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Pharmaceutics > Oral Suspensions > Flashcards

Oral Suspensions Flashcards

1
Q

What is a disperse system?

A

Two-phase heterogenous system in which an insoluble or immiscible dispersed phase is distributed through continuous phase

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2
Q

What are dispersed systems classified upon?

A

Size of dispersed phase

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3
Q

What is a colloidal system?

A

Particle size less than 1 micro meter

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4
Q

What is a coarse system?

A

Particle size more than 1 micro meter

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5
Q

What is a pharmaceutical suspension?

A

Liquid disperse system consisting of particles distributed within liquid vehicle

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6
Q

What is the particle size of pharmaceutical suspension?

A

0.1-10 micro meter

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7
Q

What is the ideal suspension?

A

Solid materials monodispersed as spheres + evenly suspended

THIS IS A CHALLENGE THO

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8
Q

To ensure uniform dose, a suspension must have what properties?

A

Particles settle slowly
Particles readily + uniformly re-dispersed upon shaking
Particle size remains constant over time
Viscosity high enough to ensure uniform dose

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9
Q

Why can’t the viscosity be too high?

A

As it wouldn’t be easy to pour

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10
Q

What is the solvent for particle-liquid interaction?

A

H2O

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11
Q

How do hydrophobic drug particles acquire charge?

A

Due to ionisation of H2O

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12
Q

What happens if a drug can be ionised?

A

Show reasonable degree of aq solubility

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13
Q

What happens in aq solution?

A

H2O undergo self-ionisation + produce ions

H2O ⇌ H+ + OH-

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14
Q

What happens in electrical double layer interaction?

A

Drug particle surface give apparent negative charge in liquid
System needs to maintain overall neutral charge
Cations form layer round “anionic” solid particle = electrical double layer

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15
Q

Can excipients affect suspension properties?

A

YES

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16
Q

What do ionic salts do?

A

Increase no. of mobile charges

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17
Q

At a low conc of ionic salt what happens?

A

Affect diffuse layer

= easier to neutralise particle charge, thinning diffuse layer

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18
Q

At high conc of ionic slat what happens?

A

Affect fixed layer

= charge of particle surface decrease

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19
Q

What is the critical micelle conc (CMC)?

A

Conc of surfactants above micelle form

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20
Q

What happens when above CMC?

A

Micelles form hydrophobic core in which hydrophobic drug may dissolve

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21
Q

What happens when below CMC?

A

Surfactants will cover particles surface

= reduce interfacial tension between particle + liquid medium

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22
Q

What is the DVLO theory?

A

Explains aggregation of aq dispersions + forces between charged surfaces interacting within liquid

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23
Q

What does DVLO theory calculate?

A

Attraction + repulsion energies between particles, together with energy of interactions

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24
Q

What is the DVLO used to do?

A

Predict behaviour of suspension
Will particle coalesce + settle?
OR
Will particle remain homogenously dispersed in suspension?

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25
Q

What do particles dispersed in a liquid exhibit?

A

Van der Waals + electrical repulsion forces

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26
Q

What do forces at surface of particle determine?

A

Degree of flocculation + aggregation

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27
Q

What is the deflocculated system?

A

A system in which particles are individually + uniformly dispersed throughout liquid medium

28
Q

When will system remain deflocculated?

A

When repulsive energy between suspended particle are high

29
Q

What happens if deflocculated particles settle?

A

Form a layer of particle sediment at bottom of suspension = difficult to re-suspend

30
Q

What is a flocculated system?

A

A system in which suspended particles are formed into floccules rather than separate particles

31
Q

When does a flocculated system occur?

A

When attractive forces between particles slightly greater than repulsive forces

32
Q

What does controlled flocculation prevent?

A

Particles caking in suspension formulations

33
Q

What is one way of inducing flocculation?

A

Reducing surface of charge of particle

= adding surfactants + ionic salts

34
Q

What is particle movement caused by?

A

Brownian motion
Gravity
External agitation - eg. shaking

35
Q

What does particle motion affect?

A

Inter-particulate distance = affecting flocculation status of suspension

36
Q

Which particles are subject to Brownian motion?

A

Small particles

Less than 2 micro meters

37
Q

What does diffusion provide?

A

More homogenous movement within medium

38
Q

Why is diffusion less likely to be seen in flocculated system?

A

Larger particles to be above affective diffusion size

39
Q

What happens to diffusion if you increase viscosity?

A

Decreases

40
Q

What is sedimentation?

A

Downward particle movement due to gravity

41
Q

When does sedimentation occur?

A

Particles less than 0.5 micro meters

42
Q

What happens to sedimentation if you increase viscosity?

A

Decreases

43
Q

How do you control sedimentation?

A

Reduce rate

44
Q

What is 1st way of controlling sedimentation?

A

Decrease particle size = increase diffusion

45
Q

What is 2nd way of controlling sedimentation?

A

Decrease particle density

46
Q

What is 3rd way of controlling sedimentation?

A

Increase medium density

eg. add dextrose

47
Q

What is 4th way of controlling sedimentation?

A

Increase medium viscosity

eg. add polymers

48
Q

What is 5th way of controlling sedimentation?

A

Increase temp = increase diffusion constant

49
Q

Which excipients improve palatability?

A 
Flavours, sweeteners + colouring
Preservatives
Buffers
Suspending agents 
Chemical stabilisers 
Wetting agents
Flocculating agents
50
Q

What are common sweeteners?

A

Saccharin sodium

Acesulfame potassium

51
Q

What do you have to consider with sweeteners?

A

Effect on double electrical layer

52
Q

Why are preservatives used?

A

Prevent microbe growth

53
Q

What are examples of preservatives?

A

Sorbic acid + benzoic acid

Parabens

54
Q

What do you have to consider with preservatives?

A

Effect on flocculation

55
Q

Why are buffers used?

A

Maintain pH of aq system

56
Q

What do you have to consider with buffers?

A

Effect flocculation behaviour

57
Q

Why are suspending agents used?

A

Reduce particle sedimentation

58
Q

What is 1st choice for suspending agents?

A

H2O soluble cellulose polymers

eg. hydroxypropyl methylcellulose (HPMC)
eg. sodium salt of carboxymethylcellulose (NaCMC)

59
Q

What is 2nd choice for suspending agents?

A

Sodium alginate

60
Q

What are problems with sodium alginate?

A

Easily ionised = affect flocculation

61
Q

Why are chemical stabilisers used?

A

Improve chemical stability of drug

62
Q

What are examples of chemical stabilisers?

A

Antioxidants

Chelators

63
Q

Why are wetting agents used?

A

Reduce interfacial tension between particle + liquid medium

64
Q

What do wetting agents improve?

A

Homogeneity of drug particle distribution

65
Q

Why are flocculating agents used?

A

Adjust flocculation status of particles

66
Q

What is an example of flocculating agent?

A

Ionic material - eg. NaCl

67
Q

Why are sweeteners used?

A

Improve patient acceptability + palatability

Pharmaceutics (21 decks)

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