Achieving polymorph selectivity in the crystallization of pharmaceutical solids: basic considerations and recent advances.

Controlling the appearance of crystal polymorphs of pharmaceuticals is essential in developing robust large-scale crystallization processes in the pharmaceutical industry. This review describes many of the thermodynamic and kinetic factors that are important for controlling crystal polymorphism and discusses recent advances in the understanding of the molecular mechanisms of polymorph appearance. Case studies in the development of crystallization processes of pharmaceutical solids, where process analytical technology was applied to resolve the complexities introduced by crystal polymorphism, are discussed.