Oral Suspensions

Question 1

What is a disperse system?

Answer 1

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

Question 2

What are dispersed systems classified upon?

Answer 2

Size of dispersed phase

Question 3

What is a colloidal system?

Answer 3

Particle size less than 1 micro meter

Question 4

What is a coarse system?

Answer 4

Particle size more than 1 micro meter

Question 5

What is a pharmaceutical suspension?

Answer 5

Liquid disperse system consisting of particles distributed within liquid vehicle

Question 6

What is the particle size of pharmaceutical suspension?

Answer 6

0.1-10 micro meter

Question 7

What is the ideal suspension?

Answer 7

Solid materials monodispersed as spheres + evenly suspended

THIS IS A CHALLENGE THO

Question 8

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

Answer 8

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

Question 9

Why can’t the viscosity be too high?

Answer 9

As it wouldn’t be easy to pour

Question 10

What is the solvent for particle-liquid interaction?

Answer 10

H2O

Question 11

How do hydrophobic drug particles acquire charge?

Answer 11

Due to ionisation of H2O

Question 12

What happens if a drug can be ionised?

Answer 12

Show reasonable degree of aq solubility

Question 13

What happens in aq solution?

Answer 13

H2O undergo self-ionisation + produce ions

H2O ⇌ H+ + OH-

Question 14

What happens in electrical double layer interaction?

Answer 14

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

Question 15

Can excipients affect suspension properties?

Answer 15

YES

Question 16

What do ionic salts do?

Answer 16

Increase no. of mobile charges

Question 17

At a low conc of ionic salt what happens?

Answer 17

Affect diffuse layer

= easier to neutralise particle charge, thinning diffuse layer

Question 18

At high conc of ionic slat what happens?

Answer 18

Affect fixed layer

= charge of particle surface decrease

Question 19

What is the critical micelle conc (CMC)?

Answer 19

Conc of surfactants above micelle form

Question 20

What happens when above CMC?

Answer 20

Micelles form hydrophobic core in which hydrophobic drug may dissolve

Question 21

What happens when below CMC?

Answer 21

Surfactants will cover particles surface

= reduce interfacial tension between particle + liquid medium

Question 22

What is the DVLO theory?

Answer 22

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

Question 23

What does DVLO theory calculate?

Answer 23

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

Question 24

What is the DVLO used to do?

Answer 24

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

Question 25

What do particles dispersed in a liquid exhibit?

Answer 25

Van der Waals + electrical repulsion forces

Question 26

What do forces at surface of particle determine?

Answer 26

Degree of flocculation + aggregation

Question 27

What is the deflocculated system?

Answer 27

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

Question 28

When will system remain deflocculated?

Answer 28

When repulsive energy between suspended particle are high

Question 29

What happens if deflocculated particles settle?

Answer 29

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

Question 30

What is a flocculated system?

Answer 30

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

Question 31

When does a flocculated system occur?

Answer 31

When attractive forces between particles slightly greater than repulsive forces

Question 32

What does controlled flocculation prevent?

Answer 32

Particles caking in suspension formulations

Question 33

What is one way of inducing flocculation?

Answer 33

Reducing surface of charge of particle | = adding surfactants + ionic salts

Question 34

What is particle movement caused by?

Answer 34

Brownian motion Gravity External agitation - eg. shaking

Question 35

What does particle motion affect?

Answer 35

Inter-particulate distance = affecting flocculation status of suspension

Question 36

Which particles are subject to Brownian motion?

Answer 36

Small particles | Less than 2 micro meters

Question 37

What does diffusion provide?

Answer 37

More homogenous movement within medium

Question 38

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

Answer 38

Larger particles to be above affective diffusion size

Question 39

What happens to diffusion if you increase viscosity?

Answer 39

Decreases

Question 40

What is sedimentation?

Answer 40

Downward particle movement due to gravity

Question 41

When does sedimentation occur?

Answer 41

Particles less than 0.5 micro meters

Question 42

What happens to sedimentation if you increase viscosity?

Answer 42

Decreases

Question 43

How do you control sedimentation?

Answer 43

Reduce rate

Question 44

What is 1st way of controlling sedimentation?

Answer 44

Decrease particle size = increase diffusion

Question 45

What is 2nd way of controlling sedimentation?

Answer 45

Decrease particle density

Question 46

What is 3rd way of controlling sedimentation?

Answer 46

Increase medium density | eg. add dextrose

Question 47

What is 4th way of controlling sedimentation?

Answer 47

Increase medium viscosity | eg. add polymers

Question 48

What is 5th way of controlling sedimentation?

Answer 48

Increase temp = increase diffusion constant

Question 49

Which excipients improve palatability?

Answer 49

``` Flavours, sweeteners + colouring Preservatives Buffers Suspending agents Chemical stabilisers Wetting agents Flocculating agents ```

Question 50

What are common sweeteners?

Answer 50

Saccharin sodium | Acesulfame potassium

Question 51

What do you have to consider with sweeteners?

Answer 51

Effect on double electrical layer

Question 52

Why are preservatives used?

Answer 52

Prevent microbe growth

Question 53

What are examples of preservatives?

Answer 53

Sorbic acid + benzoic acid | Parabens

Question 54

What do you have to consider with preservatives?

Answer 54

Effect on flocculation

Question 55

Why are buffers used?

Answer 55

Maintain pH of aq system

Question 56

What do you have to consider with buffers?

Answer 56

Effect flocculation behaviour

Question 57

Why are suspending agents used?

Answer 57

Reduce particle sedimentation

Question 58

What is 1st choice for suspending agents?

Answer 58

H2O soluble cellulose polymers eg. hydroxypropyl methylcellulose (HPMC) eg. sodium salt of carboxymethylcellulose (NaCMC)

Question 59

What is 2nd choice for suspending agents?

Answer 59

Sodium alginate

Question 60

What are problems with sodium alginate?

Answer 60

Easily ionised = affect flocculation

Question 61

Why are chemical stabilisers used?

Answer 61

Improve chemical stability of drug

Question 62

What are examples of chemical stabilisers?

Answer 62

Antioxidants | Chelators

Question 63

Why are wetting agents used?

Answer 63

Reduce interfacial tension between particle + liquid medium

Question 64

What do wetting agents improve?

Answer 64

Homogeneity of drug particle distribution

Question 65

Why are flocculating agents used?

Answer 65

Adjust flocculation status of particles

Question 66

What is an example of flocculating agent?

Answer 66

Ionic material - eg. NaCl

Question 67

Why are sweeteners used?

Answer 67

Improve patient acceptability + palatability