Emulsions Theory and Practice Flashcards
What are pharmaceutical emulsions (5)
- A system composed of two immiscible liquid phases
- Preparations contain one or more active ingredients
- Droplet diameter typically: 0.1μm - 100μm
- Disperse phase is distributed throughout a continuous phase
- The disperse phase will tend to coalesce (come together to form a mass/whole) to reduce surface area
How are thermodynamically unstable pharmaceutical emulsions stabilised
Stabilised by the addition of an emulsifying agent
What are examples of liquid emulsions (4)
- Oral emulsions (eg Arachis Oil)
- Lotions (eg Oily Calamine Lotion)
- Applications
- Liniments
What are examples of semi-solid emulsions
Creams
What effects do creams have without emulsions (2)
- Occlusive effect
- Skin-cleansing effect - helps remove oil-soluble dirt
What is the occlusive effect (2)
- Hydrate upper skin layers
- Inhibit moisture evaporation
What are the applications of pharmaceutical emulsions (5)
- Enhance absorption of lipid-based material at the intestinal wall
- Taste masking (i.e. CLO)
- TPN preparations (made up ofamino acid/dextrose solution and a lipid emulsion solution)
- IM (intramuscular) injections
- Delivery of oils and oil-soluble drugs
What are the types of emulsions (3)
- Oil in Water (O/W)
- Water in Oil (W/O)
- Water in Oil in Water (W/O/W)
What are the emulsion tests to test whether the emulsion is O/W or W/O (2)
- Miscibility tests
- Staining test (identify whether the emulsion is oil-in-water (O/W) or water-in-oil (W/O))
What are miscibility tests (2)
- The emulsion will mix with a liquid that is miscible with the continuous phase
- For example: An O/W prep will mix with water
What is the miscibility test (4)
- mixing the emulsion with a liquid that is miscible with its continuous phase
- allowing you to determine whether the emulsion is oil-in-water (o/w) or water-in-oil (w/o) by observing if the mixture remains homogeneous or separates
- if the emulsion mixes readily with water, it’s an o/w emulsion
- if it mixes with oil, it’s a w/o emulsion.
What is the process of staining tests (5)
- Filter paper
- Soak in cobal chloride solution
- Allow to dry
- Add a stable O/W (oil in water) emulsion
- Colour change from blue to pink (if the emulsion is of the oil-in-water type)
If the staining cobalt chloride test result is blue what does this mean
emulsion is oil in water type
If the staining cobalt chloride test result is blue, what does this mean
emulsion is water in oil type
What may be the result of a conductivity measurements test of emulsions (2)
- Aqueous continuous phase: Emulsion will conduct electricity
- Oily continuous phase: Emulsion will not conduct electricity
What is the emulsion dye test (2)
- Water & oil-soluble dyes are used here
- The dyes will dissolve in and colour the continuous phase
What are the characteristics of the ideal emulsion (4)
- Globules of the disperse phase should retain their character over time
- The disperse phase should remain evenly distributed throughout
- Emulsion to be formulated such that creaming/cracking is unlikely
- Minimal chance of dispersed phase coalescence
What is creaming in relation to emulsions (3)
- Similar idea to cream forming on the surface of milk
- A layer of ‘relatively concentrated emulsion’
- Preparation can be recovered by shaking
Why is emulsion creaming undesirable (4)
- Poor product presentation
- Risk of inaccurate dosing
- Globule closeness favours interface breakdown
- This can lead to globule coalescence & cracking
What is emulsion cracking (4)
- Coalescence of disperse phase globules turns into a disperse phase separation as alternate layer
- Redispersion is not possible on shaking
- Preparation viability is lost
- Produces a rancid smell
What are the causes of emulsion cracking (4)
- Chemical Effects
- Physical Effects
- Biological Effects
- Results in changes to the interfacial film
What is emulsion phase inversion (2)
- Emulsions shift from one form to another
- e.g. oil in water (O/W) to water in oil (W/O)
What is emulsion phase inversion caused by (3)
- Excessive amounts of disperse phase - (emulsions with 70% + disperse phase can invert)
- Any agent that can affect the HLB parameter
- The application of heat to the product
What do emulsifying agents do (2)
- Decrease the likelihood/degree of coalescence
- Can dictate the type of emulsion formed
What are the types of emulsifying agents (3)
- monomolecular films
- multimolecular films
- solid particle films
What are examples of monomolecular films (3)
- Lecithin laurate
- cholesterol laurate
- potassium laurate
What are examples of multimolecular films (2)
- Acacia
- gelatin
What are examples of solid particle films (2)
- Magnesium hydroxide
- aluminium hydroxide
What are the types of emulsifier chemical properties (3)
- Synthetic
- Natural
- Finely divided solids
What are synthetic emulsifying agents (4)
- Anionic
- cationic
- sulfonates
- non-ionics
What are natural emulsifying agents (2)
- Plant & animal sources
- i.e. Acacia & gelatin
What are finely divided emulsifying agents (2)
- Solid particle films → coarse-grained products
- e.g. Bentonite & Veegum
What are the characteristics of the ideal emulsifying agent (6)
- Colourless
- Odourless
- Tasteless
- Non-toxic
- Non-irritant
- Produces a stable emulsion at low concentration
What is the HLB scale (6)
- Conceived by Griffin in 1949
- Reflects the polarity of the emulsifying agent
- A high number indicates hydrophilic/lipophobic character = O/W emulsion
- A low number indicates hydrophobic/lipophilic character = W/O emulsion
- Numerical scale: 1 – 50 (of relevance 1-20)
- An effective emulsifier has a balance of both hydrophilicity and lipophilicity
How does microbial growth occur in emulsions
Microbial growth may occur due to water content
Why is microbial growth undesirable in emulsions (5)
- Poor product appearance
- Emulsion cracking
- Health hazard
- Unpleasant odours
- Altered product consistency
How can microbial contamination be minimised (4)
- Using high quality ingredients
- Boiling water prior to use
- Using equipment that can be cleaned easily
- Choosing well-fitting vessel closures
What are examples of preservatives (3)
- Chloroform (chloroform water DS)
- Quaternary ammonium species (cetrimide)
- Benzoic acid
What are the characteristics of the ideal emulsion preservatives (6)
- Bactericidal
- Rapud
- Activity independent of emulsion ingredients
- Resistant to microbial attack
- Npn-toxic
- Wide antibacterial spectrum
What are the practical points for preparing emulsions (5)
- Ensure all surfaces are thoroughly clean & dry
- Follow the correct order for material addition
- Use sufficient force in the pestle and mortar
- Produce a primary emulsion 1st (thick & stable)
- Consider the potential for anaphylactic shock
What does the amount of emulsifying agent depend on (2)
- Amount of oil to be emulsified
- Type of oil to be emulsified
What is the ratio for an emulsion of fixed oil (2)
4:2:1
oil:aqueous: gum
What is the ratio for an emulsion of mineral oil (2)
3:2:1
oil:aqueous: gum
What is the ratio for an emulsion of volatile oil (2)
2:2:1
oil:aqueous: gum
How much of each ingredient would be required to produce 100ml of a 20% emulsion of a fixed oil?
- fixed oil = 4:2:1 ratio (oil:aqueous: gum)
- 100/4 = 20ml of oil
- 20/2= 10mL of aqueous phase
- 10/2 = 5g of gum
What is effective emulsion storage (5)
- store at room temperature
- do not freeze
- use amber bottles
- air-tight seal
- child-resistant closure
What advice is given for emulsions (4)
- shake well before use
- store in a cool place
- use before the expiry date
- for external use only
