L4: Emulsions Flashcards
Why could an emulsifying agent be nessecary?
To stabilise the emulsion
What is an emulsion?
System consisting of two IMMISCIBLE LIQUID phases,
One of which is dispersed throughout the other as fine droplets.
How could you achieve a very low interfacial tension? (Micro emulsions)
Include a second surfactant, co surfactant, that is corporated into the interfacial film around the droplets.
Name the 3 forms of administration of emulsions
Topical
Oral
Parenteral
How can emulsions be administered orally? (3)
Administration of oils in nutritional products
Administration of oil soluble drugs as a liquid
Can enhance oral absorption of some drugs
How can emulsions be administered parenterally? (2)
Oils May be injected intramuscularly, in small volumes.
Emulsions for intravenous injections must be o/w
–> to avoid embolic effect.
What can multiple emulsions and micro emulsions be used for?
Controlled release drug delivery systems
Name an advantage for using emulsions.
Delivery
Delivery of drugs with low aqueous solubility.
- -> drug dissolved in oily phase.
- -> oil droplets absorbed via fat adsorption mechanism
Name an advantage for using emulsions.
Taste
Taste masking.
- -> drug dissolved in the internal phase
- -> sweeteners added to external phase
Name an advantage for using emulsions.
Ease
Ease of swallowing than solid dosage forms
Name an advantage for using emulsions.
Reduction
Reduction of irritation of topical drugs
Name advantages for using emulsions (4)
1) Drugs with low aqueous solubility can be delivered.
2) Taste masking.
3) Ease of swallowing than solid dosage form.
4) Reduction of irritation of topical drugs.
Name 4 disadvantages of using emulsions
1) needs to be shaken before use
2) storage conditions may affect stability
3) bulky, difficult to transport, container breakage
4) liable to microbial contamination
What are the 4 different stability problems which can happen with emulsions?
Flocculation
Coalescence
Creaming
Breaking
What is flocculation?
The AGGREGATION of the dispersed globules into LOOSE cluster within the emulsion.
(Before coalescence).
What is coalescence?
Droplets coalesce, form larger clusters.
After flocculation
What is creaming?
The SEPARATION of an emulsion into 2 regions, one which is richer in disperse phase than the other.
How can creaming be reduced?
By reducing rate of sedimentation.
How can phase inversion occur?
When changing the phase volumes.
Addition of an electrolyte
Name 3 ways the viscosity of an emulsion can be modified
Increase the CONCENTRATION of dispersed phase.
Increase the NUMBER of droplets
Add a viscosity MODIFIER
How does increasing concentration of the dispersed phase, increase the viscosity of emulsions?
It impedes/obstructs the movement if individual droplets.
How does increasing the no of droplets (by homogenisation), increase the viscosity?
Reduces droplet size, hence increases number.
–> causes continuous phase to be trapped between droplets.
What are the 3 groups of emulsifying agents
Surfactants
Hydrophilic colloids
Finely divided solid particles
What do emulsifying agents do?
Form coating round the dispersed globules
How do surfactants work, as emulsifying agents?
ADSORBED at oil-water interface,
to form MONOMOLECULAR FILMS around droplets,
to REDUCE interfacial tension
How do hydrophilic colloids work, as emulsifying agents?
Form a MULTIMOLECULAR FILM around the droplets of oil in o/w emulsion.
How do finely divided solid particles work, as emulsifying agents?
Absorbed at the interface, between 2 immiscible liquid phases and form a FILM OF PARTICLES around the globules.
What are the mechanisms of emulsifying agents? (4)
1) DECREASE interfacial tension at water/oil interface
2) provide PHYSICAL BARRIER between droplets to prevent coalesce
3) provide droplets with ELECTRICAL charge (repulsion)
4) increase VISCOSITY of continuous phase
What are the 3 types of monomolecular films?
Gaseous
Condensed
Expanded
Explain gaseous monomolecular films
Large spaces between surfactants allowing lots of molecular motion
Explain condensed monomolecular films
High density film with little repulsion between groups.
Explain condensed monomolecular films
Branched or rigid hydrocarbons prevent high density.
What is HLB?
Hydrophile-lipophile balance
What type of stability does a mixture of high HLBs and low HLBs give?
Good/better stability.
What type of surfactants have a high HLB; low HLB?
Water soluble surfactant –> high HLB.
Oil soluble surfactant –> low HLB.
Why might antioxidants be added to the formulation of emulsions?
Some oils may be susceptible to oxidation.
Why might humectants be added to the formulation of emulsions?
(Topical)
Reduces rate of EVAPORATION of water from formulation on skin.
- -> increased hydration of skin.
- -> moisturising capability of formulation is enhanced.
Why might viscosity enhancers be added to the formulation of emulsions?
To improve stability.
Why might preservatives be added to the formulation of emulsions?
To prevent growth of micro organisms.
Name 2 problems with adding preservatives to emulsions
- they can be solubilised by surfactant micelles.
- they can partition into oil phase.
–> reduces concentration of preservative in aqueous phase.
Name 3 ways the stability of an emulsion can be assessed.
Microscopic examination
Globules size analysis
Viscosity.
What is microscopic examination?
–> observe the extent of creaming/coalescence over a period of time.
–> droplet sizes can be determined by microscopy
What can be assessed by globule size analysis
Coalescence leads to the increase of mean globule size with time.
How is viscosity an assessment of stability?
Droplet growth will be accompanied by decrease in no of particles.
–> viscosity will decrease.
Name 4 accelerated test techniques
Store at increased temp.
Freeze-Thaw cycling
Centrifugation
Rheological assessment
What does ‘storing at increased temp’ do to an emulsion?
Decreases viscosity of emulsion
–> droplet coalescence accelerated.
What does ‘freeze-thaw cycling’ do to an emulsion?
Microcrystals of ice disrupt the film at the o/w interface of droplets.
What does ‘centrifugation’ do to an emulsion?
Increases droplet acceleration.
What does ‘rheological assessment’ do to an emulsion?
Measure the residual apparent viscosity after destroying the structure of the emulsion.
