Suspensions Flashcards
What is a pharmaceutical suspension?
a coarse dispersion containing:
-finely divided particulate material suspended in a liquid or
semisolid medium (continuous phase or vehicle)
What is the criteria for a suspension?
particles are uniformly distributed
particles have minimal solubility in the continuous phase
the size distribution of the particles ranges from 1-100um
- 1-50um: fine dispersion
- 50-100um: coarse dispersion
What are the advantages of suspensions?
deliver poor water-soluble drugs
suitable for patients with difficulty in swallowing a tablet or capsule
palatability (masking taste)
chemical stability
sustained release
can be given for both systemic (antibiotics) and local therapeutic effects (activated charcoal to adsorb excess Gi fluids)
What are the disadvantages of suspensions?
physical instability, settling over time results in lack of uniformity of the dose
manufacturing difficulties
Describe the preparation of acceptable suspensions.
should not precipitate rapidly
redispersed quickly by shaking
correct viscosity to pour from the bottle/flow through an administration needle
for topical formulations sufficiently fluid to spread over the skin
What are the two phases of a suspension?
internal phase (drug, active, or dispersed phase)
external phase (dispersion medium, vehicle)
What are the solids that can be used in the internal phase of a suspension?
hydrophilic solids: readily wetted by water
-clays (kaolin, talc, magnesium aluminum silicate)
-hydroxides and oxides of calcium, magnesium, zinc,
aluminum & titanium
hydrophobic solids: not wetted by water, but “wetted” by oils
-most pharmaceutical substances: charcoal, sulfur, aspirin,
phenobarbital
What is the selection of the external phase based on?
safety
density
viscosity (important in stability)
taste stability
What are some liquids that can be used in the internal phase of suspensions?
polar liquids:
-water: up to 100%
-simple syrup (sucrose): 50-100%
-cherry syrup: 50-100%
non-polar liquids:
-oils: up to 100%
-fatty esters: up to 100%
-hydrocarbons: up to 100%
structured vehicles:
-acacia: 0.5-2%
-tragacanth: 0.5-5%
-carbopol: 0.5-5%
-methyl cellulose derivatives: 0.5-5%
-colloidal silicon dioxide: 1.5-3.5%
What are structural vehicles?
0.5-5% polymer in final composition
aqueous dispersions of polymeric materials
What are the properties of structured vehicles?
protective colloids at low concentrations, while they function as viscosity-inducing agents at higher concentrations
-concentration varies based on viscosity requirement
some thixotropic behaviour may also be observed (by stirring or shaking)
-not used for parenteral administration
What are the other ingredients used in suspensions?
buffers
colouring agents
flavours
sweetening agents
preservatives
suspending (flocculating) agents
viscosity modifiers
What are examples of suspending (flocculating) agents?
electrolytes
ionic surfactants
polymeric flocculating agents
Describe electrolytes as suspending agents.
capable of reducing zeta potential
ex: sodium chloride, calcium salts
concentration of electrolyte used: 0.01-1%
Describe ionic surfactants as suspending agents.
capable of decreasing zeta potential
Describe polymeric flocculating agents as suspending agents.
form a gel-like network to cross-link the suspended particles
also increase viscosity (i.e methylcellulose)
What are examples of viscosity modifiers?
polysaccharides
water soluble cellulose derivatives
hydrated silicates
acrylic acid polymers
colloidal silicon dioxide
Describe polysaccharides as viscosity modifiers.
used only for extemporaneous compounding because of their increased susceptibility to microbial growth
ex: acacia gum, tragacanth, alginates
Describe water soluble cellulose derivates as viscosity modifiers.
semi-synthetic cellulose derivatives make greater viscosity ranges available by combining agents in specific proportions
ex: methylcellulose, MCC
What is an examples of a hydrated silicate?
bentonite
Describe acrylic acid polymers as viscosity modifiers.
high molecular weight cross-linked polymers of acrylic acid forms gels in neutralized aqueous dispersions
ex: Carbopol (carboxypolyethylene)
Describe colloidal silicon dioxide as viscosity modifiers.
“fluffy” white powder used as either a suspending/thickening agent or a tablet/capsule diluent
What are the properties of an ideal suspending agent/viscosity modifier?
readily dissolved/dispersed without special techniques
readily and uniformly incorporated into the formulation
ensures formulation of loosely packed system (flocculated)
no effect on the bioavailability of the drug
inert, no incompatibilities with other components
stability over wide pH range
What are some examples of oral suspensions?
antibiotics
antacids
radiopaque suspensions
