Suspensions

Question 1

What is a suspension

Answer 1

dispersion of finely divided solid particles in a liquid medium

liquid medium may be aqueous or non-aqueous

Question 2

Coarse suspension size?

Answer 2

particle size > 1 micron

1 or less micron size is colloidal suspension

Question 3

What are the uses of oral suspensions?

Answer 3

Able to administer insoluble drugs in liquid form
Can make it easy to mask distasteful drugs i.e chloramphenicol palmitate
Provide effective means of administering insoluble compounds for their absorptive or antacid properties

Question 4

Injection suspension allows for?

Answer 4

sustaining drug release as depot therapy

Question 5

what are the desirable properties of suspensions

Answer 5

chemically stable
low rate of sedimentation of particles
particles should be readily redispersed upon gentle shaking of container
size of particle should remain fairly constant throughout storage
should pour readily from container
suspensions for injection should flow readily through a syringe needle
suspensions for external use should spread easily and yet not so mobile that they run off the surface when applied.

Question 6

What type of flow is preferred in a suspension?

Answer 6

Pseudoplastic flow exhibiting thixotropy

Upon shaking, can administer easily via syringe or PO

Question 7

Which suspension will form a compact sediment (Cake): flocculated or deflocculated

What are some properties of it?

Answer 7

deflocculated, difficult to redisperse

supernatant is cloudy

displays dilatant flow, troublesome during production.

Question 8

Properties of flocculated suspension?

Answer 8

Forms a porous sediment upon prolonged standing, easy to redisperse.

Supernatant is clear instead of cloudy.

Displays plastic flow with thixotropy

Question 9

What are lyophilic solids?

Answer 9

Solvent loving solids that do not require the use of wetting agent for dispersion in the liquid vehicle.

may also increase the viscosity of suspension.

Question 10

What is the function of wetting agent?

Answer 10

make the solid particles more penetrable by the dispersion medium

Question 11

What are the modes of action of wetting agents?

Answer 11

reduces solid-liquid interfacial tension

imparts hydrophilicity to particle surface.

Question 12

Examples of wetting agents for aqueous dispersion medium

Answer 12

Surfactants (spans, used at concentrations below CMC)
hydrophilic polymers
polyhydric alcohols

Question 13

Types of flocculating agents?

Answer 13

Electrolytes
surface active agents
hydrophilic polymers

Question 14

How does electrolyte cause flocculating?

Answer 14

affect the zeta potential which governs interparticulate repulsion/ attraction

Question 15

At high or low concentration of electrolyte will it be easy to redisperse the flocs? (i.e give a flocculated suspension)

Answer 15

Low concentration.

At high concentration, the electrolytes will lead to too much interparticulate repulsion, hence floccules will not form. Causes caking on prolonged standing

Question 16

Based on Schulze-Hardy rule, increase in valency of ions lead to?

Answer 16

Increased effectiveness of particles aggregating (formation of floccules)

Question 17

Which surface active agents behave like electrolytes?

Answer 17

Ionic agents

Question 18

How are non-ionic agents used as flocculating agents?

Answer 18

Used at concentrations above CMC, the micelles are adsorbed at the surface of the particles where they serve as bridges between particles.

Flocculation is brought about by a bridging mechanism between the particles.

Question 19

Does hydrophilic polymers work like micelles (non-ionic surface active agents) to bring about flocculation?

Answer 19

Yes, they are adsorbed at the surface of particles, where they serve as bridges between particles.

Question 20

At higher concentration of hydrophilic polymers, what effects could occur?

Answer 20

Protective colloid effect (0.05 to 0.1%) - polymer forms a protective coat around each particle, separating them from one another (doesn’t bring about flocculation)

viscosity enhancing effect (>0.1%) - improves stability but reduces flowability of the suspension.

Question 21

What is a thickening agent’s function

Answer 21

assist in the suspension of the solid particles

Question 22

examples of thickening agent?

Answer 22

gums, gelatin, bentonite, CMC, PVP

Question 23

examples of hydrophilic polymers?

Answer 23

acacia, tragacanth, alginates

Question 24

What are the preparation techniques for suspensions?

Answer 24

Dispersion technique (Small and large scale)
Precipitation technique

Question 25

Explain the difference between small and large scale dispersion technique?

Answer 25

Tools and apparatus are different.
Small scale uses mortar and measuring cylinder
Large scale uses mixer with high shear equipment

Question 26

What are the different types of precipitation techniques?

Answer 26

Organic solvent precipitation

pH-induced precipitation (only applicable to drugs whose solubility is affected by pH)

Question 27

What are the ways for evaluation of suspensions

Answer 27

Stability of suspension

Redispersibility of suspension

Question 28

How can stability of suspension be determined?

Answer 28

To obtain the index of stability F,
measure volume of sediment at time t vs the initial volume of total suspension.

lower the index for a certain time t, higher the instability.

Question 29

How to determine the degree of flocculation in a suspension?

Answer 29

Allow suspension to stand until volume of sediment become constant Vt

Centrifuge the suspension and determine the resultant volume of sediment (Vc)

determine Vt/Vc

Greater the Vt/Vc, the less the flocculation.

Question 30

How does redispersibility of suspension work?

Answer 30

Use a mechanical device to shake suspension, find out number of shakes to disperse the sediment.

Ease of redispersibility is inversely proportional to the number of shakes.