The invention is related to a method for preparing 5-amino-2,3-dihydrophthalazine-1,4-dione salt with alkali metals of the formula II wherein 5-nitro-2,3-dihydrophthalazine-1,4-dione is solved in water solution of MOH1 where M has the below mentioned meaning, with formation of solution of 5-nitro-2,3-dihydrophthalazine-1,4-dione alkali metal salt, which is catalytically transformed into 5-amino-2,3-dihydrophthalazine-1,4-dione salt at the temperature 40-900C by means of hydrogen under the pressure 1-4 MPa in at the presence of a transition metal catalyst (Pt, Pd) on activated carbon, and separation of crystalline 5-amino-2,3-dihydrophthalazine-1,4-dione salt is performed by water solution diluting with lower alcohol or cyclic lower ether with cooling to the temperature −5° C. to −15° C., providing that there is used 5-nitro-2,3-dihydrophthalazine-1,4-dione formed in the reaction of anhydride of 3-nitrophthalic acid with hydrazine hydrate in anhydrous acetic acid at the temperature 100-110° C. with distilling the mixture of acetic acid and water off. There was also presented a pharmaceutical composition containing such obtained 5-amino-2,3-dihydrophthalazine-1,4-dione salt with alkali metals and its application in medicine. There was also presented new use of 5-amino-2,3-dihydrophthalazine-1,4-dione sodium salt for production of a drug for treatment of heart diseases, pancreas diseases and diabetes as well as application of sodium salt optionally in combination with lithium salt for treatment of the nervous system diseases. Besides, the methods of treatment of these diseases were also presented Formula II where M represents Li, Na, K.
