L3: Suspensions Flashcards
Why may a flocculated suspension cause an inaccurate dose?
Due to the high sedimentation rate.
Name the properties of a well formulated suspension
CEMENTS
Chemically stable,
Easy to redisperse no hard cake at bottom,
Microbiologically stable,
Easy to pour out of bottle or injected through needle,
Nongritty,
Taste, smell, appearance, patient friendly
Slow sedimentation
What enables a deflocculated suspension to have an accurate dose?
It’s low sedimentation rate.
Which type of suspension allows a proper dose to be taken from the container?
Deflocculated
What type of suspension may cause an inaccurate dose?
Flocculated suspension.
Which type of suspension (f/d) is likely to cause caking during storage?
Deflocculated, as the sediment becomes very closely packed, hard to redisperse
What are the features of controlled flocculation?
Particles reside in secondary minimum
Enables easy redispersion, minimises settling
Products look elegant
What are the ways in which controlled flocculation can be achieved? (7)
WDPPFVC
Using Wetting agents, controlling Density,
Controlling Particle size, changing PH,
Using Flocculating agents, increasing Viscosity,
Using Co solvent
If particle size is reduced, this will also reduce……
Sedimentation rate of particles.
Why might particle size change during storage?
Due to the crystallisation
Particle size might change during storage due to crystallisation, how could this be prevented?
Using surfactants could prevent crystal growth
What could changing the pH of a medium achieve?
A desired surface CHARGE.
Why must a buffer be carefully considered?
It can influence solubility of API.
It can influence ionisation of preservatives.
It can influence the other ionic agents.
Name one type of flocculating agent? (S)
Surfactant
As flocculating agents, why is optimum conc. necessary for surfactants?
Because they are used as wetting agents as well.
What can a flocculated ionic surfactant do?
NEUTRALISE the surface charge of the drug particles.
What can a deflocculated ionic surfactant do?
Provide HIGHER surface charge.
Name one type of flocculating agent? (P)
Polymers
Low concentrations of polymers causes…
Flocculation
High concentration of polymers causes….
Deflocculation.
As a flocculating agent, how are polymers spread within suspensions?
Long chain is adsorbed on the surface of particles.
Remaining part projects out into dispersing medium.
As Flocculating agents, polymers can have dual functions. What are they?
Can increase viscosity of medium.
Can affect rheological properties of medium.
Name a Flocculating agent. (E)
Electrolytes
As flocculating agents, how do electrolytes work?
They alter the zeta potential of particles.
–> reduces thickness of electric double layer.
What are suspending agents used for?
To modify viscosity.
What does increasing viscosity do to sedimentation?
Slows down the sedimentation rate.
Name a general characteristic of an ideal suspending agent.
R
Must have favourable rheological properties.
Name a general characteristic of an ideal suspending agent.
IF
Must be readily/uniformly incorporated in the formulation.
Name a general characteristic of an ideal suspending agent.
DD
Must be readily dissolved and dispersed in water.
Name a general characteristic of an ideal suspending agent.
CF
Must ensure a controlled flocculation
Name a general characteristic of an ideal suspending agent.
Toxicity
Must be inert,non toxic, and free from incompatiblities.
Name a general characteristic of an ideal suspending agent.
D/A
Must NOT influence the dissolution rate or absorption rate.
What are the 2 things that co solvents do
Help with wetting.
Increase viscosity.
Explain how co solvents help with wetting.
Can penetrate the loose agglomerates of powder,
–> displacing air phase from particle pores.
–> therefore reduce interfacial tension between liquid and air.
Are co solvents miscible with water? Example?
YES.
Glycerol.
Name the factors on which preservatives are selected on.
S,P,W,S,N,C,TO.
- SITE of use -must have good PHYSIOCHEMICAL properties
- be effective against WIDE range of microorganisms -STABLE
- NONTOXIC, -COMPATIBLE with other ingredients, -free of TASTE/ ODOUR
Why should there be adequate airspace above the suspension when packaging?
To permit shaking.
Why should suspensions be shaken before use?
To redisperse particles, to ensure a uniform distribution of solid in the vehicle, and therefore an accurate dose.
