suspensions

define suspension

A suspension is a dispersion in which solid drug particles are dispersed throughout a liquid medium

Are suspensions homogeneous?

No, 2 phase systems are not homogeneous. Can have uniformity still.

How big are coarse suspension

particle diameter > 1 µm

How big are colloidal suspensions?

particle diameter ≤ 1 µm

How big are nanosuspensions?

< 100 nm (0.1 µm)

define sediment

particles in a suspension settle due to gravity over time

Settling of a suspension is normal and expected. It does not indicate…

• poor quality

• poor stability

s𝑒𝑑𝑖𝑚𝑒𝑛𝑡𝑎𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 (c𝑚/𝑠𝑒𝑐) =

What is this process called?

ostwald ripening

Define Ostwald ripening

• small particles get smaller and eventually disappear

• large particles get larger

Can you prevent ostwald ripening?

No, it occurs in all suspensions and can’t be prevented. We can prevent cementation from occurring.

Why is cementation uncommon for manufactured suspensions?

• They are formulated so that particles in the sediment don’t touch each other.

• the expiration date of manufactured suspensions accounts for particle redispersion

How do you help prevent cementation in manufactured suspensions?

• do not add anything (solvents, other drugs, salts etc) to a suspension

• store the suspension according to the label instructions

If you are compounding a suspension, what is the best thing you can do to account for cementation and poor redispersion after sedimentation?

• don’t compound large batches of suspensions

• assign short BUD

Even after particles have fully settled, the particles are not touching each other. Why?

This prevents cementation

What is wrong with this photo?

This is an example of a poor suspension because the particles are touching each other. Eventually, this will lead to cementation.

Which is an example of cementing and which is an example of a good suspension?

the top one is cementing and the bottom one is ideal because there is space between the particles

This is an example of what?

cementation

What are some advantages of suspensions?

• dose is easily customized by choosing volume to administer

• helps with low water solubility (don’t need cosolvents)

What are some disadvantages of suspensions

• stability is lower/ shorter shelf life b/c of 2 phase system

• packaging and transport are more expensive

Define suspending agents

increases viscosity to reduce sedimentation rate

Define gel forming solids

• Small particles naturally form a viscous 3-dimensional network in water

• The 3-dimensional gel network enhances viscosity above any dissolved polymers

• The 3-dimensional gel network can include drug particles and modify particle-particle interactions

• enhance dispersibility and reduce risk of cementation

list examples of gel forming solids

• colloidal silicon dioxide

• microcrystalline cellulose

• bentonite

• aluminum magnesium silicate/ veegum

define ionic modifier

ions in the liquid phase modify particle- particle interactions to reduce contact between particles in the sediment

Why use ionic modifiers?

particle particle interactions determine the ability of the particles to be dispersed by shaking (dispersibility/ redispersibility). Particle particle interactions determine risk of cementation

list examples of ionic modifiers

salts (NaCl, NaSO4, NaH2PO4)

define wetting agents

improve the water-particle interaction to help the liquid phase spread across the surface of the particles

list examples of wetting agents/ surfactants

• polysorbate 20, 40, 60, 80

• docusate sodium

• poloxamer 188, 407

How else can glycerin be used?

to help in the initial dispersion of particles

How to shake a suspension?

• make sure the cap is on tight

• invert the bottle

• shake vigorously until the solid is uniformly dispersed

compounding suspensions, remember…

• assign short BUD

• follow established formulation exactly

How to store suspensions

• tightly capped

• room temp unless instructed otherwise

• away from sunlight

how to dispose of suspension?

drug take back sites