Green: Emulsions Flashcards
What is phenylepherine used for?
Decongestant
What is Dextromethorphan used for?
Cough suppressant
What are emulsions and creams?
Dispersion of one liquid into another
What are the other characteristics emulsions have?
- Coalescence: given time the liquid is separated into two phases
- Surfactants and micelles are in both phases
- Surfactants form complex liquid crystalline micelles
What are the different types of emulsions that are available?
- Oil in water: Generally more comfortable and used cosmetically as they are easy to wash off with water from skin (most common)
- Water in oil:
- Are more hydrophobic so tend to release the drug more readily from the emulsion.
- More moisturising as they can provide an oily barrier to prevent water loss - Oil in water in oil
What is the purpose of having different emulsions?
- Renders oily substances like liquid paraffin more plate able
- Delivery of water insoluble drugs
- Topical administration
- Delayed and modified release
Define what flocculation and coalescence is?
- Flocculation: fine particulates caused to clump together into a floc.
- Coalescence: two or more droplets, bubbles or particles merge during contact to form a single particle
What is creaming?
When the floc floats to the top of the liquid
Why do you want to avoid creaming?
- Reduced droplet size and density difference
- Increased viscosity
- Disperse phase concentration
- Prevents flocculation and coalescence
What does a normal surfactant do and what are the advantages of each type of surfactant do?
- Surfactant: aids dispersal and reduces tendency for coalescence
- Charged surfactants:
- Increase surface charge
- Repulsive interactions between droplets - Non ionic surfactants:
- Solvated layer for steric repulsion
- Lack of toxicity
- Lower sensitivity to additives - Mixed surfactants are better
What does the hydrophile-lipophile balance (HLB) number represent and what is it for?
- Whether the surfactant is hydrophobic or hydrophilic
- This is determined by by knowledge of polar and non polar functional groups in surfactant
- Determines the appropriate emulsifier
How do you form the perfect oil in water emulsion?
- Surfactant needs to confer stability (hydrophilicity)
- Ensure adsorption (hydrophobicity)
- Optimal hydrophile-lipophile balance is determined by minimal creaming
What do the use of mixed surfactants consist of and
- Mixture of high and low HLB gives a more stable surfactant
- Keep surfactant concentration as low as possible
- Pick surfactant concentrations where molecular interaction is likely
For each specific emulsion, what can they be used for? (which route)
- Oil in water: oral, intravenously and topically
2. water in oil is more greasy but more hydrating for the skin
Give examples of different uses of emulsions
- Vehicles
- Surfactants
- Preservatives: partition in oil phase when needed in aqueous phase
- Flavouring
- Viscosity and density modifiers
- Antioxidants
- Humectants: Retain moisture on the skin
What are the two tests necessary for different emulsion types?
- Miscibility test:
emulsion only miscible (mixes) with liquids that are miscible in the emulsion phase - Conductivity:
Aqueous continuous phase (causes light to glow) that readily conducts electricity - Staining test:
- Use of water or oil soluble dyes
Explain how surfactants are used as emulsifying agents?
- Adsorbs (adhesion) at interface between immiscible liquids (barrier to coalescence)
- Use of a mix of oil and water soluble surfactants
- Non ionic, less toxic and less sensitive to electrolytes
- Increases surface area and decreases surface tension
Explain how Hydrophilic colloids are used as emulsifying agents?
- Proteins (gelatin) and Polysaccharides (acacia)
- Viscoelastic layer is formed which is many multilayers of interacting polymers
- This provides mechanical robust to prevent coalescence
Explain how finely divided solids are used as emulsifying agents?
- Adhere to interface
2. Needs to be wetted to one phase
Describe how the viscosity affects the control of which rheological properties?
- Dispersed phase concentration: increased viscosity
- Radius of dispersed phase: small size increases viscosity
- Viscosity of continuous phase
- Surfactant emulsifier
How do you measure the rate of creaming or coalescence?
- Rate of volume: creamed and total volume
- Change in size of globules
- Viscosity changes
What are the different uses of emulsions?
- Oral, rectal and topical administration of oil soluble drugs
- Sustained release of dosage form
- Intramuscular injections of water soluble vaccinations: slower release of antigens and greater immune response - w/o/w
- Prolonged release and lower viscosity than w/o subcutaneous or intramuscular
