An Overview on Polymorph Preparation Methods of Active Pharmaceutical Ingredients

Polymorphism, which plays an important role in the pharmaceutical industry, is quite common for active pharmaceutical ingredients (API). Owing to the structural differences between polymorphs, they often possess remarkably different physical and chemical properties, thus leading to diversity in curative effects and shelf life. How to precisely control the polymorph of API has attracted the attention of researchers around the world. In this paper, the regulation methods of drug polymorphs are comprehensively reviewed, to give a better view for the future research. The traditional method, including the control of the nucleation and growth process, is systematically introduced and analyzed from the aspects of the action mechanism and their application in recent years. In addition, novel techniques, including templates, microfluidics technology, ultrasound, laser, ionic liquids, and supramolecular gels, are expounded and analyzed in detail. Considerable studies indicate that polymorph control of API is a promising research field. Finally, the existing problems are discussed and the future prospects are given.