The purpose of the present invention is to provide: a pharmaceutical composition that contains the pyridylaminoacetic acid compound of the present invention, said pyridylaminoacetic acid compound being stable within the pharmaceutical composition； and a method for improving the stability of the pydridylaminoacetic acid compound within the pharmaceutical composition. The pharmaceutical composition contains: (6{[4-(pyrazol-1-yl)benzyl](pyridine-3-ylsulfonyl)aminomethyl}pyridine-2-ylamino)isopropyl acetate or a salt thereof； and polyoxyethylene castor oil. The polyoxyethylene castor oil preferably contains a polyoxyethylene castor oil selected from the group consisting of polyoxyl 5 castor oil, polyoxyl 9 castor oil, polyoxyl 15 castor oil, polyoxyl 35 castor oil, and polyoxyl 40 castor oil.本發明之目的在於提供一種醫藥組成物、及使醫藥組成物中之本化合物之穩定性提高之方法，該醫藥組成物係含有本化合物者，且其中之本化合物穩定。本發明之醫藥組成物含有(6-{[4-(吡唑-1-基)苄基](吡啶-3-基磺醯基)胺基甲基}吡啶-2-基胺基)乙酸異丙酯或其鹽、與聚氧乙烯蓖麻油(polyoxyethylene castor oil)。聚氧乙烯蓖麻油較佳為包含選自由聚氧乙烯5蓖麻油(polyoxyl 5 castor oil)、聚氧乙烯9蓖麻油(polyoxyl 9 castor oil)、聚氧乙烯15蓖麻油(polyoxyl 15 castor oil)、聚氧乙烯35蓖麻油(polyoxyl 35 castor oil)及聚氧乙烯40蓖麻油(polyoxyl 40 castor oil)所組成之群中之聚氧乙烯蓖麻油。
