gel

1. Creams and Gels
Md. Saiful Islam
BPharm, MPharm (PCP)
North South University
Fb Group: Pharmacy Universe

2. Creams
Definition:
Pharmaceutical creams are semisolid preparations containing one or
more medicinal agents dissolved or dispersed in either a water-in-oil
emulsion or an oil-in-water emulsion or in another type of water-
washable base
Properties of creams:
• The so-called vanishing creams are o/w type emulsions containing
large percentages of water, stearic acid or other oleaginous
components
• After application of the cream , the water evaporates, leaving behind
a thin residue film of the stearic acid or other oleaginous
components

3. Properties of creams:
• The primary application of creams is as topical skin
products
• Sometimes creams are preferable to ointments because
they are easier to spread and remove
• Pharmaceutical manufacturers frequently manufacture
topical preparations of a drug in both cream and
ointment bases to satisfy the preference of the patient
and physician

4. Gels
Definition:
Gels are semisolid systems consisting of dispersions of
small or large molecules in an aqueous liquid vehicle
rendered jelly like by the addition of a gelling agent
• The concentration of the gelling agents is mostly less
than 10%, usually in o.5 to 2.0% range, with some
exceptions

5. Terminology related to gel
A number of terms are commonly used in discussing some
of the characteristics of gels. These are:
1) Imbibition:
- Taking up of a certain amount of liquid without a
measurable increase in volume
2) Swelling:
- Taking up of a liquid by a gel with an increase in volume
- Only liquids that solvate a gel can cause swelling

6. Terminology…….
3) Syneresis:
- This occurs when the interaction between particles of the
dispersed phase becomes so great that on standing, the
dispersing medium is squeezed out in droplets and the
gel shrinks
- This is a form of instability in aqueous and non-aqueous
gels
- Separation of a solvent phase is thought to occur
because of the elastic contraction of the polymeric
molecules (in the swelling process during gel formation,
the macromolecules become stretched and the elastic
forces increase as swelling proceeds)

7. Terminology…..
4) Thixotropy:
- A reversible gel-sol formation with no change in volume
or temperature, a type of non-Newtonian flow
5) Xerogel:
- A xerogel is formed when the liquid is removed from a
gel and only the framework remains

8. Classification and types of gels
Depending on the appearance and number of phases, the
gels are primarily divided into two classes:
1) Single-phase gels:
- Gels in which the macromolecules are distributed so that
no apparent boundaries exist between them
- these gels look as clear as water
2) Two-phase system:
- Gels in which the mass consists of floccules of small,
distinct particles and may not be completely molecularly
dispersed
- these gels look turbid and frequently called magma or a
milk

9. Classification…….
Single-phase and two-phase gels are further classified into
two schemes. The first scheme divides gels into 2 types:
1) Inorganic hydrogels:
- These are two-phase systems
- Examples: Aluminum hydroxide gel, Bentonite magma
2) Organic gels:
- These are single-phase systems
- Examples: Carbopol, Tragacanth

10. Classification…….
The second scheme divides gels into 2 types:
1) Hydrogels:
- Include ingredients that are dispersible as colloids or
soluble in water
- They include organic hydrogels, natural and synthetic
gums and inorganic hydrogels
- Examples: Pectin paste, Tragacanth jelly, Methyl
cellulose, Sodium CMC, Bentonite gel, Veegum, Silica

11. Classification…….
2) Organogels:
- These include the hydrocarbons, animal and vegetable
fats, soap base greases, hydrophilic organogels
- Examples: Petrolatum, Lard, cocoa butter, Aluminum
stearate with heavy mineral oil gel, carbowax bases

12. Preparation of magmas and gels
Magmas and gels are prepared by one of the two ways:
1) By freshly precipitating the disperse phase:
- The disperse phase is precipitated to achieve a fine
degree of subdivision and a gelatinous character to
those particles
- When the solutions of inorganic agents react to form an
insoluble chemical, the desired gelatinous precipitates
results
- As the microcrystalline particles of the precipitate
develop, they strongly attract water to yield gelatinous
particles, which combine to form the desired gel

13. Preparation of……
2) By directly hydrating the inorganic chemical:
- The inorganic chemicals are hydrated directly which
produces the disperse phase of the dispersion
- In addition to the water vehicle, other agents as
propylene glycol, propyl gallate, and hydroxypropyl
cellulose may be used to enhance gel formation