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Jihong Han's lectures > Creams, Ointments and gels > Flashcards

Creams, Ointments and gels Flashcards

1
Q

What type of newtonian characteristics do creams,ointments and gels have? and provide examples

A

Non-Newtonian

-e.g plastic , pseudoplastic or thixotropic type of flow

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2
Q

What are hydrous creams also refered as?

A

Oily creams

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3
Q

What are creams?

A

-Semi solid preparations intended for external use

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4
Q

What type of emuslions form aqueous creams? and determine which is the external and internal phase?

A

Oil in water

  • Oil - internal phase
  • Water - External phase
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5
Q

What type of emulsions form oily creams? and state which is the internal and external phase?

A
  • Water in oil
  • water - internal phase
  • oil - externnal phase
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6
Q

What is the extrenal phase of the cream structured by?

A

-Structured by the addition of structuring materials such as clay particles and polymers

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7
Q

why does lamellar gel network phases form in the aqueous phase of a cream?

A

-They form as a result of the interaction between some emulsifiers and water

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8
Q

In hydrophilic creams, which phase is known as the continuous phase?

A

Aqueous phase

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9
Q

What type of emulsions form hydrophilic creams?

A

-Oil in water

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10
Q

Are hydrophilic creams water water washable, if so why? -

A

They are water washable because the external phase is water

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11
Q

Hydrophilic ccreams are occlusive. TRUE OR FALSE?

A

FALSE

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12
Q

When the continuous phase evaporates, does the drug concentration in adhering film increase or decrease?

A

Increases

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13
Q

Give examples of most commonly used emulsifiers?

A
  • Lipophilic amphiphiles such as fatty acids and fatty alcohols
  • Ionic water soluble surfactants
  • Non-ionic water soluble surfactants
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14
Q

Give examples of some fatty amphiphiles and surfactants used?

A
  • Cetyl alcohol / sodium stearate
  • Stearyl alcohol / Triethanolamine stearate
  • Cetosteryl alcohol / sodium lauryl sulphate
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15
Q

Excess amount of lipid amphiphiles are used in creams, more than that can be absorbed at the o-w interface. TRUE OR FALSE?

A

TRUE

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16
Q

When are alpha crystalline gel network phase formed?

A

-When they come into contact with water

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17
Q

What is the self bodying effects?

A

-More fluid at low concentrations, more rigid (semisolids) at high concentrations

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18
Q

What are the three different polymorphs that long chain alcohols exists as?

A
  • alpha form
  • Beta form
  • Gama form
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19
Q

alpha form long chain alcohols, are at high temperatures and come out first when cooled. TRUE OR FALSE?

A

TRUE

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20
Q

Beta and gama form of long chain alcohols can coexist, and are usually at low and room temperature. TRUE OR FALSE?

A

TRUE

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21
Q

Which form does pure cetyl or stearyl alcohol exists in?

A

-beta and gama crystalline polymorphs

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22
Q

which form does cetostearyl alcohol exists as?

A

-Alpha crystalline forms

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23
Q

Formation of alpha crystalline si the prerequisite to form liquid crystalline and swollen crystalline phases. TRUE OR FALSE?

A

TRUE

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24
Q

alpha crytsalline shows limited swelling in excess of water. TRUE OR FALSE?

A

TRUE

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25
Q

How are creams stabilised?

A

-The crystalline gel network traps and immobilises the oil droplets, hence stabilises the cream

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26
Q

Alpha crystalline forms waxy crystalline hydrates with limited swelling in the presence of water. TRUE OR FALSE?

A

TRUE

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27
Q

Alpha crystalline gel phase changes to a less swollen liquid crystalline form upon heating to Tc. TRUE OR FALSE?

A

TRUE

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28
Q

What is the Tc for cetostearyl alcohol and other common used amphiphiles in creams?

A

40-50 degrees

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29
Q

At high temperatures the cream is less viscous. TRUE OR FALSE?

A

TRUE

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30
Q

What is the transtion temperature known as?

A

-The setting temperature, when cream is cooled and becomes more viscous

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31
Q

How is the dispersed oil droplets stabilised?

A

Stabilised by monolayer emulsifier film and charge

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32
Q

Describe the alpha crystalline gel phase?

A

-Bilayers of fatty alcohol and surfactants seperated by interlamellar fixed water

33
Q

Between alpha crystalline gel phase and alpha crystalline hydrate, which one has siginficant and limited swelling?

A
  • alpha crystalline gel phase - significant swelling

- alpha crystalline hydrate - limited swelling

34
Q

What does the viscoelastic continuous phase contain?

A
  • alpha crystalline gel phase
  • alpha crystalline hydrate
  • Bulk continuous free water
35
Q

What occurs in liquid emulsions?

A
  • Oil droplets are free moving
  • May coalesce
  • May flocculate
  • May move to form a cream layer
36
Q

what occurs in Creams (O/W)?

A
  • Oil droplets are effectively immobilised in the gel phase
  • No creaming
  • No coalescence
  • No flocculation
37
Q

What are the rheological properties of creams strongly dependent on?

