Suspensions, dry syrups and instant granules

Various auxiliaries with different functions are used in suspensions or dry syrups and instant granules for the preparation of suspensions. These include thickeners, hydrophilic polymers as dispersing agents, sugars, surfactants, electrolytes, colorants,etc. [296]. 

All povidone types can be used as hydrophilic polymers to physically stabilize suspensions [39,119]. Their most important and primary function in all suspensions is as protective colloids, which hydrophilize the individual solid particles and sterically separate them. This increases the volume of any sediment and makes it easier to redisperse by shaking. Povidone also prevents the dissolved portion of the active substance from crystallizing out by forming soluble complexes with it [389] (see also Sections 2.2.7 and 2.4.5). The Zeta potential of many substances, e. g. iron oxide pigments, can also be reduced with povidone [421]. 

In addition to the functions given above, the thickening effect of povidone is also used in oral suspensions. This particularly applies to povidone K 90, which gives solutions of significantly higher viscosity than, for example, povidone K 25 (Section 2.2.3). The effect of the viscosity on the sedimentation rate of a suspension is given by Stokes Law for Newtonian fluids  

T) = Viscosity of the suspension r = Radius of the particles dl = Density of the suspended phase d2 = Density of the continuous phase g = Gravity 

If the suspension has pseudoplastic properties, the sedimentation rate is greater according to the difference between the gravitational force on the suspended par- 

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