Kh Sadique Faisal Asst. Lecturer Northern University Bangladesh

The empirical method of producing pharmaceutical suspensions is based on an attempt to prepare a stable deflocculated dispersion of a drug in a suitable suspension vehicle. The main problem is that settling of the solid phase causes formation of a solid cake, re-dispersion of that solid cake is a arduous work. Deflocculated suspension is a method to prevent this problem. This technique involves make the external phase equal or more viscous than the crystal of the drug.

the crystal density of most organic drug particles lies somewhere between 1.1 and 1.5 g/cm3, the only liquid vehicles for oral use with densities (at 25C) high enough to be considered are Sorbitol Solution USP (1.29 g/cm3), Syrup USP (1.31 g/cm3), and highfructose corn syrup (1.41 g/cm3). In practice, however, it is extremely difficult to prepare oral suspensions by the matched-density technique alone because dilution with water and other liquids reduces the vehicle density. Nevertheless, the use of high-density liquids as suspending vehicles often has a beneficial effect on physical stability.

 Deflocculated suspensions are produced by three methods.  Mutual repulsion to large Z-potential, a large surface z-potential increase the stability of the dispersion.  Zeta potential [mV] Stability behavior of the colloid from  to ±5, Rapid coagulation or flocculation  from ±10 to ±30 Incipient instability  from ±30 to ±40 Moderate stability  from 40 to ±60 Good stability  more than ±61 Excellent stability

Adsorption of a smaller hydrophilic or lyophilic colloid on larger suspended particles.When a strongly hydrated hydrophilic protective colloid, such as gelatin, is adsorbed on the surface of the suspended particles, the affinity for water exceeds the mutual attraction of adjacent particles for each other. The protective colloid and hydrogen-bonded water molecules form a protective hydration layeraround each suspended particle.

Steric hindrance due to adsorption of an oriented non- ionic surfactant or polyelectrolyte Adsorption of a non-ionic polymer (gum or cellulosic) or surfactant (polysorbate 80) of sufficient chain length creates steric hindrance and prevents adjacent suspended particles from coming close enough to join each other. Steric stabilization has the advantage over electrostatic stabilization in that it is relatively insensitive to the presence of electrolyte in the aqueous vehicle.