Provided is a pharmaceutical composition which contains 5-{[(3R)-1-acryloylpyrrolidin-3-yl]oxy}-6-ethyl-3-({4-[4- (4-methylpiperazin-1-yl)piperidin-1-yl]phenyl}amino)- pyrazine-2-carboxamide (which is referred to as "compound A", hereinbelow) or a pharmaceutically acceptable salt thereof and is stabilized. The pharmaceutical composition comprises the compound A or a pharmaceutically acceptable salt thereof and a pharmaceutical additive having a difference in a water activity value of 0.1 or more, and is stabilized.本發明提供一種含有5-{[(3R)-1-丙烯醯基吡咯嗪-3-基]氧基}-6-乙基-3-({4-[4-(4-甲基哌嗪-1-基)哌啶-1-基]苯基}胺基)吡嗪-2-甲醯胺(以下,化合物A)或其在製藥學上被容許的鹽,並經安定化而成之醫藥組成物。前述醫藥組成物含有化合物A或其在製藥學上被容許的鹽、及水活性值的差分為0.1以上之醫藥品添加物,並經安定化而成。
