Amorphous powders, drug substance

Investigations for the occurrence of polymorphism have been undertaken by ir spectroscopy, differential scanning calorimetry and x-ray powder diffraction (Guinier-de Wolff). No polymorphism has been observed so far. An amorphous form may be prepared artificially by rapid evaporation of a methanolic solution of the drug substance. 

Fig. 3 X-ray diffraction patterns for powdered amorphous and crystalline samples of an experimental drug substance. (From Ref.. )...

Many drug substances appear in more than one polymorphic form. The form is determined by certain conditions during the crystallization step. Occasionally drug substances are precipitated in such a way that molecules do not organize themselves in any set pattern, resulting in an amorphous powder. It is also possible for solids to entrap solvents stoichiometrically to form solvates. 

Not all drug substances are prepared as crystalline solids. Amorphous solids, such as nelfmavir mesylate [8], often display increased solubility and bioavailability [7], Lyophilized powders, which are prepared by freeze-drying solutions of the drug substance, may be crystalline or amorphous before they are reconstituted by adding water [7]. Whether the form is crystalline or amorphous, the goal is to prepare medicines that offer the most benefit to the consumer. 

An amorphous drug substance is a powdered material without crystalline structure. Thus, no X-ray powder diffraction pattern or thermal peaks in the DSC can be observed. Amorphous powder can be prepared by rapid cooling of a solution, coprecipitation with an organic solvent, or freeze-drying or from the melt. Because the entropy of the amorphous powder is high, the solubility... 

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