D8-D9 Emulsions, creams and ointments Flashcards
what is an emulsion?
- a liquid medicine in which an immiscible liquid is dispersed as microscopic globules in another liquid (the 2 liquids are immiscible)
- the boundary between the 2 liquids are the emulsifying agents at the oil/water interface
what are the external and internal phases in an emulsion?
- external / continuous phase: the vehicle
- internal / dispersed phase: the droplets
what are the different types of emulsions?
o/w
w/o
w/o/w
o/w/o
describe o/w emulsions
oil in water
milky white
most common
describe w/o emulsions
water in oil
translucent, like diluted oil
describe w/o/w and o/w/o emulsions
- multiple emulsions
- droplets within the droplets
- least common
what are the 3 types of oils used in emulsions?
- natural oils
- mineral oils
- volatile oils
describe natural oils that can be used in emulsions
- triglycerides (3 fatty acids and glycerol)
- eg. vegetable oils, fish oil
describe mineral oils that can be used in emulsions
- hydrocarbons (petroleum industry)
- more used for external use emulsions
- eg. liquid paraffin
describe volatile oils that can be used in emulsions
- complex mixtures
- better smells, masks tastes unlike worse-smelling ones (natural and mineral oils)
- eg. plant oils
describe some issues surrounding emulsions
- instable
- the 2 liquids want to separate
- creaming will occur until it becomes cracked
state a feature of a good quality emulsion
- will look uniform and homogenous
- oil droplets evenly distributed throughout the water phase
what will happen to an emulsion if you leave it for a while?
- creaming will start to occur
describe creaming of emulsions
- oil droplets fuse together to form bigger droplets and collect near the surface of the emulsion
- usually creaming is reversible (droplets can be broken back into smaller ones and redispersed)
what is cracking?
- when creaming of an emulsion becomes irreversible
- oil and water have completely separated and the oil can’t be redispersed
state 4 factors that can be controlled to prevent creaming and cracking
- droplet size
- temperature
- type
- emulsifiers (surfactants)
explain how droplet size can prevent creaming and cracking in emulsions
- small droplets = more stable
- less likely to fuse together if smaller
how does the pharmaceutical industry make a small droplet size in emulsions?
- using high shear mixers
- impossible in hand-made emulsions
explain how temperature can prevent creaming and cracking in emulsions
- high risk of creaming / cracking if exposed to heat or temperature fluctuations
- higher temp increases kinetic energy of droplets and likelihood of them fusing
- freezing / thawing causes rapid separation (crystals will form which can destabilise the oil / water interface, causing instant cracking)
what 2 labels regarding storage conditions should be on emulsion products?
- do not freeze
- store in a cool place
explain how the type of emulsion can prevent creaming and cracking
- o/w is more stable than w/o
- w/o cracks straight away (no creaming phase)
- o/w has creaming phase so can be shaken and reversed
- creams are more stable than liquid emulsions as the droplets can’t move as fast
explain how emulsifiers can prevent creaming and cracking in emulsions
- ‘surface active’ long molecules at the oil / water interface
- forms a molecular film which stabilises emulsions
what are emulsifiers? how do they position themselves?
- amphiphiles (they have a hydrophilic head and a hydrophobic tail)
- position themselves at oil / water interfaces or between water and air
- hydrophilic head goes towards water and hydrophobic tail goes towards oil / air
what are the 3 types of emulsifiers?
- anionic
- cationic
- non-ionic
describe anionic emulsifiers, give an example
- widely used but can react with oppositely charged species and be inactivated
eg. sodium dodecyl sulphate (SDS)
- sulphate is the head
- carbon chain is the tail
describe cationic emulsifiers, give an example
- widely used but can react with oppositely charged species and be inactivated
eg. Cetrimide
- carbon chain is the tail
describe non-ionic emulsifiers, give an example
- more compatible with charged ingredients
eg. cetostearyl alcohol
- OH is the head
- carbon chain is the tail
what is the hydrophobic tail of most emulsifiers?
carbon chain
what is good and bad about using a single, charged emulsifier?
