Internal & External Emulsions Flashcards
Define what an emulsion is and the medicines in which they may be used
Defined as a dispersion of liquid droplets in an immiscible liquid.
Immiscible liquids do not mix- such as oil and water.
- Without the emulsifying agent the oil would simply float on top of the water (as it usually has a lower density)
- they can be o/w or w/o
Reason for formulating:
- to dissolve a poorly-soluble drug in the oil phase
- to administer oil into the body either orally or through injections
- to create a range of liquids for applications to skin
Application of different medicinal formulations of emulsions include:
- oral emulsions and formulations for IV/IM injections
- total parenteral nutrition
- external creams, ointments, liniments and lotions
Examples of medicines outside pharmacy include milk, vinaigrette’s, mayonnaise and paint
Know different types of emulsions, lotions and collodion
Surfactant: surfactant molecules have hydrophobic and hydrophilic parts, so they are but like oil and a bit like water, the naturally self assemble at an oil/water interface, interface is stabilised so the oil and water mix, resulting product is an emulsion like.
Emulsion: continuous and dispersed phase, o/w w/o type will depend on emulsifying agent for example lotion would be o/w and ointment would be w/o, properties will be affected by the drug and droplet size , factors in wk0
Understand common excipients and their functions
Antioxidants – stabilise the emulsion from degradation
- Oils are liable to oxidations
- Added to the oil phase
Preservatives
- Water supports microbe growth and may feed on the emulsifying agent
- Needs to inhibit bacterial growth to maintain the safety of the product
- e.g. benzoic acid, chloroform, chlorocresol, cetrimide
- e.g. parabens (methyl-, ethyl- and propyl- parahydroxybenzoate)
Buffers – to maintain pH
- Same considerations as oral solutions
Acidity modifiers – to change pH
- Same considerations as oral solutions
Colouring agents, flavourings and sweeteners
Same considerations as oral solutions
Describe the stability and packaging of different formulations
When formulating emulsions aims are to:
- Retain the distribution of droplets globules at an optimum size
- Prevent extremes of temperature that can result in changing droplet size
- Use stabilisers to prevent coalescence of droplets
- Limit degradation of the component with suitable packaging
- Prevent microbial contamination
Discuss similarities and differences between different types of emulsions
A
Discuss advantages and disadvantages of the use of emulsions
A
Emulsion stability
Coalescence: droplets start to combine into bigger droplets irreversibly which the leads to breaking/cracking
Flocculation: droplets aggregate but do not combine, shaking can redisperse
Creaming: oil rises to the top or sinks to the bottom in an o/w emulsion, shaking can redisperse
Breaking: two phases separate irreversibly with the lower-density liquid floating on top of the higher-density liquid (also known as cracking)
Phase intervention: changes in temperature can interchange o/w and w/o
Emulsifying agents
can be found in wk 1 (internal and external emulsions)
hydrophilic-lipophilic balance (HLB
The hydrophilic-lipophilic balance (HLB) is a number usually between 1 and 20 that is attributed to the relative proportions of the hydrophilic and lipophilic parts of an emulsifying agent, where:
Low number = oil soluble agent (w/o)
High number = water soluble agent (o/w)
Emulsifying agents with a low HLB of less than about 8 will be predominantly lipophilic or oil-like in nature, and as they stabilise or wet oil better than water, a water-in-oil emulsion results. An example is sorbitan stearate with an HLB number of 4.7. Those with a higher HLB of more than about 8 will be predominantly hydrophilic or water-like in nature, and as they stabilise or wet water better than oil, an oil-in-water emulsion results. An example is tragacanth with an HLB number of 13.2
Emulsion identification
Miscibility test
- o/w: addition of water can be performed
- w/o: the emulsion breaks
Conductivity test
- o/w: electricity will be conducted when the continuous phase is water
- w/o: conduction does not occur
Staining test
- o/w: emulsion will spread rapidly on filter paper
- w/o: spreading does not occur
Dye test
- o/w: addition of a water-soluble dye will change the colour evenly
- w/o: the colour change will be less pronounced
