Green: suspensions Flashcards
What are the advantage of oral administration routes for suspensions?
- More pleasant in suspension form compared to solution for children
- Required to be in finely divided form in the GI tract
Give examples of topical administration of suspensions?
- Calamine solution (leaves light deposit after evaporation)
- Zinc cream (suspended powdered drug)
Give a reason why a parental suspension is used?
Controls the rate of absorption of a drug
Give a reason why inhalations are used?
Prolonged release of volatiles
What are the advantages of using suspensions?
- Formulation of low soluble drugs
- Effective as masking taste
- Ideal for patients with swallowing difficulty (after stroke or impairment)
- May require to be finely divided in solid form
- Formulations of drug to control drug delivery rate
What are the disadvantages of using suspensions?
- Fundamentally unstable
- Aesthetic suspension is difficult to attain
- Often be bulky
What are the desired features when applying a suspension of a therapeutically?
- Particles must be able to disperse slowly and easily when shaken
- medium particle size must remain constant
- Suspension should pour readily and evenly (homogenous)
- Therapeutic efficacy, stabiltiy, Aesthetic look
What are the parameters that can be controlled in making a suspension?
- Dispersed phase
- Particle size
- Surface properties of particles - Vehicle (continuous phase)
- Controlling viscosity
- Using electrolytes
- Addition of surfactants - All of these control sedimentation and aggregation of particles
Describe why particle size is important when developing suspensions?
- Parental devices can only handle 25 micrometer particles
- Particles control rate of dissolution
- Small fine powder form for slow sedimentation
- Beware of crystal growth, smaller particles dissolve and large particles grow
Explain why the surface properties of particles in a suspension phase is important?
- According to DVLO theory, if there is surface potential of a charge in the particle
- This will lead to repulsion and a more stable suspension due to no reaction occurring
- Steric hindrance: (polymer chains)
- Repulsion between hydrated surfaces
When a particle is coated with a hydrated polymer, what does that lead to?
- Steric repulsion: Positive enthalpy change and negative entropy
- Osmotic pressure
What are the problems you want to overcome when choosing excipients to be used in suspensions?
- Sedimentation
- Caking: thickening
- Flocculation: clumping together into a floc into the surface
- Particle growth
- Adhesion to wall
What are the common excipients used for oral suspension formulation?
- Vehicle: purified water, buffers, co-solvents
- Electrolytes
- Surfactants
- Hydrophilic polymers
- Preservatives
- Sweeteners and flavours
- Anti-oxidants
Describe the purpose of wetting agents? Give examples of some?
- Reduce interfacial tension between particle and dispersion medium (improves wetting
- Examples: Hydrophilic colloids, surface active agents, solvents
- Lead to deflocculated system
What is the problem when deflocculation on a suspension leads to “caked”?
- Very difficult to redisperse
2. Problem occurs when sedimentation occurs
What is the most ideal controlled flocculation system?
Deflocculated system with sufficient high viscosity to prevent sedimentation
What is the real flocculation like in a suspension?
- Partially flocculated
- Control the particle size
- Control zeta potential
- Addition of polymers
- Flocculating agents support the floc and increase sedimentation volume
Give example of flocculating agents?
- Electrolytes
- Ions of opposite charge will create a secondary minimum of thickness layer (flocculation) - Surface active agents
- Affect electric (zeta) potential - Hydrophilic polymers
- Adsorb to particles- leads to loose flocculated structures
Define what rheology is?
The study of flow, viscosity and characteristics of powders, fluid and semi-solids
When a suspension has high and low shear, what does that mean of the viscosity?
- High shear (break apart)= lower viscosity (on shaking and pouring from bottle)
- Low shear= higher viscosity
How do you adjust the viscosity of a suspension?
- Polysaccharides
- celluloses
- silicates
How do you clarify the stability of a suspension?
The ratio of the sedimentation layer volume to total suspension is used
Describe the drug release from the suspension?
- Orally: drug is presented to GI fluids in a finely divided form
- Dissolution occurs rapidly
- Rate of release from the suspension depends on viscosity (high viscosity = slow dissolution)
- If slow dissolution= good for intravenous injection
What are the qualities an extemporaneous suspension (dry powder, made up with water) should have?
- Readily and uniformly in-corporated in formulation
- Readily dispersed in water without special techniques
- No caking
- Doesn’t affect dissolution rate or absorption rate
- Be non toxic
