Emulsions Flashcards
what is an emulsion
a dispersed system containing at least 2 immiscible liquids
what are advantages of an emulsion
Unpalatable drugs can be administered in palatable form
Aqueous phase easily flavored
Oily sensation easily removed
Increased rate of absorption
Ease of parenteral administration where lipid component (phase) is important
Possible to include two incompatible ingredients
oil phase for oral administration
Liquid paraffin
Castor oil
Cod liver oil
Arachis oil
oil phase for IV administration
cottonseed oil
cod liver oil
safflower oil
fixed oils
Castor oil
Cod liver oil
Olive oil
water phase
Water
Glycerol
Propylene glycol
Polyethylene glycols
requirements of an emulsifying agent
Stable interface Chemical stability Inertness Non-toxic, non-irritating Odorless, tasteless, colorless Not cost-prohibitive
plant derived emulsifying agents form what type of emulsion
Form o/w
Tragacanth, xanthan gum
animal derived emulsifying agents form what type of emulsion
Make o/w emulsions
Gelatin, cholesterol, lecithin Lanolin (w/o)
what are some semi-synthetic emulsifying agents
Methylcellulose, carboxymethylcellulose
Improve the stability of the emulsions by improving viscosity
polymer emulsifying agents
® PVP, PEG, or carbomer
o/w emulsions
Often viscosity building
soft soaps form what type of emulsion
Can be formed in situ
o/w emulsions
Sodium, potassium, ammonium, triethanolamine-stearate
Incompatible with electrolytes
ONLY ATTACH ONE FATTY ACID TO THE MONOVALENT IONS
hard soaps form what type of emulsion
w/o emulsions
Used to form w/o emulsions because the divalent ion can attach to more than one fatty acid meaning the hydrophobic portion is much more than the hydrophilic
Soluble in oil, water insoluble
Calcium oleate
detergents form what types of emulsions
o/w emulsion
Sodium lauryl sulfate
cationic surfactants are useful because
Not used very often as an emulsifying agent but is used for its antibacterial properties Quaternary ammonium compounds (benzylalkonium chloride, benethonium chloride)
Can be toxic in high concentrations because there are many negatively charged membranes in the body and these are permanently charged
non-ionic surfactants form what types of emulsions
◊ Can vary the size of the hydrophilic head and the hydrophobic tail
If hydrophobic portion predominates: surfactant is oil soluble
If the hydrophilic portion predominates: surfactant is water soluble
SPANS AND TWEENS
zwitterionic surfactants are useful for what
injectables
ex: lecithin
finely divided solids are used for what type of emulsion
most support o/w emulsions
what are auxiliary emulsifiers?
Stabilize the system by thickening (increasing the viscosity)–>retard inter-particle movement
Ex: fatty acids (stearic acid), fatty alcohols (stearyl or cetyl alcohol) or fatty esters (glycerol mono stearate)
what is the mechanism of action of surfactants?
Mono-molecular film:
Move to liquid: liquid interface–>higher concentration at interface compared to the bulk–>reduces the surface interfacial tension
what is the mechanism of action of hydrocolloids
Multi-molecular film:
Causes NO change in interfacial tension and protects coalescence by:
Protective sheath around the droplets
Imparting charge to the droplets–>repel each other welling to increase viscosity–>less likely to merge
what is the mechanism of action of finely divided solids
Solid particle film:
Forms particulate layer–>swells–>increases viscosity–> retards droplet movement
Do you want a surfactant with a low CMC or high CMC value?
A surfactant with a low CMC means emulsifications is not as efficient as one whose CMC is higher
Low CMC are very potent and are attracted to one another and therefore form micelles instead of forming a micelle around the oil droplets
CMC is low–>surfactant will form micelles before oil (or water) droplets can be coated–>therefore a surfactant with a low CMC emulsification is not as efficient as one whose CMC is higher
What does a low HLB value mean?
lipophilic surfactant
forms w/o emulsions
ie. SPANS
What does a high HLB value mean?
hydrophilic surfactant
forms o/w emulsions
ie. TWEENS
what is the formula to calculate the HLB value
HLBmix=x(HLBa)+(1-x)(HLBb)
when making an emulsion does the water go into the oil phase or does the oil phase go into the water?
WATER GOES INTO THE OIL SLOWLY OR PHASE REVERSION CAN OCCUR
when should antioxidants be used
when an oil other than mineral oil is used
hydrophobic antioxidants
BHA, BHT, ascorbyl palmitate
hydrophilic antioxidants
ascorbic acid
what are examples of preservatives
Methylparabens (water phase) and propylparabens (oil phase)
examples of humectants and when to use
topical formulations
EX: propylene glycol, glycerol
labelling of emulsion
shake well
+/- external use only
what is creaming
internal phase to the top (o/w) because oil is less dense
what is sedimentation
internal phase to the bottom w/o because water is denser
how to prevent creaming/sedimentation
Shake well
Decrease in droplet size (homogenization)
Decrease in the density difference between the two phases
Change the density of the hydrophilic phase: add glycerol or propylene glycol
Cannot change the density of the oil
Increase viscosity of the continuous phase (hydrocolloids)
Control of the disperse phase concentration
what is flocculation
Process of aggregation of dispersed droplets into loose clusters within an emulsion
what is coalescence
Coalescence is the complete fusion of droplets within an emulsion, which leads to a decreased number of droplets and ultimately separation of the two immiscible phases
what should the BUD be on a emulsion
14 days with water containing products
1 month for external use preparations
