| Member | Definition | Role |
|---|
| 3-oxo-2-[(6-oxo-1-phenyl-3-pyridazinyl)oxy]butanoic acid ethyl ester | | 3-oxo-2-[(6-oxo-1-phenyl-3-pyridazinyl)oxy]butanoic acid ethyl ester |
| 6-hydroxy-2-phenylpyridazin-3-one | | 6-hydroxy-2-phenylpyridazin-3-one |
| 6-hydroxy-4-methyl-2-phenyl-2,3-dihydropyridazin-3-one | | 6-hydroxy-4-methyl-2-phenyl-2,3-dihydropyridazin-3-one |
| maleic hydrazide | | Maleic hydrazide |
| norflurazone | A pyridazinone that is pyridazin-3(2H)-one which is substituted at positions 2, 4, and 5 by m-(trifluoromethyl)phenyl, chloro, and methylamino groups, respectively. A pre-emergence herbicide used to control grasses and broad-leafed weeds in a variety of crops. Not approved for use within the European Union. | norflurazon |
| or 1259 | | levosimendan |
| pimobendan | | pimobendan |
| pyrazon | A pyridazinone that is pyridazin-3(2H)-one substituted by an amino group at position 5, a chloro group at position 4 and a phenyl group at position 2. | chloridazon |
| pyridaben | | pyridaben |
| pyridafenthion | | pyridaphenthion |
| siguazodan | | 1-cyano-2-methyl-3-[4-(4-methyl-6-oxo-4,5-dihydro-1H-pyridazin-3-yl)phenyl]guanidine |
| y 23684 | | Y 23684 |
| zardaverine | A pyridazinone derivative in which pyridazin-3(2H)-one is substituted at C-6 with a 4-(difluoromethoxy)-3-methoxyphenyl group. It is a phosphodiesterase inhibitor, selective for PDE3 and 4. | zardaverine |