Suspensions are biphasic, heterogeneous systems in which finely divided insoluble solid particles (disperse phase) are dispersed or suspended in a vehicle (dispersion medium).
• The diameter of disperse
phase may range from 0.5 µm to 100 µm.
• Systems in which
particle size is below this range are called colloidal (1 nm – 0.5 µm diameter).
• Suspension can be used in
oral dosage form, applied topically to the skin, or given parenterally.
Properties of Good Suspension
1. The dispersed particles should settle slowly and
should redisperse immediately on shaking.
2. The product should remain sufficiently homogeneous
for at least the period between shaking the container and removing the required
dose.
3. The viscosity of suspension should be such that it
can be easily removed from the container and transferred to the site of
application without any difficulty.
4. The sediment produced on standing should not form a
hard cake.
5. Suspension particles should be small and uniformly
sized to give a smooth, elegant product
free from grittiness.
6. The suspension should be physically and chemically
stable during handling and storage conditions.
7. It should have good syringibility in case of
parenteral suspension.
8. It should produce thixotropic properties, gel to
sol upon shaking, and sol to gel on storage.
Advantages of Suspensions
1. Insoluble drugs may be made more palatable (masking
bitter taste). For example:
Chloramphenicol.
2. Insoluble drugs can be prepared in a more stable
manner. For example: Procaine penicillin G.
3. Suspensions result in more bioavailability compared
to any other dosage form. Solution >
Suspension > Capsule > Compressed tablet > Coated tablet.
4. Duration and onset of action can be controlled. For
example: Protamine Zinc-insulin injection.
5. Lotion leaves a cooling layer of medicament on the skin.
6. It can be prepared for both immediate and sustained
drug release preparations.
Disadvantages of Suspensions
1. Suspensions require shaking before use, to ensure uniformity of dose.
2. If suspension is not shaken well, the accuracy of the
dose is affected.
3. Improper storage conditions can affect the disperse
system.
4. Sufficient care must be taken during handling and
transport.