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PY4 > PHARMACEUTICAL DISPERSIONS > Flashcards

PHARMACEUTICAL DISPERSIONS Flashcards

1
Q

Define dispersed and continous phase

A

Disperse phase, dispersed as particles/droplets/bubbles within a continuous phase

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2
Q

What is a colloidal system and name some examples

A
  • If dispersed partices are 1-1000nm
  • Thermodynamically unstable
  • Suspensions and emulsions
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3
Q

How to prepare a suspension

A
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4
Q

How do we measure size of dispersed particles?

A
  • Can be done by both kinetic and light scattering method
  • Kinetic property: These will measure size dependant on the concentration so number of particles in the sample (total weight of particles divided by total number of particles).
  • Light scattering will measure size based on weight as larger particles scatter light more so skewing (dominating) the measurement.
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5
Q

How do dispersed phases gain a charge

A
  • Surfaces will have a surface electric charge when brought into contact with a polar medium
  • Changes distribution of the ions in the solution
  • Ions of opposite charge (counter-ions) are attracted to the surface
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6
Q

What is the electrical double layer?

A
  • This is a region of charge that forms between a solid surface and liquid solution
  • First layer is the ‘stern layer’ that are oppositely charged and strongly attracted
  • Second layer ‘diffuse’ layer are ions that are less strong attracted and more spread out
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7
Q

Define counter ions and co ions in terms of distribution of of ions in a colloidal system

A

Ions of opposite charge (counter-ions) are attracted to the surface
Ions of like charge (co-ions) are repelled

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8
Q

Interactions between particles are depedent on which two forces

A
  • Repulsive forces: Electrical double layer or steric repulsion
  • Attractive forces: Van der Waals
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9
Q

What is dvlo theory, include equation

A
  • Its the total interaction energy
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10
Q

Label interactive distance curve

A
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11
Q

Attractive interactions, Va

A
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12
Q

Attractive interactions, Va

A
  • Depends on Van der Waals and hamaker constant
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13
Q

What are repulsive interactions dependent on

A
  • Surface charge - as charge increases, repulsive interactions increase
  • Conc of ions in solution - increased concentration, lead to increased , but reduced thickness of the double layer => repulsive interaction decrease
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14
Q

Do repulsive or attracted forces increase stability

A

REPULSIVE
Prevents aggregation and flocculation

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15
Q

What is steric hindrance

A
  • Bulky molecules stop attractive forces from occurring
  • Act as a barrier preventing molecules from getting close so now VDW forces
  • This prevents aggregation and flocculation
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16
Q

Three main types of PD

A
17
Q

Define a pharmaceutical suspension

A
  • A dispersion system in which the API (as solid) is dispersed in the external medium (the vehicle).
  • This means the API sediments over time
18
Q

What factors should you consider when formulating a PD

A
  • Suspension should not settle too rapidly or too slowly
  • Should be readily dispersed on shaking
  • Should not be too viscous – easily pour
  • Particle size needs to be small enough to give smooth product – not gritty
19
Q

How can we apply DVLO theory to making a PD coarse dispersion

A
  • DVLO theory says to produce a system with a suitable secondary medium
  • Add small amounts of electrolytes to slightly reduce repulsive and interaction forces
20
Q

How can we apply knowledge of ‘steric stabilising’ to producing a stable PD coarse suspension

A
  • Larger hamakers constant = more ruplsion
  • By incorporating bulky groups into the surface of suspended particles, you can create repulsive forces that hinder their aggregation, thus maintaining suspension stability.
  • This approach involves selecting appropriate polymers or surfactants with bulky side chains or incorporating steric stabilizers into the formulation
21
Q

What is secondary minimum flocculation

A
  • It has an energy barrier, the system then forms flocs
  • This is useful when particle size is larger than colloidal as flocs are easily dispersed
  • This flocculation is good, when excessive it sedements
22
Q

What can we change/add to make PD suspension stable - what THREE EXCIPIENTS are added

A
  • {Particle size decrease
  • Solution viscosity}
  • ADD Electrolyte concentration - These create an electric double layer, leading to electrostatic repulsion between particles. This prevents particles from aggregating or settling
  • ADD Surfactants: reduce interface tension between two phases - prevents seperation
  • ADD Add hydrophilic polymer - cause steric hind, increase viscosity and wetting agents
23
Q

What is schulze-hardy rule

A

Efficiency of flocculation increases with charge number of counter ion of the added electrolyte

24
Q

Name some applications of Schulze-Hardy rule

A
  • Added ions of opposite charge to colloid act as flocculating agents
  • Efficiency of flocculation increases with ionic charge ….. Useful for diagnoses of particle charge
  • Charge number of co-ions has no effect on CCC
25
Q

Problems you need to overcome to create a stable formulation

A
  • Sedimentation
  • Caking
  • Excess flocculation (only good in small amounts)
  • Particle growth
  • Adhesion to containers
25
Q

Function of wetting agents and viscosity agents as excipients in suspensions

A
  • Wetting agent: Must reduce interfacial tension between particle and dispersion medium to improve wetting e.g. surfactants and hydrophilic polymers
  • Viscosity agents: Slow diffusion rate and slow sedimentastion e.g. hydrophilic polymerd
26
Q

Suspensions are thermodynamically unstable and require BLANK to provide kinetic stability.

A

Suspensions are thermodynamically unstable and require excipients to provide kinetic stability.

27
Q

Electrolytes act as BLANK in suspensions.

A

Electrolytes act as flocculating agents in suspensions.

28
Q

What factors effect emulsion stability but not suspension

A

Coalescence - given time the liquids will separate into two phases (break)
Excipients in both phases – e.g. surfactants and micelles can exist in both dispersed and continuous phases

29
Q

Describe why emulsions arent thermodynamically stable

A

Dispersion leads to high surface area of the dispersed phase
High surface area -> high surface tension
High surface tension -> high interfacial Gibbs energy
The system tries to correct this by completely separating the two phase, i.e. unstable system

30
Q

How can stability of EMULSIONS be increased

A
  • Reduced droplet size – Smaller droplets flocculate slower!
  • Increase viscosity (of continuous phase) – make it harder for the droplets to move!
  • Reduced density difference between phases – Lower difference gravity effects are lowered!
  • Disperse phase concentration – Lower dispersed phased concentration, slower coalescence.
  • Prevention of coalescence – Additives to reduce creaming.
  • ADD surfactants or hydrophilic polymers
31
Q

How can you test the stability of an emulsion

A
32
Q

Advantages and disadvantages of emulsions

A

PY4 (7 decks)

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