Define micro-emulsion
dispersed globules whose colloid dispersion’s are less than 1microm
What are the uses of emulsions?
oral emulsions, IV/IM, external creams and lotions (semi solids)
Give an example of an oral emulsion and what is the active ingredient?
Cod liver oil emulsion
The active ingredient is usually oil and so its o/w
What are the property differences of o/w compared to w/o?
o/w is less greasy, viscous and quicker absorption than w/o
What are properties of the ideal emulsion?
The globules should remain the same size and evenly dispersed. Cracking (where water comes out of the dispersed phase and cant be re-dispersed) and creaming (where oil rises/sinks) should be prevented.
What are emulsifying agent used for?
to prevent droplets joining together
Give examples of natural emulsifying agents
polysaccharides (acacia, starch, tragacanth), semi synthetic polysaccharides (methylcellulose) and sterols (beeswax, wool fat)
Give examples of synthetic surfactants as emulsifying agents
anionic (soaps - SDS), cationic (anti microbial - cetrimide), non ionic (glycerol, polysorbates, emulsifying wax)
What does it mean if an emulsifying agent has a low number?
it is an oil soluble agent (w/o)
Discuss finely divided solids as emulsifying agents
they form stable emulsions and include bentonite and colloidal silicon dioxide
Give the 3 types of emulsifying agents
- natural
- synthetic surfactants
- finely divided solids (powdered)
What other excipients are needed in emulsions?
antioxidants, preservatives (chloroform, benzoic acid) and colours and flavour.
How can you prevent creaming and cracking?
- retain globule size
- prevent extreme temperatures
- use stabilisers to prevent globules joining
- prevent microbial contamination
What are the advantages of internal emulsions?
- makes oils palatable
- easy to swallow
- fast absorption
- enables oils to be given as IV
What are the disadvantages of internal emulsions?
- not very stable
- problems with cracking and creaming
- difficult to manufacture
- can be inconvinenit to patient
- must shake before use
What are the advantages of external emulsions?
- can have a cooling effect on the skin
- local effect (no systemic side effects)
- can be greasy or non greasy
- can be used to treat a large area
- can be used as soaps
What are the disadvantages of external emulsions?
- stability problems
- difficult to apply
- must shake the bottle
- bath additives can cause slips
- paraffin can be flammable
- preservatives can irritate the skin
What are collodions?
They form a waterproof film on the skin e.g. bazuka
What are the excipients needed in collodions?
solvents, proxylin, camphor (waterproof excipient), plasticiser (makes the film flexible)
