Levothyroxine EP Impurity H

Levothyroxine EP Impurity H is a diiodinated tyrosine derivative featuring a fully iodinated benzene ring (four iodine atoms) and a 3,5-dihydroxybenzoic acid moiety. It lacks the 3'-iodo substitution present in the parent levothyroxine structure, resulting in a truncated side chain. This impurity arises via oxidative degradation pathways during API synthesis, retaining the core aromatic framework but with altered iodination patterns. The compound exhibits strong UV absorbance due to conjugated aromatic systems and hydroxyl groups, enabling detection in chromatographic profiles. It serves as a critical HPLC reference standard for quantifying process-related impurities in levothyroxine formulations.