Emulsions Flashcards
What is an Emulsion?
the dispersed phase is composed of small globules of a liquid
distributed throughout a vehicle (dispersion medium) in which it is
immiscible.
Why are Emulsions not transparent?
Because light is scattered by the suspended particles in the mixture
How do emulsifiers help form Emulsions?
-They are surfactants and amphiphile (hydrophilic and lipophilic component
-Depending on the type of Emulsion (w/o or o/w) the hydrophilic part will be directed towards the trapped medium or to the outer medium
When are high or low HLB surfactants needed for emulsions?
For oil in water o/w, we need higher HLBs 8-18 bc higher are more water-soluble
For w/o lower HLBs 3-6
What are multiple emulsions?
-An emulsion (f.e. o/w) can be dispersed in a dispersed medium (oil) -> which makes it o/w/o
-For the modified release of DDS: a drug can be packed in the first oil phase -> slowly move into the 2. water phase -> and then move into the 3. oily phase before it gets absorbed
-Taste masking, by closing it into the first emulsion (o/w) it is not getting in contact with the taste buds
How are microemulsions formed?
-Emulsions that are turbid can be made clear by adding an emulsifier cosurfactant and a co-emulsifier, the interfacial tension between oil and water is reduced to a degree that very small globules are formed -> no light scattered
-Droplet size (10-200 nm)
-clear, like solutions
-more stable than traditional emulsions
What are self-emulsifying DDS?
all ingredients added except water in a capsule -> the emulsion is formed once the DDS is in the body where there is a lot of water
composed of drugs, oil, surfactant, and cosurfactant - no water
bc it is an emulsion it gets into chylomicrons and lipoproteins -> lymphatic system
-a fine emulsion is formed in the GI tract and absorbed through the lymphatic system and thereby passing the liver bc lipid-soluble drugs are absorbed differently (f.e. a product with testosterone -> Testosterone is prone to first-pass metabolism)
Purpose of Emulsions:
-Stability: for drugs that are not stable in water -> incorporate in f.e. oil and make an emulsion
-Taste-masking: The taste of Drugs and oil can be masked and dispersed in a sweetened, flavored aqueous vehicle
-Therapeutic efficacy: by putting the drugs in small globules -> thereby reducing particle size and increasing the surface area -> and absorption of the drug
Which DRUG DELIVERY SYSTEMS are used with Emulsions?
-Oral Liquids (common)
-Parenterals (caution: Precipitation can lead to the death of patients)
-Creams, Lotion, Shampoo
What are some application for o/w and w/o Emulsions:
-Oral preparations: o/w -> taste masking oil globules and faster absorption
-Topical: o/w: retain moisture in skin
w/o: spreads more readily on the skin
IN-CLASS ACTIVITY:
Describe the Vials and explain observation
Vial #1 oil and water layer: no emulsifier added
Vial #2: turbid/translucent, it has mixed: Emulsion
Vial #3: transperent: Microemulsion
What are the most important factors determining the type of Emulsion?
Order of mixing and the type of emulsifying agent
-To make an emulsion there are always at least 3 ingredients needed: Dispersed (internal phase), Dispersion medium (continuous phase), and Emulsifying agent (mostly surfactant)
Why is the amount of ingredients of the internal and external phases relative?
-Mostly the internal phase is less than the external, but it is possible to have 74% of the internal phase and still form a stable emulsion -> because the globules can be very well packed together
-it is the emulsifying agent that tells if it is o/w or w/o -> acacia f.e. always form o/w emulsions
Why is the Order of Mixture important in Emulsions?
-It determines the type of emulsion:
-creating a primary emulsion is important
-oil soluble-components should be added to the oil phase and water-soluble components to the water phase (drugs, preservatives)
-2 preservatives for each phase (the preservatives will partionate into the different phases - we need combined effect??)
What are the different types of emulsifying agents?
