Emulsions and Creams Flashcards
What is a emulsion
A homogeneous liquid or semisolid preparation consisting of TWO immiscible liquids (oil and water) mixed together by the addition of an emulsifying agent
- one of the liquids (dispersed phase) is uniformly distributed as droplets throughout the other (continuous phase)
- o/w: oil droplets dispersed in aqueous continuous phase
- w/o: water droplets dispersed in oil continuous phase
- multiple emulsions, microemulsions, nanoemulsions
What are microemulsions and nanoemulsions?
- o/w nanoemulsions: used in cosmetics, pharmaceutical, food, agricultural industries as delivery systems for active lipophilic compounds and drugs
- Translucent nanoemulsions: extremely small droplet size provides long-term stability, high concentrations of active, solubilize lipophilic actives, improves skin absorption and enables the delivery of exceptionally high concentrations of active substances.
- High-power ultrasound and other techniques used in the preparation.
How to identify emulsions?
- Miscibility tests: add small quantity of emulsion to water or oil – will mix only if continuous phase is same as solvent
- Microscopic examination after staining with oil soluble dye (eg Scarlet Red: w/o -red; o/w – pink) or water soluble dye such as methylene blue
- Conductivity measurement: o/w will conduct electricity
What are types of emulsion instability?
- Creaming: dispersed phase rises or sediments - reversible
- Cracking/coalescence: irreversible (may be caused by any chemical, physical or biological effect that changes the nature of the interfacial film)
- Phase inversion: o/w becomes w/o or vice versa
What are some examples of oral emulsions? What are their advantages and disadvantages?
- Milk
- Rationale for pharmaceutical emulsions
- Oil in water (o/w)
General: oil phase divided into minute droplets, coated with emulsifying agent, then suspended in aqueous phase.
> Used for flavouring, colouring presrevative
Advantages
- Formulation of unpalatable drugs
- Aqueous phase easily flavoured
- Increased rate of absorption
- Can incorporate 2 incompatible ingredients
- Useful for enteral nutrition: high calorie
Disadvantages
- Require effective shaking before use
- Storage conditions may affect stability
- Liable to microbial contamination which can cause instability
What are some components of oral emulsions?
Emulgents
- Emulsifying gum eg acacia –
- Methylcellulose, magnesium hydroxide, aluminum hydroxide
Oil
- Fixed oils eg Arachis, castor, cod liver oil
- Mineral oils eg liquid paraffin
- Volatile oils eg cinnamon, peppermint oil
Water
- Freshly boiled and cooled purified water
- Preservative, flavoring, coloring agents
How to prepare oral emulsions?
- A thick, primary emulsion must by firstly prepared (ratios for this is in attached image)
- Wet gum method: triturate the acacia with water to produce a mucilage. Then add oil.
- Dry gum method: triturate acacia with oil first, just for a short time, then add all the water at once and triturate thoroughly
What are some examples of topical formulations and external emulsions
See attached image
- o/w and w/o emulsions
- Liniments, lotions, creams, foams
What are some formulation components of external emulsions?
Aqueous phase: Water, alcohol, preservative (e.g. benzoic acid, chlorocresol, phenoxyethanol, cetrimide, parabens)
Oil phase: – Mineral oils eg liquid paraffin – Vegetable oils eg arachis, coconut, olive oil – Synthetic oils eg dimethicone
Emulgent: determined using the HLB method by the type and quantity of oil present in the formula
Why mix both phases after warming
- Used for waxes that require heat to melt
- Emulgent added to phase in which miscible or soluble
- Water temperature slightly above oil temperature (≈65C)
- Phases mixed – water generally added to the oil and stirred to cool
- Slow cooling to prevent granular product
- Adjust to weight
How does emulsification by precipitation happen? Provide an example
- Oil dissolved in solvent such as ethanol containing emulgent
- Solution added to large volume of water
- Emulsion formed
Example: Coal tar solution to water with polysorbate 80 (Tween 80)
> Coal tar solution is 20% coal tar in alcohol with polysorbate 80
What is the method of adding the emulgent?
- Add in water phase or oil phase – dependent on the solubility of the emulgent
- Nascent soap (formed in situ)
> Formed from combination of fatty acid (in oil) and alkali (in aqueous phase)
> Type of soap formed determines o/w or w/o emulsion as product
> Eg potassium oleate – o/w
> Eg calcium oleate – w/o
What are some properties of emulsifying agents?
Surface-active agents or surfactants
- Polar group = hydrophilic
- Non-polar group = lipophilic
HLB: hydrophilic-lipophilic balance of surfactant effects type of emulsion:
- high HLB – high hydrophilicity
- low HLB – high lipophilicity
Ideal properties: colourless, odourless, tasteless, non-toxic, non-irritant, form stable emulsions at low conc
Uses: topical formulations, parenteral formulations, solubilisers, cleaning/disinfecting
What are the types of emulsifiyng agents?
Synthetic or semi-synthetic emulgents
- Anionic, cationic, non-ionic, ampholytic surfactants
Natural products
- Polysaccharides, sterols
Finely divided solids
- Natural clays, bentonite
- Preferential wetting determines emulsion type
What are anionic surfactants? Provide some examples?
Dissociate in aqueous solution to form large surface active anion (negative)
- Alkali metal soaps
- Ammonium soaps
- Di and tri-valent metallic soaps
- Amine soaps
- Alkyl sulphate soaps
Aqueous cream is anionic, what is found in aqueous cream?
Discuss the properties and incompatibilities of cationic surfactants
See attached image for ingredients for cetrimide cream aqueous APF (cationic)
- Quaternary ammonium compounds
- o/w emulsifying agents
- General formula: (R1R2R3R4N)+. X-
- Eg. Cetrimide: C16H33CH3CH3CH3N+.Br -
- Emulsifying power poor if used alone
- Used in combination
Properties
- Water soluble (use hot water to reduce froth)
- Bactericidal (also benzalkonium chloride – antibacterial and preservative, not emulgent)
- Relatively toxic: external use only
- Stable pH 3-7 therefore good skin compatability
- Unaffected by di and trivalent cations
Incompatabilities
- Anionic agents, iodine, alkali hydroxides
- Strong w/o non-ionic emulsifiers
- Bacteriocidal activity reduced by Cetomacrogol emulsfiying wax
Cetamoacrogol cream aqueous APF (sorbolone cream) is non-ionic, what is found in non-ionic cream?
Compare anionic, cationic and non-ionic emulgents/ointments/creams
How to incorporate ingredients into a cream base?
See attached image
