Suspensions Flashcards
What is the definition of a suspension?
A pharmaceutical suspension that is a coarse dispersion that contains the following:
- Finely divided insoluble particulate
- Suspended in a liquid or semi-solid medium
What is the particle size of suspensions?
Ranges from 1-100 micrometers
FIne dispersion (1-50 micometers)
Coarse dispersion (50-100 micrometers)
What are some advantages of suspensions?
Ability to deliver poor water soluble drugs
Suitable for patients who have difficulty swallowing
Easier to mask taste
Chemical stability
Sustained release (
Can be given for systemic or local effects/treatment
What are some disadvantages of suspensions?
Physical instability, will settle relatively quickly due to a lack in uniformity of the dose
Manufacturing difficulties
What are some qualities expected in a good suspension?
PArticles should not precipitate quickly
Should redispersed quickly by shaking product
Correct viscosity to pour the bottle/flow though an administration needle
Finer particles allow us to easily spread our product
What is the internal phase?
This includes the drug/active ingredient
They are also divided into hydrophobic (not wetted by water, but by oils) and hydrophobic solids (readily wetted by water)
What are some examples of a hydrophillic solid used in a suspension
Clays (kaolin, talc, magnesium
What are some examples of hydrophobic solids in suspensions?
Most drugs are hydrophobic
ex. Charcoal, sulfur, aspirin, and phenobarbital
What is the external phase?
It is the dispersion medium
What is considered when selecting an external phase/dispersion medium?
Safety
Density
Viscosity (important for formulation stability)
Taste
Stability
Can alcohol content be above 10% and still be classified as a suspension?
No, if alcohol content is higher than 10%, it is not considered a suspension
What are structured vehicles?
They are aqueous dispersions of polymeric materials
Ex. Acacia (0-2%)
Tragacanth - 0.5-5%
Carbopol (0-0.5%)
Methyl cellulose derivatives are set between (0.5-5%)
Colloidal silicon dioxide (1.5-3.5%)
What are the properties of structured vehicles depending on their concentration?
At low concentrations, structured vehicles are effectively protective colloids
At high concentrations, it is a viscosity-inducing agent
What are some flocculating agents used in suspensions?
Electrolytes (capable of reducing zeta potential, deflocculation is reduced)
Ionic surfactants (neutralize some of the surface charges, increase flocculation)
Polymeric Flocculating Agents (form a gel-like network to cross-link the suspended particles)
What are some viscosity modifiers used in suspensions?
- Polysaccharides (only used in extemporaneously compounding) ex. Acacia gum, tragacanth, alginates
- Water Soluble Cellulose Derivatives
Ex. Methylcellulose and microcrystalline cellulose - Hydrated silicates
Ex. Bentonite - Acrylic acid polymers
Ex. Carbopol - Colloidal Silicon Dioxide
What are the different types of suspensions according to administration type ?
Oral suspensions (antibiotics, antacids, radiplaque suspensions)
Topical suspensions (calamine lotions)
Parenteral suspensions (I.M, S.C, intralesional, intrarticular)
Sterile Topical Suspension (ophthalmic suspensions)
Cosmetics
What are the different types of suspensions according to physical structure?
Deflocculated suspensions:
Small discrete units, settle slower and pack tighter (cake formation)
Flocculated suspension (most common form):
Dispersed particles form loose aggregates (flocs)
Rate of sedimentation is rapid (water is trapped)
Easily redispersed
What are the properties of a well formulated pharmaceutical suspension?
Must be easily resuspendable
The dispersed phase must also be long enough to remove a dose
Particles should be sufficiently small to appear smooth
Has suitable viscosity (for stability, function, and aesthetic)
What happens when zeta potential is high?
Repulsive forces are greater than attractive forces
System will be dispersed or deflocculated (individual particles), therefore harder to resuspend
What happens when zeta potential is low?
Attractive forces dominate repulsive potential
System is flocculated (prevents caking), can be resuspended relatively easily
Review slide 39 to study suspension strategy
What are some general compounding tips?
Wear a dust mask if you are working with powders
Wet powders that aerosolize easily with alcohol, water, or mineral oil
What is the reason and solution for caking in a suspension?
Reason: High zeta potential, therefore deflocculated
Solution: Flocculate
What is the reason and solution for crystal growth in suspensions?
Reason: Partial solubility, temp fluctuations, and heterogenous particle size
Solution: Select insoluble form of the drug, keep at constant temp, ensure narrow particle size distribution
