The Rigaku Journal Vol. 22 / No. 1 / 2005, 2–15

X-ray powder diffraction assumes many roles in the analysis of pharmaceuticals. Pharmaceuticals, typically organic solids, exist in numerous solid forms that feature different physical and chemical properties. The vast majority of pharmaceuticals are administered as oral tablet dosage forms. In order for a drug molecule to be absorbed by the body, it must first dissolve. One of the most effective means of modifying the physical properties of an active pharmaceutical ingredient (API) is through formation of a salt, if the molecule possesses a basic or acidic functional group. In general, salt forms of drugs are more soluble in aqueous environments, potentially leading to improved bioavailability when compared to administration of a drug in its neutral form. Furthermore, there are opportunities to modify a pharmaceutical’s physical properties by isolation of different crystallographic forms of the same chemical substance in different polymorphic, solvated, desolvated and amorphous solids. This phenomenon presents an opportunity for pharmaceutical scientists who are interested in understanding the structure-property relationships in organic solids. Thus the importance of polymorphism has prompted much interest in the characterization of pharmaceutical solids. Different polymorphs require different strategies and techniques for development. Researchers have access to many different analytical techniques that allow them to study many aspects of polymorphism. Single crystal provides the best structural evidence for polymorphism, however the stringent sample requirements limit its applications to high-quality, single crystals. X-ray powder diffraction allows characterization of materials that do not meet these criteria. This technique has been improved through the advances in beam intensity using rotating anodes or synchrotron radiation sources, advances in parallel beam optics, and advances in detector technology with solid-state detectors, linear and area position sensitive detectors. These advances allow for rapid data collection times and time-resolved studies of phase transformations. Controlled environment stages allow studies of polymorphic conversions as a function of temperature and humidity. Analysis of powder diffraction has become more sophisticated, thus enabling extraction of greater amounts of information from a diffraction pattern than ever before. Crystal indexation packages now offer a high success rate even for low symmetry materials [1]. Powder diffraction data are widely used for quantitative polymorphic mixtures. Rietveld and other whole-powder pattern methods enable superior accuracy than single peak methods. The powder diffraction file, the PDF, THE RIGAKU JOURNAL VOL. 22 / NO. 1 / 2005, 2–15