- good because it repels the other internal phase droplets (all have negatively charged surfaces so can’t fuse easily)
- bad because the emulsifiers repel each other at the oil / water interface (causes sparse interfacial film)
explain the use of mixed emulsifiers, give an example
- mix of charged and non-ionic emulsifiers
- dense interfacial film
- better for stabilising emulsions
eg. Emulsifying Wax BP
- sodium dodecyl sulphate (anionic)
- cetostearyl alcohol (non-ionic)
- instant stable emulsions and creams
state some stability issues with o/w emulsions
- internal phase has huge surface area between all oil droplets and water phase
- continuous phase is water
explain the issue of a large surface area in emulsions between the oil droplets and the water phase. what is often needed to prevent this issue?
- very sensitive to chemical degradation by hydrolysis and fat oxidation (ester bond is sensitive to water, double bond is sensitive to oxidation)
- oil soluble antioxidant often needed
what can oxidation of double bonds and hydrolysis of ester bonds in emulsions lead to?
- rancidity
- bad smell
- change in appearance / taste
explain the issue of the continuous phase being water in emulsions
- microorganisms grow well in continuous phase (feed on oil droplets which speeds up growth)
what must be added to an emulsion to prevent microorganism growth in water (the continuous phase)? what issues come with this?
- preservative must be added
- can destabilise the emulsifier film
- can partition into the oil (makes it ineffective)
- should not be charged (may destabilise emulsifier film)
- uncharged are usually more hydrophobic (soluble in oil), don’t want preservative to migrate into oil, must stay in water (would be ineffective in oil)
what routes of administration are there for emulsions?
- oral
- topical
- injections
describe the oral route of administration for emulsions
- administer oils or oil soluble drugs by mouth
- more palatable
- easier to administer and swallow (eg. feeding through nasogastric tube - pure oils block the tube)
- more digestible due to large surface area of droplets
describe the topical route of administration for emulsions
- used for skin infections, inflammation, contact allergy, insect bites etc.
- lotions (runny) are good to treat large / hairy areas and spread very well
- creams (semi-solid) are less messy to use
what is a cream?
- a thick emulsion to be applied on the skin in which one of the 2 phases is a semi-solid or a wax
- can be w/o or o/w (o/w is more common)
- may contain ingredients that are soluble either in the oily or aqueous phase or insoluble powders
what can creams be packed into? how does packaging affect stability and shelf life?
- jar or tube
- easier to pack into jar
- creams in jars are more susceptible to water, microorganisms, contamination, air etc.
- creams in jars are less stable than creams in tubes (tubes protect against the environment, therefore longer shelf life)
state some uses of o/w creams
- wounds, bites, inflammation etc.
- water can mix with wound fluids
- feels cool and dries the wound (helps with healing)
- not greasy or sticky
- smooth and easy to rub in
where can glucocorticoid creams not be used?
- wounds or broken skin
- if the drug is absorbed into the blood they can have serious adverse effects
describe w/o creams
- ‘oily’ so occlusive (forms hydrophobic oil layer to stop water evaporation from skin)
- hydrates the skin (moisturising)
- protects against water (nappy rash, suncream)
- not as common
why are w/o creams not as common as o/w creams?
- very unstable
- crack within a very short amount of time
what is an ointment?
- spreadable, greasy semi-solids that might contain dispersed powders and small amounts of aqueous liquids
- not an emulsion
what is the base of an ointment?
- a uniform mixture of waxes, fats and oils (hydrophobic, water repellent)
- drugs are added to the base as drug powders or a small amount of liquid
what is an ointment with a high powder content called?
- a paste
- these aren’t as common
- they’re very stiff and difficult to work on the surface of the skin
what kinds of ointments must be sterile?
