A 60-year-old woman has been suffering from weakness, dizziness, and fatigue over the last year. Recently she has also developed dyspnea, paresthesia. Objectively: the skin and mucous membranes are pale and slightly icteric. The tongue is smooth due to the loss of lingual papillae. Liver and spleen are located at the costal margin. Blood count: Hb- 70 g/l, RBC- 1,7 × 1012/l, color index -1,2, macrocytes. Administer the patient a pathogenetically justified drug: