Emulsions Flashcards
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What is an emulsion?
A dispersed system with at least 2 immiscible liquids. One is always aqueous and one is always oleaginous.
What is the internal phase?
The liquid that is finely subdivided into droplets and is dispersed through the external phase.
What is O/W emulsions and what properties do they have?
Oil in water
Water is >45%= external phase
non greasy, water washable
What is W/O emulsions and what properties do they have?
Water in oil
water is <45%= internal phase
greasy, occlusive, forms water repellant film
What are the two types of multiple emulsions?
W/O/W= water droplets in larger oil droplets dispersed in water
O/W/O= oil droplets in larger water droplets dispersed in oil
Pros of emulsions compared to other dosage forms?
-Easier to eat/ taste
- bypass dissolution= faster
- combine 2 incompatible ingredients
- better for parental administration if lipid component is necessary.
Which emulsion is used for oral?
O/W= because better taste
Which emulsion for IV?
O/W= because serious embolism if W/O is used
Which emulsion for IM?
W/O= because of sustained release (depot effect)
What oils do we choose for oral emulsions
castor oil, cod liver oil, olive oil, liquid paraffin (mineral oil)
What oils for IV emulsions
Cotton seed
What oil for topical emulsions?
turpentine, benzyl-benzoate, liquid paraffin
What are our choices for water phase?
water
glycerol
PEG
What is the mechanism of action for emulsifying agents?
Lowers the interface tension making it more miscible
puts charges on droplets
What is part of egg yolk that acts as a emulsifying agent?
lecithin
What type of emulsions would lotions, creams, and ointments be?
L=o/w
C=both
O= w/o
What are the natural emulsifying agents?
Plant= tragacanth, xanthin gum= o/w
Animal= gelatin, lanolin= w/o
What are some semi synthetic emulsifying agents?
MC
CMC
What are anionic surfactants?
have a negative changed head
Soft and hard soaps
What are soft soaps and give examples?
alkali metal and ammonium soaps
ie) sodium,K, NH3 stearate
What are hard soaps and give examples
Divalent or trivalent metals
Ie) calcium oleate
What is special about soft soaps?
can be formed in situ
What emulsions do soft soaps make
o/w
What emulsions do hard soaps make?
w/o emulsions
What emulsions do detergents make?
o/w
What is a detergent agent?
sodium lauryl sulfate
Of the three anionic surfactants (soft, hard soaps, detergent) which is most common and why?
detergent because resistant to hydrolysis
What are cationic surfactants and give examples?
Have a positive charged head.
Ie) quaternary ammonium compounds like benzylkonium chloride and benethonium chloride
What is special about cationic surfactants?
can be used as preservative in ophthalmic formations
What are non-ionic surfactants and give examples?
have a hydrophilic head no charge.
ie) usually an alcohol, or fatty acid has moiety
Of all surfactants which is most common and why?
non-ionic due to neutral at pH and resistant to acids and electrolytes
If hydrophobic portion of non-ionic surfactant which phase is it soluble in?
oil phase
Of span and tween which is hydrophobic and which is hydrophilic
tween= hydrophilic
span= hydrophobic
What is a zwitterionic surfactant?
carries both cationic and anionic charge.
What are finely divided solids?
form a particulate layer around droplets to increase inter particle distances.
What emulsions are formed from finely divided solids?
o/w emulsions but bentonite can also form w/o
Examples of finely divided solids?
bentonite, veegum
What are auxiliary emulsifiers?
are weak and need another one as well.
They act by thickening
Examples of aux emulsifiers?
stearic acid, cetyl alcohol
When should we NOT use ionic emulsifiers and why?
NO for oral due to cationic being toxic and bad taste
anionic is basic= NO for broken skin
Which surfactants may be used in Parenteral?
NON-ionic= lecithin, polysorbate 80
What are the three MOA of emulsifying agents?
1= Mono film- go to interface and reduces surface tension(surface agents)
2= Multi film- makes protective sheath and gives charge to droplets= repel (hydrocolloids)
3= Solid particle film- layer then swell to increase viscosity (FDS)
CMC is a term we learned about, What does it mean and what does a LOW number indicate?
CMC= concentration of surfactant where micelles will form micelles
WE WANT a High number because if it is low it will be coated before forming micelles.
What does a low HLB indicate
lipophilic
What does a high HLB indicate?
hydrophilic
>10
What is the formula for finding HLB of a mixture
HLB= y x HLB + (1-y) x HLB
If we want a O/w emulsion what HLB are we expecting?
> 8
WHICH PHASE ALWAYS GETS POURED INTO THE OTHER ONE?
water phase into oil phase due to not wanting the oil phase to precipitate out.
What are antioxidants we can add?
BHA,BHT, Vit e, Vit C
What are some preservatives we can add and which phase do they like?
Methylparaben= water
propylparaben=oil phase
What can happen with the common preservatives and tweens?
parabens can bind and inactivate
What are humectants and give examples?
Absorb water from air= keep moist
ex) PEG, glycerol, sorbitol
What is the dry gum method?
add gum to oil then add water to oil all at once to get emulsion
What is the wet gum method?
add water to gum then get mucilage then slow addition to oil phase
What type of mortar for natural ingredients?
not glass due to high energy to break it down
Which method wet or dry is better?
no clear answer but wet gum works better for tragacanth
What is special about lime water and cottonseed oil?
form in situ calcium oleate = hard soap= w/o emulsion
What ways can we mix emulsions?
Mechanical stirrers= for low viscosity
Homogenizers= no for high viscosity
Ultrasonifiers= gentle and powerful
Colloid mills= when need scaling up production
What aux labels always?
for external use and shake well
What three things can happen if the stability of emulsion is super low?
cream/ sediment
flocculate
coalescence
Which way do particles move if creaming is happening
up
Which way do particles move if sedimentation is happening
down
How can we predict whether creaming or sedimentation may happen?
density of droplets and density of continuous phase
How can we reduce creaming/sedimentation?
lower droplet size
increase viscosity of continuous phase
Is creaming or sedimentation reversible
Yes
In stokes law what does a negative value indicate?
creaming
What is stokes law?
V=d^2(Pint-Pext)/(18xnext) x g
What does primary minimum mean?
very attractive potential
What does primary maximum mean?
repulsion is greater= ideal for dispersion
What does secondary minimum mean?
shallow attraction for easy dispersion
Which is okay Primary max/min or secondary minimum
Primary min= NO hard to disperse
Primary max= IDEAL
Secondary min= not bad. just need to shake
What is coalescence?
fusion of droplets which can eventually lead to separation
How can we stop coalescence?
o/w= strength of mono films
w/o= need long hydrocarbon chains of surfactants into oil phase
What does flocculation mean?
aggregate
Can coalescence be fixed?
NOOOOOOO
What to do if it foams?
lower surfactant and mix slower
What is BUD if water containing?
14 days
What is BUD for external preps?
1 month
