflourophosphate
 Triclosan
 Strontium chloride
Preparing tooth paste

11.  Pastes are prepared by trituration and fusion methods.
 Trituration method is used when the base is liquid or
semisolid.
 Fusion method is used when the base is solid in nature.
Compound zinc paste is prepared by both fusion and trituration
methods.
Trituration method:
 Zinc oxide and starch powder are passed through sieve no.
180.
 Soft paraffin is melted on a water bath.
 Required amount of powder is taken in mortar , triturated with
little melted base untill it gets smooth and gradually the rest
of the base is added.
Methods of preparation

12.  Fusion method:
Zinc and coal tar paste B.P.C. is prepared by fusion method.
Method 1:
 The components are melted in decreasing order of their
melting points.
 The medicament is added slowly in the melted
ingredients and stirred thoroughly until the mass cools
down.
Method 2:
 All the components are taken in subdivided state and
melted together.

13. Pastes can be packed in various container types,
including
 intermediate bulk containers (IBCs),
 plastic or metal containers,
 glass bottles,
 metal canisters,
 and plastic bags or boxes.
The best choice depends on factors like the paste's
specific characteristics (e.g., potential for
contamination), the quantity of paste being packed,
and the intended use (e.g., storage, transportation).
Packaging and labeling of pastes

14. Labels
1. Foe external use only ( most pastes are applied to
the skin)
2. Apply to affected area only( prevents application to
healthy or sensitive area)
3. Do not apply to broken or inflamed skin( important
for irritating or drying pastes)
4. Store in a cool place/ below 25º. ( stability of certain
pastes depends on the storage temperature)

15. “ A semisolid system consisting of a network of
polymer chains or colloidal particles that are
dispersed in a liquid vehicle, and have a high
degree of fluidity, yet exhibit no flow in the
steady state”
Examples
 Carbopol gel
 Gelatin gel
 Xanthan gum gel etc
Introduction to Gels

16.  gels have several important properties that make
them effective for various drug delivery systems and
therapeutic applications.
 Viscosity: Gels have a high viscosity compared to liquids,
giving them a thick, semi-solid consistency.
 Adhesion: Gels adhere well to surfaces such as the skin or
mucous membranes.
 Transparency: Many gels are transparent or translucent,
which can be beneficial for aesthetic reasons, particularly in
cosmetic and dermatological formulations.
Properties of gels

17.  Controlled Release: Gels can be designed to control the release of
an active ingredient over time. This allows for sustained drug delivery
and can improve the therapeutic effect while reducing side effects by
avoiding peak drug concentrations.
 Hydration: Gels often contain water as a primary component. This
provides hydration to the skin, mucous membranes, or wounds.
 Non-greasy Texture: Gels are typically non-greasy, making them
more appealing for patients, especially in hot or humid conditions.
 Drug Penetration: Gels can improve the penetration of drugs
through the skin or mucous membranes due to their water-based
structure. The gel matrix can enhance the solubility and bioavailability
of certain drugs. Ease of Application: Gels are easy to apply and
spread evenly on the skin or affected area. This makes them user-
friendly, particularly in topical and ophthalmic applications.

18. 1. Topical Medications
Gels are frequently used as a vehicle for topical drugs. They are ideal for
delivering active ingredients to the skin due to their smooth texture,
ability to spread easily, and quick absorption. For example, gels
containing anti-inflammatory agents, antibiotics, or corticosteroids are
applied to treat conditions like eczema, acne, or muscle pain.
2. Controlled Release Formulations
Some gels are designed for controlled release of drugs. These gels release
the active ingredient over an extended period, improving the therapeutic
effect while reducing the frequency of dosing. For example, gels used in
the treatment of certain chronic conditions like pain or inflammation.
3. Ophthalmic Gels
Gels are used in eye care for the treatment of eye infections, dry eyes, or
glaucoma. They can hold moisture longer on the surface of the eye,
helping to hydrate and deliver active ingredients effectively.
Applications of gels

