FIELD: medicine. SUBSTANCE: invention relates to the use of sodium salt of diethyl ester of 4-oxo-1,4-dihydropyrazolo[5,1-c]-1,2,4-triazine-3,8-dicarboxylic acid, monohydrate of the formula I as a drug for the treatment and prevention of long-term consequences of diabetes mellitus. Sodium salt of diethyl ester of 4-oxo-1,4-dihydropyrazolo[5,1-c]-1,2,4-triazine-3,8-dicarboxylic acid, monohydrate is an effective drug for the treatment and prevention of such diabetic complications as nephropathy, cardiomyopathy, neuropathy, encephalopathy, endothelial dysfunction and hemorheological disorders; it can be widely used in medicine in the field of therapy of late complications of diabetes mellitus. EFFECT: obtaining a drug for the treatment of complications of diabetes mellitus.