PH2107 - Emulsions 3

Question 1

What is DPPC?

Answer 1

dipalmitoylphosphatidyl choline

Question 2

What is POPC?

Answer 2

palmitoyloleoylphosphatidyl choline

Question 3

What are poloxamers?

Answer 3

Non-ionic triblock copolymers

Question 4

What is the structure of poloxamers?

Answer 4

Composed of a central hydrophobic chain of polyoxypropylene flanked by two hydrophilic chains of polyoxyethylene

Question 5

What are poloxamers used for?

Answer 5

Pharmaceutical formulations
- surfactants
- emulsifying agents
- solubilising agents
- dispersing agents
In vivo absorbance enhancers
Topical dosage forms
Rectal suppositories

Question 6

What is Span 80?

Answer 6

Sorbital oleate - biodegradable non-ionic surfactant

- ester of a fatty acid (oleic acid, C18) and sugar alcohol, sorbitan (dehydrated sorbitol)

Question 7

What is a highly effective liquid w/o emulsifier and o/w emulsion stabiliser, particularly when used together with its ethoxylated derivative, Tween 80?

Answer 7

Span 80

Question 8

What are the features of Span 80?

Answer 8

More lipophilic than Tween 80

Question 9

What is Span 80 used for?

Answer 9

• wetting agent

- dispersant for materials such as Zinc Oxide, calamine and penicillin in lipophilic pharmaceutical bases

Question 10

Give four example of different Spans

Answer 10

Span 20
Span 60
Span 65
Span 80

Question 11

What is polysorbate 80?

Answer 11

Tween 80

Question 12

Describe Tween 80

Answer 12

Polysorbate 80 is also a biodegradable non-ionic surfactant

- derived from polyethoxylated sorbitan and oleic acid

Question 13

What are the hydrophilic groups in polysorbate 80 called?

Answer 13

Polyethers - polyoxyethylene groups which are polymers of ethylene oxide

Question 14

What is often used to construct a stronger, more stable complex film at an interface in an emulsion?

Answer 14

A combination of emulsifiers

Question 15

What will a good emulsifier mixture produce?

Answer 15

A closely packed and/or compelx film by using two agents with different hydrophilicities

Question 16

How does the chemical structure of the chosen emulsifiers in a mixture affect the film produced?

Answer 16

• emulsifiers with long, saturated hydrocarbon groups produce closely packed film by allowing maximum cohesion between adjacent molecules
• the most stable emulsions are formed when both emulsifiers are of a similar chain length

Question 17

What is the difference between Span molecules and Tween molecules?

Answer 17

Spans are lipophilic

Tweens are hydrophilic

Question 18

How do Spans and Tweens work as emulsifiers?

Answer 18

Spans are good emulsifiers but they have bulky heads which don’t allow the tails to get close enough to each other for van der Waals to develop

If a Tween molecule is placed between the two Spans, the Spans can each form van der Waals with the Tween, strengthening the interfacial film and the resistance of the emulsion to coalescence

Question 19

What is a finely divided solid?

Answer 19

These agents form a particulate layer around dispersed particles

• most will swell in the dispersion medium to increase viscosity and reduce the interaction between dispersed droplets
• most commonly they support the formation of o/w emulsions but some may support w/o emulsions

Question 20

Give examples of finely divided solids

Answer 20

• bentonite
• veegum
• hectorite
• magnesium hydroxide
• aluminium hydroxide
• magnesium trisilicate

Question 21

What considerations need to be made when choosing an emulsifier?

Answer 21

1. Desired type of emulsion (o/w or w/o)
2. Conferred stability
   - emulsifying ability/stability
   - compatability with other excipients
   - stability towards acids, alkalis, salts, or electrolytes
3. Route of administration
   - some emulsifiers may only be used externally
4. Adverse effects
   - irritancy of cationic > anionic
   - some anionics have low pH
   - ionics can act as laxatives
5. Cost

Question 22

What is used when you want the final product to exhibit aqueous characteristics i.e. to dilute readily with water?

Answer 22

A water soluble emulsifier

Question 23

When would you choose an oil soluble emulsifier?

Answer 23

• to make a w/o emulsion
• couple water soluble materials into an ion
• to produce another type of non-aqueous emulsion system

Question 24

What is the Bancroft rule?

Answer 24

The phase in which the emulsifier is more soluble usually becomes the continuous phase
e.g. Proteins emulsifiers tend to produce oil-in-water emulsions - depends on the emulsifiers polar/non-polar characteristics

Question 25

What is PVR?

Answer 25

Phase volume ratio - the phase present in the greater amount usually becomes the continuous phase

Question 26

What type of emulsion are most pharmaceutical emulsions?

Answer 26

Oil-in-water so require an o/w emulsifier

Question 27

What is HLB?

Answer 27

Hydrophile-lipophile balance

Question 28

What is each emulsifier assigned in the HLB system?

Answer 28

A numerical value (0-20)

Question 29

What do all emulsifiers consist of?

Answer 29

A molecule that combines both hydrophilic and lipophilic groups
- they are amphiphiles

Question 30

What does a low HLB number (< 9) indicate?

Answer 30

An emulsifier that is lipophilic in character

0 = completely lipophilic

Question 31

What does a high HLB number (> 11) indicate?

Answer 31

An emulsifier that is hydrophilic in character

20 = completely hydrophilic