The invention relates to the field of medicine and pharmaceuticals and particularly to a novel dosage form of an antitumor preparation, which ensures the hydrolytic and physical stability of said preparation, as well as to a method for producing a dosage form of this type. The stable dosage form is a lyophilizate comprising an etidronate-cytarabine conjugate or a pharmaceutically acceptable salt thereof, and a stabilizer, which is a divalent metal salt, in a molar ratio of stabilizer to conjugate of 1 : 1 to 20 : 1. A dosage form of this type ensures the hydrolytic and physical stability of the conjugate during long-term storage, and the stability of solutions of the conjugate for parenteral administration during clinical use.