Unit 2 - Topical formulations 2

Question 1

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

Answer 1

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

Question 2

How are absorption bases made?

Answer 2

Anhydrous vehicles composed of a hydrocarbon base and an emulsifier

• sterols
• sorbitan monosterate

Question 3

How do absorption bases as an ointment base work?

Answer 3

Deposits a greasy, occlusive film on the skin surface

- less suppression of trans-epidermal water loss than hydrocarbons

Question 4

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

Answer 4

They hydrate the stratum corneum (w/o emulsion)

Question 5

What is the opposite of an absorption base?

Answer 5

Emulsifying base (o/w emulsion)

Question 6

What are the three types of emulsifying base?

Answer 6

• anionic (negatively charged)
• cationic (positively charged)
• non-ionic

Question 7

Why do emulsifying bases as an ointment base contain surfactants?

Answer 7

May help with spreading

Question 8

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

Answer 8

Mix with aqueous secretions and readily wash off skin

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

Question 9

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

Answer 9

Polyethylene glycols

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

Question 10

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

Answer 10

• non-occlusive (water soluble)

- do not stain clothing

Question 11

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

Answer 11

Incompatible with many chemicals

- limits what you can add to it

Question 12

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

Answer 12

Lignocaine as a topical anaesthetic

- can be used to incorporate drugs dissolved in water

Question 13

How are ointments prepared?

Answer 13

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

Question 14

What is a paste?

Answer 14

Ointment containing 20 - 60% powder dispersed in base

• soft paraffins
• glycerol
• emulsifying ointments

Question 15

What are the disadvantages of pastes?

Answer 15

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

Question 16

Why are pastes useful for localised drug action?

Answer 16

Pastes spread less well
Reduced irritancy
Reduced staining

Question 17

What are the advantages of pastes?

Answer 17

Less greasy than ointments

Question 18

Give some uses for pastes

Answer 18

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

Question 19

Which regions of the body are pastes unsuitable for?

Answer 19

Hairy areas - pull on hairs as hard to spread

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

Question 20

What can pastes be used to treat?

Answer 20

Splinter removal (magnesium sulphate)
Plaque psoriasis

Question 21

What can affect the stability of a cream?

Answer 21

Anything which affects the emulsifying agent

Question 22

What forms the basis of many o/w creams?

Answer 22

Emulsifying waxes and ointments

Question 23

What is needed to make a cream?

Answer 23

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

Question 24

Which oil-soluble alcohol do all emulsifiers contain?

Answer 24

Cetostearyl alcohol

Question 25

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

Answer 25

- surfactants | - oil-soluble alcohols (cetostearyl alcohols)

Question 26

What contributes to the emulsion stability via electron repulsion?

Answer 26

Charge | - stops droplets coalescing

Question 27

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

Answer 27

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

Question 28

What makes up emulsifying wax BP?

Answer 28

Sodium lauryl sulphate + Cetostearyl alcohol

Question 29

What makes up emulsifying ointment BP?

Answer 29

Emulsifying wax BP White soft paraffin Liquid paraffin

Question 30

What makes up aqueous cream BP?

Answer 30

Emulsifying ointment BP | Water

Question 31

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

Answer 31

- 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

Question 32

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

Answer 32

The adsorption of a surfactant

Question 33

What determines whether the surfactant will stabilise an emulsion?

Answer 33

The type of film (barrier) formed at the interface

Question 34

Describe hydrophilic creams

Answer 34

- 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)

Question 35

What type of cream is a hydrophilic cream?

Answer 35

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

Question 36

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

Answer 36

Propylene glycol

Question 37

Why is aqueous cream an anionic cream?

Answer 37

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

Question 38

Describe the emulsifying system in hydrophobic creams

Answer 38

Oil-soluble (low HLB)

Question 39

How is Wool Alcohols Ointment (WAO) BP made?

Answer 39

Wool alcohols Hard paraffin White soft paraffin Liquid paraffin

Question 40

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

Answer 40

Wool Alcohols Ointment BP | Water

Question 41

What does Wool Alcohols Ointment act as?

Answer 41

Absorption base AND emulsifier

Question 42

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

Answer 42

Anionic surfactant

Question 43

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

Answer 43

Cationic surfactant

Question 44

Why can creams support the growth of microorganisms?

Answer 44

They contain water

Question 45

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

Answer 45

Purified water | - freshly boiled and cooled

Question 46

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

Answer 46

Preservative