A Study on Pharmaceutical Drug Substances | Original Article

ABSTRACT:

It has been known since the middle of 18thcentury that many substances could be obtained in more than one crystallineform but the subject of drug polymorphism has received extensive academic andindustrial attention since the early pioneering reports of Aguiar andcolleagues at Parke-Davis in which effect of polymorphism on dissolution andbioavailability were highlighted for Chloramphenicol palmitate. The existenceof different crystal structures of the various polymorphs of a substance oftencauses these solids to exhibit a variety of different physical and chemicalproperties. Because of differences in the dimensions, shape, symmetry, capacityi.e. number of molecules and void volumes of their unit cells, the differentpolymorphs of a given substance have different physical and chemical propertiesarising from differences in molecular packing. Such properties includemolecular volume, molar volume i.e., molecular volume multiplied by Avogadro’snumber, density, refractive index along a given crystal axis, thermalconductivity, electrical conductivity, hygroscopicity, hardness, solubility,rate of dissolution in different solvents, chemical stability and interactionswith biological systems. Differences in melting points of the variouspolymorphs arise from differences of the cooperative interactions of themolecules in the solid state compared with the liquid state.