Phenylpyridazine compounds and medicines containing the same

A phenylpyridazine compound represented by the following formula (I):

• wherein
• R1 represents phenyl, pyridyl, substituted phenyl or substituted pyridyl, wherein the substituents are selected from the group consisting of halogen, hydroxyl, alkyl, lower alkoxy and phenylthio;
• R2 represents lower alkoxy, lower alkylthio, lower alkylsulfinyl or lower alkylsulfonyl;
• R3 represents hydrogen or lower alkoxy;
• or R2 and R3 may be fused together to form an alkylenedioxy group;
• R4 represents hydrogen, halogen, cyano, carboxy, lower alkyl, lower alkyl substituted by halogen, hydroxy, cyano, nitro, amino, carboxy, aminocarbonyl, N-hydroxy,N-loweralkylaminocarbonyl or lower alkyl substituted aminocarbonyl;
• lower alkenyl, halogen or phenyl substituted lower alkenyl, lower alkylthio, phenyl substituted lower alkylthio, lower alkylsulfinyl, phenyl substituted lower alkylsulfinyl, lower alkylsulfonyl, phenyl substituted lower alkylsulfonyl, lower alkylsulfonyloxy, phenyl substituted lower alkylsulfonyloxy, phenyl, phenyl substituted by halogen, lower alkyl, lower alkoxy, cyano, nitro, or amino;
• pyridyl, pyridyl substituted by halogen, lower alkyl, lower alkoxy, cyano, nitro or amino;
• phenoxy, phenoxy substituted by halogen, lower alkyl, lower alkoxy, cyano, nitro or amino;
• phenylthio, phenylthio substituted by halogen, lower alkyl, lower alkoxy, cyano, nitro or amino;
• phenylsulfinyl, phenylsulfinyl substituted by halogen, lower alkyl, lower alkoxy, cyano, nitro or amino;
• phenylsulfonyl, phenylsulfonyl substituted by halogen, lower alkyl, lower alkoxy, cyano, nitro or amino;
• pyridyloxy, pyridyloxy substituted by halogen, lower alkyl, lower alkoxy, cyano, nitro or amino;
• morpholino, morpholino substituted by halogen, lower alkyl, lower alkoxy, cyano or nitro;
• morpholinocarbonyl, morpholinocarbonyl substituted by halogen, lower alkyl, lower alkoxy, cyano or nitro;
• piperidinocarbonyl, piperidinocarbonyl substituted by halogen, lower alkyl, lower alkoxy, cyano or nitro;
• 1-piperazinylcarbonyl, 1-piperazinylcarbonyl substituted by halogen, lower alkyl, lower alkoxy, cyano, nitro or amino;
• amino substituted by phenyl, phenyl substituted by halogen, cyano, nitro, amino, lower alkyl or lower alkoxy, or benzyl;
• and
• n is 0 or 1,
• with the proviso that when R1 is 4-methoxyphenyl, R2 is methoxy and R3 is hydrogen, R4 can not be hydrogen or halogen and with the proviso that R1 can not be 4-(methylsulfonyl)phenyl or 4-(aminosulfonyl)phenyl and with the proviso that when R4 is halogen, R1 can not be lower alkoxyphenyl and R2 can not be lower alkoxy;
• or a salt thereof.