Suspensions

Question 1

What are the particle sizes of suspensions?

Answer 1

> 1micrometers

Question 2

What is the definition of a suspension?

Answer 2

Formulation of small insoluble solid particles distributed throughout a liquid continuous phase

Question 3

What are the advantages compared to a tablet?

Answer 3

Faster absorption

Question 4

What are the disadvantages compared to solution?

Answer 4

Slowe absorption

Question 5

Most pharmaceutical suspensions are solid drug particles in aqueous vehicles, but what are the other possible aqueous phases and why are they sometimes used?

Answer 5

Oily or Organic liquids are sometimes used to slow the rate of absorption in some injections.

Question 6

What is the concept of wetting?

Answer 6

THe ability of a solid to stay in contact with the liquid.

Question 7

WHy is wetting related to suspensions?

Answer 7

Weting is the first step in the formulation of a suspension to stop the particles from remaining on the surface, attaching to container, or form large clumps within the liquid.

Question 8

How easy is it to wet diffisuable and indiffusable solids?

Answer 8

Diffusable solids are easily wetted and straightforward to suspend
Indiffusable solids are hydrophobic and not easily wetted. They require a wetting agent.

Question 9

WHat are wetting agents?

Answer 9

They decrease the interfactial tension of indiffusable solids to promote wetting and help dispersion
e.g. alcohol

Question 10

What type of particles are difficult to wet?

Answer 10

Finly divided substances are difficult to wet due to the precense of an adsorbed layer of air around the particels.

Question 11

Describe the concept of interfacial tension:

Answer 11

Molecules rather be in contact with molecules like themselves rather than with different molecules.
Interfacial tension involves cohesive and adhesive forces. The bigger the difference between these forces, the bigger the interfacial tension and therefore the higher the degree of wetting is required.

Question 12

What are cohesive and adhesive forces?

Answer 12

Cohesive forces are those that form between ‘like’ molecules

Adhesive factors are those that form between different molecules

Question 13

What are the different types of Wetting agents?

Answer 13

SurfaceActive Agents (detergents)
Hydrophilic colloids
Solvents

Question 14

How do SurfaceActive Agents (detergents) work?

Answer 14

Hydrocarbon chains are absorbed by hydrophobic particle surfaces while polar groups enter the liquid and become hydrated. They can cause excessive foaming or deflocculate the system.

Question 15

How do Hydrophilic colloids work?

Answer 15

They coat the hydrophobic particles with a layer, giving the particle a hydrophilic character.
They can be used in combination with SAAs,
but can also lead to deflocculation.

Question 16

How do solvents work?

Answer 16

Water miscible solvents decrease the interfacial tension by penetrating the powder clumps and displacing the air.

Question 17

How do we asses suspension stability?

Answer 17

• Rate of sedimentation
• Final volume or height of sedimentation (how densly sedimentated)
• Ease of redispurion
• Particle size distribution.

Question 18

What rate of shear should be used during the measurement of stability and why?

Answer 18

A low rate of shear should be used to mimic the change in strucutre upon different storage.

Question 19

What would a high rate of shear do during the measurement of stability?

Answer 19

A high rate may damage the suspension and give an inacurate representation of what would happen on the shelf.

Question 20

What is the advantage and disadvantage of using ACCELERATED STABILITY TESTING?

Answer 20

Shortens time of experiments

Not always possible to accurately predict the normal behaviour from the results.

Question 21

What are the two types of Accelerated stability testing:

Answer 21

1. Centrifugation

2. Temperature cycling

Question 22

Describe Centrifugation:

Answer 22

This works by increasing the rate of sedimentation.
A disadvantage is that if the system is flocculated, then the system will be destroyed when centrifuged forming a tightly packed sediment which would not happen in real conditions.

Question 23

Describe Temperature cycling:

Answer 23

This is useing two extreme temperatures (very cold and very hot) as a worse case scenario of storage conditions. A disadvantafe is that it increases the rate of crystal growth which wouldn’t happen in normal conditions

Question 24

What is the equation of sedimentation volume?

Answer 24

Sedimentation vol (F) = Vu (ultimate vol) / Vo (original volume)

Question 25

In the sedment/time graphs, what does a constant line tell us?

Answer 25

That sedimentation is complete

Question 26

What if F (Sedimentation volume) is = to 1?

Answer 26

If F = 1, then the volume of sediment is equal to the original volume (think of the sediment equation) and the product is said to be at ‘Flocculation equilibrium’. This is a desirable state in pharmaceuticals.

Question 27

What is the normal values of F?

Answer 27

F is normally less than 1, becasue the volume after sedimentaton is normally lower than the volume of the original suspension.

Question 28

What happens if the F is >1?

Answer 28

This is not desirable because the floccs in the system become loose and fluffy.

Question 29

What is the equation for the degree of flocculation?

Answer 29

Degree of flocculation = Flocculated sedementation / Deflocculated sedementation.
It is more useful than F but takes longer.