Emulsions

Question 1

What are emulsions?

Answer 1

Two or more imiscible liquids mixed together. The dispersed phase being small globules throughout the continuous phase.

Question 2

What is the stbility of elumsions?

Answer 2

Emulsions are UNSTABLE because Globules will try to reduce their overall surface area in contact with the continuous phase by either coalescing (come toghether) or/and adapt a spherical shape.

Question 3

What is tho posible globule size, but the size most often seen?

Answer 3

Possible = 0.01-100 micrometer
Often = 0.1-10 micrometer

Question 4

What is almost always added to an emulsion to try to stabilise it?

Answer 4

An emulsifier.

Question 5

What is an emulsion without an emulsifier?

Answer 5

A temprorary emulsifier.

Question 6

What are the different types of emulsions?

Answer 6

Oil dispersed in water (o/w)
Water dispersed in oil (w/o)
Multiple emulsion e.g. water in oil in water (vica versa)

Question 7

What are the advantages of an emulsion as an oral formulation?

Answer 7

• A way of giving water insoluble drugs
• Mask unpleasent tasting of drug with flavouring agent
• Better absorption in GI due to the small particle size
• Increased compliance (no pain, easy to swallow etc)

Question 8

What are the advantages of an emulsion as a Parenteral formulation?

Answer 8

• Increase onset of action if delivered straight into blood
• w/o injection can be given intramuscularly which can act as depots for slower release
• o/w used to administer lipids for nutrition

Question 9

What are the advantages of MULTIPLE EMULSIONS?

Answer 9

Multiple emulsions are carrier systems for proteins or peptide drugs e.g. insulin.
Encapsulate drugs to protect from the environment
A way of controlled release drug delivery

Question 10

What are the characteristics of an o/w emulsion for topical use?

Answer 10

Absorbs water, used for local effects (not absorbed well), washable, not greasy.

Question 11

What are the characteristics of a w/o emulsion for topical use?

Answer 11

Feels greasy, occlusive, decreases water loss, water repellant, enahnces drug penetration

Question 12

What are the possible tests for determining emulsion type?

Answer 12

Miscibillity test (mixing)
Stain with dyes
Conductivity test.

Question 13

WHat is the miscibility test?

Answer 13

o/w - add water and would mix, adding oil and would not mix and would sink to the bottom.
w/o - add oil and would mix, ad water and would not mix

Question 14

What is the test involving staining with dyes?

Answer 14

o/w - add a water soluble dye, and continuous phase will be coloured
w/o - add an oil soluble dye and the continuous phase will be coloured. Adding water soluble dye would cause the dye to form little globules throughut the emulsions

Question 15

What is the conductivity test?

Answer 15

This involves electricity.
o/w - will conduct electricity because water conducts electric
w/o will not conduct electricity because oil doesn’t conduct electricity.

Question 16

What are the definitons of a stable emulsion?

Answer 16

-when the globules (drug) remain uniformly distributed throughout the continuous phase, and the globules retain their original character. The two phases remain mixed and the emulsion retains its original physocal properties (appearance, colour, odour)

Question 17

What are the different definitions of an instable emulsion?

Answer 17

1. Flocculation
2. Creamed
3. Cracked
4. Phase inversion

Question 18

What is meant by a flocculated emulsion?

Answer 18

There are 2 types :
-Coaggulation (irreversible):
Primary minimul phenomenon. Particles re very closely aggreagted and sedimentation rate is very rapid. Formulation is very viscous due to trapping of continuous phase between aggregates. Impossible to re-disperse.
-Partial-flocculation (reversible on shaking)
Flocculation is the secondary minimum phenomenon where loose aggregates form. Sedimentation rate is rapid due to quite bulcky aggregates. Has a high sedimentation value due to continuous phase being trapped on sedimentation.

Question 19

What is meant by a creamed emulsion?

Answer 19

This is as a result of flocculation.
If an o/w solution would cream, would see a layer of oil at the top.
If a w/o solution would cream, would see a layer of oil at the bottom.
(oil alwasy at the top)
Shaking will easily redisperse the emulsion becuase each globule is still surrounded by protective emulsifier. Fine for patient to use.

Question 20

What is a cracked solution?

Answer 20

This is coalescence / breaking. Dispersed particels have been too close for too long (have been creamed for too long) and have merged into one layer. This is irreversible seperation of the emulsion into its constituent phases. Not suitable for use. Normally caused by a change in pH or chemical instability.

Question 21

What is a phase inverted emulsion?

Answer 21

This can happen at extreme temperatures., if there is chemical instability, or if the phase vol ratio is >60-70% dispersed phase (more dispersed phase than continuous phase). It forms an emulsion that is still a homogenously distributed, but the original physical properties haven’t been retained. Can happen spontantpusly (due to instability), but is sometimes used in manufacturing to obtain a finer product.

Question 22

What are the result of instabile emulsion in Pharmacy?

Answer 22

• Won’t look right - soen’t give patient confidence in their pharmacist
• Isn’t homogenous so risk of all the drug being at the top therefore risk of overdose
• Cracking in parenteral emulsions have killed people due to overdose
• An unstable w/o depot injection could give a patient a 6 months etc dose at one time