Liquid Dosage Forms: Emulsions Flashcards
Emulsion
-system of 2 immiscible liquids
-one is dispersed as droplets -dispersed phase
-continuous phase
continuous phase of emulsion
-external phase
-determines touch, taste, smell of emulsion
Applications of emulsion
-oral
-external
-IV
oral emulsion
-O/W to mask taste of oil and enhance absorption of oil
External emulsion O/W
-water-washable
-vanishing cream
External emulsion W/O
-for cleansing skin
-cold cream
IV lipid emulsion
-O/W
-parenteral nutrition
-100mL of 20% lipid emulsion provides 200kcal, while 100 mL of 5% dextrose only provides 20kcal
-critical that droplet size is less than 1mcm to avoid embolisms in capillaries
Interfacial phenomena
-molecules attracted to each other equally in all directions except at boundary between phases
-imbalance of interaction forces leads to random movement of molecules from interface to bulk phase
=fewer molecules by area at the interface
water force of attraction
H bond
oil force of attraction
london dispersion forces
Interfacial tension
-interface resists expansion in response to attempt to reverse random movement of molecules
-force of tension per unit length of interface
-stronger force in bulk phase = higher interfacial tension
-larger tendency to interact = less interfacial tension
-high temp = lower tenstion (forces are reduced at high heat)
Emulsifiers
-stabilize emulsion
types of emulsifiers
-surfactants
-hydrophilic colloids (polymers)
-finely divided solid particles
Monomolecular film
surfactant
multimolecular film
hydrophilic colloid
solid particle film
fine partivles
Surfactants
-contain hydrophobic and hydrophilic regions
-orient ar interface and LOWER interfacial/surface tension
-acts as clamp to bind oil and water together
Surfactant classification
-anionic
-cationic
-zwitterionic
-nonionic
Hydrophile-lipophile balance (HLB)
-measure relative concentration of hydrophilic and lipophilic regions of surfactant
-calcualted via formula
HLB value for non-ionic surfactants
-ranges from 0-20
low HLB indicates
greater lipid solubility
How to get desired HLB
-mixture of emulsifying agents
-HLB = aX + (1-a)Y
-X=HLB of surfactant 1
-Y = HLB of surfactant 2
-a = fraction of surfactant 1 in surfactant mixture
Rule of Bancroft
-relative solubility of surfactant determines type of emulsion
-i.e.the phase in which a surfactant is more soluble becomes the continuous phase
Rule of Bancroft example
-a surfactant with a high HLB (>10, soluble in water) forms an o/w emulsion
1 L of O/W emulsion contains 3g of Span 80 (HLB 4) and 7g of Tween 80
(HLB 15). What is the HLB value of the emulsion product?
idk
Micelles
-hydrophobic core
-hydrophilic shell
Micelle formation
-surfactant molecules aggregate as the concentration increases above CMC (critical micelle concentration)
Center of micelle
-lipid-like region
-capable of dissolving water-insoluble drugs
Hydrophillic colloids
-polymers
-used in O/w emulsions
-form multimolecular film at interface = increase viscosity of water
-does NOT lower interfacial tension - instead blocks particles from bumping into ea other
hydrophilic colloid examples
-acacia
-tragacanth
-gelatin
Finely Divided solid particles
-less than 1micron can absorb at interface
-form film of fine particles
finely divided solid particle examples
-bentonite, mgAl silicate, Al hydroxide: hydrophilic (o/w)
-charcoal: hydroPHOBIC (w/o)
Phase in which the emulsifier is most soluble
-external (continuous) phase
W/O emulsion if
-HLB LESS than 10
-contact angle of solid particles is GREATER than 90 degrees
O/W emulsion if
-HLB GREATER than 10
-HYDROPHILLIC COLLOIDS
-contact angle of particles is LESS than 90
Hydrophilic emulsion
-O/W
Hydrophobic emulsion
-W/O
Instability of Emulsion
- Creaming
- Coalescence
- Phase Inversion
Creaming
-Stokes Law
-reversible as long as. interfacial film maintains integrity of individual droplets
-low density starts floating
-shake before use
Stokes law
kys
Coalescence
-droplet size increase bc interfacial film unable to maintain individual droplets
-irreversible
-ultimately leads to layer of oil and layer of water (broken emulsion)
-cannot fix by shaking
-must be reformulated
Phase Inversion
-due to phase volume ration exceeding 74% (it should be under 50%)
-O/W emulsion stabilized with sodium stearate can be inverted to W/O type using heard water (containing calcium)
Conversion of Na Stearate to Ca stearate
-high HLB to low HLB
-O/W to W/O
-phase inversion by using hard water (containing calcium)
matching
matching
