Emulsions Theory and Practice Flashcards
(47 cards)
1
Q
What are pharmaceutical emulsions (5)
A
- 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
2
Q
How are thermodynamically unstable pharmaceutical emulsions stabilised
A
Stabilised by the addition of an emulsifying agent
3
Q
What are examples of liquid emulsions (4)
A
- Oral emulsions (eg Arachis Oil)
- Lotions (eg Oily Calamine Lotion)
- Applications
- Liniments
4
Q
What are examples of semi-solid emulsions
A
Creams
5
Q
What effects do creams have without emulsions (2)
A
- Occlusive effect
- Skin-cleansing effect - helps remove oil-soluble dirt
6
Q
What is the occlusive effect (2)
A
- Hydrate upper skin layers
- Inhibit moisture evaporation
7
Q
What are the applications of pharmaceutical emulsions (5)
A
- 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
8
Q
What are the types of emulsions (3)
A
- Oil in Water (O/W)
- Water in Oil (W/O)
- Water in Oil in Water (W/O/W)
9
Q
What are the emulsion tests to test whether the emulsion is O/W or W/O (2)
A
- Miscibility tests
- Staining test (identify whether the emulsion is oil-in-water (O/W) or water-in-oil (W/O))
10
Q
What are miscibility tests (2)
A
- The emulsion will mix with a liquid that is miscible with the continuous phase
- For example: An O/W prep will mix with water
11
Q
What is the miscibility test (4)
A
- 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.
12
Q
What is the process of staining tests (5)
A
- 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)
13
Q
If the staining cobalt chloride test result is blue what does this mean
A
emulsion is oil in water type
14
Q
If the staining cobalt chloride test result is blue, what does this mean
A
emulsion is water in oil type
15
Q
What may be the result of a conductivity measurements test of emulsions (2)
A
- Aqueous continuous phase: Emulsion will conduct electricity
- Oily continuous phase: Emulsion will not conduct electricity
16
Q
What is the emulsion dye test (2)
A
- Water & oil-soluble dyes are used here
- The dyes will dissolve in and colour the continuous phase
17
Q
What are the characteristics of the ideal emulsion (4)
A
- 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
18
Q
What is creaming in relation to emulsions (3)
A
- Similar idea to cream forming on the surface of milk
- A layer of ‘relatively concentrated emulsion’
- Preparation can be recovered by shaking
19
Q
Why is emulsion creaming undesirable (4)
A
- Poor product presentation
- Risk of inaccurate dosing
- Globule closeness favours interface breakdown
- This can lead to globule coalescence & cracking
20
Q
What is emulsion cracking (4)
A
- 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
21
Q
What are the causes of emulsion cracking (4)
A
- Chemical Effects
- Physical Effects
- Biological Effects
- Results in changes to the interfacial film
22
Q
What is emulsion phase inversion (2)
A
- Emulsions shift from one form to another
- e.g. oil in water (O/W) to water in oil (W/O)
23
Q
What is emulsion phase inversion caused by (3)
A
- 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
24
Q
What do emulsifying agents do (2)
A
- Decrease the likelihood/degree of coalescence
- Can dictate the type of emulsion formed
25
What are the types of emulsifying agents (3)
1. monomolecular films
2. multimolecular films
3. solid particle films
26
What are examples of monomolecular films (3)
1. Lecithin laurate
2. cholesterol laurate
3. potassium laurate
27
What are examples of multimolecular films (2)
1. Acacia
2. gelatin
28
What are examples of solid particle films (2)
1. Magnesium hydroxide
2. aluminium hydroxide
29
What are the types of emulsifier chemical properties (3)
1. Synthetic
2. Natural
3. Finely divided solids
30
What are synthetic emulsifying agents (4)
1. Anionic
2. cationic
3. sulfonates
4. non-ionics
31
What are natural emulsifying agents (2)
1. Plant & animal sources
2. i.e. Acacia & gelatin
32
What are finely divided emulsifying agents (2)
1. Solid particle films → coarse-grained products
2. e.g. Bentonite & Veegum
33
What are the characteristics of the ideal emulsifying agent (6)
1. Colourless
2. Odourless
3. Tasteless
4. Non-toxic
5. Non-irritant
6. Produces a stable emulsion at low concentration
34
What is the HLB scale (6)
1. Conceived by Griffin in 1949
2. Reflects the polarity of the emulsifying agent
3. A high number indicates hydrophilic/lipophobic character = O/W emulsion
4. A low number indicates hydrophobic/lipophilic character = W/O emulsion
5. Numerical scale: 1 – 50 (of relevance 1-20)
6. An effective emulsifier has a balance of both hydrophilicity and lipophilicity
35
How does microbial growth occur in emulsions
Microbial growth may occur due to water content
36
Why is microbial growth undesirable in emulsions (5)
1. Poor product appearance
2. Emulsion cracking
3. Health hazard
4. Unpleasant odours
5. Altered product consistency
37
How can microbial contamination be minimised (4)
1. Using high quality ingredients
2. Boiling water prior to use
3. Using equipment that can be cleaned easily
4. Choosing well-fitting vessel closures
38
What are examples of preservatives (3)
1. Chloroform (chloroform water DS)
2. Quaternary ammonium species (cetrimide)
3. Benzoic acid
39
What are the characteristics of the ideal emulsion preservatives (6)
1. Bactericidal
2. Rapud
3. Activity independent of emulsion ingredients
4. Resistant to microbial attack
5. Npn-toxic
6. Wide antibacterial spectrum
40
What are the practical points for preparing emulsions (5)
1. Ensure all surfaces are thoroughly clean & dry
2. Follow the correct order for material addition
3. Use sufficient force in the pestle and mortar
4. Produce a primary emulsion 1st (thick & stable)
5. Consider the potential for anaphylactic shock
41
What does the amount of emulsifying agent depend on (2)
1. Amount of oil to be emulsified
2. Type of oil to be emulsified
42
What is the ratio for an emulsion of fixed oil (2)
4:2:1
oil:aqueous: gum
43
What is the ratio for an emulsion of mineral oil (2)
3:2:1
oil:aqueous: gum
44
What is the ratio for an emulsion of volatile oil (2)
2:2:1
oil:aqueous: gum
45
How much of each ingredient would be required to produce 100ml of a 20% emulsion of a fixed oil?
1. fixed oil = 4:2:1 ratio (oil:aqueous: gum)
2. 100/4 = 20ml of oil
3. 20/2= 10mL of aqueous phase
4. 10/2 = 5g of gum
46
What is effective emulsion storage (5)
1. store at room temperature
2. do not freeze
3. use amber bottles
4. air-tight seal
5. child-resistant closure
47
What advice is given for emulsions (4)
1. shake well before use
2. store in a cool place
3. use before the expiry date
4. for external use only
