Suspension Dosage Forms Flashcards
What is a suspension?
Course dispersion in which insoluble particles, generally >1micrometer, are dispersed within a liquid medium which is usually aqueous
What are the characteristics of an ideal suspension?
Homogeneous during dosing
Easy to redisperse
Poor viscosity
Particles should be small and uniform
What does ratio r compare?
Sedimentation layer volume (Vs) to total suspension volume (Vt)
How do you prevent caking in a suspension?
Use a flocculating agent
What is zeta potential?
Magnitude and type (+ or -) of the electrical potential at the slipping plate
What happens when there is entropic (steric) effects?
Two particles come into close contact, the polymer chains start to overlap
Which leads to a loss in the freedom of motion of the polymer chains
The is situation is thermodynamically unfavourable and forces droplets apart again
What happens when there is osmotic forces (solvation)?
When two particles come into close contact the polymer chains start to overlap, effectively lending to a concentrated polymer solution.
This induces osmotic gradient
What is flocculation?
Form into an aggregated lumpy or fluffy mass
What happens when the attractive forces (Va)>(Vr)?
Weakly attracted clusters form
Re disperse upon shaking
What happens when attractive forces (Va)<(Vr)?
Close packed arrangement at the bottom of container
Cannot be redispersed
What are the characteristics of flocculated systems?
Particles are aggregated
Fast sedimentation
Fluffy sediment
Large sedimentation volume
What are the characteristics of deflocculated systems?
Particles remain as discrete units
Slower sedimentation
Compact sediment
Small sedimentation volume
how to achieve controlled flocculation?
particle size
use of electrolytes to control the electrostatic repulsion
addition of floccuating agents