- eye ointments
- skin ointments don’t have to be sterile
explain why there aren’t many stability issues with ointment bases
- base is ONE greasy phase (it can’t separate, could be frozen and still won’t separate)
- don’t contain water (microbial growth is limited, hydrolysis is unlikely)
what stability issues can ointment bases face (despite them being relatively stable)
- can be sensitive to fat oxidation and light
- this depends on the composition of the greasy material
- may need protection against light and air
state 3 common ingredients in ointment bases
- glycerides
- hydrocarbons
- lanolin
what types of glycerides can be ingredients in ointment bases?
mono, di or tri
describe the hydrocarbons that may be used in ointment bases
- ‘paraffins’
- eg. liquid paraffins, white soft paraffin, hard paraffin
- no reactive groups
- chemically very stable
- flammable!
describe lanolin that may be used as an ingredient in ointment bases
- yellow wax obtained from sheep wool (wool fat)
- can cause allergic reaction (contact allergy on skin or in eyes, must ask patients if they are allergic to lanolin to their knowledge)
- cheap
state advantages of ointments
- occlusive (moisturising)
- make skin more supple (emollients)
- suitable for dry skin conditions eg. eczema
- can be used in a bath
- no preservatives needed
- suitable for patients with allergy
what must ointments contain if they are to be used in a bath and why?
must contain emulsifiers to form emulsion between ointment and water
state disadvantages of ointments
- very greasy
- not suitable for wounds
what can happen due to ointments being very greasy?
- stain clothes
- difficult to rub onto or remove from the skin
- not very popular with patients
why are ointments not suitable for wounds?
- increase water content in wound
- increase temperature at the surface of skin
- these 2 things combined increase risk of microbial growth and infection
what are the 2 steps involved in preparing an ointment?
- make the base by fusion
- disperse the powders manually by trituration
what are the 2 methods for dispersing powders into an ointment by trituration? when would each method be used?
- on a tile (small amount of powder, traditional ointment)
- in a mortar (large amount of powder, main method for pastes)
how do you prepare an ointment base by fusion?
- melt and mix over a steam bath
- base ingredients are added in order of decreasing melting point
describe the process of dispersing powders into an ointment base by trituration on a tile
- warm the tile (a cold tile will stiffen the base and make mixing in the powders harder)
- mix the powders on the tile
- add a portion of the base similar to volume of the powders
- using an ointment spatula, disperse the powders into the base by smearing side to side
- keep adding the base until all added
why do you mix ointment powders on the tile before trituration rather than in a pestle and mortar?
you would lose powders in a pestle and mortar as you would have to transfer it to the tile and some would be left behind
describe the process for packing an ointment into an ointment jar
- place the jar on a balance
- add the quantity to be dispensed into the jar
describe the process of packing an ointment into a metal tube
- weigh required amount of ointment onto greaseproof paper and roll it up quite tightly
- insert rolled up paper and ointment into tube
- use large ointment spatula to flatten the end of the tube
- pull out the paper
- seal the tube by folding the end of the tube over the ointment spatula twice
how should the label be placed on a metal tube of ointment?
- along the tube
- not around it
what should be considered when assessing the quality of an ointment?
- any lumps?
- are the powders mixed evenly?
- is it gritty?
- is it elegantly packed in the jar? is the jar shiny and not greasy?
what should be done to ensure elegant packing of ointments / creams in a jar?
- tap jar on flat surface or use spatula to smooth top
- clean rim with blue roll
- clean jar with soapy water to make shiny
- add labels after cleaning the jar to make sure they stick
describe the process of preparing an o/w cream
- dissolve water-soluble ingredients in aqueous phase and dissolve oil-soluble ingredients in the melted oily phase
- warm both of these to the same temperature (the melting point of the oily phase)
- mix while stirring (slowly add water phase whilst stirring oily phase
- stir with glass rod until cold
how should o/w creams be made up to their final weight and why is this necessary?
- water evaporates during warming process of preparation
- this means there is less water in the final cream so the cream is too concentrated
- lukewarm water must be added up to the final weight at the end
what should be considered when assessing the quality of an o/w cream?
- any sign of separation?
- any lumps?
- is it shiny?
- is it elegantly packed in the tube?
signs of a cream packed elegantly into a tube
- not greasy
- well-sealed
- not squashed
what does it mean if an o/w cream is shiny?
- the droplets of the dispersed phase are small
- this is good
