Structural Characterization and Pharmaceutical Evaluation of Telmisartan Hydrochloride Salts

Abstract

Telmisartan is an anti-hypertensive drug that exhibits poor aqueous solubility. In this work, salt formation was utilized to address this issue. Three hydrochloride salts of telmisartan (TELHCl), a trihemihydrate hydrochloride salt (TELHCl-Hyd), and two anhydrate forms (TELHCl-A and TELHCl-B) were obtained. The crystal structures of TELHCl-Hyd and TELHCl-A were determined using single-crystal structure analysis. TELHCl-Hyd is a channel hydrate that has structural similarities with TELHCl-A. The structures of both crystals are mainly composed of chain structures formed by centrosymmetric dimers connected via carboxylic–benzimidazole hydrogen bonding. Despite their structural similarities, the dehydration of TELHCl-Hyd led to the formation of TELHCl-B. The solubility, intrinsic dissolution rate (IDR), powder flowability, and tabletability of TELHCl-Hyd and TELHCl-B were characterized and compared with those of the telmisartan free base form (TEL). The hydrochloride salts enhanced the solubility of telmisartan approximately 10 to 20 times and maintained the spring parachute effect up to 24 h. The IDR was also improved due to the existence of a hydrophilic channel that facilitates the dissolution of telmisartan cations. The resulting salts had a larger particle size and a more favorable crystal morphology that led to a better powder flowability. However, the tabletability was not improved by salt formation. The TEL exhibited a defined slip plane and a higher specific surface area that may assist the tableting process.

Keywords

• telmisartan
• crystal structure analysis
• salt formation
• hydrate
• solubility
• intrinsic dissolution