A perfect suspension provides content uniformity. Some problems occurs in the formulating of suspensions and many parameters should be consider such as particle size distribution, specific surface area, inhibition of crystal growth and changes in the polymorphic form. These and other properties should not change after long term storage and do not adversely affect the performance of suspension. Choice of pH, particle size, viscosity, flocculation, taste, color and odor are some of the most important factors that must be controlled at the time of formulation.

Suspensions Formulation Components and Ingredients
The various components, which are used in suspension formulation, are as follows.

Components Function
API Active drug substances
Wetting agents to disperse solids in continuous liquid phase
Flocculating agents to floc the drug particles
Thickeners/Suspending Agent to increase the viscosity of suspension
Buffers and pH adjusting agents to stabilize the suspension to a desired pH range
Osmotic agents to adjust osmotic pressure comparable to biological fluid
Coloring agents to impart desired color to suspension and improve elegance
Preservatives to prevent microbial growth
External liquid vehicle to construct structure of the final suspension

Combination of all or few of the above mentioned components are required for different suspension formulation. In the manufacture of suspension, there are two kinds of systems, namely:
a. Deflocculation system
b. flocculation system

In the flocculation system, flocculate particles are weakly bound, settles quickly and easily re-suspended and did not form a cake. While in the deflocculation system, Deflocculated particles settle slowly and will eventually form sediment and aggregation occurs and then subsequent harsh cakes and difficult to suspended again.

Manufacturing of Suspension

Suspension can be made by using two methods, namely:
1. Dispersion methods
2. Precipitation method, this method is divided again into three kinds :
  • precipitation with organic solvents
  • precipitation with a pH change of media
  • precipitation with double decomposition

1. Dispersion methods
Finely divided powder, dispersed in the carrier solvent. Generally, as the carrier solvent is water. In formulating suspension, the important thing is particles must be dispersed well in water, dispersing powder that is not soluble in water, sometimes difficult. This is caused due to the presence of air, fat and other contaminants on the surface of the powder.

2. Precipitation method
With organic solvents made with substances that are insoluble in water, was dissolved in an organic solvent which can be mixed with water, then add distilled water to certain conditions. Organic solvents used are ethanol, methanol, propylene glycol and glycerin. To note with this method is control of particle size, ie the occurrence of polymorph or hydrate form of crystals.