*Article* **Pharmaceutical Salts of Enrofloxacin with Organic Acids**

**Hong Pang <sup>1</sup> , Yu-Bin Sun <sup>1</sup> , Jun-Wen Zhou <sup>1</sup> , Meng-Juan Xie <sup>1</sup> , Hao Lin <sup>1</sup> , Yan Yong <sup>2</sup> , Liang-Zhu Chen <sup>2</sup> and Bing-Hu Fang 1,2,\***


Received: 1 July 2020; Accepted: 24 July 2020; Published: 27 July 2020

**Abstract:** Enrofloxacin is a poorly soluble antibacterial drug of the fluoroquinolones class used in veterinary medicine. The main purpose of this work was to investigate the structural and pharmaceutical properties of new enrofloxacin salts. Enrofloxacin anhydrate and its organic salts with tartaric acid, nicotinic acid and suberic acid formed as pure crystalline anhydrous solids. All the crystals were grown from a mixed solution by slow evaporation at room temperature. These products were then characterized by field-emission scanning electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry. Further, X-ray single crystal diffraction analysis was used to study the crystal structure. The intermolecular interactions and packing arrangements in the crystal structures were studied, and the solubility of these salts in water was determined using high-performance liquid chromatography. The results show that the new salts of enrofloxacin developed in this study exhibited excellent water solubility.

**Keywords:** enrofloxacin; salts; crystal structure; organic acids; solubility
