The present invention addresses the problem of providing a combination medicine that is capable of preventing or inhibiting acquisition of resistance to a pyrimidine antimetabolite, a drug for preventing or inhibiting pyrimidine antimetabolite-resistance acquisition, and a method for treating a disease with the use of the combination medicine. Provided is a combination medicine that comprises a pyrimidine antimetabolite and 5-hydroxy-1H-imidazole-4-carboxamide, wherein the single dosage of Compound A is 50-500 mg/m2 and the daily dosage thereof is 100-1000 mg/m2.
