Heterogeneous Dispersion: EMULSIONS Flashcards
define an emulsion
a dispersion in which the dispersed phase is composed of small droplets of a liquid dispersed throughout a vehicle in which it is immiscible
according to the USP definition of emulsions:
emulsions are ______ systems in which….
emulsions are TWO-PHASE systems in which one liquid is dispersed throughout another liquid in the form of small droplets
what are the “2 phases” of an emulsion
internal phase (discontinuous) and external phase (continuous)
the internal phase is ____ while the external phase is _____
internal phase = dispersed liquid droplet (discontinuous)
external phase = dispersion medium (continuous)
in an O/W dispersion, _____ is the dispersed phase and ____ is the continuous phase
dispersed phase = oil
continuous = water
what is the dispersed particle size of an emulsion? can emulsions be injected?
0.1-100 micrometers in diameter
larger than an RBC, but we can still inject because they are LIQUID DROPLETS not SOLID PARTICLES (like suspensions)
emulsions must be injected slowly
true or false
emulsions are thermodynamically stable
FALSE
they are thermodynamically unstable
this is due to the fact that the droplets are small –> large surface area —> large surface tension
the surfactant TEMPORARILY reduces surface tension
true or false
emulsions exhibit coalescence
true (when small particles merge)
what are the emulsifying agents that can be used in an emulsion?
3 types:
-surfactants
-hydrophilic colloids
-finely divided solid particles
(finely divided solid particles is normally not used bc emulsions are LIQUID dispersed in liquid)
true or false
emulsions are two phase systems
true
N-cetyl N-ethyl morpholinum ethosulfate is also known as…..
Atlas G-263
cationic surfactant
forms o/w emulsion
a high HLB value usually means a o/w or w/o emulsion?
o/w
what is something to consider when choosing surfactants as emulsifying agents?
some may carry out an anionic/cationic charge which may not be compatible with the formulation.
therefore, a non ionic surfactant agent might be preferred
name 2 non-ionic surface active agents used as emulsifying agents
Atlas Span 80 (Sorbitan mono-oleate)
Atlas Tween 80 (polyoxyethylene sorbitan mono-oleate)
name 2 hydrophilic colloids and their properties
acacia and gelatin (NATURAL)
forms o/w emulsion
Atlas Span 80 and Atlas Tween 80:
o/w or w/o? what are their chemical names?
Atlas Span 80 = w/o
Atlas Tween 80 = o/w
Atlas Span 80 = sorbitan mono-oleate
atlas tween 80 = polyoxyethylene sorbitan mono-oleate
name 3 examples of “finely divided solid particles” used as emulsifying agents, as well as if they are o/w or w/o
bentonite
veegum
carbon black
bentonite = o/w and w/o
veegum = o/w
carbon black = w/o
carbon black is an adsorbent and not really used in ceutics
bentonite and veegum work by coating the surface of the particles and preventing aggregation
salts of d-glucuronic acid
acacia
hydrated aluminum silicate
bentonite
polypeptides and amino acids
gelatin
magnesium aluminum silicate
veegum
which has a high HLB value – Atlas Span 80 or Atlas Tween 80?
Atlas Tween 80.
good for o/w emulsions
what are 3 routes in which emulsions can be administered
oral
topical
parenteral
name 4 applications of emulsions in terms of oral administration
-can enhance bioavailability of water-insoluble drugs
-improve drug stability
-improvement of palatability
-laxative emulsion
as mentioned, emulsions can enhance the bioavailability of water insoluble drugs
give an example of this
Vitamin A is difficult to dissolve in water, but it will dissolve easier in an o/w emulsion
as mentioned, emulsions can improve drug stability.
