emulsions cream and ointements Flashcards
what’s an emulsion
a liquid medicines where one insoluble liquid is dispersed as microscopic globules in another liquid
continuous phase in emulsions
is the liquid vehicle
dispersed phase
is the droplets
types of emulsions
-oil in. water: milky white
-water in oil : translucent
-multiple emulsions: this droplets in droplets
types of oils that can be used in emulsions
-natural oils: triglycerides (veg or fish oils)n
-mineral oils: hydrocarbons, liquid parafins
-volatlie oils: complexs mixtures eg. plant oils
issues with emulsions
-physical stability
- the two liquids want to separate and this can lead to creaming (oil collects near the surprise) or cracking which is phase seperation
how to prevent creaming and cracking
- control droplet size: small drops are usually more stable the industry makes small drops using shear mixers (up to two years shelf life) can’t do this with hand made emulsions hence why shelf life is very short
-tempreture: cool place is the best, fluctuation increases separations
-oil in water is more stable than water in oil
-use emulsifiers (surfactants): long molecules that are on the oil water interface
emulsifiers structure
they at amphiphiles which mean they have a hydrophilic head and hydrophobic tail
three types of emulsifiers
- anionic
-cationic
widely used but when they react with a charged species they become in active
-non ionic ( more compatible with charges ingredients)
why is using mixed emulsifiers better
- single charged is good as they repel internal phase droplets however they repel each other on the surface so there is sparse coverage
-mixed emulsifiers means charged and non ionic means a dense interfacial film
why we need antioxidants
-the internal phase has large surface are and is very sensitive to hydrolysis and fat oxidation so and oil soluble antioxidant is required
why we need preservative
microorganisms grow well in water and feed on the oil droplets, preservatives can be added but then they can destabilise emulsifier film and partition into in to the oil
different instabilities of emulsions
-physicially
-chemically
-microbiologically unstable
uses of emulsions oral routes
-oral route: used to administer oils or oil soluble drugs, this is good because its : more palatable, easier to administer eg through feeding tubes and its more digestible to large surface area of droplets
topical route of emulsions
used for skin infections, inflammations, allergy
-lotions (large areas)
-creams (less messy)
whats a cream
an emulsions where one of the two phases is semi solid or wax
can contain insoluble powders and ingredients that are only soluble in the oil and aqueous phase
o/w creams uses
- Wounds*,bites,acute inflammation, etc…
- Can mix with wound exudates
- Feels cool and dry the wound/skin
- Not greasy or sticky
- Easy to rub on to the skin
- Well accepted by patients
w/o cream uses
‘oily’, so seals off areas
* Hydrate the skin
(‘moisturising’)
ex: Cold Cream BP
* Protect against water (nappy rash, sunscreen)
ex: Zinc Cream BP
super unstable tho
what is ointments
Spreadable greasy semi-solids that might contain dispersed powders and small amounts of aqueous liquids
The base is a uniform mixture of waxes, fats and oils
→ hydrophobic, so water repellent
paste
An ointment with a high powder content is called a paste
Stability issues with ointment bases
Notmany!
* 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
Common ingredients in ointment bases
-glycerides
-Lanolin: yellow wax obtained from sheep wool ( can cause allergic reactions)
-hydrocarbons: no reactive groups meaning they are very chemically stable
advantages of using ointments
-occlusive (seals off areas)
-makes skin more supple
-suitable for dry skin conditions
-can be used in bath
-no preservatives needed so its suitable for patients with allergy
disadvantages of ointments
-very greasy
-stain
-difficult to rub or remove of skins
-not suitable for wounds