A

-On the concentration of the mixture of emulsifiers due to the swelling properties of the lamellar gel network phase

38
Q

What occurs at low concentrations of emulsifiers?

A
  • Structureed liquid and high proportion of free water

- More fluidic

39
Q

What occurs at high concentrations of emulsifiers

A
  • Increased proportion of swollen lamellar gel network phase
  • Reduced proportion of free water
  • More viscous
40
Q

In external swelling, water layer is 10 times thicker than the carbon layer. TRUE OR FALSE?

41
Q

What happens when electrolytes are added?

A
  • Reduction in repulsion between adjacent bilayers
  • Reduction in the volume of the lamallar gel network phase
  • Reduction in viscosity
42
Q

What is PEO? (polyoxyethylene)

A

A surfactant polymer

43
Q

In steric stabilisation, PEO chain extends into the water layer. TRUE OR FALSE?

44
Q

When is PEO more hydrated?

A

At low temperature

45
Q

PEO containing surfactants are more soluble at low temperature. TRUE OR FALSE?

46
Q

Vanishing cream appears to be vanishing when being applied leaving a non greasy residue on the skin. TRUE OR FALSE?

47
Q

Stearate creams are stearic acids partially neutralised by alkali. TRUE OR FALSE?

48
Q

Give examples of alkali used in stearate creams and state what they form?

A
  • Triethanolamine : forms swollen lamellar structure
  • NaOH and KOH : does not form swollen lamellar structure , forms disordered interlinking bilayers of mixed emulsifiers, entrapping large amounts of water
49
Q

What does an ointment consist of?

A

Consists of a single phase basis in which solids or liquids may be dispersed

50
Q

Are ointments highly viscous?

51
Q

Medicaments cannot be dissolved or dispersed in ointments. TRUE OR FALSE?

52
Q

Provide characteristics of hydrophobic ointments?

A
  • Can absorb only small amounts of water

- Occlusive effect

53
Q

Give examples of typical bases for hydrophobic ointments?

A

-Hard, liquid and light liquid paraffins, vegetable oils, animal fats and waxes

54
Q

Provide characteristics of water-emulsifying ointments?

A
  • Can absorb larger amounts of water

- Results in water in oil or oil in water emulsions

55
Q

Provide characteristics of hydrophilic ointments?

A
  • Bases are miscible in water
  • May contain appropriate amounts of water
  • Less emollient
56
Q

How are ointments prepared?

A
  • Melt at high temperature (above melting point)
  • Mix excipients, drugs
  • Cool
  • May need special equipments e.g rollers to maintain smoothness
57
Q

What are gels?

A

Semi-solids (usually)

58
Q

In gels, liquid vehicles interact with colloidal particles. TRUE OR FALSE?

59
Q

In gels, bonds from between adjacent particles resulting in a 3D network formation. TRUE OR FALSE?

60
Q

Where is the continuous phase held in gels?

A

-Held between 3D network

61
Q

Gels usually thin after application of a smaller sheer stress, and are amendable to topical application. TRUE OR FALSE?

62
Q

Describe the characterstics of type 1 gels?

A
  • Covalent bonds between the macromolecules
  • Irreversible system
  • The crosslinjing system created by the polymer is not dissolvable
  • Polymeric implants
  • Sustained release of drugs
63
Q

Describe the characterstics of type 2 gels?

A
  • Hydrogen bonds or van der waals forces

- Heat reversible (heating or cooling)

64
Q

Give an example of polymer used in type 1 gels?

A

Polymer e.g HEMA cross linked with ethylene glycol dimethacrylate

65
Q

Give an example of polymer used in type 2 gels?

A

-Polymer e.g polyvinyl alcohol

66
Q

Which type of gels would show a change in viscosity when stress is applied?

67
Q

Gelation of lyophobic colloids consist of floccules of small particles such as bentonite and aluminium magnesium silicate. TRUE OR FALSE?

68
Q

What type of attraction is between the particles in lyophobic colloids?

A

Electrostatic attraction

69
Q

Give examples of some semi synthetic gelling agents?

A
  • Methylcellulose (MC)
  • Carboxymethylcellulose (CMC)
  • HEC
  • HPC
70
Q

Give examples of natural gelling agents?

A
  • Natural gums e.g acacia
  • Clays e.g Bentonite
  • Synthetic materials e.g Carbomer
71
Q

Poly vinyl alcohol turns into gel upon cooling. TRUE OR FALSE?

72
Q

Gelling temperature is equals to mp of gelling agent. TRUE OR FALSE?

73
Q

Higher concentration, will have higher Tg. TRUE OR FALSE?

74
Q

Increasing Tg suggests that a higher energy is required to break the structure of the gel networks. TRUE OR FALSE?

75
Q

Concentrated poloxamer solutions do not turn into gel upon heating. TRUE OR FALSE?

76
Q

OH groups are better hydrated at low temperature. TRUE OR FALSE?

77
Q

At what concentration do poloxamers form micelles

A

At high concentrations above CMC

78
Q

Increasing temperature will result in more micelles being formed, which can compact together to form gels. TRUE OR FALSE?

Jihong Han's lectures (11 decks)

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