give an example of this
erythromycin
give an example of a laxative emulsion
mineral oil
as mentioned, emulsions can improve the palatability of a drug
give a specific example of this
valproic acid is very bitter. When dissolved in oil, the taste won’t be noticeable
true or false
only O/W emulsions are widely used topically, not W/O
FALSE
they’re both widely used depending on the effect desired
W/O emulsions are OCCLUSIVE (create physical barrier) and EMOLLIENT (soothe. soften)
O/W emulsions are removed more easily by water
give 3 examples of how emulsions are given parenterally
IV nutrient emulsions (solution preferred but some pts can’t have dextrose)
antineoplastic agents (anticancer – methotrexate emulsion.) prolong action and minimize dosing frequency
influenza vaccine emulsion
what is the size of a RBC
~7 micrometers
give 3 examples of IV nutrient emulsions
cotton seed oil
dextrose
lecithin
name 4 advantages of emulsions
-therapeutic properties and spreading ability increases
-unpleasant taste or odor of an oil is masked
-absorption/penetration of drugs controlled (depending on o/w or w/o)
-aqueous and oil soluble drugs can be administered SIMULTANEOUSLY
true or false
emulsions can increase drug stability
TRUE
many drugs are more stable in emulsion rather than aqueous.
hydrolysis is more easily avoided
how can emulsions prolong drug action?
IM and SUBQ injections.
the drug can partition between the oil and water phases
how can the activity of a drug be maintained or enhanced in an emulsion?
through the partitioning of the drug from the oil phase to the water phase
there are ___ components in an emulsion:
3 components:
-oil phase
-water phase
-emulsifying agent
the smaller the particle size, the ____ the surface energy.
what is the job of the surfactant?
HIGHER
job of surfactant (emulsifying agent) is to reduce this energy
what are the 3 theories of emulsification
surface tension theory
oriented wedge theory
plastic or interfacial film theory
all have same meaning— surface tension, interfacial tension, surfactants, wetting agents
name the 4 desirable properties of emulsifying agents
-be surface active and REDUCE SURFACE TENSION TO BELOW 10 DYNES/CM
-be adsorbed QUICKLY around the dispersed droplets. (a condensed, nonadherent film will prevent coalescence)
-impart to the droplets enough electrical potential so that MUTUAL REPULSION occurs
-be effective in a REASONABLY LOW CONCENTRATION (surfactants considered toxic)
one of the desirable properties of emulsifying agents is to impart to the droplets an adequate electrical potential so that mutual repulsion occurs
are there any potential problems with this?
yes
the charge might have an interaction with the drug formulation. sometimes nonionic is preferred
Span 40
Span 60
Span 65
Span 80
rank them according to HLB value (highest to lowest)
highest HLB = Span 40
Span 60
Span 80
Lowest HLB = Span 65
Tween 20
Tween 60
Tween 80
rank them according to HLB value (highest to lowest)
highest = Tween 20
Tween 80
lowest = tween 60
which have higher HLB – span or tween?
tween
are span and tween natural or synthetic emulsifying agents?
synthetic
name some natural emulsifying agents
gelatin
egg yolk
casein
wool fat
cholesterol
lecithin
Sorbitan tristearate
span 65
sorbitan monostearate
span 60
sorbitan monooleate
span 80
sorbitan monopalmitate
span 40
polyoxyethylene sorbitan monolaurate
tween 20
polyoxyethylene sorbitan monostearate
tween 60
polyoxyethylene sorbitan monooleate
tween 80
what is the desired HLB for a w/o emulsion
3-6
what is the desired HLB for o/w emulsions
8-18
what is the desired HLB for detergents
13-15
what is the desired HLB for antifoaming
1-3
what is the desired HLB for wetting agents
7-9
what is the desired HLB for solubilizers
15-20
explain why we would use 2 surfactants
sodium cetyl sulfate is an anionic surfactant. if we just used that, there would be a lot of empty space around the oil droplet due to the repulsion of like charges. thus, we can use a nonionic surfactant (such as cholesterol) to fill in the gaps.
the ultimate goal is to lower the interfacial tension below 10 dynes/cm
if the gaps weren’t filled in, adjacent particles would aggregate (coalescence)
is cetyl alcohol + sodium oleate a good combination of surfactants?
no
is sodium cetyl sulfate + oleyl alcohol a good combination of surfactants?
no
is sodium cetyl sulfate + cholesterol a good combination of surfactants?
yes
what are the 3 methods of emulsion preparation?
