Doxycycline-d3 hydrochloride is deuterium labeled Doxycycline (hydrochloride). Doxycycline hydrochloride, an antibiotic, is an orally active and broad-spectrum metalloproteinase (MMP) inhibitor[1]. Doxycycline hydrochloride shows antibacterial activity and anti-cancer cell proliferation activity[1][2][3][4][5][6].