Identification and structural characterization of lactose adduct impurities in isosorbide dinitrate and hydralazine hydrochloride tablets by liquid chromatography‐mass spectrometry and nuclear magnetic resonance studies

Abstract Isosorbide dinitrate and hydralazine hydrochloride tablets are approved for the treatment of heart failure, prolonged hospitalization for heart failure, and enhanced patient‐reported functional status. It has been administered orally. Isosorbide dinitrate and hydralazine hydrochloride tablets contained two additional major unknown peaks (Degradation Product 1 and Degradation Product 2) in the stability studies (25°C/60% relative humidity and 40°C/75% relative humidity). These two unknown degradation peaks formed due to the heat (thermal) and humidity stress of hydralazine hydrochloride. Liquid chromatography separated these unknown degradant peaks. Initially, liquid chromatography‐mass spectrometry assessed the degradation pathways and mass of two degradants. Afterward, preparative‐liquid chromatography isolated the two major unknown degradation impurities formed under heat (thermal) and humidity stress conditions. Further, to confirm the structures, nuclear magnetic resonance spectroscopy evaluated these two degradants. The liquid chromatography‐mass spectrometry and nuclear magnetic resonance spectral data confirmed that the two degradation impurities are hydralazine lactosone ring‐opened adduct (Degradation Product 1) and s‐triazolo [3,4‐α] phthalazine (Degradation Product 2).