Define suspension.
Heterogeneous mixture in which insoluble solid particles are dispersed evenly in a liquid medium.
What two types of suspensions are there?
Colloidal suspension - 1nm to 1mcm
Coarse suspension - 1mcm to 100mcm
Why should a suspension be formulated?
- drug is insoluble in the delivery vehicle.
- masks the bitter taste of the drug.
- increases drug stability.
- patient unable to swallow the solid dosage form of drug.
What are the disadvantages of suspensions?
- issues with physical stability - sedimentation and compaction
- bulky formulation in comparison to solid dosage forms
- uniform/accurate doses cannot be achieved unless bottle is shaken really well.
- more expensive to manufacture.
List 4 stability and solubility concerns.
Drug degrades in water.
Physical/chemical instability.
Insoluble/poorly water soluble drug.
Drug physiochemical stability in water.
Why is smaller particle size preferred?
Less sedimentation occurs - improves stability and storage.
Increases dissolution rate and solubility.
What is meant by sedimentation?
Sedimentation of particles or floccules as a result of gravitational forces in the liquid.
What are flocculated systems?
Flocculated suspensions - floccules form, increased sedimentation rate, forms loose porous sediment, easily resuspended by shaking.
What are deflocculated systems?
Deflocculated suspensions - slower sedimentation rate, particles start to sediment, forms dense cakes, uniform dosing before sedimentation, not easily resuspended.
What is unique about Nyastin oral suspension?
It shouldn’t be swallowed (it can be) as it is for localised treatment of fungal infections in mouth and throat by candida albicans.
Describe topical suspensions.
Can be applied to body surfaces.
Skin/mucous membranes - vagina, rectum, throat, eyes and ears.
What is calamine lotion?
Combination of zinc oxide with 0.5% iron (III) oxide. Treatment of mild itchiness.
- designed to leave a light residue/deposit of active drug on skin after evaporation of the continuous phase.
Describe parenteral suspensions.
- control the rate of drug absorption
- varying particle size controls the dissolution rate and thus the duration of activity
- drugs may be suspended in an oil - product remains as oil globule after administration.
Describe how vaccines are formulated?
- formulated as dispersions of killed microorganisms e.g. cholera vaccine.
- dispersions of constituent toxoids absorbed onto alum e.g. diphtheria and tetanus vaccine
e. g. hepatitis A/B vaccine - absorbed onto aluminium oxide core
What is the benefit of vaccine suspensions?
The prolonged antigenic stimulus leads to a high antibody titre.
Describe vehicle and suspending agents.
- used in deflocculated systems.
- are aqueous solutions that increase the viscosity of the formulation - system will take longer to sediment.
Name 4 suspending agents.
Methyl cellulose
Gelatin
Acacia
Tragacanth
Why are wetting agents used?
Wetting agents are required for insoluble drugs to allow a suspension to form.
- achieve a reduced surface tension between drug and water.
Give 3 examples of wetting agents (type not actual excipient name)
Surfactants - lipophilic drug transport
Hydrophilic colloids
Co-solvents
What are diffusible solids?
Spreads evenly throughout formulation.
Does not require a suspending agent.
What are indiffusible solids?
Does not spread evenly throughout formulation.
Requires a suspending agent.
