Emulsiona and Suspensions

Question 1

Define an emulsion

Answer 1

Mixture of 2 immiscible liquids. Contains tiny particles of 1 liquid suspended in another - colloids where both phases are liquids

Question 2

Two main types of emulsion

Answer 2

Water in oil = dispersed phase is water, continuous phase oil
Oil in water = dispersed phase oil, continuous phase water

or get o/w/o

Question 3

What are emulsions mainly used for

Answer 3

Topical e.g creams, rectal, oral
Delivery of water insoluble drugs
Can administer oils and fats via IV
Delay or modify release

Question 4

Why is o/w/o not commonly used?

Answer 4

Unstable- will break down to o/w

Question 5

What is the most common type of emulsion

Answer 5

o/w - it is the most comfortable, acceptable, less greasy and easily washed off

Question 6

What happens to emulsions due to instability?

Answer 6

Creaming e.g migration of dispersed phase of emulsion due to buoyancy.
Particles flocculate float upwards or sink depending ontheir size/density and viscosity of continuous phase
- Droplets could coalese - join together to form large globules e.g fat

Question 7

How to avoid creaming?

Answer 7

1. reduce droplet size as smaller flocculate slower
2. Reduce density difference - effects lowered
3. Reduce the [dispersed phase]
4. Increase viscosity of continuous phase so they cant move and merge
5. additives to reduce creaming

Question 8

What can be added to the mixture to control stability? What do these do?

Answer 8

surfactants - aid dispersal and reduce tendency coalesence

Question 9

What do charged & non-ionic surfactants do?

Answer 9

Charged increase the surface charge so increase repulsive interactions between droplets.
Whereas the non ionic create a solvated later to produce steric repulsion

Question 10

Is it better to have 1 surfactant i.e charged/uncharged or a mixture of both?

Answer 10

Mixture of 2 or more different surfactants is better

Question 11

Why are non ionic surfactants more commonly used to stabilise emulsions?

Answer 11

Less toxic & not affected by electrolyte conc- use in very small amounts

Question 12

What is the HLB number?

Answer 12

Used to determine the ratio of surfactants that will best stabilise the system - depending on the length of the chains will have a HLB between 1-20

Question 13

Name some common non ionic surfactants - oral

Answer 13

Span 20 - 8.6 HLB
Tween 20 - 16.7 HLB
Poloxamers - 1-20

Question 14

What surfactant could be used for external applications?

Answer 14

Anionic sodium lauryl sulphate

Question 15

Disadvantages to the use of non ionic surfactants in emulsions

Answer 15

Excessive foaming

Deflocculation possible

Question 16

What are the pre requisities for a good surfactant in o/w emulsion?

Answer 16

must have stability (hydrophilicity), and ensure adsorption (hydrophobicity).

Question 17

How is optimal HLB determined in o/w? and name optimal HLB for oils

Answer 17

Optimal HLB is determined by the system with minimal creaming. 
Optimal HLB: 
- cotton seed oil 7.5 
- vaseline oil 8.5
- Mineral oil 10-12
- Cyclohexane 12

Question 18

What do you need to ensure when selecting an appt surfactant?

Answer 18

Need to identify the nature of the surfactant such that they interact well i.e ionic surfactants - ensure that we select ions that are not in the emulsion so as to NOT introduce the same ons - which would cause repulsion - done via trial and error

Question 19

Name 3 tests to identify emulsion type i.e o/w or w/o?

Answer 19

1. Miscibility test - adding liquid to an emulsion - phase that increases is the miscible continuous phase
2. Conductivity - water is a conductor but fat is not
3. Staining - use water soluble dyes - the fat part of the system will get coloured see whether fat is dispersed or vehicle.

Question 20

Name 3 types of emulsifying agents

Answer 20

1. Surfactants - non ionic, Adsorb to the surface between 2 phases and act as a barrier - use 2 different ones to stabilise
2. Hydrophilic colloids - proteins form a network around droplets
3. Finely divided solids - not common but powders sit and adhere to surface

Question 21

Define a suspension

Answer 21

Heterogenous mixture - solid suspended ina . liquid. Particles are dispersed but not fully dissolved, mixed by agitation

Question 22

Advantages of suspensions

Answer 22

Formulate suspensions from tablets for people who cannot swallow

• Taste better
• Good for insoluble drugs
• Control drug delivery rate
• Certain drugs can only work as suspensions e.g detoxifying agents

Question 23

Disadvantages of suspensions

Answer 23

• bulky
• thermodynamically unstable - form cakes over time
• Not aesthetically pleasing

Question 24

What are the 3 desired features of suspensions?

Answer 24

1. Must settle slowly and easily redisperse on gentle shaking
2. Particles sizes must all be the constant in the dispersion
3. Suspension should pour readily and evenly

Question 25

What does electrolyte excipient do in suspensions?

Answer 25

Control flocculation

Question 26

What do surfactant excipients do in suspensions?

Answer 26

Wetting agents & flocculating agents - controlled flocculation

Question 27

What do hydrophilic polymers do in suspensions

Answer 27

1. Enhance physical stability - wetting/flocculating | 2. Enhance rheological stability - viscosity agent

Question 28

What antioxidants are used in suspensions?

Answer 28

Sodium phosphate, chelating agents e.g citric acid

Question 29

What property of suspensions make it preferred option for controlling drug rate of release?

Answer 29

Slower dissolution than solutions

Question 30

What is a disadvantage of suspending a tablet into a suspension?

Answer 30

Lack of knowledge regarding the stability of the drug in liquid form (despite having dispersion, non toxic, uniformly incorporated into formulation)

Question 31

What is polysorbate 80?

Answer 31

Surfactant