Suspensions

Question 1

Define suspensions and its criteria (size distribution)

Answer 1

2 phase system
- Dispersed phase (insoluble)
- Dispersion medium (liquid or soluble)

Criteria
- uniformly distributed, minimal solubility
- Size distribution
Fine dispersion: 1-50 microm
Coarse dispersion: 50-100 microm

Question 2

What are some advantages of suspensions

Answer 2

Alternate solid dosage form
Solubility
Palatability (taste)
Drug stability
Improved bioavailability
Sustained release

Question 3

What are some disadvantages of suspensions

Answer 3

Sedimentation may occur
Manufacturing difficulties (large mixing vessels, uniformity of product difficult to
maintain)
Bulkiness of final product (handling and shipping bottles, heavy boxes difficult)

Question 4

*****Define Deflocculated and Flocculated particles and the zeta potential in each systems

Answer 4

Flocculated (colloidly unstable, pharm. stable)
- Particles remain dispersed (easy to redisperse)
- low zeta potential
- faster sedimentation
- clumps
- no caking
- attractive forces

Deflocculated (colloidly stable)
- Particles form loose aggregations (difficult redispersion)
- High zeta potential
- slower sedimentation
- no clumps
- Caking
-repulsive forces

Question 5

List components of suspensions

Answer 5

Internal phase (disperse phase)
- Hydrophobic solids, not wetted by water but wetted by soils
- eg. charcoal, sulfur, aspirin, phenoarbital
- Hydrophilic solids: readily wetted by water
- eg, clays, hydroxides and oxides, vitamins etc..

External phase (dispersion medium)
- polar & non-polar liquids
- Structured vehicle

Question 6

Define structured vehicle. What effect does it have on the vehicle

Answer 6

Protective colloids at low concentrations, while they function at viscosity-inducing agents at higher concentration

Reduces sedimentation rate

Question 7

Define wetting agent. Provide 3 example

Answer 7

Allows incorporation of a solid into liquid by moving air from the powder surface; only surfactant can lower the interfacial tension

Surfactants, protective colloids, or solvents

Question 8

Define deflocculating and flocculating agent

Answer 8

Deflocculating
- alter the surface charge of particles by physical adsorption causing repulsion among particles
- have no influence on surface tension

Flocculating
- achieve loose aggregation of suspended particles to provide fluffy, high volume sediment that is easily redispersible

Question 9

Define thickeners and provide examples

Answer 9

Thickeners are protective (hydrophilic) colloids that function to increase the strength of the hydration layer

Polysaccharides, water soluble cellulose derivatives, Carbopol, -ite, gum

Question 10

Define wetting and how we measure it

Answer 10

-First step in preparing suspensions
-The liquid displaces the air at the surface of the solid before becoming wetted
- Described by CONTACT angle

Question 11

What does a large and small contact angle correspond to

Answer 11

Large contact angle = hydrophobic surface = poor wetting

Small contact angle = hydrophilic surface = good wetting

Question 12

What does delta F stand for. How do you decrease this value and what does it mean when you decrease it

Answer 12

F= surface free energy
- the smaller the value the more stable it is

To get this:
- surfactant can lower YSL (interfacial tension)
- decrease interfacial area

Question 13

When assessing stability of a suspension which parameters are important

Answer 13

1. Physical stability: rate of sedimentation, easy re-dispersion
2. Rheological assessment: viscosity
3. Assessment of crystal growth: temperature

Question 14

What considerations provide a well-formulated suspension product (4)

Answer 14

1. drug particle size
2. Wetting
3. Flocculation
4. microbial stability

Question 15

What are 2 important factors in decreasing sedimentation rate of dispersion?

Answer 15

1. Increase viscosity
2. Decrease particle size