Suspensions

Question 1

Define suspension

Answer 1

A heterogenous system where fine particles are evenly DISPERSED throughout the liquid medium.
- particles are partially soluble and not fully dissolved

Question 2

Outline 3 benefits of suspension dosage forms

Answer 2

1. Dosing flexibility - beneficial to give to paediatric patients
2. Ease of swallowing and formulation
3. Flavour-adding flexibility to mask bitter tase

Question 3

Outline 6 main characteristics of a good suspension

Answer 3

1. Optimal viscosity
2. Controlled flocculation (i.e. the level of closeness of the particles where they get re-dispersed immediately upon shaking
3. Good wettability
4. Good taste
5. pH stability to maintain API stability

Question 4

What does the stokes equation predict?

Answer 4

predicts the sedimentation rate of the particles over time (i.e. how fast the particles will settle at the bottom of the bottle)

Question 5

Define caking

Answer 5

Particles at bottom are compressed over time

Question 6

Define flocculated suspension

Answer 6

Double check slides and then write the answer.

Question 7

List 3 factors that influence sedimentation rate

Answer 7

1. Particle size
2. Density difference
3. Viscosity of medium

Question 8

How does partial size affect sedimentation rate?

Answer 8

SMALLER particles are dispersed for a longer time and settles at a slower rate
- THUS, decreases sedimentation rate
LARGER particles settle faster
-THUS, increases SR

Question 9

How does density difference (between particles and medium) affect SR?

Answer 9

• If PD (particle density) is higher than medium density (MD), the particles settle at a faster rate which increases SR
• If MD is higher than PD = floating of particles
  OVERALL with a lower density difference particles will settle at a slower rate

Question 10

How does viscosity of medium affect SR?

Answer 10

A thicker more viscous liquid slows the movement of particles which makes them settle at a slower rate THUS reduce in SR
In comparision, the more thin and flowing the liquid is, promotes faster particle movement leading to faster settling THUS SR.

Question 11

When we reduce/decreasethe SR of particles what happens?

Answer 11

Particles are dispersed in the system for a longer period which STABILISES the suspension

Question 12

List components that helps to stabilise a suspension

Answer 12

1. Small particles
2. Fluccolating agents
3. electrolytes
4. Preservatives
5. Stabilisers

Question 13

List the key excipients used in suspensions

Answer 13

1. Wetting agents
2. Flucoolating agents
3. Viscosity enhancers
4. Surfactants
5. Buffering agents

Question 14

Outline specific examples and the role of each class of excpieint

Answer 14

• Check ED discussion if we need to remember this

Question 15

The particle diameter in the Stokes Law equation needs to be which unit

Answer 15

(m) - metres

Question 16

how do you convert micrometers to m

Answer 16

divide by a million

Question 17

What is the stern layer?

Answer 17

It is the layer that directly interacts with particles outer surface
- It is immobile (this layer moves with the drug particle)
- comprised of ion charges that is opposite to the particles charge

Question 18

What is the slipping plane (shear plane)?

Answer 18

the outermost layer and located next to the stern plane
- it can freely move in the liquid
- I

Question 19

Define Nernst potential

Answer 19

the effective charge on the surface of the particle

Question 20

Define zeta potential

Answer 20

the charge of the particle that appears to other particles

Question 21

What does a decrease in zeta potential mean?

Answer 21

Less negative or more positive charge:
1. Decrease in repulsive forces
2. Higher chances of aggregation/clumping
3. decrease in the STABILITY of the suspension

Question 22

What does an increase in zeta potential mean?

Answer 22

More negative or less positive
1. Increase in repulsive forces
2. Lower chances of aggregation/clumping
3. Increase in the STABILITY of suspension

Question 23

List the 3 factors that affect zeta potential

Answer 23

1. Ionic strength
2. Surfactants
3. pH

Question 24

How does ionic strength affect zeta potential?

Answer 24

With a higher ionic strength, there’s a decrease in repulsive forces therefore a decrease in zeta potential

Question 25

How does surfactants affect zeta potential (refer to both cationic and anionic surfactants)

Answer 25

Cationic surfactants:
- increase in positive charge on the particle’s surface
- therefore a DECREASE in zeta potential = decrease in stability
Anionic surfactants
- increase in negative charge on particles surface
- INCREASE in zeta potential = increase in stability

Question 26

How does pH affect zeta potential?

Answer 26

low pH:
- particles will gain a proton (H+) making them more positively charged
- decreased zeta potential
high pH
- particles will lose a proton (H+) making them more negatively charged = increased zeta potential = higher stability of suspension