Emulsions Flashcards by Denisse E

What is an emulsion?

Dispersed system containing at least two immiscible liquids

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What is the dilution test?

Determines emulsion type- relies on the fact that o/w emulsions can be diluted with water and w/o can be diluted with oil

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What is the conductivity test?

An o/w emulsion will be a better conductor than a w/o one

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What is the dye-solubility test?

Determines emulsion type- uses oil soluble and/or water soluble dyes.

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What type of emulsion is used for IV administration?

O/W

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What type of emulsion is used for oral administration?

O/W to ensure a pleasant taste

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What type of emulsion is used for IM administration?

W/O

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What additives are used for emulsions?

Antioxidants, preservatives, humectants

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Which specific oils can be used for IV administration?

Cottonseed, soya bean oil. safflower oil

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What types of anionic emulsifying agents are there?

Alkali metal and ammonium soaps (o/w)
Amine soaps (o/w)
Sulfated and sulfonated compounds (o/w)
Soaps of divalent and trivalent metals (w/o)

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What types of non-ionic emulsifying agents are there?

Polysorbates (o/w)
Fatty alcohol polyglycol ethers (o/w)
Fatty acid polyglycol esters (o/w)
Poloxalcohols (o/w)
Glycol and glycerol esters (w/o)
Sorbitan esters (w/o)
Higher fatty alcohols (emulsion type depends on other surfactant)

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Which surfactants are soluble for parenteral injections?

Lecithin, polysorbate 80, poloxamers

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What is an in situ emulsifier?

Emulsifier is formed upon mixing of separate components during the compounding process

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What are quaternary ammonium compounds? When are they best used at?

Surfactants that form cations in aqueous solutions. Best at a pH of 4-6, and incompatible with anionic surfactants and polyvalent anions.

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What are spans? HLB range?

Sorbitan esters (w/o emulsions)-- hydroxyl groups of sorbitan esterified with acids.
HLB range 2-10

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What are tweens? HLB range?

Polysorbates (o/w)– polyethylene glycol derivatives of sorbitan esters.
HLB range 10-18

What are the advantages of tweens (polysorbates) as surfactants?

Versatile, can be used in all dosage forms, safe, non-toxic, non-irritating.

What’s an example of a semisynthetic polysaccharide?

Methylcellulose (o/w)

What is the relationship between surfactant concentration and interfacial tension?

More surfactant=less interfacial tension, up to a point which we call the CMC of the surfactant. At the CMC (surface layer is saturated with surfactant), micelles start to form, which don’t affect interfacial tension.

What equation can we use to describe the interfacial tension and adsorption of surfactant molecules? What is surface excess surfactant concentration?

Gibb’s adsorption equation. Represents surface excess surfactant concentration, which is the portion of surfactant that occupies that interface and contributes to lowering the interfacial tension.

What is a mixed micelle?

Blend of surfactants used in the preparation of an emulsion

What is the aggregation number?

Number of surfactant molecules that form one micelle

What does HLB describe?

Describes the hydrophilic-hydrophobic characteristics. 0-10 means it’s lipophilic. 10-20 represents hydrophilic characteristics.

Which emulsifying agents form monomolecular films around the disperse phase?

Ionic and non-ionic surfactants

Which emulsifying agents form multimolecular film around the disperse phase?

Hydrocolloids- acacia, gelatin

How does bentonite exert its emulsifying properties?

Forms a solid particle film on the surface of oil droplets

Describe the properties of non-ionic and ionic emulsifiers

Non-ionic: less toxic, less irritant. Includes those that can be used for parenteral administration Ionic: should not be given orally, irritates the GIT. Cationic are toxic at low concentrations and should only be used externally, while anionic have a high pH and are unsuitable for broken skin.

What is the role of antioxidants?

Prevents it from going rancid by preventing auto-oxidation of oil and lipid components

What is the role of preservatives?

Prevents growth of micro-organisms

How are preservatives inactivated in emulsions?

Micellar binding of preservatives with surfactants may inactivate them

What equipment can be used for emulsification?

Mechanical stirrers (allow for mixing of large quantities, used for low viscosity preparations) Homogenizers (pressure through a small hole, not suitable for viscosities over 2000cP) Ultrasonifiers Colloid mills (frequently used)

What is coalescence?

Complete fusion of droplets within an emulsion. Leads to a decrease in the number of droplets and irreversible separation of the two immiscible phases.

How can you determine the rate of creaming/sedimentation in an emulsion?

Stoke's law of sedimentation can be used. Creaming will result in a negative number.

What stress conditions are used for assessing emulsion shelf life?

Aging and temperature Centrifugation Agitation

What is the reason for coalescence and how can you prevent it?

Can be caused by a low zeta potential, high surface free energy, or high interfacial tension. Can be prevented by adding protective colloids, adding more surfactant, or optimizing particle size.

What is the reason for creaming and how can you prevent it?

Can be caused by flocculation and upward sedimentation. | Can be prevented by adding protective colloids or more surfactant.

What is the reason for foaming and how can you prevent it?

Caused by too much surfactant in the formulation. | Can be prevented by reducing surfactant concentration.

What is the reason for microbial growth in an otherwise preserved emulsion and how can you prevent it?

Can be caused by the preservative-surfactant interaction leading to reduced antimicrobial function. Can be prevented by adding more, or a different preservative.

What is the reason for unpleasant taste, and how can you prevent it?

Can be caused by an inappropriate amount of certain excipients, preservatives, or lack/inappropriate amount of sweetener and flavouring agent. Can be prevented by reducing/optimizing excipient concentrations or adding more/different sweetener/flavour.