A drug for inhibiting vascular intimal hyperplasia which is effective in the prevention of restenosis after percutaneous transluminal coronary angioplasty (PTCA) and stent placement in a blood vessel or effective in treatments for the progress thereof. The drug for inhibiting vascular intimal hyperplasia contains either a 3(2H)-pyridazinone compound represented by the formula (I): (wherein R1, R2, and R3 each independently represents hydrogen or C1-6 alkyl group； X represents halogeno, cyano group, or hydrogen； Y represents halogen, trifluoromethyl, or hydrogen； and A represents optionally hydroxylated C1-8 alkylene) or a pharmacologically acceptable salt thereof.提供對於治療經皮之冠狀動脈形成術(PTCA，氣球導管擴張術)及血管內放置支架後再狹窄之預防、進展有效之使用於抑制血管內膜肥厚之醫藥組成物。；[式中，R1、R2及R3係表示分別獨立之氫原子或C1-6烷基，X係表示鹵素原子、氰基或氫原子，Y係表示鹵素原子、三氟甲基或氫原子，A係表示以羥基取代亦可之碳原子數為1至8個伸烷基。]所表示之含3(2H)-噠嗪酮化合物或其藥理學上所容許鹽之使用於抑制血管內膜肥厚之醫藥組成物。
