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PM2B Spring Amy L > Emulsion Dosage Forms > Flashcards

Emulsion Dosage Forms Flashcards

1
Q

What are emulsions and creams?

A

Dispersions of 1 liquid into another

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2
Q

What are the 3 types of emulsions in pharmaceuticals?

A

Oil in water (o/w)
Water in oil (w/o)
Multiple emulsions (e.g. o/w/o)

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3
Q

Describe oil in water (o/w) creams

A

More comfortable and cosmetically acceptable as they are less greasy and more easily washed off using water

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4
Q

Describe water in oil (w/o) creams

A

More difficult to handle
Many drugs incorporated into creams are hydrophobic - will be released more readily from this type of cream
They are also more moisturising - provide an oily barrier which reduces water loss from the stratum corneum

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5
Q

Define: Flocculation

A

The process by which individual particles aggregate into clot-like masses or precipitate into small lumps - of the dispersed phase

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6
Q

Define: Coalescence

A

The process by which 2 or more particles merge during contact to form a single particle - of the dispersed phase
(Groups of particles from flocculation forming fewer but larger masses)
Irreversible

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7
Q

Define: Rapid creaming

A

The migration of a dispersed phase of an emulsion under the influence of buoyancy
The particles float upwards (or sink) depending on their mass and the viscosity of the continuous phase
This is reversible - by shaking
Can happen at any stage of the separation of an emulsion

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8
Q

Define: Cracking/breaking

A

The complete separation and fusion of the dispersed phase

Irreversible

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9
Q

List 5 ways of avoiding creaming

A
  1. Reduced droplet size
  2. Increase viscosity
  3. Reduced density difference (between the 2 phases)
  4. Disperse phase concentration
  5. Prevent flocculation and coalescence
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10
Q

How do surfactants affect the stability of emulsions?

A

Surfactants aid dispersal and reduce tendency for coalescence

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11
Q

How do charged surfactants prevent flocculation and coalescence?

A

Charged surfactants increase surface charge = repulsive interactions between droplets
Phospholipids surround the oil droplet with the charged hydrophobic heads pointing outwards
Prevents flocculation and coalescence

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12
Q

How do non-ionic surfactants prevent flocculation and coalescence?

A

Non-ionic surfactants create a solvated layer leading to steric repulsion (due to tails)
Head of phospholipid in aqueous droplet, tails pointing outward
They lack toxicity and lower sensitivity to additives

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13
Q

What is the best kind of surfactant?

A

Mixed surfactant = mixture of those with high/low HLB numbers give more stable emulsions

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14
Q

What is an HLB number?

A

Hydrophile Lyophile Balance
Determines whether a surfactant is predominantly hydrophobic or hydrophilic
Decided based on the polar/non-polar functional groups in the surfactant
High HLB number (18) = hydrophilic, water-soluble

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15
Q

What does a high HLB number imply?

A

That the surfactant is hydrophilic and water-soluble
e.g. solubilising agents and detergents
18

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16
Q

What does a low HLB number imply?

A

That the surfactant is hydrophobic and oil-soluble
e.g. anti-foaming agents
3 or 0

17
Q

What does a medium HLB number imply?

A

That the surfactant is water dispersible
e.g. wetting/spreading agents
9

18
Q

Name a method used to decrease the size of droplets

A

Passage through colloid mill

19
Q

Which type of emulsion should only be used for oral and IV preparations?

A

Oil in water

20
Q

In which situations are oil in water emulsions best?

A

Oral
IV
Topical - but water in oil more hydrating

21
Q

In which situations are water in oil emulsions best?

A

Topical - more greasy formulation but more hydrating than o/w
Not for use in oral or IV preparations

22
Q

How do viscosity modifiers affect the stability of emulsions?

A

Can decrease the rate of creaming by addition of hydrophilic colloids (polymers)
e.g. methylcellulose

23
Q

Define: Colloid/Colloidal dispersions

A

A solution which contains particles between 1-1000 nanometers in diameter
But are able to stay evenly distributed throughout the solution

24
Q

What is a possible issue with preservatives in an emulsion?

A

They may partition into the oil phase when they are required in the aqueous phase

25
Q

What is the purpose of including humectants in an emulsion?

A

Humectants help to retain moisture on the skin

26
Q

List 3 tests used to identify the emulsion type

A
  1. Miscibility test - o/w emulsion will be miscible in water
  2. Conductivity - aqueous continuous phases readily conduct electricity
  3. Staining test - use of water-soluble or oil-soluble dyes
27
Q

List 3 emulsifying agents

A

Surfactants
Hydrophobic colloids
Finely divided solids

28
Q

How do surfactants act as emulsifying agents?

A

Adsorb at interface between immiscible liquids = barrier to coalescence
Lower the surface tension by increasing surface area
Use of a mix of oil & water soluble surfactants
Non-ionic surfactants = less toxic and less sensitive to electrolytes/pH

29
Q

How do hydrophilic colloids act as emulsifying agents?

A

Polymers
Form viscoelastic layer = multi-layer of interacting polymers (network)
This provides mechanical robustness to prevent coalescence
Don’t significantly reduce surface tension

30
Q

How do finely divided solids work as emulsifying agents?

A

They adhere to interface
Need to preferably wetted to 1 phase
Can act to provide mechanical robustness to prevent coalescence

31
Q

What type of emulsion has the greater viscosity?

A

Water in oil emulsion exhibits a higher apparent viscosity

32
Q

Define: Rheological properties

A

Those relating to flow

33
Q

List 4 factors which affect the rheological properties

A
  1. Dispersed phase concentration = increases viscosity
  2. Radius of dispersed phase = small size increases viscosity
  3. Viscosity of continuous phase
  4. Surfactant emulsifier
34
Q

How can the rate of creaming or coalescence be measured?

A
  1. Ratio of volumes - creamed:total volume
  2. Changes in size of globules
  3. Viscosity changes

Used to investigate properties of the emulsion

35
Q

What are microemulsions?

A

Isotropic liquid mixtures, thermodynamically stable
Contain high percentage of oil, water and 15-25% emulsifier
Can form spontaneously - swollen micelle

PM2B Spring Amy L (16 decks)

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