DERIVADOS DE PIRIDAZINONA

Pyridazinone derivatives represented by the formula (I) and antiplatelet agents containing them: Äwherein R is a hydrogen atom or a C1-C4 alkyl group, X is a hydrogen atom, a chlorine atom or a bromine atom, Ar is a pyridyl group or a phenyl group substituted with OR (wherein R is a hydrogen atom or a C1-C4 alkyl group) and A äwherein A is a hydrogen atom, a halogen atom, a C1-C4 alkyl group or OR (wherein R is a hydrogen atom or a C1-C4 alkyl group)ü, Y is C1-C8 alkylene wherein one carbon atom on the straight chain is substituted with one OR group (wherein R is the same as defined above), and Z and Z are independently a hydrogen atom, a halogen atom, a C1-C4 alkyl group or a OR group (wherein R is the same as defined above)Ü. These compounds have strong antiplatelet effects, are excellently safe, and can be used as active ingredients of prophylactic and therapeutic drugs for various thrombotic diseases.