D8 and D9- Medicine design and manufacturing (emulsions, creams and ointments) Flashcards
what is an emulsion?
A liquid medicine in which one insoluble liquid is
dispersed as microscopic globules in another
liquid (the two liquids are ‘immiscible’)
what is the external or continuous phase in an emulsion?
liquid vehicle
what is the internal or dispersed phase in an emulsion?
droplets- there is Molecular film of emulsifying
agent(s) at the oil/water interface
what are the different types of emulsion?
-o/w ‘Oil in Water’: Milky white
-w/o ‘Water in Oil’: Translucent
-w/o/w and o/w/o multiple emulsions: Droplets within
the droplets
pictures on one note!
what types of oils are used in emulsions?
natural oils, mineral oils, volatile oils
Describe natural oils
Triglycerides- e.g Vegetable oils (sunflower, olive, sesame)
Fish oil (cod liver oil)
Describe mineral oils
Hydrocarbons
(petroleum industry)- e.g Liquid paraffin
Describe volatile oils
Complex mixtures- e.g Plant oils- used as flavour and aromas (peppermint,
lemon)
what is the issue with emulsions?
-stability
-two liquids separate- emulsions are physically unstable. creaming and cracking occur (one note for diagram)
what is creaming?
Droplets coalesce
Oil collect near surface
what is cracking?
complete phase separation
how to prevent creaming and cracking through droplet size?
-Small droplets = more stable.
-Industry uses high shear mixers for small droplets
-Shelf-life: up to 2 years
Impossible with hand-made emulsions!
-Shelf-life: very short!
how to prevent cracking and creaming through temperature?
-High risk if exposed to heat or temperature
fluctuations
→ Label: ‘Store in a cool place’
Freezing/thawing causes rapid separation (crystals)
→ Label: ‘Do not freeze’
which kind of emulsion is more stable
o/w more stable than w/o (immediate cracking with w/o)
are creams or liquid emulsions more stable?
creams
what are Emulsifiers
(surfactants)?
‘surface active’ long molecules that locate at
the oil-water interface
what are emulsifiers? (structure?)
-amphiphiles
-a hydrophilic head and hydrophobic tail
-position themselves at interfaces (diagram on one note)
what are the types of emulsifiers
anionic, cationic, non- ionic
(charged can react with other charged species and be inactivated) (non- ionic more compatible with charged)
one note for diagram
what other stability issues are with o/w emulsions? (sensitivity)
- The internal phase has a huge surface area
→ very sensitive to hydrolysis and fat oxidation (ester bonds hydrolyse and unsaturated bonds oxidise)
→ oil soluble antioxidant often needed
-this leads to ‘rancidity’ (bad smell, change in appearance/ taste)
look one one note
what other issues are with o/w emulsions? (water)
- The continuous phase is water
→ microorganisms grow well in continuous phase
(feed on the oil droplets!)
→ a preservative must be added BUT can destabilise the emulsifier film
can partition into the oil – will be ineffective
How unstable are emulsions?
physically, chemically and microbiologically unstable
what are the uses of emulsions?
oral route and topical route
Describe the oral route of emulsions
administer oils or oil soluble drugs by mouth
* More palatable
* Easier to administer (ex: feeding through nasogastric tube)
* More digestible due to large surface area of droplets
Describe the topical route of emulsions
skin infections, inflammation,
allergy, etc…
-Lotions (runny): good to treat hairy or large areas
-Creams (semi-solid): less messy!
what is a cream?
-An emulsion to be applied on the skin in which one of the two phases is a semi-solid or a wax (o/w or w/o)
-may contain ingredients that are soluble either in oily or aqueous phase and insoluble powders
what are the uses for o/w creams?
-Wounds, bites, acute
inflammation, etc…
-Can mix with wound
exudates
-Feels cool and dry the
wound/skin (due to water evaporation)
-Not greasy or sticky
-Easy to rub onto the skin
-Well accepted by patients
what are the uses of w/o creams?
-‘oily’, so occlusive
-Hydrate the skin (‘moisturising’)
ex: Cold Cream BP
-Protect against water
(nappy rash, sunscreen)
ex: Zinc Cream BP
-not common as very unstable
why do we use mixed emulsifiers? (charged and non- ionic)
-when using only charged amphiphiles, positive charges repel the interphase droplets and negative charges repel each other at interface creating a sparse interfacial film
-mixed emulsifiers (charges and non- ionic) creates a dense interfacial film for better stability
what is an ointment?
-Spreadable greasy semi -solids that might contain dispersed powders and small amounts of aqueous
liquids
-base is a mixture of waxes, fats, oils
-hydrophobic
-paste is an ointment with high powder content
what are the stability issues with ointments?
-base is ONE greasy phase (can’t separate)
-do not contain water (microbial growth is limited, hydrolysis is unlikely)
-can be sensitive to fat oxidation and light
what are common ingredients in ointment bases?
-glycerides (mono, di or tri)
-hydrocarbons (paraffins)
-lanolin
Describe hydrocarbons (paraffins)
-no reactive groups
-chemically very stable
-flammable
Describe Lanolin
-yellow wax obtained from sheep wool
-can cause allergic reaction
What are the advantages of using ointments
-Occlusive
→ Make skin more supple
(‘emollients’)
→ Suitable for dry skin
conditions (ex: eczema)
-Can be used in a bath
(must contain emulsifiers)
ex: Emulsifying Ointment BP
-No preservatives needed
→ Suitable for patients with
allergy
Disadvantages of ointments?
-Very greasy
→ Stain clothes, difficult to
rub onto or remove from
the skin
-Not very popular with
patients!
-Not suitable for wounds (increases temp and water content of skin, increasing risk of infection)
what are the two main steps to prepare an ointment?
-Step 1: make the base by fusion
-Step 2: disperse the powders manually by
trituration
How can you do trituration?
-On a tile – small amount of powder
-In a mortar – large amount of powder
How do you prepare the base?
-By fusion, i.e., melting and mixing over a steam
bath
-base ingredients are added in order of decreasing melting point
(one note for diagram)
How to disperse powders into base by trituration on a tile?
- (Warm the tile)
- Mix the powders on the tile
- Add a portion of base similar
to volume of powders - Using an ointment spatula,
disperse the powders into the
base by side to side smearing - Keep adding the base
(one note for diagram)
How to pack ointments and creams elegantly in a jar?
-flat surface
-clean rim
-shiny and clean jar
-add labels
How to assess the quality of your ointment?
-Any lumps?
-Are the powders evenly mixed?
-Is it gritty? (use greaseproof paper)
-Is it elegantly packed in the jar?
-Is the jar shiny and not greasy?
How to prepare o/w cream?
-dissolve water soluble ingredients in aqueous phase
-dissolve oil soluble ingredients in the melted oily phase
-warm both to the same temp (melting point of oily phase)
-mix while stirring (with glass rod until cold)
how to make o/w creams to the final weight?
-issue is that water evaporates during warming
→ Lukewarm water must be added up to the final weight at the end (weigh evaporating dish before starting!)
How to assess the quality of your o/w cream?
-Any sign of separation?
-Any lumps?
-Is it shiny (means the droplets of dispersed
phase are small)
-Is it elegantly packed in the tube ?
