PH2107 - Emulsions 3 Flashcards
What is DPPC?
dipalmitoylphosphatidyl choline
What is POPC?
palmitoyloleoylphosphatidyl choline
What are poloxamers?
Non-ionic triblock copolymers
What is the structure of poloxamers?
Composed of a central hydrophobic chain of polyoxypropylene flanked by two hydrophilic chains of polyoxyethylene
What are poloxamers used for?
Pharmaceutical formulations - surfactants - emulsifying agents - solubilising agents - dispersing agents In vivo absorbance enhancers Topical dosage forms Rectal suppositories
What is Span 80?
Sorbital oleate - biodegradable non-ionic surfactant
- ester of a fatty acid (oleic acid, C18) and sugar alcohol, sorbitan (dehydrated sorbitol)
What is a highly effective liquid w/o emulsifier and o/w emulsion stabiliser, particularly when used together with its ethoxylated derivative, Tween 80?
Span 80
What are the features of Span 80?
More lipophilic than Tween 80
What is Span 80 used for?
- wetting agent
- dispersant for materials such as Zinc Oxide, calamine and penicillin in lipophilic pharmaceutical bases
Give four example of different Spans
Span 20
Span 60
Span 65
Span 80
What is polysorbate 80?
Tween 80
Describe Tween 80
Polysorbate 80 is also a biodegradable non-ionic surfactant
- derived from polyethoxylated sorbitan and oleic acid
What are the hydrophilic groups in polysorbate 80 called?
Polyethers - polyoxyethylene groups which are polymers of ethylene oxide
What is often used to construct a stronger, more stable complex film at an interface in an emulsion?
A combination of emulsifiers
What will a good emulsifier mixture produce?
A closely packed and/or compelx film by using two agents with different hydrophilicities
How does the chemical structure of the chosen emulsifiers in a mixture affect the film produced?
- 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
What is the difference between Span molecules and Tween molecules?
Spans are lipophilic
Tweens are hydrophilic
How do Spans and Tweens work as emulsifiers?
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
What is a finely divided solid?
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
Give examples of finely divided solids
- bentonite
- veegum
- hectorite
- magnesium hydroxide
- aluminium hydroxide
- magnesium trisilicate
What considerations need to be made when choosing an emulsifier?
- Desired type of emulsion (o/w or w/o)
- Conferred stability
- emulsifying ability/stability
- compatability with other excipients
- stability towards acids, alkalis, salts, or electrolytes - Route of administration
- some emulsifiers may only be used externally - Adverse effects
- irritancy of cationic > anionic
- some anionics have low pH
- ionics can act as laxatives - Cost
What is used when you want the final product to exhibit aqueous characteristics i.e. to dilute readily with water?
A water soluble emulsifier
When would you choose an oil soluble emulsifier?
- to make a w/o emulsion
- couple water soluble materials into an ion
- to produce another type of non-aqueous emulsion system
What is the Bancroft rule?
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
What is PVR?
Phase volume ratio - the phase present in the greater amount usually becomes the continuous phase
What type of emulsion are most pharmaceutical emulsions?
Oil-in-water so require an o/w emulsifier
What is HLB?
Hydrophile-lipophile balance
What is each emulsifier assigned in the HLB system?
A numerical value (0-20)
What do all emulsifiers consist of?
A molecule that combines both hydrophilic and lipophilic groups
- they are amphiphiles
What does a low HLB number (< 9) indicate?
An emulsifier that is lipophilic in character
0 = completely lipophilic
What does a high HLB number (> 11) indicate?
An emulsifier that is hydrophilic in character
20 = completely hydrophilic
