Suspensions Flashcards
What is a suspension?
Heterogenous mixture in which insoluble solid particles are dispersed evenly in a liquid medium
What two types of suspensions are there?
Colloidal- 1nm to 1um- small
Coarse- 1um-100um - more liable to settling out
Why are suspensions used?
*mask taste
*increase drug stability
*patient unable to swallow solids
What are the disadvantages of suspensions?
*physical stability of suspension itself- sedimentation and compaction
*bulky formulation- 500ml bottles sometimes
*uniform doses can’t be given unless formulation well shaken just before use
At what particle size does sedimentation happen fastest?
Larger particle size
What is the difference between flocculated and deflocculated systems?
*flocculated- flocs form - increased sedimentation rate- loose porous sediment - preferred as redispersibility easier
* deflocculated- dense caking - takes longer to sediment- hard to redisperse
What are characteristics of parenteral suspensions?
*can control rate of drug absorption
*varying particle size = controls dissolution rate= controls duration of activity
*drugs may be suspended in oil= drug administered in oil globule
What is a vaccine made from?
Dispersions of killed microorganisms
Prolonged exposure= prolonged antigenic stimulus= antibody’s build up
What are the three formulation considerations when making an ideal suspension?
*use an appropriate vehicle
*control flocculations with wetting agents
*combine both of these
When are suspending agents used?
In deflocculated systems
They increase viscosity
Eg tragacanth
What is a wetting agent?
Surfactant- decrease interfacial tension between solid and liquid
-tweens, spans (oral suspensions)
-SLS (topical)
-polysorbates (parenteral)
What does a suspension made with an indiffusible solid need?
Suspending agent- tragacanth