-Natural: Acacia, tragacanth, alginates, xanthan
-Finely Divided Solids: Bentonite, Veegum
-Synthetic: Surfactants (Tweens and Spans) and Co-surfactants (reduces interfacial tension even further, i.e. Ethanol)
-High molecular weight alcohols: Cetyl alcohol, stearyl alcohol
Describe the Dry Gum Method: 4:2:1
The goal of the Methods is the create the primary emulsion!
4 oil: 2 water: 1Gum –> with FIXEX OILS that are not volatile
-Acacia is emulsifying agent -> o/w
-good for smaller scale
-need Wedgwood mortar and pestle (rough surface for nice friction)
-First triturate Oil (all at once) and Gum before adding water (DRY GUM METHOD) -> cracking sound indicates that the primary emulsion is ready -> add water and other ingredients (color, preservatives)
-If alcohol is used, add it diluted with water and as close at last as possible, bc it can precipitate water and gum out -> Emulsion breaks
How should the formulation be adjusted when working with volatile oils?
Reduce the amount of oil (3:2:1 or 2:2:1) or increase the amount of gum
Describe the WetGum Method: 4:2:1
-The same ratio, just the order of mixture has changed
-First Water and Gum, triturate -> add oil gradually (not at once)
Which method is used for volatile oils?
-Bottle Method (closed system) bc the oil is volatile and would be lost -3:2:1 or 2:2:1 ratio
-Dry Gum Method: Add acacia and oil -> mixing -> add water slowly to make the primary emulsion
How are MULTIPLE EMULSIONS created?
-Two steps f.e. w/o/w
-1. create w/o by adding an emulsifier that is lipophilic bc it interacts with oily medium
-2. now I have a w/o emulsion -> add an emulsifier that is hydrophilic bc it needs to interact with water medium -> w/o/w
How are Microemulsions created?
-The process is spontaneous and requires simple mixing
-The hard part is to create the formula with high amounts of surfactants and co-surfactants
Can the principles of Stokes Law used in Suspension also be used in Emuslions?
Yes, the only difference is that in Suspension we describe the settling of particles, whereas in emulsions we talk about globules
-The same factors are adjusted to prevent the separation of the two phases
-For o/w the oil globules are lighter than water, so they may move upwards (creaming) -> density value (difference between globule and medium density) can be negative
Instability in Emulsions: Creaming
After a period there will be separation
-for o/w the oil globules will move up bc they are lighter
-for w/o the water globules moving down bc they are heavier
-Emuslion is not broken -> can be recovered by shaking
Instability in Emulsions: Aggregation
-Droplets come together and form flocks and move up or down (depending on o/w or w/o)
-It is reversible as long as individual droplets exist
Instability in Emulsions: Coalescence
-Exposed to extreme temperature -> damages the interfacial tension reduction of the surfactant, so there is nothing that separates globules and media -> BREAK
-CANNOT be redispersed -> separate layer visible
Which parameters can be adjusted to enhance the stability of an emulsion?
Prevent separation
-Increase viscosity of continuous phase
-Reduce the particle (droplet) size of the internal phase
-Increase the fractional volume of the internal phase (enable better packaging -> 74% internal phase)
-Increase the amount of emulsifying agent
Wich auxiliary labels are added to Emulsions?
Shake well. Different storage conditions. (never freeze -> it will break)
Which ingredients should not be administered to the elderly and neonates?
-No preservatives, colors, flavors, or alcohol for neonates
-No benzyl alcohol or Propylene glycol for neonates
-No alcohol-containing drugs for elderly and patients taking anti-depressants
How are BUDs determined?
for Nonpreserved aqueous dosage form (Solutions, Suspensions, Emulsions) -> the active amount of water that supports microbial growth is determinant -> 14 DAYS; 35 DAYS with preservatives
Liquid but Nonaqueos (f.e. oil): 90 days (microbes don’t grow in oil)
Nonaqueos (nonoral -> topical): 180 days
