Formulation of emulsions
1.Formulation by the method of HLB
(hydrophile-Lipophile Balance);
•Surface-active agents are amphiphiles in which the molecule or ion
contains both hydrophilic and lipophilic portions.
•Griffen developed a scale based on the balance between these two
opposing tendencies. This so called HLB scale.
nA numerical scale,
extending from 1 to 50.
nThe more hydrophilic
surfactant have high HLB numbers (in excess of 10),
nsurfactants with HLB
numbers from 1 to 10 considered to be lipophilic.
•the type of emulsion is related to the balance between hydrophilic
and lipophilic solution tendencies of the surface-active emulsifying agent.
•Surfactants with a proper balance in their hydrophilic and
lipophilic affinities are effective emulsifying agents since they tend to
concentrate at the oil / water interface.
•The relationship between HLB values and the application of the surface active agent is shown in the table
•The relationship between HLB values and the application of the surface active agent is shown in the table
HLB Pharmaceutical use
0 –3 Antifoaming
4 –6 w/o emulsifier
7 –9 Wetting agent
8 –18 o/w emulsifier
13 –15 Detergent
10 -18 Solubilizer
•If the HLB of the oil phase is known and
the type of emulsion desired is known (o/w or w/o), the formulator chooses two
emulsifying agents, one with an HLB value above and the second with an HLB
value below ,that required by the oil. These are blended to give a mixture of
the correct HLB. The following formula, should serve as an example.
•R/
Liquid
petrolatum (HLB 10.5) 50 gm
Emulsifying
agent 5 gm
Span 80
(HLB 4.3)
Tween 80
(HLB 15)
Water,Q.S
100 ml
Prepare o/w
emulsion
•Calculation
Tween 80
(HLB 15) 6.2 parts
Required
HLB =10.5
Span 80
(HLB 4.3) 4.5 parts
10.7 parts
•The required weight of tween = 5*6.2/10.7=2.9 gm
•The required weight of tween = 5*6.2/10.7=2.9 gm
•The
required weight of span = 5*4.5/10.7=2.1 gm
Preparation
•The
oil soluble span is dissolved in oil and heated to 75 C,
•The
water soluble tween is added to the aqueous phase, which is heated to 70 C.
•Mix
the oil phase with the aqueous phase and stirred until cool.
•Formulation additives:
•Formulation additives:
1-Antioxidants
2-Preservatives
3-Humectants
4-Colors and flavorings.
1-Antioxidants:
•Some oils are liable to degradation by oxidation and therefore
antioxidants may be added to the formulation. They should be preferentially
soluble in the oily phase. Antioxidants used in oral emulsions which are
odorless and tasteless include ascorbic acid, citric acid, sodium
metabisulphite and sodium sulphite.
•Antioxidant is commonly used at concentrations ranging from 0.001
to 0.1%.
2-Preservatives:
2-Preservatives:
•Emulsions contain water, which will support microbial growth.
Microbes produce unpleasant odors, color changes and gases, pH change and
breakdown of the emulsion
•Microbial growth normally occurs in the aqueous phase of an
emulsion, therefore it is important that a sufficient concentration of
preservative is, present in the aqueous phase.
•Some preservatives in use are listed below:
nMethylparahydroxybenzoate
in 0.2% & Propyl parahydroxybezoate in 0.02%. ,They are suitable for both
external and internal use.
nBenzoic acid, which is
effective at a concentration of 0.1% at pH below 5.
nChloroform, as
chloroform water (0.25% v/v).
nChlorocresol (0.1 %).
3-Humectants:
3-Humectants:
nTo reduce the
evaporation of the water either from the packaged product when the closure is
removed or from the surface of the skin after application.
nE.g., Propylene glycol,
glycerol and sorbitol at a concentration around 5%.
4-Colours and flavourings:
nColour is rarely needed
in an emulsion, as most have an elegant white colour and thick texture.
nEmulsions for oral use
will usually contain some flavouring agent.
Example of emulsion formulations
Example of emulsion formulations
R/
Code liver oil 30 ml
Chloroform 0.2 ml
Cinnamon water to 100 ml
•Prepare 100 ml cod liver oil emulsion (o/w emulsion for internal
use)
•Formulation
nCod liver oil is a fixed
oil that requires the addition of acacia gum as an o/w emulsifying agent
nPreparation of primary
emulsion
0 w G
4 2 1
30 ml 15ml 7.5 g
nTherefore 30 ml cod liver oil, 15 ml of cinnamon water and 7.5 g
of acacia gum will be used to prepare the primary emulsion. Cinnamon water acts
as a flavouring agent and vehicle. .chloroform is dense only slowly soluble and
act as a preservative.
