A 60-year-old woman started feeling weakness, vertigo, rapid fatigability during the last year. Recently she has developed dyspnea and paresthesia observed. Objectively: skin and mucous membranes are pale and icteric. Lingual papillae are smoothed out. Liver and spleen are at the edge of costal arch. Blood test: Hb- 70 g/L, erythrocytes – 1.7 × 1012/L, blood color index – 1.2, macrocytes. What drug can be prescribed on pathogenetic grounds?