Lec 14: Suspensions

Question 1

Suspension

Answer 1

A disperse system in which one substance (the dispersed phase) is distributed in particulate form throughout another (the continuous phase)

Question 2

Uses of suspensions

Answer 2

1. Low water solubility medicaments
2. Swallowing difficulties of patients
3. Change things to insoluble form to mask taste (hydrolysed in GI tract)
4. Hydrolysis of medicaments -> prolong action
5. Depot injections: prolong release of drugs
6. External Use: Lotion of suspended insoluble solids leave a thin coating medicament on skin.

Question 3

What to do when there is low water solubility?

Answer 3

1. Wetting agent to reduce surface tension
2. Hydrophilic suspending agent coats hydrophobic particle
3. Flocculated: dispersible sediment

Question 4

Stability

Answer 4

Large surface area= high surface free energy = thermodynamically unstable
- store under 25 degrees
Test: sediment size and re-dispersiblity

Question 5

Additives

Answer 5

• buffers
• flavourants
• colourants
• preservatives

Question 6

Advantages of suspensions

Answer 6

1. Insoluble drugs may be more palatable
2. Insoluble drugs may be more stable
3. Suspended powders are easier to swallow
4. Enables easy admin of bulk insoluble powders
5. Absorption will be quicker than solid form
6. Lotions will leave a cooling layer of medicament on skin

Question 7

Disadvantages of suspensions

Answer 7

1. Requires shaking before use
2. Accuracy of dose likely to be less than equivalent solution
3. Storage conditions can affect dispersed systems
4. Bulky, difficult to transport and prong to container breakages

Question 8

Properties of good suspension

Answer 8

1. Ready re-dispersion of any sediment which accumulates
2. After gentle shaking, medicament stays in suspension long enough for dose to be measured
3. Pourable
4. Particles in suspension are small and relatively uniform in size- > free from gritty texture

Question 9

How to compound suspensions

Answer 9

1. Grind solids finely in mortar w pestle
2. Mix in solid suspending agent
3. Use small amount of vehicle or suspending mucilage to make smooth paste
4. If glycerol or syrup in formula, use to make paste
5. Dissolve soluble ingredients in vehicle and add to paste gradually until it is pourable