19. 4. Wound Care
Hydro gel dressings are used for wound management. They help keep
wounds moist, promote faster healing, and provide a barrier to bacteria.
5. Cosmetic and Dermatological Uses
Gels are often used in skincare products, such as moisturizers, sunscreens,
and anti-aging treatments. They have a light, non-greasy feel, making
them ideal for use on the skin, particularly in hot or humid climates.
6. Drug Delivery Systems:
Gels can also be used as drug delivery systems in the form of transdermal
patches or implants. These systems allow for the slow release of
medication directly into the bloodstream through the skin.
7. Oral Gels:
Some oral gels are formulated for conditions like sore throats, ulcers, or
dental issues. These gels soothe irritation and can provide localized relief.
8. Suppositories:
Gels are used in the formulation of suppositories, which can be inserted
into body cavities (like the rectum or vagina) for localized or systemic
drug delivery.

20.  Gels are prepared by dispersing gelling agents in a suitable solvent
(usually water or an organic solvent), followed by swelling and/or cross-
linking to form a semi-solid structure. The choice of method depends on
the type of gelling agent, solubility, and desired properties of the gel.
1. Cold Method
Used when gelling agents are water-soluble and swell without heat.
Steps:
 Dissolve the gelling agent in cold water with constant stirring.
 Allow to swell for a few hours or overnight.
 Adjust pH (if needed) to trigger gel formation.
 Add other ingredients like preservatives or active drugs .
Examples: Carbopol GelHydroxypropyl Methylcellulose (HPMC) Gel.
Note: Carbopol requires neutralization with Triethanolamine (TEA) or
Sodium Hydroxide to form a gel.
Methods of preparation of gels

21.  2. Hot Method
Used when gelling agents require heat to dissolve
properly.
Steps:
 Heat the solvent (usually water) to around 60–80°C.
 Slowly add the gelling agent with continuous stirring.
 Cool the solution to room temperature.
 Add other ingredients once cooled.
 Examples : Gelatin GelMethylcellulose Gel (requires
heating and cooling for setting)

22. 3. Dispersion Method
A general technique for both organic and inorganic gelling agents.
Steps:
 Disperse the gelling agent in the vehicle (water, alcohol, etc.).
 Use a high-shear mixer or magnetic stirrer.
 Allow to hydrate and swell over time.
 Add active ingredients after gelatin.
 Examples : Xanthan gum gels , Bentonite gels
4. Fusion Method
Used when components (including the drug) are heat-stable and need to
be melted.
Steps:
 Melt the base (e.g., polyethylene glycol) at a suitable temperature.
 Add gelling agent and active ingredient.
 Stir until uniform.
 Cool and pour into containers.
Examples : Organogels ,Thermally set gels

23. 1. Purpose
To prepare and dispense clindamycin 1 % gel, a topical antibiotic
used for acne vulgaris treatment.
2. ingredients
EXAMPLE: Preparation and
dispensing of clindamycin gel 1%
Ingredients Quantity (for 100g gel)
Clindamycin phosphate 1g
Carbopol 1g
Propylene glycol 5g
Methylparaben 0.2g
Triethanolamine (TEA) q.S to adjust Ph (5.5_6)
Purified water q.S to make 100g

24. 3.Procedure / compounding
 Soak carbopol 940 in purified water and allow to swell.
 Dissolve clindamycin phosphate in a portion of water with
propylene glycol and methylparaben.
 Mix the solution and slowly add to swollen carbopol.
 Adjust the pH using triethnolamine to form a clear gel.
 Mix thoroughly to ensure uniformity.
4. Dispensing
o Name : clindamycin gel %
o Directions : apply a thin layer to affected area twice a day
o Storage :store in a cool , dry place. Do not freeze.
o Precautions : for external use only. Avoid contact with eyes.
o Expiry : use within 30 days of preparation.

25.  Explain how to apply gel properly
 Advise on possible side effects (eg: dryness,
irritation).
 Instruct them not to use other harsh skin products
simultaneously.
Counseling of the patient