PROBLEM TO BE SOLVED : To provide : a method of synthesis of thyroid hormone analogs, such as pyridazinone compounds, and their prodrugs; and pharmaceutical compositions for use in treating a resistance to thyroid hormone (RTH) that contain the compound.SOLUTION : A pharmaceutical composition for use in treating a resistance to thyroid hormone (RTH) in a subject having at least one TRβ mutation contains a pyridazinone compound having a specific chemical structure represented by 2-(3, 5-dichloro-4-((5-isopropyl-6-oxo-1, 6-dihydropyridazin-3-yl)oxy)phenyl)-3, 5-dioxo-2, 3, 4, 5-tetrahydro-1, 2, 4-triazine-6-carbonitrile.SELECTED DRAWING : Figure 1COPYRIGHT : (C)2019, JPO&INPIT