emulsions Flashcards
What is an emulsion?
A two-phase system consisting of two immiscible liquids, one dispersed as droplets (USP) through-out another.
to mix immiscible liquids and make an emulsion we need an ___
emulsifying agent
dispersed phase
internal phase
dispersion medium
external or continuous phase
advantages of emulsions
- stable and homogenous mixture
- good palatability of distasteful oil in sweet flavored aqueous vehicle
- small oil globules are digested and absorbed well
-less irritation of skin
based on viscosity emulsions are
liquids and semi-solids
administration of emulsions
oral (liquid)
topical (liquid & semi-solid)
parenteral (liquid)
What are the two types of emulsions?
Oil-in-water (O/W) and water-in-oil (W/O).
factors determining emulsion type
- emulsifier
- phase ratio
- order of mixing
emulsifier
favors a particular emulsion type
overcomes unfavorable phase ratio
external phase
- greater concentration
- the one that is being added
inversion of emulsion
O/W –> W/O and vice versa
inversions happen due to
emulsion made by heating is being cooled
concentration of internal and/or external phases is changed
internal concentration increases
inversion occurs
stable emulsion
dispersed phase does not exceed 50% of total volume
True or False: Emulsions are always stable.
False. Emulsions are (physically) thermodynamically unstable and require emulsifying agents.
internal phase tends to form aggregates (globules)
upon standing
The dispersed phase in an O/W emulsion is ____.
Oil.
instability types
creaming
flocculation
coalescence
breaking
creaming
migration of droplets of internal phase to top or bottom of emulsion
creaming happens due to
improper dose (no longer even distribution)
creaming is esthetically
unacceptable
flocculation
small spheres of oil stick together to form flocs (larger drops)
drops remain separated
___ is a prerequisite step to coalescence
flocculation
coalescence
merging of small droplets into large droplets
___ is coalescence and creaming combined
breaking
breaking
oil separates completely from the water
floats at the top as single continuous layer
additional emulsifier is needed
reversible ___
reversible and irreversible ___
irreversible ___
creaming (redistributed upon shaking)
flocculation
breaking
theories of emulsification mechanism of action of emulsifier
surface tension theory
oriented-wedge theory
plastic or interfacial film theory
surface tension theory
liquid’s surface tension
emulsifiers facilitate breaking up large globules
liquids have ___ minimal surface area
minimal
if drops of the same liquid come into contact
they join
new larger drop has a smaller surface area than
total surface area of small drops
Emulsifying agents work by…
Reducing interfacial tension
reduce repellent force between two immiscible liquids
diminish each liquid’s attraction for its own molecules
interfacial force
force resisting breaking up liquids into smaller molecules
oriented-wedge theory
molecular layer of emulsifying agent is curved around a droplet of internal phase
molecules of an emulsifier orient themselves into each phase
hint: think of surfactants
true or false: all emulsifiers have hydrophilic and hydrophobic parts
true
plastic or interfacial film theory
emulsifier surrounds the droplets of internal phase as thin layer of film
film prevents
contact and join of internal phase
emulsification is a two-step process
- lowering interfacial force
- formation of protective wedge film around droplet (stability)
maintaining stability of emulsions prevents
coalescence of droplets
emulsifying agent with relatively strong hydrophilic groups produces
O/W emulsion
emulsifying agent with relatively strong hydrophobic groups produces
W/O emulsion
emulsifying agents must be
stable
nontoxic
compatible
effective concentration 2.5-5% v/w
little odor, taste, color
do not affect therapeutics agents
emulsifiers can be
surfactants
stabilizers
thickeners
surfactants are classified as
anionic pH >8
cationic pH 3-7
nonionic pH 3-10
anionic surfactants
soaps (triethanomine oleate)
sulfonates (sodium laurel sulfate)
cationic surfactant
benzalkonium chloride (bacterial agent)
nonionic surfactants
sorbitans esters
polyoxyethylene derivatives
___ should be used in combination with ___
primary emulsifier
stabilizer (secondary emulsifier)
hydrophilic ointment USP
sodium laurel sulfate - primary emulsifier
acetyl alcohol - auxiliary emulsifier
stabilizers
high-molecular-weight alcohol
colloidal clays
high-molecular-weight alcohol
steryl alcohol
acetyl alcohol
cholesterol and derivatives (W/O emulsions)
colloidal clays
Mg hydroxide
Al hydroxide
bentonite
thickeners (viscosity)
carbohydrate materials (O/W)
proteins (O/W)
carbohydrates
ACACIA (compounding)
pectin
tragacanth
agar
microcrystalline cellulose
proteins
gelatin
egg yolk
casein
gelatin
too fluid emulsions which become more fluid upon standing
What is the HLB scale used for?
