[Crystallization and solid state properties of molecules of pharmaceutical interest]

Polymorphism characterizes the ability of a molecule to crystallize in different crystallographic systems (in the case of a simple atom the term allotropy is used). This phenomenon, known for a long time, leads to significantly different physicochemical properties between the different crystalline forms. In the pharmaceutical domain, the potential polymorphism of the active substances and the excipients could affect Since most of the pharmaceutical products consist of solid dosage forms administered by the oral route, it is not surprising that studies on polymorphism have become a mandatory chapter of any pharmaceutical dossier whether it concerns a new chemical entity or a generic. In fact, beyond the polymorphism phenomenon, it is the crystallization process which deserves to be highlighted. We will show how it controls the appearance of the polymorphism and the crystalline growth which is a second feature at least as important as the polymorphism itself (external aspect of the solid particles/habit) in terms of processability and dissolution. After having recalled some thermodynamic considerations which characterize the polymorphism, we will illustrate succinctly the impact of these phenomena on some important aspects of the pharmaceutical development such as the dissolution, the bioavailability and the stability.