A 55-year-old man presents with macrocytic anaemia and a vitamin B12 level of 90 ng/L, with a history of pernicious anaemia. Which treatment is most appropriate to initiate?

• A. Folic acid
• B. Iron
• C. Hydroxocobalamin
• D. Vitamin C

Answer: (C)

B12 deficiency from pernicious anaemia requires replacement with vitamin B12 through a route that bypasses gut absorption. In this setting, the appropriate action is intramuscular hydroxocobalamin, which reliably replenishes stores despite lack of intrinsic factor. This corrects the macrocytosis and helps prevent neurological complications that can occur with prolonged B12 deficiency.

Folic acid would not treat the underlying B12 deficiency and can mask it, potentially allowing neurological damage to progress. Iron targets iron deficiency, not B12 deficiency. Vitamin C has no role in treating B12 deficiency.