Medicinal Emulsions Flashcards
Tutorial on Emulsions
1. Consider the following formulation for a topical cream:
Component Amount (%w/v) Required HLB
Glyceryl Stearate 5 3.8
Cetyl Alcohol 5 15.0
Liquid Paraffin 40 12.0
Surfactants 10 -
Distilled Water to 100 mL
(a) Calculate the Total Required HLB for the non-aqueous components.
Glyceryl Stearate = 5/50 x 3.8 = 0.38
Cetyl Alcohol = 5/50 x 15.0 = 1.50
Liquid Paraffin = 40/50 x 12.0 = 9.60
Total RHLB = 0.38 + 1.50 + 9.60 = 11.48
Tutorial on Emulsions
1. Consider the following formulation for a topical cream:
Component Amount (%w/v) Required HLB
Glyceryl Stearate 5 3.8
Cetyl Alcohol 5 15.0
Liquid Paraffin 40 12.0
Surfactants 10 -
Distilled Water to 100 mL
(b) Calculate the relative amounts of Tween 80 (HLB = 15.0) and Span
60 (HLB = 4.7) required to produce a stable emulsion.
Fraction of Tween 80 = (11.48 – 4.7)/(15.0 – 4.7) = 0.66
Fraction of Span 60 = 1.00 – 0.66 = 0.34
For 10 g of surfactants ⇒ 6.6 g of Tween 80
3.4 g of Span 60
- Draw the chemical structure of glycerol monostearate and state the type of emulsifying agent (surfactant).
Non-ionic EA. Monosubstituted ester of glycerol and stearic acid.
What is an emulsion?
Liquid formulations for internal application, Composed of two phases consisting of fine
droplets of oil or water (0.1 – 100 mm) dispersed
in water or oil.
emulsions for external application are normally
referred to as lotions, applications or liniments.
‘Semi-solids’ are commonly known as ‘creams’
Oral emulsions are almost exclusively oil in water.
What is Oil in Water?
Oil in Water (O/W)
Oil is the disperse phase.
Water is the continuous phase
Used in invariability for oral and IV medicines
What is water in Oil?
Water in oil (W/O)
Water is the disperse phase
Oil is the continuous phase
* Mainly external uses as emollients (‘greasy bases’)
although can be used as IM or ‘depot’ injections.
What ARE Multiple Emulsions?
Multiple emulsions (O/W/O or W/O/W)
Oil droplet enclosing a water droplet suspended in water!
Water droplet enclosing an oil droplet suspended in oil!
* Have uses as delayed action delivery systems.
What are microemulsions?
When the dispersed droplets are 1 nm – 1 mm in size, the formulation is referred to as a ‘microemulsion’.
These systems have many similarities to colloids
and are sometimes termed ‘colloidal emulsions’.
They are homogeneous, transparent systems that are (generally) thermodynamically stable.
Contain more than one surfactant
Typically O/W or W/O, they are 10-200 nm in size
and constitute form 20-80% of the total volume.
Have been used as IV delivery systems but are more
commonly used as topical delivery systems.
They are thermodynamically stable
How do you determine O/W or W/O
Use of hydrophilic/hydrophobic (lipophilic/lipophobic) dyes
Conductivity Test - O/W conducts electricity much better than W/O
Miscibility in Oil or Water?
Better in Oil is W/O Better in water is O/W
What is interfacial tension? What does it allow?
Boundary between two phases is termed the interface
Interfacial tension causes both phases to remain seperate
Total energy contained within interfacial tension is dependent on the surface area in contact with the other phase.
the cohesive force between the molecules of seperate liquids is greater than the adhesive force between the two liquids
What is the disperse phase? What is the interfacial tension between the droplets low or high? and why?
Finally what happens?
The phase that remains in droplet form the longest
should become the disperse phase. As interfacial tension between droplets is high,
(exacerbated by the extremely high surface area)
droplets quickly coalesce to lower the tension.
Complete phase separation eventually occurs.
What emulsion is used for fatty or oily medications or for oil soluble drugs?
O/W emulsions
What is used to mask taste in medications, what emulsion are they?
Water soluble flavouring (sugar) will mask any unpleasant taste ( for liquid paraffin, cod-liver oil or caster oil)
What are the most common emulsifying agents in oral preparations?
Synthetic non-ionic surfactants (polyoxyethylene sorbitan esters) hydrocolloids (acacia, tragacanth) and gelatine are commonly used as emulsifying agents in oral preparations.
What is TPN and what emulsion is used?
These emulsions are formulated for IV injection to patients who are unable to feed orally. This is known as Total Parenteral Nutrition (TPN).