Suspension Dosage Forms (w9) Flashcards
What is a suspension ?
A course dispersion In which insoluble particles, generally > 1 micrometer (less than) are dispersed within a liquid medium which is usually aqueous.
- you need to let it settle out and shake it so it stays suspended (can easily separate)
What are properties of an ideal suspension ?
- homogeneous during dosing
- easy to re-suspend
- proper viscosity
- particles should be small and uniform in size
What happens to suspensions in deflocculated systems ?
The particles in the suspension are not associated
What happens to suspensions during flocculation ?
The particles come together attracted by weak forces of attraction to form flocs.
What does pressure on the individual particles in the suspension cause ?
Pressure on the individual particles leads to close packing of the particles at the bottom, irreversibility bound together to from a cake
What can prevent caking of the suspension ?
Flocculating agents
What are some examples of flocculating agents ?
-Electrolytes
Reduce electrical forces of repulsion
-Surfactants
Ionic and/or non-ionic
Hydrated layers around particles and formation of liquid bridges
-Polymers
Lyophilic polymers
Structured vehicles and interparticulate interactions
What are two examples of stabling suspensions ?
-electrostatic stabilization
-steric stabilization
What is zeta potential and what type of stabilization does this come under ?
Zeta potential = magnitude and type (+ or –) of the electrical potential at the slipping plane
Comes under electrostatic stabilization
What are steric (entropic) effects of stabilization ?
When two particles come into close contact, the polymer chains start to overlap
This leads to a loss in the freedom of motion of the polymer chains, i.e. a loss of entropy
This situation is thermodynamically unfavourable and forces the droplets apart again
What are osmotic (solvation) forces ?
When two particles come into close contact the polymer chains start to overlap, effectively leading to a concentrated polymer solution
This induces an osmotic gradient in the solution: a concentrated polymer solution in the overlap region and a dilute solution in the bulk solution
Water enters the concentrated region in an attempt to dilute it and in doing so forces the polymer chains (and droplets) apart
What are properties of a flocculated system ?
Flocculated systems
-Particles are aggregated
-Fast sedimentation
-“Fluffy” sediment
-Large sedimentation volume
What are properties of deflocculated systems ?
Deflocculated systems
-Particles remain as discrete units
-Slower sedimentation
-Compact sediment
-Small sedimentation volume
