A 60-year-old woman started feeling weakness, vertigo, rapid fatigability during the last year. Recently there have been dyspnea and paresthesia observed. Objectively: skin and mucous membranes are pale and icteric. Lingual papillae are smoothed out. Liver and spleen are situated 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?