An agent for overcoming resistance to anti-cancer agent is characterized by using xanthine oxidase inhibitor as an active pharmaceutical ingredient, containing 2-[3-cyano-4-(4-fluorophenoxy)phenyl]-4-hydroxy-thiazolo [5,4-d]pyrimidine potassium salt, 2-[3-cyano-4-(4-fluorophenoxy)phenyl]thiazole [5,4-d]pyrimidine, 2-(3-cyano-4-phenoxyphenyl)-4-hydroxy-thiazolo [5,4-d]pyrimidine, 2-(3-cyano-4-phenoxyphenyl)-4-hydroxy-thiazolo[5,4-d]pyrimidine potassium salt, 2 - [3-cyano-4-phenoxyphenyl)thiazolo[5,4-d]pyrimidine, TMX-67 and FYX-051,etc.一種抗癌劑之抗性克服劑,其特徵為使用含有2-〔3-氰基-4-(4-氟苯氧基)苯基〕-4-羥基噻唑〔5,4-d〕嘧啶 鉀鹽、2-〔3-氰基-4-(4-氟苯氧基)苯基〕噻唑〔5,4-d〕嘧啶、2-(3-氰基-4-苯氧基苯基)-4-羥基噻唑〔5,4-d〕嘧啶、2-(3-氰基-4-苯氧基苯基)-4-羥基噻唑〔5,4-d〕嘧啶 鉀鹽、2-〔3-氰基-4-苯氧基苯基)噻唑〔5,4-d〕嘧啶、TMX-67及FYX-051等之黃嘌呤氧化酵素抑制劑(Xanthine Oxidase inhibitor)作為有效成份的藥劑。
