Lec 14: Suspensions Flashcards
1
Q
Suspension
A
A disperse system in which one substance (the dispersed phase) is distributed in particulate form throughout another (the continuous phase)
2
Q
Uses of suspensions
A
- Low water solubility medicaments
- Swallowing difficulties of patients
- Change things to insoluble form to mask taste (hydrolysed in GI tract)
- Hydrolysis of medicaments -> prolong action
- Depot injections: prolong release of drugs
- External Use: Lotion of suspended insoluble solids leave a thin coating medicament on skin.
3
Q
What to do when there is low water solubility?
A
- Wetting agent to reduce surface tension
- Hydrophilic suspending agent coats hydrophobic particle
- Flocculated: dispersible sediment
4
Q
Stability
A
Large surface area= high surface free energy = thermodynamically unstable
- store under 25 degrees
Test: sediment size and re-dispersiblity
5
Q
Additives
A
- buffers
- flavourants
- colourants
- preservatives
6
Q
Advantages of suspensions
A
- Insoluble drugs may be more palatable
- Insoluble drugs may be more stable
- Suspended powders are easier to swallow
- Enables easy admin of bulk insoluble powders
- Absorption will be quicker than solid form
- Lotions will leave a cooling layer of medicament on skin
7
Q
Disadvantages of suspensions
A
- Requires shaking before use
- Accuracy of dose likely to be less than equivalent solution
- Storage conditions can affect dispersed systems
- Bulky, difficult to transport and prong to container breakages
8
Q
Properties of good suspension
A
- Ready re-dispersion of any sediment which accumulates
- After gentle shaking, medicament stays in suspension long enough for dose to be measured
- Pourable
- Particles in suspension are small and relatively uniform in size- > free from gritty texture
9
Q
How to compound suspensions
A
- Grind solids finely in mortar w pestle
- Mix in solid suspending agent
- Use small amount of vehicle or suspending mucilage to make smooth paste
- If glycerol or syrup in formula, use to make paste
- Dissolve soluble ingredients in vehicle and add to paste gradually until it is pourable
