A chemically stable formulation of (E)-7-[4-(4-fluorophenyl)-6-isopropyl-2-[methyl(methylsulfonyl)amino]pyrimidin-5-yl]-(3R, 5S)-3,5-dihydroxyhept-6-enoic acid or a pharmaceutically-acceptable salt thereof for oral use, such as tablets, capsules, powders, granules has been developed using the substances which stabilize against formation of degradation products: lactone and oxidation product.