Definition : A pharmaceutical suspension is a coarse dispersion in which the internal phase ( therapeutically active ingredient )...
Definition: A pharmaceutical suspension is a coarse dispersion in which the internal phase (therapeutically active ingredient) is uniformly dispersed throughout the outer phase
The internal phase consists of insoluble solid particles having a size range (
0.5 to 5 microns) that throughout the vehicle suspension is uniformly maintained
using unique combination or suspending agent
The (suspending medium) or external phase is aqueous generally in some cases, and can be an organic liquid or grease for non-oral use.
Examples:
Antacid oral suspensions
Antibacterial oral suspension
Dry powders for oral suspension (antibiotic)
Analgesic oral suspension
Anthelmentic oral suspension
Anticonvulsant oral suspension
Antifungal oral suspension
Magmas: suspensions
of finely divided material in a small amount of water.
Drugs may be packed dry to avoid instability in aqueous
dispersions.
Advantages:
Sustained effect: requires
dissolution or diffusion step. Stability: drug degradation is slower
than in a solution. Taste: for insoluble drugs used in suspension. Solubility:
when solvent is not available.
Example: only water can be used in ophthalmics, but suspension offer an
alternative.
Preparation: first
solids are wetted by levigation (addition of nonsolvent levigating agent to
solid material to form a paste). A
surfactant can be used. Then suspending
agent is added as aqueous dispersion by geometric dilution.
Suspending agents:
- Hydrophilic colloids
↑ viscosity by binding with water. Support microbial growth and require
preservation. Mostly anionic, except
methyl cellulose (neutral) and chitosan (cationic), therefore incompatible with
quaternary antimicrobials. Insoluble in
alcohol.
Acacia: used as
35% water dispersion (mucilage). Neutral
pH.
Tragacanth: 6%
mucilage (less needed).
Methyl cellulose: heat
and light stable polymer. Soluble in
cold but not hot water. Prepared using
boiling water.
Carboxy methyl
cellulose: anionic and water soluble.
- Clays
Anionic silicates.
Strongly hydrated and exhibit thixotropy. Examples: bentonite (5% magma), veegum.
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