- continental/dry gum method
- english/wet gum method
- bottle/forbes bottle method
explain the continental/dry gum method
used to prepare emulsions
primary emulsion is made of:
fixed oil, water, acacia in 4:2:1 Ratio
oil is added to the acacia and the micture is titurated until the powder is evenly distributed throughout the oil. forms a PASTE
water is then added all at once followed by rapid tituration to form the PRIMARY EMULSION
any remaining water + other ingredients are added to finish the product
in the continental/dry gum method, the last step is to add any remaining water and other ingredients to finish the product
explain this further
electrolytes (in high concentration) tend to crack an emulsion, thus they should be added LAST in as dilute a form as possible
also, alcoholic solutions tend to dehydrate and precipitate hydrocolloids, so they should be added in as dilute a concentration as possible
explain the english/wet gum method for preparing emulsions
-primary emulsion of fixed oil, water, acacia in a 4:2:1 ratio
2 parts of water are added all at one to 1 part of acacia and the mixture is titurated until a smooth mucilage (glue) is formed
then, oil is added in small incremements (1-5mL) with continuous tituration until the primary emulsion is formed
the mixture is titurated for another 5 mins (o/w) and can be brought up to volume with water and mixing
explain the bottle/forbes bottle method of preparing emulsions
oil is added to acacia in a bottle
ratio of oil:water:acacia is 3:2:1 OR 2:1:1
why is the ratio of oil:water:acacia 4:2:1 in the dry gum/wet gum methods, but in the bottle/forbes bottle method it is 3:2:1 or 2:1:1?
because the low viscosity of the volatile oil used in the bottle method requires a higher proportion of acacia
is a mortar and pestle used for all 3 methods of preparing emulsions?
NO
only the dry and wet gum methods
a stable emulsion is defined as…..
an emulsion that would maintain the same number of dispersed particles per unit volume of the continuous phase
what is creaming?
the creaming of emulsions is when the dispersed particles/droplets rise or sediment (depending on the differences in densities between the phases)
how can the creaming emulsion be reconstituted?
by shaking
the rate of creaming is _______ proportional to the viscosity of the emulsion
inversely
ie: high viscosity = low rate of creaming
the _____ droplets cream more rapidly than _____ ones
LARGER DROPLETS CREAM MORE RAPIDLY THAN SMALLER ONES
how can aggregation/coalescence of emulsion droplets be prevented?
by forming a thick interfacial film (in the use of macromolecules like natural gums or protein)
or finely divided solids (veegum and bentonite)
besides creaming and coalescence, what are 3 other considerations for the stability of emulsions?
temperature, microorganisms, alcohol content
alcohol may cause dehydration and everything will crack
what are microemulsions?
liquid dispersions of water and oil that are made HOMOGENEOUS, TRANSPARENT, AND STABLE by the addition of a relatively large amount of surfactant and cosurfactant
true or false
emulsions are homogeneous, transparent, and stable
FALSE – only microemulsion
what is the droplet diameter of microemulsions?
~100-1000 angstroms
true or false
like normal emulsions, microemulsions can be W/O or O/W
true
true or false
microemulsions are thermodynamically stable
TRUE
bc of the large amount of surfactant
can microemulsions be given IV?
yes
which has a higher bioavailability – microemulsions or conventional emulsions?
microemulsions
can surfactants enhance absorption?
YES they can enhance permeation through the reduction of interfacial tension – affect the absorption rate of the drug
are span and tween natural or synthetic?
synthetic
is an emulsifying agent used in all 3 methods of emulsion preparation?
NO
acacia is used in dry and wet gum, but none is used in the bottle method
mixing is done in the bottle method to reduce the particle size. emulsifying agent not used
besides the main 3 methods of preparing emulsions, name 2 others
auxiliary methods
in situ soap method
name 4 equipment pieces used in emulsification
high speed mixer
blenders
colloid mills
homogenizers
they all give energy to reduce the particle size
