Irbesartan (IBS) is a tetrazole derivative and antihypertensive drug that has two interconvertible structures, 1H- and 2H-tautomers. The difference between them lies in the protonation of the tetrazole ring. In the solid-state, both tautomers can be isolated as crystal forms A (1H-tautomer) and B (2H-tautomer). Studies have reported that IBS is a polymorphic system and its forms A and B are related monotropically. These reports indicate form B as the most stable and less soluble form. Therefore, the goal of this contribution is to demonstrate through a complete solid-state characterization, thermodynamic study and dissolution properties that the IBS forms are desmotropes that are not related monotropically. However, the intention is also to call attention to the importance of conducting strict chemical and in solid-state quality controls on the IBS raw materials. Hence, powder X-ray diffraction (PXRD) and Raman spectroscopy (RS) at ambient and non-ambient conditions, differential scanning calorimetry (DSC), hot stage microscopy (HSM), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM) techniques were applied. Furthermore, intrinsic dissolution rate (IDR) and structural stability studies at 98% relative humidity (RH), 25 °C and 40 °C were conducted as well. The results show that in fact, form A is approximately four-fold more soluble than form B. In addition, both IBS forms are stable at ambient conditions. Nevertheless, structural and/or chemical instability was observed in form B at 40 °C and 98% RH. IBS has been confirmed as a desmotropic system rather than a polymorphic one. Consequently, forms A and B are not related monotropically.

厄贝沙坦 (IBS) 是一种四唑衍生物和抗高血压药物，具有两种可相互转换的结构：1H-和 2H-互变异构体。它们之间的区别在于四唑环的质子化程度。在固态下，两种互变异构体均可分离为晶型 A（1H-互变异构体）和 B（2H-互变异构体）。研究表明IBS是一个多态性系统，其A型和B型是单向相关的。这些报告表明 B 型是最稳定且溶解度较低的形式。因此，本贡献的目标是通过完整的固态表征、热力学研究和溶解特性来证明 IBS 形式是不单向相关的促分子。然而，其目的还在于提醒人们注意对 IBS 原材料进行严格的化学和固态质量控制的重要性。因此，环境和非环境条件下的粉末 X 射线衍射 (PXRD) 和拉曼光谱 (RS)、差示扫描量热法 (DSC)、热台显微镜 (HSM)、傅里叶变换红外 (FT-IR) 和扫描电子显微镜（SEM）技术被应用。此外，还在 98% 相对湿度 (RH)、25 °C 和 40 °C 下进行了固有溶出率 (IDR) 和结构稳定性研究。结果表明，事实上，A 型的溶解度大约是 B 型的四倍。此外，两种 IBS 形式在环境条件下都很稳定。然而，在 40°C 和 98% 相对湿度下，B 型中观察到结构和/或化学不稳定性。 IBS 已被证实是一种趋向性系统，而不是多态性系统。因此，形式 A 和 B 不单向相关。