1. Pharmaceutical Technology
Lec 6
Dr Athmar Dhahir Habeeb
PhD in Industrial pharmacy and pharmaceutical formulations

2. Dispersed systems
Dispersion (dispersed system) is a mixtures of two substances, one of which (dispersed phase) is distributed in form of subdivided particles throughout another substance (dispersion medium).
Classification of dispersed systems
Molecular dispersions
Molecular dispersion is a true solutions. The dispersed phase (solute) is in form of separate molecules homogeneously distributed throughout the dispersion medium(solvent). The molecule size is less than 1 nm. Example of molecular dispersions is aqueous solutions of salts.
Colloids
Colloids are micro-heterogeneous dispersed systems, in which the size of the dispersed phase particles is within the range nm. The colloids phases can not be separated under gravity, centrifugal or other forces. Dispersed phase of colloids may be separated from the dispersion medium by micro-filtration. Example is emulsions.

3. Coarse dispersions
Coarse dispersions are heterogeneous dispersed systems, in which the dispersed phase particles are larger than 1000 nm (1 μm). Example suspensions.
Suspensions are finely divided insoluble material suspended in a liquid medium or available in dry form to be distributed in the liquid when desired.
Qualities of oral suspensions
Reasoning for suspensions
Particles size range should be between (0.5-5 μm) while aggregates of the particles may attain sizes of 50 μm or larger

4. Collision of particles may cause
Particles with diameter less than 5 μm show Brownian movement(the irregular motion of small particles suspended in a liquid or gas, caused by the bombardment of the particles by molecules of the medium)
Collision of particles may cause
Agglomeration
Dense clumps (hard cake)
Difficult to redisperse
Flocculation
Light fluffy clumps
Redisperse easily

5. In injectable suspension the shape of particles is important (needle shaped crystals are desirable) to produce thixotropic suspensions (for sustained and depot preparations).
Note: Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick, or viscous, under static conditions will flow (become thin, less viscous) over time when shaken, agitated, sheared or otherwise stressed (time dependent viscosity)
Ophthalmic suspension particle size should be less than 10 μm to avoid pain and discomfort
Topical suspension have the same criteria as ophthalmic suspensions (particle size also affect the rate of dissolution and penetration).

6. Formation of oral suspension
The primary process is mixing
Main problem is physical stability
Generally they are prepared by mixing powder in a vehicle
Occasionally the powder is prepared in situ by taking a solution of the drug in a suitable solvent then precipitate it (chang in temperature, change in pH, double decomposition reaction).
Note: A double decomposition reaction is a reaction in which the positive ions and negative ions in two compounds switch partners to form two new compounds.
Thickening agent is generally used to reduce sedimentation of the particles
Wetting agent is also used to assist in initial dispersion of particles
Frequently colouring , preservatives and flavouring also used.