Suspensions Flashcards
(45 cards)
Suspensions
-solid particles dispersed in a liquid phase in which they are not soluble
Peptobismol example
-active ingredient: bismuth subsalicylate
-suspension of insoluble salt of salicylic acid linked to bismuth cation
suspensions vs solutions
-solubility
-chemical stability (0 vs1st order)
-palatability (taste)
suspesions vs tablets
-flexibility of dose
-ease of swallowing
-dissolution rate
Components of Suspension
-active ingredient (solid particles)
-vehicle
-buffer
-preservative
-flocculating agent
-structured vehicle system
-wetting agent
-antifoaming
-flavor and sweetener
Desirable properties of Suspensions
-suspended material should not settle rapidly
-particles that settle must not form a hard cake and readily be redispersed when shaken
-easy to admin
-particle size remains constant in storage
Viscosity of suspension
-should not flow thru syringe needle
-fluid enough to spread over affected area
Settling equations
-Stokes Law
Particle size
-micropulverization (10-50mcm)
-fluid energy grinding (10mcm)
-spray drying (5 mcm)
Micropulverization
-10-50mcm
-high speed attrition or impact mills
fluid energy grinding
-less than 10 mcm
-jet milling, micronizing
-shearing action of high-velocity compressed airstreams on the particles in a confined space
Spray drying
-5mcm
-spray dryer: cone-shaped apparatus into which a solution of drug is sprayed and rapidly dried by current of warm, dry air circulating in the cone
Suspension Formulation Designs
-dispersed phase (solid particles)
-dispersion medium
Types of suspension
-dispersed suspension
-flocculated suspension
-structured vehicle system
Thermodynamic stability
slide 13
Interparticle forces
-van der Waals ATTRACTIVE
-hydration REPULSIVE
-electrostatic REPULSIVE
-steric REPULSIVE
van der waals attractive force
-operates at moderate distance from the surface but becomes very strong close to the surface
-NOT affected by formulation factors
Hydration REPULSIVE force
-due to absorbed water molecules at surface of particle
-NOT affected by formulation factors
Electrostatic repulsive force
-due to surface charge on the particles
-may be affected by formulation
Steric REPULSIVE force
-due to an absorbed layer of neutral polymer at surface of a particle
-may be affected by formulation
forces NOT affected by formulation factors
-van der waals ATTRACTICE
-hydration REPULSIVE
forces that might be affected by formulation
-electrostatic REPULSIVE force
-steric REPULSIVE force
Net effect of interparticle forces
slifde 15?
Dispersed suspension
-make REPULSIVE forces dominant
-particles repel each other
-no aggregation
