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MPharm 2 - PH2107 > Unit 2 - Topical formulations 2 > Flashcards

Unit 2 - Topical formulations 2 Flashcards

1
Q

What is the function of an absorption base as an ointment base?

A

Absorb water (from skin or air) to form water-in-oil emulsions (cf. cream)

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2
Q

How are absorption bases made?

A

Anhydrous vehicles composed of a hydrocarbon base and an emulsifier

  • sterols
  • sorbitan monosterate
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3
Q

How do absorption bases as an ointment base work?

A

Deposits a greasy, occlusive film on the skin surface

- less suppression of trans-epidermal water loss than hydrocarbons

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4
Q

Which structure in the skin is targeted by absorption bases as an ointment base?

A

They hydrate the stratum corneum (w/o emulsion)

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5
Q

What is the opposite of an absorption base?

A

Emulsifying base (o/w emulsion)

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6
Q

What are the three types of emulsifying base?

A
  • anionic (negatively charged)
  • cationic (positively charged)
  • non-ionic
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7
Q

Why do emulsifying bases as an ointment base contain surfactants?

A

May help with spreading

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8
Q

What are the advantages of emulsifying bases as an ointment base?

A

Mix with aqueous secretions and readily wash off skin

  • useful for scalp treatments
  • get a much more even layer
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9
Q

What are water soluble bases as an ointment base prepared from?

A

Polyethylene glycols

  • high molecular weight
  • low molecular weight (less viscous)
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10
Q

What are the advantages of water soluble bases as an ointment base?

A
  • non-occlusive (water soluble)

- do not stain clothing

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11
Q

What are the disadvantages of water soluble bases as an ointment base?

A

Incompatible with many chemicals

- limits what you can add to it

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12
Q

What can be added to water soluble bases as an ointment base?

A

Lignocaine as a topical anaesthetic

- can be used to incorporate drugs dissolved in water

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13
Q

How are ointments prepared?

A

Insoluble ingredients must be finely powdered (but do not grind fine powders!)
Medicament incorporated into base by geometric dilution

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14
Q

What is a paste?

A

Ointment containing 20 - 60% powder dispersed in base

  • soft paraffins
  • glycerol
  • emulsifying ointments
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15
Q

What are the disadvantages of pastes?

A

Absorb noxious chemicals (e.g. ammonia from bacteria)

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16
Q

Why are pastes useful for localised drug action?

A

Pastes spread less well
Reduced irritancy
Reduced staining

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17
Q

What are the advantages of pastes?

A

Less greasy than ointments

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18
Q

Give some uses for pastes

A

Sun and wind filters (e.g. cricket players noses)

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19
Q

Which regions of the body are pastes unsuitable for?

A

Hairy areas - pull on hairs as hard to spread

Widespread areas - hard to spread (imagine hard butter on bread)

20
Q

What can pastes be used to treat?

A 
Splinter removal (magnesium sulphate)
Plaque psoriasis
21
Q

What can affect the stability of a cream?

A

Anything which affects the emulsifying agent

22
Q

What forms the basis of many o/w creams?

A

Emulsifying waxes and ointments

23
Q

What is needed to make a cream?

A
  • emulsifying wax (contains the emulsifying agent)
  • oily phase (to produce an emulsifying ointment)
  • water (to produce the cream)
24
Q

Which oil-soluble alcohol do all emulsifiers contain?

A

Cetostearyl alcohol

25
Q

What substances are mixed together to form stable, complex condensed films at the o/w interface in emulsions?

A
  • surfactants

- oil-soluble alcohols (cetostearyl alcohols)

26
Q

What contributes to the emulsion stability via electron repulsion?

A

Charge

- stops droplets coalescing

27
Q

How do non-ionic surfactants retard coalescence of droplets in emulsions?

A

Steric hindrance - physically get in the way through repulsion of hydrated ethylene oxide chains

28
Q

What makes up emulsifying wax BP?

A

Sodium lauryl sulphate + Cetostearyl alcohol

29
Q

What makes up emulsifying ointment BP?

A

Emulsifying wax BP
White soft paraffin
Liquid paraffin

30
Q

What makes up aqueous cream BP?

A

Emulsifying ointment BP

Water

31
Q

Which phase forms the dispersed phase and which forms the continuous phase in an emulsion?

A
  • phase that persists in the droplet phase the longest
  • phase in which the emulsifying agent is more soluble tends to form the continuous phase
  • function of phase concentration and interfacial tension
32
Q

What lowers the o/w interfacial tension enhancing stability (which determines shelf life)?

A

The adsorption of a surfactant

33
Q

What determines whether the surfactant will stabilise an emulsion?

A

The type of film (barrier) formed at the interface

34
Q

Describe hydrophilic creams

A
  • non occlusive/slightly occlusive
  • ‘vanishing creams’ - thin oily film (heat from skin evaporates water)
  • promote percutaneous absorption (via concentration gradient - concentration increases as water evaporates)
35
Q

What type of cream is a hydrophilic cream?

A

Oil-in-water cream
Oil - dispersed phase
Water - continuous phase

36
Q

What is added to a hydrophilic cream to reduce drug precipitation?

A

Propylene glycol

37
Q

Why is aqueous cream an anionic cream?

A

It contains sodium lauryl sulphate, which is negatively charged (lauryl sulphate)

38
Q

Describe the emulsifying system in hydrophobic creams

A

Oil-soluble (low HLB)

39
Q

How is Wool Alcohols Ointment (WAO) BP made?

A

Wool alcohols
Hard paraffin
White soft paraffin
Liquid paraffin

40
Q

How is Oily Cream BP (AKA Hydrous Ointment BP) made?

A

Wool Alcohols Ointment BP

Water

41
Q

What does Wool Alcohols Ointment act as?

A

Absorption base AND emulsifier

42
Q

Which type of surfactant should be used with an anionic drug?

A

Anionic surfactant

43
Q

Which type of surfactant should be used with a cationic drug?

A

Cationic surfactant

44
Q

Why can creams support the growth of microorganisms?

A

They contain water

45
Q

What type of water must be used to make topical creams?

A

Purified water

- freshly boiled and cooled

46
Q

What needs to be added to a cream to prevent microbe growth?

A

Preservative

MPharm 2 - PH2107 (26 decks)

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