To classify surfactants based on their hydrophilic-lipophilic balance.
surfactants have HLB value
1 - 20
True or False: A higher HLB value indicates greater lipophilicity.
False. A higher HLB value indicates greater hydrophilicity.
What is the typical HLB range for O/W emulsifiers?
8-18.
What is the typical HLB range for W/O emulsifiers?
3-6.
emulsifiers should have HLB value similar to
external or internal phase
(stable emulsion)
two or more emulsifiers can be combined to
achieve proper HLB value
What are common methods for emulsion preparation?
Dry gum method (continental)
Wet gum method (English)
Bottle method (Forbes)
What is the dry gum method?
Oil, water, and gum are mixed in a 4:2:1 ratio
O/W emulsifier: acacia
emulsifier is triturated with oil in rough mortar (Wedgwood)
then add water
creamy white mixture
solid compounds (preservatives, stabilizers) are dissolved in water and added to primary emulsion
idk how to condense this my bad
dry method is used to make
mineral oil emulsion USP
What is the wet gum method?
method 4:2:1
gum (1 part) and water (2 parts) are mixed first, oil (4 pasts) is added after
trituration to emulsify oil and ensure uniformity
then add other ingredients
for both dry gum and wet gum methods at the end
transfer emulsion to graduate and bring to volume with water
Forbes bottle method
emulsions of volatile oil or oils with low viscosity
oil is added to acacia (powder) in dry bottle
shake and add water
shake again
in Forbes bottle method volume of water is
equal to volume of oil
added in portions
in Forbes bottle method primary emulsion should be diluted to
proper volume by water or aqueous solution of other ingredients
What are microemulsions?
stable transparent emulsions with very small droplet sizes
rapid and efficient absorption
both O/W and W/O
absorption of microemulsions
oral and transdermal
What is the function of preservatives in emulsions?
to prevent microbial growth and contamination
required by USP
preservatives for emulsions
benzoic acid/sodium benzoate or sorbic acid 0.2% (acidic pH)
methylparaben 0.2% + propylparaben 0.02%
stability of emulsions
physical
chemical
oxidation
__ is added to emulsions to prevent oxidation.
Antioxidants (chelating agents)
most oil undergo oxidation
chelating agents
organic compounds that form complexes with metal ions and inactive oxidation process
properties of antioxidants/chelators
compatible
do not affect therapeutic agents
soluble
stable anf effective
nontoxic
little odor, taste color
unreactive with containers
antioxidants for aqueous systems
ascorbic acid USP 0.05-3%
sodium bisulfate/metabisulfate 0.1%
sodium thiosulfate USP 0.02-1%
which antioxidants for aqueous systems might cause allergic reactions?
sodium bisulfate
metabisulfate
antioxidants for oil systems
ascorbic palmitate 0.01-0.2%
butylated hydroxytoluene 0.05-0.02
tocopherol 0.01-0.1%
sulfur dioxide 0.005-0.15%
chelating agents
eidetic acid/edetate disodium/calcium disodium edetate 0.1%
citric acid USP 0.3-2.0%
protect emulsions from
freezing
excessive heat
light-resistant containers for
light sensitive emulsions
addition of antioxidants
oxidative decomposition of emulsions
label warning
container must be tightly closed
internal (oral) emulsions should be stored in ___ while external ones at ___
refrigerator
room temperature
labeling
SHAKE WELL
lotion (emulsions)
calamine - antiseptic 5%
zinc oxide - antiseptic 5%
oxybenzone - sunscreen 6%
almond oil - part of emulsion vehicle system
acacia - emulsifying agent
rose water - part of emulsion vehicle system
oral emulsions
mineral oil emulsion
castor oil emulsion
simethicone emulsion
topical emulsion
estradiol emulsion
for oral emulsion use
spoonful
droperwise
avoid drug interactions
cholestyramine (oral suspension) and warfarin, oral diabetes drugs, tetracycline
aluminum hydroxide gel and antibiotics, digoxin
