Vitamins Pharmacology

Which vitamin acts as a coenzyme in the transamination and decarboxylation of amino acids?

A 58-year-old male from rural Maharashtra presents with progressive weakness, paresthesias in both feet, and difficulty walking for 3 months. On examination, he has diminished vibration and proprioception sense in lower limbs, hyperreflexia, and a positive Romberg sign. His diet consists mainly of polished rice and minimal protein intake. Blood investigations show macrocytic anemia (Hb 9.2 g/dL, MCV 104 fL) and serum cobalamin level of 145 pg/mL (normal >200). What is the most appropriate initial pharmacological intervention?

A 42-year-old woman from Delhi presents with a 6-month history of progressive fatigue, dyspnea on exertion, and recurrent mouth ulcers. On examination, she has glossitis, angular cheilitis, and mild hepatomegaly. Full blood count shows macrocytic anemia (Hb 8.5 g/dL, MCV 108 fL, reticulocyte count 0.8%). Serum folate is 2.1 ng/mL (normal 5.4–16), and serum B₁₂ is 580 pg/mL (normal). Peripheral blood smear shows hypersegmented neutrophils. She denies alcohol use. What is the most appropriate initial pharmacological management?