Structural elucidation of the Rifaximin Ph. Eur. Impurity H.

Rifaximin, a semisynthetic, rifamycin-based non-systemic antibiotic is used in the treatment of acute and chronic gastrointestinal disorders. The aim of this study was the elucidation of the molecular structure of the 802 Dalton impurity which was found in Rifaximin industrial batches and reported with an erroneous structure in European Pharmacopoeia 6.5 (2009) [7] monograph as Rifaximin Impurity H. This impurity was isolated from Rifaximin by preparative HPLC and purified by column chromatography. The molecular structure was evidenced by means of (1)H and (13)C NMR spectroscopy, mass spectrometry and FT-IR.