What are the different formulations of suspensions?
oral, drops, sprays, lotions, shampoo, aerosols, enemas, injection
What is the difference between diffusible and indiffusible solids?
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.
What are the desirable movements of particles in suspension?
Brownian movement - random movement and collision of particles
Diffusion/osmosis - from a high conc to a low conc
What are the undesirable movements of particles in suspension?
Sedimentation - according to stokes law
Flocculation - where electrostatic charges increase as particles get closer, resulting in coagulation
How can you control the movement of particles in suspension?
- Reduce the particle size as this will increase diffusion rates and decrease sedimentation rates
- 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
What are the excipients needed in suspensions?
- 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
Which are more stable, suspensions or solutions?
solutions
What are the advantages of oral suspensions?
- 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
What are the disadvantages of oral suspensions?
- not convenient for the patient
- less stable than solutions
- can separate and sediment
- must shake to re-disperse
- difficult to manufacture
