L3 Suspensions Flashcards
(27 cards)
What is a suspension?
It is a dispersion of finely divided solid particles in a liquid medium
Name 3 applications of suspensions
Oral Use, Injection, External Use
How are suspensions used as injections?
For sustained release (as in depot therapy).
Only for IM and SC. Avoid IV
Why are suspensions used in oral formulations?
Able to administer insoluble drugs in liquid form.
Able to make drugs have a more pleasant taste
For treatment of GI conditions (e.g. antacids)
What are the 6 desirable properties of suspensions?
- Chemically stable
- Low rate of sedimentation
- Easily redispersed
- Size of particle should not change throughout storage
- Pour readily from container/syringe
- Spread easily for external use, but not run off surface when applied
What is the application of Stokes Law in suspensions and emulsions?
Suspensions - Determine rate of sedimentation
Emulsions - determine rate of creaming
Name 2 ways to decrease the rate of sedimentation.
- Reduce particle size
2. Increase viscosity of dispersed medium
What are the characteristics of flocculated suspensions?
- Aggregated particles
- Fast sedimentation
- Clear supernatant + Porous sediments (easily redispersed)
- Plastic flow with thixotropy (shear thinning)
What are the characteristics of deflocculated suspensions?
- Dispersed particles
- Slow sedimentation
- Cloudy supernatant + Compact sediments
- Dilatant flow (issues in production/stirring)
What is the difference between lyophilic solids vs lyophobic solids?
Lyophilic solids easily dissolve in the solvent and do not require a wetting agent.
Lyophobic solids require a wetting agent for dispersion.
Name 2 ways wetting agents allows for the suspension of particles in the dispersion medium.
- Reduces solid-liquid interfacial tension.
2. Imparts hydrophilicity to particle surface
Name 3 examples of wetting agents
- Surfactants (HLB 7-9)
- Hydrophilic polymers
- Polyhydric alcohols
Name 3 examples of flocculating agents
- Surfactants
- Hydrophilic polymers
- Electrolytes
How are ionic surfactants used as flocculating agents?
Similar action as electrolytes. Increases interparticulate attraction when zeta potential is reduced below critical value.
How are non-ionic surfactants used as flocculating agents?
Forms micelles, which are adsorbed at surface of solid particles and form ‘bridges’
Used at concentrations above CMC.
How are hydrophilic polymers used as flocculating agents?
Similar to non-ionic surfactants. Polymers are adsorbed at surface of solid particles and form ‘bridges’
How are electrolytes used as flocculating agents?
Increases interparticulate attraction when zeta potential is reduced below critical value. This promotes flocculation of particles.
What is the purpose of thickening agents?
To increase the viscosity of the dispersion medium so that the particles remain suspended in the medium.
What are the 2 deflocculating effects when hydrophilic polymers are added at high conc?
- Protective colloid effect
2. Viscosity enhancing effect
Describe the protective colloid effect.
Polymers cover the particle completely and prevents aggregation, thus there is less flocculation.
Describe the viscosity enhancing effect.
Improves stability but reduces flowability due to formation of polymer mesh/complex.
Describe the dispersion technique used in preparation of suspensions (Small scale).
- Mix solid and wetting agent in a mortar.
- Add small portion of liquid vehicle containing additives.
- Transfer mixture into measuring cylinder and make up to remaining volume with liquid vehicle
Describe the dispersion technique used in preparation of suspensions (Large scale).
- Mix solid and wetting agent in a mixer.
- Add liquid vehicle containing additives.
- Transfer mixture into a high shear equipment
(Avoid excessive high shearing)
Describe the Organic solvent precipitation technique used in preparation of suspensions.
Water insoluble drug is dissolved in water miscible organic solvent.
When water is added, drug will precipitate out to form suspension.
