Emulsions Flashcards
What is an Emulsion?
Dispersed system containing 2 insoluble liquids
Droplet size for emulsions?
0.1-100 um
Define a O/W Emulsion
Oil droplets dispersed in water/aqueous phase with water >45% of total weight
Define W/O emulsion
water droplets dispersed in oil phase, water<45% of total weight
Can you have multiple emulsions?
Yes, W/O/W, O/W/O; an emulsion within an emulsion
What are advantages of using emulsions as a dosage form?
- Administration of unpalatable drugs
- aqueous phase easily flavored
- oily sensation easily removed
- increase rate of absorption
- easy parenteral admin where liquid phase is important
- possible to include 2 incompatible ingredients
Type of Emulsion for Oral Admin?
Mostly O/W to ensure pleasant taste
Type of emulsion for IV admin?
Must be O/W b/c serious embolization may occur
Type of emulsion for IM admin?
Usually W/O for depot therapy (sustained release)
Characteristics of O/W external use emulsions?
Not Greasy
water-washable
Characteristics of W/O external use emulsions?
Greasy
occlusive
form water-repellent film
Advantages of using O/W oral emulsions?
Mask taste
Render oil more digestible
Increase bioavailability of the drug by icreasing the solubility
Most common dosage form for emulsions?
Topical formulation
What emulsion type would you use for unbroken skin?
W/O –> easily spreads
What type of Emulsion is a Lotion?
Ointment?
Cream?
Lotion: O/W
Cream: both
Ointments: W/O
Oil phase choices for Oral?
Liquid paraffin
Castor oil
cod liver oil
arachis oil
–> all of these are laxatives
oil phase for IV?
Cottonseed oil
soya bean oil
safflower oil
Oil phase for external use?
Turpentine oil
benzyl-benzoate
various oils as carriers for AI –> liquid paraffin
What are fixed oils? Exs?
non-volatile/fatty oil of anomal or plant derivations, a mixture of esters of fatty acids, TGs.
Ex: Castor oil, cod liver oil, olive oil
Essential or volatile oils? Exs?
non-fatty oils from plants
Ex: mint oil, rose oil, peppermint oil
Mineral Oil? Exs?
a grade of liquid petrolatum
Ex: liquid paraffin
Water phase Exs?
Water
Glycerol
Propylene glycol
Polyethylene glycols
Sorbitol
How do emulsifiers stabilize the system?
reduce the inferfacial tension
imparting a charge on the droplets creating electrostatic repulsion
What are requirements for emulsifying agents?
Molecular structure
stabe interface
chemical stability
inertness
non-toxic
non-irritating
odorless
tasteless
colorless
not cost-prohibitve
Classes of emulsifying agents?
Chemical structure:
- synthetic and semi-synthetic
- Natural
- Finely dispersed solids
- Auxillary agents
MOA:
- surface active agents
- hydrophilic colloids
- finely divided solid particles
Most common emusifying agents?
Surfactants:
- anionic
- cationic
- non-ionic
- zwitterionic
What structural classification do polymers and surfactants fall under?
Synthetic
WHat are semi-synthetic emulsifying agents derived from?
cellulose
Types of anionic surfactants?
Soft soaps: alkali metal and amminium soaps
Hard Soaps: divalent and trivalent metals
Detergents: sulfated and sulfonated compounds
Most common anionic surfactant? why?Ex?
Detergents b/c resistant to hydrolysis
Ex: Sodium lauryl sulfate
What area has the negatvie charge for anionic surfactants?
The hydrophilic head
What area has the positive charge for cationic surfactants?
The hydrophilic head
What other purpose are cationic surfactants used for opthalmically?
As a preservative/ antiseptic/ disinfectant
What is a non-ionic surfactatn where a hydrophobic portion predominates soluble in?
Oil-soluble
What is a non-ionic surfactatn where a hydrophillic portion predominates soluble in?
Water-soluble
What are some Exs of non-ionic surfactants?
Sorbital esters (SPANS) and Polyoxyethylene sorbitan esters (TWEENS)
Most common surfactants?Why?
Non-ionic
Neutral pH, resistant to added acids and electrolytes, superior in compatibility, stability, ands saftey
What is the cationic part of synthetic zwitterionic surfactants?
Primary/Secondary/tertiary amines or ammonium
Which area is variable for zwitterionic surfactants?
Anionic area
How do finely divided solids work as emulsifying agents
form particulate layer around dispersed droplets, swell in dispersion medium, increase inter-particle distance, minimize inter-particle interaction
What does the viscosity depend on for finely divided solids?
the internal concentration, relative volume of the internal phase
What are auxillary emusifiers? How do they work?
weak emulsifiers used always in combonation with other emulsifiers.
