Green: Emulsions

Question 1

What is phenylepherine used for?

Answer 1

Decongestant

Question 2

What is Dextromethorphan used for?

Answer 2

Cough suppressant

Question 3

What are emulsions and creams?

Answer 3

Dispersion of one liquid into another

Question 4

What are the other characteristics emulsions have?

Answer 4

1. Coalescence: given time the liquid is separated into two phases
2. Surfactants and micelles are in both phases
3. Surfactants form complex liquid crystalline micelles

Question 5

What are the different types of emulsions that are available?

Answer 5

1. Oil in water: Generally more comfortable and used cosmetically as they are easy to wash off with water from skin (most common)
2. Water in oil:
   - Are more hydrophobic so tend to release the drug more readily from the emulsion.
   - More moisturising as they can provide an oily barrier to prevent water loss
3. Oil in water in oil

Question 6

What is the purpose of having different emulsions?

Answer 6

1. Renders oily substances like liquid paraffin more plate able
2. Delivery of water insoluble drugs
3. Topical administration
4. Delayed and modified release

Question 7

Define what flocculation and coalescence is?

Answer 7

1. Flocculation: fine particulates caused to clump together into a floc.
2. Coalescence: two or more droplets, bubbles or particles merge during contact to form a single particle

Question 8

What is creaming?

Answer 8

When the floc floats to the top of the liquid

Question 9

Why do you want to avoid creaming?

Answer 9

1. Reduced droplet size and density difference
2. Increased viscosity
3. Disperse phase concentration
4. Prevents flocculation and coalescence

Question 10

What does a normal surfactant do and what are the advantages of each type of surfactant do?

Answer 10

1. Surfactant: aids dispersal and reduces tendency for coalescence
2. Charged surfactants:
   - Increase surface charge
   - Repulsive interactions between droplets
3. Non ionic surfactants:
   - Solvated layer for steric repulsion
   - Lack of toxicity
   - Lower sensitivity to additives
4. Mixed surfactants are better

Question 11

What does the hydrophile-lipophile balance (HLB) number represent and what is it for?

Answer 11

1. Whether the surfactant is hydrophobic or hydrophilic
2. This is determined by by knowledge of polar and non polar functional groups in surfactant
3. Determines the appropriate emulsifier

Question 12

How do you form the perfect oil in water emulsion?

Answer 12

1. Surfactant needs to confer stability (hydrophilicity)
2. Ensure adsorption (hydrophobicity)
3. Optimal hydrophile-lipophile balance is determined by minimal creaming

Question 13

What do the use of mixed surfactants consist of and

Answer 13

1. Mixture of high and low HLB gives a more stable surfactant
2. Keep surfactant concentration as low as possible
3. Pick surfactant concentrations where molecular interaction is likely

Question 14

For each specific emulsion, what can they be used for? (which route)

Answer 14

1. Oil in water: oral, intravenously and topically

2. water in oil is more greasy but more hydrating for the skin

Question 15

Give examples of different uses of emulsions

Answer 15

1. Vehicles
2. Surfactants
3. Preservatives: partition in oil phase when needed in aqueous phase
4. Flavouring
5. Viscosity and density modifiers
6. Antioxidants
7. Humectants: Retain moisture on the skin

Question 16

What are the two tests necessary for different emulsion types?

Answer 16

1. Miscibility test:
   emulsion only miscible (mixes) with liquids that are miscible in the emulsion phase
2. Conductivity:
   Aqueous continuous phase (causes light to glow) that readily conducts electricity
3. Staining test:
   - Use of water or oil soluble dyes

Question 17

Explain how surfactants are used as emulsifying agents?

Answer 17

1. Adsorbs (adhesion) at interface between immiscible liquids (barrier to coalescence)
2. Use of a mix of oil and water soluble surfactants
3. Non ionic, less toxic and less sensitive to electrolytes
4. Increases surface area and decreases surface tension

Question 18

Explain how Hydrophilic colloids are used as emulsifying agents?

Answer 18

1. Proteins (gelatin) and Polysaccharides (acacia)
2. Viscoelastic layer is formed which is many multilayers of interacting polymers
3. This provides mechanical robust to prevent coalescence

Question 19

Explain how finely divided solids are used as emulsifying agents?

Answer 19

1. Adhere to interface

2. Needs to be wetted to one phase

Question 20

Describe how the viscosity affects the control of which rheological properties?

Answer 20

1. Dispersed phase concentration: increased viscosity
2. Radius of dispersed phase: small size increases viscosity
3. Viscosity of continuous phase
4. Surfactant emulsifier

Question 21

How do you measure the rate of creaming or coalescence?

Answer 21

1. Rate of volume: creamed and total volume
2. Change in size of globules
3. Viscosity changes

Question 22

What are the different uses of emulsions?

Answer 22

1. Oral, rectal and topical administration of oil soluble drugs
2. Sustained release of dosage form
   - Intramuscular injections of water soluble vaccinations: slower release of antigens and greater immune response
3. w/o/w
   - Prolonged release and lower viscosity than w/o subcutaneous or intramuscular