PH2107 - Emulsions 1 Flashcards
What is an emulsion?
A dispersed system comprised of two or more immiscible liquids
- oily
- aqueous
What are the two phases that make up an emulsion?
Disperse phase
Continuous phase
What state are emulsions in?
Emulsions may be semi solids or liquids
What determines the state of an emulsion?
The oil and water proportions
Route of administration
How is an emulsion formed?
High energy input needed as they are thermodynamically incompatible
Why are emulsions thermodynamically unstable ?
Globules tend to:
adopt a spherical shape, due to surface tension
coalesce, merge with other globules – without an emulsifier
What can be added to an emulsion to increase kinetic stability?
An emulsifier (emulgent)
What is the general size of an emulsion ?
Emulsions can have broad droplet sizes not always nano, often micro range, but generally a mean diameter of ~1µm
Mini-emulsions and nano-emulsions can be formed with droplet sizes in the 100-500 nm range.
What are microemulsions typically used for?
To kill microbes (bacteria, viruses), blood and sperm
How much force is needed to make a microemulsion?
The smaller the droplet, the greater the surface tension and thus the greater the force to merge with other lipids
How is a microemulsion made?
The oil is emulsified with a high shear mixer with detergents to stabilise the emulsion, so when they encounter lipids in the membrane or envelope of bacteria/viruses, they force the lipids to merge with themselves, disintegrating pathogen membrane
What is a vesicle?
A supramolecular assembly of lipid molecules in an aqueous environment
What is a bilayer?
A fundamental structural feature of a biological membrane
What is a micelle?
A spherical aggregate, ~150nm of surfactant molecules dispersed in a liquid colloid
What is a normal phase micelle?
A micelle with the headgroups facing away from the centre (oil-in-water micelle)
What is an inverse micelle?
A micelle with the headgroups at the centre with the tails extending out (water-in-oil micelle)
What are the two types of emulsions?
Oil in water (o/w)
Water in oil (w/o)
What is a multiple layer emulsion?
Multiple emulsions - concentric multi-layer structures
Give some uses for multiple layer emulsions
- carrier systems for protein or peptide drugs e.g. insulin
- to encapsulate drugs to protect them from physiological environment
- controlled release drug delivery e.g. synthesis of PLGA nanoparticles
What is the ‘double emulsion technique’?
Encapsulation of hydrophilic or lipophilic molecules in polymeric nanoparticles
What are the advantages of using emulsions for oral use?
- convenient way of giving water insoluble drugs (o/w)
- mask unpleasant tasting drugs (only taste continuous phase)
- some oil soluble compounds have increased absorption from GI tract when emulsified than when given as an oily oral solution
What are the advantages of using emulsions for parenteral use?
- some parenteral formulations work better/faster as an emulsion than as an oil
- w/o injections given intra-muscularly (IM) can act as depots (slow drug release)
What is TPN?
Total parenteral nutrition - a method of feeding that bypasses the gastrointestinal tract
- fluids are given into a vein to provide most of the nutrients the body needs
What are used to supply total nutrition or specific components e.g. lipids in IV nutrition?
o/w systems
What are the advantages of using emulsions for ocular use?
Eye is sensitive - emulsions have a more pleasant feel
Give an example of an emulsion used to treat dry eye
Cationorm - o/w emulsion formulation to treat dry eye. It restores moisture (moisturises) from water + electrolytes but also helps to prevent fluid loss or evaporation (oil)
- oil phase also helps lubricate movements
What is a common form of drug delivery?
Topical delivery
- skin
- mucous membranes
- gingiva
- rectum
- vagina
What are creams?
Emulsions, as semi-solid (high viscosity) preparations of oil and water
Give two examples of unmedicated creams that are used in a variety of skin conditions (dermatoses)
Emollients
Humectants
What is an emollient?
Cosmetic preparations used for protecting, moisturising and lubricating the skin (barrier)
What is a humectant?
Have an emollient effect but they act by drawing water or urea into stratum corneum
What is a medicated emulsion?
Facilitate drug uptake
- oil absorbed into skin along with the drug
What are the properties of o/w emulsions?
- absorbs water
- used for local effects
- washable
- non-greasy
What are the properties of w/o emulsions?
- occlusive
- water repellant
- decreases water loss from skin
- enhances drug penetration
- feels greasy
How can you determine the emulsion type?
Feel
- emulsions feel like the continuous phase (water or oil)
Miscibility
- o/w emulsion should dilute readily upon adding more water
Staining
- water soluble dye (e.g. food colourant) will colour o/w emulsion
Conductivity
- o/w conducts electricity
- w/o does not conduct electricity
Why are emulsifiers essential in keeping the oil dispersed throughout the water phase?
Emulsions are thermodynamically unstable
What happens when an emulsifier is added to a mixture of water and oil?
Polar groups associate with water molecules while non-polar parts enter the oil phase
Where is an emulsifier located in an emulsion?The globule/continuous phase interface
The globule/continuous phase interface
What factors determine the effectiveness of an emulsifier?
Balance between its hydrophilic and lipophilic characteristics relative to oil and water phases
What are the five processes that determine how effective an emulsifier is?
- Emulsifiers form a flexible interfacial film (physical barrier) to help prevent coalescence when globules come into contact
- Emulsifiers provide a surface charge to globules, causing electrostatic repulsion with adjacent molecules
- Emulsifiers reduce interfacial tension
- Emulsifiers prevent globules coming into close contact by steric hindrance of hydrated side chains
- Increased continuous phase viscosity slows globule movement and decreases likelihood of collision and coalescence (semi-solids = cream)
Describe the barrier around the oil globules in o/w emulsions
Either due to
- electrical (polar)
- steric repulsion (non-polar) effects
What causes repulsion between water droplets in w/o emulsions?
Non-polar effects from the hydrocarbon part of interfacial film
Which groups are better barriers to coalescence in a barrier?
Polar groups compared to non-polar groups
Which type of emulsions are generally more stable?
o/w are generally more stable than w/o
