Suspensions

Question 1

What are the different formulations of suspensions?

Answer 1

oral, drops, sprays, lotions, shampoo, aerosols, enemas, injection

Question 2

What is the difference between diffusible and indiffusible solids?

Answer 2

Diffusible solids are insoluble and are easily wetted and mix easily with water. They are easily re-dispersed on shaking.
Indiffusible solids are more common, they form clumps in the liquid and aren’t easily re-dispersed.

Question 3

What are the desirable movements of particles in suspension?

Answer 3

Brownian movement - random movement and collision of particles
Diffusion/osmosis - from a high conc to a low conc

Question 4

What are the undesirable movements of particles in suspension?

Answer 4

Sedimentation - according to stokes law

Flocculation - where electrostatic charges increase as particles get closer, resulting in coagulation

Question 5

How can you control the movement of particles in suspension?

Answer 5

1. Reduce the particle size as this will increase diffusion rates and decrease sedimentation rates
2. Increase viscosity of the vehicle which leads to decreased diffusion and sedimentation
   - you can also decrease the density of the particle or increase the density of the vehicle but these methods are less common

Question 6

What are the excipients needed in suspensions?

Answer 6

• Vehicle; water, syrup, alcohol, glycerol
• Preservatives; chloroform, benzoic acid, ethanol
• Stabilisers; antioxidants, chelating agents
• Buffers; carbonates, citrates, gluconates
• Density modifiers; dextrose, sucrose
• Suspending agents/thickeners; clays, gelatin, glycerol, semi synthetic polysaccharides, gums
• Wetting agents; surfactants (conc below CMC), solvents
• Flavourings
• Sweeteners
• Colouring agents

Question 7

Which are more stable, suspensions or solutions?

Answer 7

solutions

Question 8

What are the advantages of oral suspensions?

Answer 8

• easier to swallow
• fast GIT absorption
• drug is in a finely divided form
• the taste isn’t as noticeable
• can be used for insoluble drugs and can prevent hydrolysis

Question 9

What are the disadvantages of oral suspensions?

Answer 9

• not convenient for the patient
• less stable than solutions
• can separate and sediment
• must shake to re-disperse
• difficult to manufacture