Special characteristics and problems of pharmaceutical agglomerates

The most important aspect of all pharmaceutical products is that they are consumer products therefore, consumer appeal is of great concern which means for agglomerated specialties that they must have uniform, esthetically pleasing, and reproducible shape and weight. 

The latter is also an essential requirement in that agglomerated products are supposed to facilitate measurement of or, in the case of tablets, define the dosage unit. Particularly for tablets, the weight accuracy is of the utmost importance. Since, in most cases, the medicinally active component represents only a small fraction of the commercial drug form, uniform mixing and stabilization of the mixture are a must to avoid segregation. 

During production of the agglomerated specialities a number of problems may have to be considered and overcome. They result from the specific characteristics of the highly sophisticated and often very sensitive active drug components. For example, the natural or chemical materials may not tolerate the presence of water or other liquids and may be sensitive to heat and/or pressure for selected substances shear forces must be avoided while still other materials are unstable or result in, for example, discoloration if they are brought in contact with certain chemical elements (e.g. iron ions). 

Agglomerates are porous bodies. The accretion and growth processes are normally controlled such that nearly saturated conglomerates are produced this means that a large portion (i.e. 80-90%) of the pores are filled with the liquid. During drying, evaporation at first only occurs on the surface and liquid moves from the inside by capillary flow. This mechanism continues until (at 

If the liquid flowing to the surface and evaporating there contains dissolved materials, these materials will crystallize at the pore ends and form a crust (see Section 3.3.1). As long as evaporation takes place, the temperature of the agglomerate remains low due to the removal of heat of evaporation. Vacuum drying enhances this effect. It is, however, possible that the crust becomes so dense that no additional liquid can reach the surface while the core is still wet. If this happens, two alternative processes may occur  

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