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

Creams, Ointments and gels Flashcards

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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
How are creams stabilised?
-The crystalline gel network traps and immobilises the oil droplets, hence stabilises the cream
26
Alpha crystalline forms waxy crystalline hydrates with limited swelling in the presence of water. TRUE OR FALSE?
TRUE
27
Alpha crystalline gel phase changes to a less swollen liquid crystalline form upon heating to Tc. TRUE OR FALSE?
TRUE
28
What is the Tc for cetostearyl alcohol and other common used amphiphiles in creams?
40-50 degrees
29
At high temperatures the cream is less viscous. TRUE OR FALSE?
TRUE
30
What is the transtion temperature known as?
-The setting temperature, when cream is cooled and becomes more viscous
31
How is the dispersed oil droplets stabilised?
Stabilised by monolayer emulsifier film and charge
32
Describe the alpha crystalline gel phase?
-Bilayers of fatty alcohol and surfactants seperated by interlamellar fixed water
33
Between alpha crystalline gel phase and alpha crystalline hydrate, which one has siginficant and limited swelling?
- alpha crystalline gel phase - significant swelling | - alpha crystalline hydrate - limited swelling
34
What does the viscoelastic continuous phase contain?
- alpha crystalline gel phase - alpha crystalline hydrate - Bulk continuous free water
35
What occurs in liquid emulsions?
- Oil droplets are free moving - May coalesce - May flocculate - May move to form a cream layer
36
what occurs in Creams (O/W)?
- Oil droplets are effectively immobilised in the gel phase - No creaming - No coalescence - No flocculation
37
What are the rheological properties of creams strongly dependent on?
-On the concentration of the mixture of emulsifiers due to the swelling properties of the lamellar gel network phase
38
What occurs at low concentrations of emulsifiers?
- Structureed liquid and high proportion of free water | - More fluidic
39
What occurs at high concentrations of emulsifiers
- Increased proportion of swollen lamellar gel network phase - Reduced proportion of free water - More viscous
40
In external swelling, water layer is 10 times thicker than the carbon layer. TRUE OR FALSE?
TRUE
41
What happens when electrolytes are added?
- Reduction in repulsion between adjacent bilayers - Reduction in the volume of the lamallar gel network phase - Reduction in viscosity
42
What is PEO? (polyoxyethylene)
A surfactant polymer
43
In steric stabilisation, PEO chain extends into the water layer. TRUE OR FALSE?
TRUE
44
When is PEO more hydrated?
At low temperature
45
PEO containing surfactants are more soluble at low temperature. TRUE OR FALSE?
TRUE
46
Vanishing cream appears to be vanishing when being applied leaving a non greasy residue on the skin. TRUE OR FALSE?
TRUE
47
Stearate creams are stearic acids partially neutralised by alkali. TRUE OR FALSE?
TRUE
48
Give examples of alkali used in stearate creams and state what they form?
- 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
What does an ointment consist of?
Consists of a single phase basis in which solids or liquids may be dispersed
50
Are ointments highly viscous?
yes
51
Medicaments cannot be dissolved or dispersed in ointments. TRUE OR FALSE?
FALSE
52
Provide characteristics of hydrophobic ointments?
- Can absorb only small amounts of water | - Occlusive effect
53
Give examples of typical bases for hydrophobic ointments?
-Hard, liquid and light liquid paraffins, vegetable oils, animal fats and waxes
54
Provide characteristics of water-emulsifying ointments?
- Can absorb larger amounts of water | - Results in water in oil or oil in water emulsions
55
Provide characteristics of hydrophilic ointments?
- Bases are miscible in water - May contain appropriate amounts of water - Less emollient
56
How are ointments prepared?
- Melt at high temperature (above melting point) - Mix excipients, drugs - Cool - May need special equipments e.g rollers to maintain smoothness
57
What are gels?
Semi-solids (usually)
58
In gels, liquid vehicles interact with colloidal particles. TRUE OR FALSE?
TRUE
59
In gels, bonds from between adjacent particles resulting in a 3D network formation. TRUE OR FALSE?
TRUE
60
Where is the continuous phase held in gels?
-Held between 3D network
61
Gels usually thin after application of a smaller sheer stress, and are amendable to topical application. TRUE OR FALSE?
TRUE
62
Describe the characterstics of type 1 gels?
- Covalent bonds between the macromolecules - Irreversible system - The crosslinjing system created by the polymer is not dissolvable - Polymeric implants - Sustained release of drugs
63
Describe the characterstics of type 2 gels?
- Hydrogen bonds or van der waals forces | - Heat reversible (heating or cooling)
64
Give an example of polymer used in type 1 gels?
Polymer e.g HEMA cross linked with ethylene glycol dimethacrylate
65
Give an example of polymer used in type 2 gels?
-Polymer e.g polyvinyl alcohol
66
Which type of gels would show a change in viscosity when stress is applied?
Type 2
67
Gelation of lyophobic colloids consist of floccules of small particles such as bentonite and aluminium magnesium silicate. TRUE OR FALSE?
TRUE
68
What type of attraction is between the particles in lyophobic colloids?
Electrostatic attraction
69
Give examples of some semi synthetic gelling agents?
- Methylcellulose (MC) - Carboxymethylcellulose (CMC) - HEC - HPC
70
Give examples of natural gelling agents?
- Natural gums e.g acacia - Clays e.g Bentonite - Synthetic materials e.g Carbomer
71
Poly vinyl alcohol turns into gel upon cooling. TRUE OR FALSE?
TRUE
72
Gelling temperature is equals to mp of gelling agent. TRUE OR FALSE?
TRUE
73
Higher concentration, will have higher Tg. TRUE OR FALSE?
TRUE
74
Increasing Tg suggests that a higher energy is required to break the structure of the gel networks. TRUE OR FALSE?
TRUE
75
Concentrated poloxamer solutions do not turn into gel upon heating. TRUE OR FALSE?
FALSE
76
OH groups are better hydrated at low temperature. TRUE OR FALSE?
TRUE
77
At what concentration do poloxamers form micelles
At high concentrations above CMC
78
Increasing temperature will result in more micelles being formed, which can compact together to form gels. TRUE OR FALSE?
TRUE

Jihong Han's lectures (11 decks)

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