Simvastatin Imp. A (EP) as Sodium Salt: (3R,5R)-7-[(1S,2S,6R,8S,8aR)-8-[(2,2-Dimethylbutanoyl)oxy]-2,6-dimethyl-1,2,6,7,8,8a-hexahydronaphthalen-1-yl]-3,5-dihydroxyheptanoic Acid Sodium Salt.