Stabalize system by thickening (increasing viscosity)
When do you use cationic emusifiers? Anionic?
Cationic –> low [ ] b/c can become toxic, used when antiseptic properties are required
Anionic have high pH, do not use for broken skin
Are Ionic emulsifiers used orally?
No; irritant to GIT
What surfactants are used in parenteral use?
Non-ionic, specific ones such as lecithin and polysorbate 80
What 2 structural features are common in all types of surfactants?
Hydrophillic head, hydrophobic tail
Mono-molecular film?
Move to liquid: liquid interface
reduce surface interfacial tension as higher [ ] at interface comared to bulk mixture
–> surface active agent
Multi-molecular film?
protection from coalescence via:
- protective sheath around droplets
- imparting charge on droplets, repulsion
- wetting to increase viscosity
no change in interfacial tension
–> hydrocolloids
Solid particle film?
Form particulate layer, swells, increase viscosity, impair droplet movement
–> finely divided solids
How do surfactants impact interfacial tension?
Lower it
What is the CMC?
Critical micelle [ ] –> [ ] of surfactant above which micelles form and all additional surfactants added to the system will form micelles
What is the aggregation number?
average number of surfactant monomers in a spherical micelle
do ionic surfactants require more or less [ ] to form micelles than non-ionic?
Ionic require much more [ ] than non-ionic
What is the dynamic equilibrium within the system with micelles?
Micelles in dynamic equalibrium with monomeric surfactant molecules in the emulsion
Do you want an emuslifier with a low CMC?
No, surfactant will form micelles before oil droplets can be coated
What does low HLB value mean?
low polarity, lipophilic surfactant (0-10)
What does high HLB value mean?
high polarity, hydrophilic surfactant (10-20)
WIth same oil how can HLB values differ based on w/o, o/w?
w/o emulsion will desire a low HLB value
o/w will desire a high HLB value
How do you calculate HLB of a mixture?
HLB(mixture) = y x HLBa + (1-y) x HLBb
How do you mix the oil and water phase?
Always water into oil slowly
What are antioxidants used for?
prevent auto-oxidation of oil and lipid components
What do chelating agents do?
Grab up free ions
Exs of true antioxidants?
BHA and BHT
Exs of chelating agents?
EDTA, tartaric acid, citric acid
What are chelating agents synergistic with?
reducing agents
Major preservative used?
parabens
What are Humectants? exs?
agents capable of absorbing water from the air, used to reduce evaporation of water phase
ex: propylene glycol, glycerol, sorbitol
Dry gum method?
emulsifying agent into oil phase, make water phase, add water phase to oil phase = primary emulsion
Wet gum method?
water + emulsifying agent = mucilage, add slowly to oil phase = primary emulsion
would you use a glass mortor with natural emulsifying agents?
No, b/c natural need more enery to mix
In situ soap method?
emulsifying agent is formed fresh inside the solution.
ex: cottonseed oil mix with lime water –> Calcium oleate as emulsifying agent = w/o emulsion
Surfactant based method?
HLB claculated, SPAN in oil phase and TWEEN in water phase, SPAN and TWEEN amount depends on emulsion type w/o or o/w
Mechanica stirrers use?
for low viscosity preparations, large quantities
Homogenizers use?
small inlet orfice and pressure used to incorporate oil but, limited as cannot be used for viscosity greater than 2000 cP
Ultrasonifers use?
ultrasonic waves break down emulsified droplets, produces a uniform emulsion
What external labels are needed for emulsions?
shake well
–> external use only for topical
What is a stable emulsion?
Dispersed droplets retain orignal characteristics and remain uniformly dispersed throughout the continuous phase
What is creaming?
dispersed droplets move upward within the continuous phase
What is sedimentation?
dispersed droplets move downward within the continuous phase
How can you reduce the rate of creaming/sedimentation?
decrease droplet size
decrease the density difference between the 2 phases
increase viscosity of the continuous phase
control the disperse phase [ ]
Can emulsions that have creamed or sedimented be redispursed?
Yes
what does a negatvie calue of v in stokes law indicate?
indicates upward movement = creaming
What do particles in the primary maximum zone show?
higher energy of repulsion vs attraction = more likely to remain separated or deflocculated
Is to much repulsion dangerous?
yes, can increase the risk of attraction betwee the third and second particle
What is coalescence?
complete fusion of droplets within an emulsion, leading to an ultimate separation of the 2 insoluble phases
How is coalescence resisted in o/w? w/o?
resistance provided by the strenght of mono or multimolecular films for o/w
presence of hydrocarbon chains of surfactant molecules which project into oil phase for w/o
Is coalescence reversible?
NO
BUD for simple external emulsons?
1 month
What is the usual BUD for all water containing preparations when ingredients are in solid form and chemical stability of the system is unknown?
14 days
