Understanding the Role of Water in Different Solid Forms of Avibactam Sodium and Its Affecting Mechanism

Abstract

Hydrates are common in pharmaceutical development, and the formation of hydrates affects the performance of the final product. However, the role that water plays in crystal packing remains unclear. In this study, Avibactam sodium, which has one dihydrate (Form E), one monohydrate (Form A), and two anhydrous forms (Form B and D), was chosen as the model compound to understand this subject. Single crystal structures of four solid forms were obtained and characterized by single X-ray diffraction. The dynamic vapor sorption experiments revealed the moisture-dependent stability increased in the order: Form B < Form D < Form A < Form E. It can be envisaged that the integration of water molecules could noticeably compensate the potential intermolecular interactions, thereby significantly improving the crystal stabilities of hydrates. Furthermore, the hydration of Form B was investigated to understand the integration of water molecules by measuring the critical hydration water activities (aw). The results indicated that both water activities and temperature are vital factors to determine the amount of water molecules existing in crystal lattice. Moreover, to probe the disintegration of water molecules, the dehydration of dihydrate was investigated in detail by solid-state transformation and solvent-mediated transformation experiments. Finally, two-step dehydration and one-step dehydration + recrystallization mechanisms of these different pathways were proposed by analyzing the transformation experiment results and the crystal structure of various solid forms